# Squaring off the bottom of a blind hole



## davidyat (Nov 25, 2020)

*When drilling a blind hole, you are obviously going to end up with the bottom having a 118 degree "funnel" at the bottom. I'm looking at suggestions to help me "square off" the bottom of the hole. I've tried using an end mill and my boring head but I'm not comfortable with either. Any suggestions would be appreciated.
Thanks,
Grasshopper*


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## Ramon (Nov 25, 2020)

Hello  David , 

It depends of course on how deep and what diameter the hole is but there are several options. The first and easiest is to 'flat bottom' the drill but that does require grinding the existing one or modifying another of the same diameter.  The end is ground square then a 5-10* cutting angle is applied to each flute - much like a slot drill. If you just tweak the corners of the flutes it will travel down the predrilled hole without scoring. It's just used to take out the bottom - not for drilling the hole any depth as it will not cut on the centre

If it's much shallower then a slot drill of similar diameter will have the same effect but be aware the bottom of the hole will not be truly flat. A 'D' bit could be made from drill rod or if there's enough clearance it can simply be taken out with a boring tool.

If it's a deep hole then the Flat Bottom Drill or the D Bit are your two main choices

Hope hat helps - Ramon (Tug)


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## Ken I (Nov 25, 2020)

Agree with Ramon - When I was told to do this as an apprentice - I thought my artisan was joking and checked with the foreman - but I then had to grind it back again after the job was done. (Was a dirty big Ø30mm diameter MT4 drill on a large radial arm drill - a job of 5 such holes IIRC.)
In my own workshop I hate doing this - so if I grind a drill flat bottomed - then it stays that way and gets kept in a box of flat bottomed drills.
If necessary, I buy another drill.
Otherwise I will chop off the end off a drill with worn lands - being a tad undersize is not going to be a problem as its only ever going to clean out a drill point.
Try to stick to common sizes - in my case metric - half millimeter steps - so I have most half-mil steps up to 13mm diameter.
A flat bottomed Ø3.8 hole better have a damn good reason or its going to end up Ø4.

Using an end mill is not a good idea as it doesn't cut to the center - use a 2 or 3 flute slot drill.

Regards, Ken


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## davidyat (Nov 25, 2020)

*Thanks. I like the idea of flat bottoming a drill bit. I have a lot of used bits and this idea sounds just like what I was looking for.
Grasshopper*


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## teeleevs (Nov 26, 2020)

I usually find I have a broken drill the right size in my box of such, a touch on the grinder with just a little cutting edge is all that is needed, also when sinking socket head bolts I usually have one already to size in a box.
Keep up the good work. Ted


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## L98fiero (Nov 26, 2020)

Ken I said:


> Using an end mill is not a good idea as it doesn't cut to the center - use a 2 or 3 flute slot drill.


FWIW, there are center cutting end mills, McMaster-Carr lists them up to 11 flute. McMaster-Carr
but even a 4 flute isn't good at drilling more than about a 1/4 diameter deep and then using some care so a 4 flute is marginal at cleaning up the bottom of a drilled hole, even when drilled with a 135° drill point, at least that's my experience. The problem is chip clearance as only one flute is center cutting.


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## Howder1951 (Nov 26, 2020)

Has anyone tried an end mill or modified drill in a boring head? It appears sound in theory and could probably bemused as a desperate last resort or a one off need. Just asking.


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## goldstar31 (Nov 27, 2020)

Howder1951 said:


> Has anyone tried an end mill or modified drill in a boring head? It appears sound in theory and could probably bemused as a desperate last resort or a one off need. Just asking.


Many MANY years ago it was suggested in Model Engineer when a broken  drill with one 'flank' had been shattered. There was NO tool and cutter grinder for the average little man to make.  It was fitted to a small boring head as a single lip cutting tool. I tried it, it worked.
Today, with cheap double ended grinders and tool and cutter grinders  in abundance and the introduction of cheap(ish) insert carbides- I simply doubt the logic. The world was full of Slocombe broken tips on centre drills and endless( in all ways) drills. All oof this scrap hss tooling took a second life as boring tool mends.
Today, hummmmm? I think that those people who are forced to attep such expedients should probably find another less expensive hobby.
However back to those people who who want a 'flat bottom'( no pun intended) Leonard Sparey Did write vthe Amateur's Lathe( 1948 in which apart from his excellent references to external and infernal engines mostly of his design, he demonstrated how to modify an ordinary drill for this purpose. Later George Thomas described amongst many things how to make a proper tool to successfully bore holes Better than what was available to us ordinary people in his excellent and seemingly unread Model Engineer's Worksop Manual and his Workshop Techniques.
 My opinions but shared by many more expert hobbyists

Norman


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## grahamgollar (Nov 27, 2020)

I would agree with the comments from L98fiero i.e. any end mill cutting in a blind hole would struggle with swarf clearance. This is particularly the case with centre cutting mills where the cutting end would quickly clog and overheat.
Aside from the current topic I have found that in general use the centre cutting mills are very good but, when cutting ductile steels, they produce some wickedly fine and sharp chips  to be carefully avoided by your pinkies!


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## Richard Carlstedt (Nov 27, 2020)

Be aware that center cutting endmills have a  1 - 2 degree relief ground in the flutes which
means that it leaves a convex , not flat, surface at the bottom of the hole.
This means a 1/4 " diameter hole may have a .001 crown at the bottom - not flat, but not noticeable either 
Rich


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## goldstar31 (Nov 27, 2020)

Well, yes and no. The amateur with a better than average tool and cutter grinder  cannot round the extreme tipof end mills and and slot drills.

I've been following the var ious designs and their performances. I've just given a Clarkson away. No instructions were ever published until the radius turning attachment was finally introduced for the Mark2.

Te Quorn group have prattled on about the Mar k1 and Mark2 Quorns and I'm sitting with a Quornand a Kennet and a Chinese Deckel clone- Same answer!

Sorry and all that

Norman


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## Ramon (Nov 27, 2020)

Unless held by something extremely rigid a centre cutting cutter, 2 or 3 or more flute is unlikely to cut a similar sized hole as the cutter itself unless the centre of said hole is previously relieved (drilled). Any slightest give either in the holding of the cutter, the spindle or the machine ways themselves will lead to the cutter moving off centre. Even then it is still frought with variation on diameter unless done by steps (in diameter) and even then not an 'accurate' hole as in reaming or boring will probably result

I suggested the slot drill as a 'means' to take out the corners of a previously drilled hole to 'flat bottom' but that does depend on having a corresponding size SD and certainly only on shallow holes - not really an ideal solution to the OP's question

I was shown the flat bottom drill technique circa 1975 as a means to overcome not having a counterbore for caphead screws. I have used it many times but something tells me it had been around for a lot longer before that than the time that has passed since 

I do use slot drills and endmills on occasion to spot face or to open up before boring but would never do so to achieve an accurate diameter hole.

Tug


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## Charles Lamont (Nov 28, 2020)

goldstar31 said:


> Well, yes and no. The amateur with a better than average tool and cutter grinder  cannot round the extreme tipof end mills and and slot drills.
> 
> I've been following the var ious designs and their performances. I've just given a Clarkson away. No instructions were ever published until the radius turning attachment was finally introduced for the Mark2.
> 
> ...



Norm, I don't understand. Grinding a radius on milling cutter tips with a Quorn is perfectly possible, but Chaddock explains in his Quorn 'bible' that it is tricky.


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## goldstar31 (Nov 28, 2020)

If I recall Chaddock describes the procedure  with a reference to-- and I quote a position in ballet dancing'
Obviously the Quorn group of which I am a member ( Ye Gods) have expressed concerns. It seems, and I have the Mk3 plans etc but hae n't tried, gone to fart greater lengths to correct the problem. How Chaddock could round the tips of his home made milling cutters of 1/10th of an inch in diameter- but ironically wasn't able to re-sharpen them. I have a Mark1 with all the gadgets.
Tom Walshaw writing as a retired lecturer in engineering and as Tubal Cain was aware of the problem and his solution was to 'stone; the extreme tips'.
Clearly, the treatment of milling cutters SHOULD follow what we do with lathe tools and round that little sharp end. Well, I have a Kennet designed by? but sold by Model Engineering Services and owned by Ivan Law-the boiler man and possibly Arnold Throp of Dore Engineering and author of Vertical Milling in the Home Workshop. No mention of 'rounding off'. In fact Arnold Throp was questioned why at a SME  demonstration why he was'nt sharpening tools on his Quorn. Yes, It was I! The Quorn simply took too long to set up. He's made one- incidentally!
I have a Stent- oddly a fabricated one. Is there a gadget to do  what is claimed possible.  Perhaps think again- it doesn't happen.
So, again in the Home Workshop, what does? Possibly a modification to the replacement of the Kennet by the Worden Mk3 does. I'm still on with mine. Now the Mk3 Quorn comes in at over. £600 for the kit-- and not all the gubbins to make the thing and even then it is not complete because it needs a ER32 collet set with a 25mm shaft and the 2 preceding models are planed for 1".
In addition,  I have a Chinese Deckel clone-- without the pivot point to 'round off. So I amd other withthat model will have-- to GUESS.
As you will see, I was being utterly practical and kept theory and guessing and -err fiction for another post

Cheers

N


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## Chiptosser (Nov 28, 2020)

Slot Drill,   Thats a new one to me.
From the definition of a slot drill, what I was able to find,  sounds like something to use in wood.
I have only been in this hobby cense 1972 !  Must be a regional phrase or trade specific?

I have mainly used drill bits squared off to suit the need of a flat bottom hole as big as 3".
For small flat bottom holes, I usually like to use the mill for rigidity.
 For larger pieces I will use the drill press because of its large table.  I will use up to .500 diameter modified endmills, because of chuck capacity, and flat bottom drills.   

 Now remenber, you will want to run these flat bottom tools at a slower speed!  They are more likly to cause chatter.  You have more surface contact and because of the geometry.

You can dub the outer edges of the drill or endmill, so that the edges do not cut or dig in to the side of the hole.

I have used end mills to do this also. Now, granted, I would not us a endmill with an inch of flutes sticking out, unless you obsolutly had to.     I would cut the end of a mill of to a short stub and let the shank guide throught the hole. Two flute , or four,  depends on the depth diameter ect. 

I have used Deckel grinders to make nice D shaped tools and ground radius's on the corners of drill bits, if you have that need, these I only use in the mill.

I grind most one off tools for this pupose (drills, mills) by hand, on the pedestal grinder and touch up on a diamond wheel or on the surface grinder with a indexer if needed.

A nice tool grinder over here in the USA, is a Darex tool cutter.  They are becoming very inexpensive.
They have a air spindle for the tool collet , uses 5c collets. very user friendly. 

Those of you who have not used, operated, CNC equipment have not been introduced to some of the newer end mills,  Yes, there are many center cutting endmills availiable.   Just make what you need, experiment!


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## goldstar31 (Nov 28, 2020)

A slot drill is a two cutting edged bit that surprisingly-- cuts slots.

A mill drill in the same task will probably cut oversize due to 'cutter flutter'

Next?


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## Chiptosser (Nov 28, 2020)

So,  you are calling a two fluted endmill, a slot drill?


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## Ramon (Nov 28, 2020)

Chiptosser said:


> Slot Drill, Thats a new one to me.
> From the definition of a slot drill, what I was able to find, sounds like something to use in wood.
> I have only been in this hobby cense 1972 ! Must be a regional phrase or trade specific?



Me too 'CT' - first thing I learnt though was the difference between a slot drill to an endmill - as Goldstar says the clue is in the name but like so many attributions possibly only on this side of the pond 

and as already said - taking the corners of a FB drill helps prevent potential scoring.

I'm sure you would agree though access to work funded equipment is a long way off to whats available to most in a home developed workshop.

PS Yes two flute = slot drill.

Tug


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## Chiptosser (Nov 28, 2020)

Mill drill???


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## goldstar31 (Nov 28, 2020)

But a slot drill has one flute ( Cutting edge) longer than the opposite one


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## Chiptosser (Nov 28, 2020)

Must have a specific application, material type use. ?  I have never seen one.


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## mu38&Bg# (Nov 28, 2020)

I'm am so surprised at how often this comes up, and that the understanding of terminology has somehow still not crossed the pond in either direction. 

A slot drill is a center cutting endmill. That is all. We do not call them slot drills here. I've nver seen a 2 or 3 flute end mill that wasn't center cutting. I've never seen a non center cutting (true) endmill other than the ancient stuff acquired in drawers of retired machinists tool boxes. And those were only 1/2" and larger.

Of course, if you look at modern tooling you'll find stuff that isn't center cutting, inserted and not, which requires a ramp tool path to cut axially.


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## photopro (Nov 28, 2020)

Richard Carlstedt said:


> Be aware that center cutting endmills have a  1 - 2 degree relief ground in the flutes which
> means that it leaves a convex , not flat, surface at the bottom of the hole.
> This means a 1/4 " diameter hole may have a .001 crown at the bottom - not flat, but not noticeable either
> Rich


That makes a fairly good seat for a ball if you are making a check valve.  If I don't feel like grinding a single lip cutter for the job, I will use an end mill for this.
Doug


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## Chiptosser (Nov 28, 2020)

Today at 8:29 AM
Add bookmark
#20
But a slot drill has one flute ( Cutting edge) longer than the opposite one

This is very un-clear!


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## Ken I (Nov 28, 2020)

O.K. A picture 1000 words etc.etc.






As I have always known it :-
#1, 2 & 3) are a 2 flute, 3 flute and 4 flute (resp.) slot drills - they can be run back and forward in a blind slot (like a Pratt & Whitney keyway slot) and at the end of each run you can plunge down axis to your next depth.

#4 is a 4 flute end mill which cannot be plunged down axis - you can only mill "passing through" type slots. There is no relief on the hole in the middle - you can plunge only microns before problems set in - so you don't mill blind slots with this.

#5 is a hand sharpened flat bottomed drill c/w split point.

#6 is a HSS "Bullet Point Pilot Drill" touted for rapid drilling in wood but makes an excellent drill for counterbored holes - only contrary to normal practice you drill the counterbore first - and follow with the clearance drill on the pre-drilled pilot hole.
You even get these in high Cobalt for use on stainless.

Regards, Ken


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## Charles Lamont (Nov 28, 2020)

When cutting a groove, or into a corner, any end milling cutter tends to pull to one side as a reaction to the cutting forces. With a two flute cutter, at the point in its rotation where the flutes are lined up at right angles to the direction of feed, there is no lateral reaction force, and this means that it will cut a slot pretty much the nominal diameter of the cutter even with a heavy cut. That is why it is called a slot drill. Cutters with more than two flutes will be subject to lateral forces throughout the rotation and will therefore cut a slot accurate in neither width nor position (although they are generally good enough if used delicately).


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## goldstar31 (Nov 29, 2020)

As a follow up to what. is a most. informative discussion, may I ask how one- in the restive confines of the amateur's workshop ACTUALLY round the corners of their own worn mill and end mills?
 I've researched what must be an inordinate amount of comment and some scant information of how it is done
As a non- engineer/ machinist--
Thank you


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## jack620 (Nov 29, 2020)

Chiptosser said:


> But a slot drill has one flute ( Cutting edge) longer than the opposite one
> 
> This is very un-clear!



This is a 16mm Presto brand slot drill. One cutting edge is 6.7mm long, the other is 8.2mm long. The longer edge passes through the centre of the cutter (i.e it's longer than half the diameter), so there's no "dead zone".


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## deverett (Nov 29, 2020)

goldstar31 said:


> As a follow up to what. is a most. informative discussion, may I ask how one- in the restive confines of the amateur's workshop ACTUALLY round the corners of their own worn mill and end mills?
> I've researched what must be an inordinate amount of comment and some scant information of how it is done
> As a non- engineer/ machinist--
> Thank you


Being  a metal butcher of the lowest order, when my end mills get a 'bit' worn, in other words just scratch the metal instead of cutting, I take a diamond file and just round off the blunt bit.  Brutal, I know, un-scientific, I know, usually different amounts get taken off the cutting edges and different radii result, but hey what, for a butcher it suffices for a while until I put hand in pocket and get a new cutter.

Dave
The Emerald Isle


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## Chiptosser (Nov 29, 2020)

I have hand stoned the edges of end mills and flat bottom drills to get a radius when needed.
That is the easiest way that I have found to do it. 
 Us a hard stone.  Use your radius gages, and blueing.

Now that I have seen a picture of the long sided cutting lip on the mills you are talking about, I do recall  seeing them and using them. Seems to me Weldon made some in the past. 
As I remember, they are an ; uneven cutting, unbalanced load when trying to do plunge cutting. 
Another way to discribe it is ; they liked to walk around.


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## goldstar31 (Nov 29, 2020)

Chiptosser said:


> Another way to discribe it is ; they liked to walk around.
> [/QUOT
> As Char les Lamont says and me  in my earlier remarks, it is the slot drills that are accurate whilst the end mills suffer 'cutter flutter'
> 
> ...


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## Chiptosser (Nov 29, 2020)

I am not guessing!  What happens with a drill when the the cutting edges are not equal?
It will drill a larger diameter hole, same with a endmill when plunging, as stated earlier.
If you gotem use em!
  This is the experince that I remember having while using them.         Out of quriosity,  I have been looking for a vendor that still sells them and doing online inquires I am not finding any listings over here.  I found old stock but nothing new.


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## goldstar31 (Nov 29, 2020)

My Guide and Comforter- in all things model engineering is in George Thomas's Model Engineer's Workshop Manual.  I have, as I said earlier, a number of tool and cutter grinders- some bought,, some made.  I can only suggest that  set up a slot drill and perhaps grind it yourself and come back with your own findings. 
Harking back to happier days, I have been known to bore the vertual limit( 13 inches) perfectly parallel  and to size down to an 1/8th of an inch in Africal Blackwood using nothing more than a sort of D bit fashined in silver steel( your keysteel and tempered with sticking it red hot into an old potao.
Importantly, I am not alone in doing such things. I used the tailstock on a somewhat rickety old Myford lathe.

The shepherd's who were pipe makers of Northumbrian Small Pipes( Bag Pipes) had far less equipment and sharpened things- like my father did- on  sandstone window sill.

Now I'm over 90, crippled  partially blind- sorry!


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## goldstar31 (Nov 29, 2020)

I am a somewhat weary old man and was having a break in these unfortunate proceedings and was listening to Emma Johnson playing a Peter Eaton Bflat clarinet( My daughter has a better one!) and note tha the tome holes werre not merely drilled but 'undercut'. You don't buy under cutting tools in the shops!
I mentioned GHT earlier and in his 2nd book 'Workshops Techniques' he describes the making of what he called a Small Versatile Dividing head- with a one hole plate and TWO Acme threads but to get the holding down bolts done he actually made an inverted cutter out of carbon steel hardened and tempered. And as I am NOT an engineer, never was- made one. I was a retired bean counter who has now been retired than I never needed to work. So it can be done, thousands of other model engineers with similar moderate skills have done it-- but I'm not weary- I'm tired now. Sorry


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## Ken I (Nov 29, 2020)

Chiptosser said:


> What happens with a drill when the the cutting edges are not equal?
> It will drill a larger diameter hole


Yes with a 118° drillpoint - not so with a flat pointed stubby slot drill (depending on how rigid your machinery is).

I have used the unequal grind of a drill point to deliberately drill an oversize hole - a Ø7.1 from a Ø7.0 drill for use with a rotary hexagonal broach.

A word of caution it will also drill bell bottomed - the diameter gets bigger as you go deeper - surprisingly so if you overdo the unequal.

Regards, Ken


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## Ramon (Nov 29, 2020)

Its a well known trick to grind a drill slightly offcentre when drilling drawn Phosphor Bronze to prevent the material grabbing the drill - a very difficult material to drill even with extreme care and even then it does not always work - as below. Step drilling isn't the answer in this material either. Heat builds up extremely rapidly and can result in very firmly stuck drills or reamers. Lots of coolant and slow progress is about the only road to take

This one, a ground off centre one too, took hold so quick it snapped before I could even react.





I round off worn cutters (and not so worn if I want an unimportant radius) free hand on the off hand grinder. I use the corner of the wheel and offer the corner of each flute to it in turn drawing the cutter from each side of the wheel corner (which has a radius on it from use anyway)  and holding it such to create the cutting angle. Only thing to watch out for is not to grind the front edge of the flute below which is hidden from view. There are quite a few such modified cutters sitting in a tin - a useful technique to acquire. You will only achieve that with practice though so give it a go - lets face it if the cutter isn't working well it's buggered anyway you can't make it worse by trying   

Tug


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## Ken I (Nov 29, 2020)

Tug, Best way around "snatching" is to grind the drill to zero or negative rake.
You only have to do just a small flat on the cutting edge - not more than your feed rate will stop "snatching" dead in its tracks.




Unless you intend to keep the drill in this configuration, a small flat means less regrinding to get it back to normal.
Regards, Ken


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## goldstar31 (Nov 29, 2020)

I read up the advert for the Acute Tool Grinding System which originates from  Eccentric Engineering- an Australian firm but  with a family member as an agent in the UK.
 In Pommie Bastard' prices, the drawings are only £20 plus postage and whilst a completed tool and a kit are available,  apart from a few Bristol clamps( or home made ones) can be constructed from little more than one's scrap box.
What is important is an excellent series of U Tube articles describing clearly the construction but it follows with how to grind a conventional lathe tool but, importantly here, how to completely grind a two flank end mill.  It assumes that one has a  double ended grinder with a CBN wheel on one end and a white aluminium oxide wheel at the other.
I have no financial interst in the company but would mention having bought the plans and a kit of parts.
To avoid further questions, it is not a tool which will 'do everything' but seemingly will perform adequately to saisfy the normal requirements of the home model maker.
As my sonn is also intersted, a completed tool has been ordered and perhaps it will  arrive for Christmas.
As I have intimated before, I have an ancient  Potts vertical slide with  a division plate and a No2MT spindle with a Myford threaded nose.  To stock up dwindling stocks of metal, I  have taken delivered of what can only be described as a heap of scrap metal offcuts- and will have a go to see whether with a few nutsand bolts, a decent tool and cutter can be made. 

It all should solve the problems of the impecunious as well.

Norman


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## Ramon (Nov 29, 2020)

Hi Ken - thanks for your thoughts but yes I am aware of reducing the cutting edge to negative rake when drilling 'brass' to prevent snatching and particular so when opening up previously drilled holes.
However there is a distinct difference from most brass that has that tendency to the drawn phoshor bronze referred to above. This material gets hot extremely quickly - even as said with a freshly ground drill and with a degree of offset. This doesn't snatch like brass but somehow rapidly closes on the drill or reamer in very quick order. I fear if one was to use a negative raked tool on this it would exacerbate the situation far more than resolve it.

Drawn bronze is the 'pink' or coppery colour not the yellow type. Once you have experienced a drill getting stuck in it you'll know  

Regards - Tug


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## John Antliff (Nov 29, 2020)

I so agree with Ramon - normally a hole in a piece of metal expands i.e. a 0.25 diameter hole becomes bigger as the heat builds up.  However in bronze it seems to contract because if you don't lubricate and suppress heat generation IT WILL GRAB and break your drill.   I haven't found end mill plunging causing the same distress but I'm guessing that end mills "wander" around resulting in more clearance.


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## clockworkcheval (Nov 30, 2020)

On off-center grinding drills: the old hands in my first machine shop would do it for intermediate sizes. For instance if you need a 10,3 mm diameter hole, and you don't have a 10,3 mm drill, you take a 10 mm diameter drill and grind it 0,15 mm off-center. I have never become good at replicating it with the same precision as the old hands.


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## Charles Lamont (Nov 30, 2020)

If you heat drawn phosphor bronze up to dull red and let it cool it will alter the grain structure to something more similar to a cast bronze. I have found it much easier to drill after this treatment. It also improves its bearing properties. It is a while since I needed to do this and I can't remember if I quenched it or not. Heating to red is highly unscientific anyway, it probably anneals at a lower temperature, but I have never bothered to find out.


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## Ken I (Nov 30, 2020)

Another problem I have experienced with bronze bar - is a result of its origins as a spun cast rod - it can have a corkscrewed central grain which leads the drill askew.
The deeper you drill the more it binds up on your drill. (The drill is trying to drill a corkscrewed hole.)
You can't see it but you can generally hear the screaming.
Annealing can greatly reduce this.
Similar problems with spun cast cast-iron.
Regards, Ken


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## Ramon (Nov 30, 2020)

Charles 
I have never given thought to 'heat treat' it first. That's a thought for the future so will try heating the end of a bar sometime to see if that improves matters. Thanks for the tip.

Ken 
There is a distinct machining difference between drawn and cast bronze. I use the latter a lot and only use the drawn when needs matter.
Drawn bronze machines in all other aspects with relative ease but you do need very sharp tools. It is it's ability to generate heat so quickly that makes this different from the cast bronze which is lovely stuff to work with.

Regards - Tug


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## Peter Twissell (Nov 30, 2020)

I suspect the issue with phosphor bronze is that it heats locally at the cutting edge, then cools rapidly, so a 1/4" hole at the cutting edge becomes less than 1/4" just behind the cut, grabbing the lands of the drill.


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## Charles Lamont (Nov 30, 2020)

Peter Twissell said:


> I suspect the issue with phosphor bronze is that it heats locally at the cutting edge, then cools rapidly, so a 1/4" hole at the cutting edge becomes less than 1/4" just behind the cut, grabbing the lands of the drill.


I think that might be the wrong end of a chicken and egg argument. As I understand it (which is not well)  the bar contracts as a result of releasing compressive stress in the bar.


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## L98fiero (Nov 30, 2020)

Ramon said:


> Drawn bronze is the 'pink' or coppery colour not the yellow type. Once you have experienced a drill getting stuck in it you'll know


Aluminum bronze is the same, I've had to drill 3/16 hole 6" deep in the stuff and can confirm that 'dubbing' like Ken I described isn't going to work where grinding one lip longer does.


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## Ramon (Nov 30, 2020)

I'm not sure what actually is the cause of this particular phenomenon with this material but I've been aware of it for many years. Just this morning I have experienced it using a 3.8 drill but not to the extent as the previous photo.  It's as if the hole drilled is _microscopically_ 'tapered' as the further in the drill the more difficult it is to withdraw. Heat is without doubt a major factor. The heat generated can be easily seen increasing as any oil/lubricant soon begins to smoke!  A 4mm reamer however followed without issue  

It is 'get roundable' but something to be aware of. When making the bushes for I/C conrods I always bore it to size - bore first, OD second.

I haven't machined aluminium bronze L98 but do know of it's difficult machining properties. That's a deep hole at the best of times. I think I may have a piece of something that may be similar under the bench - to all intents unworkable on my home kit.

Colphos of course is free cutting and a different matter.

Tug


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## L98fiero (Nov 30, 2020)

Ramon said:


> It's as if the hole drilled is _microscopically_ 'tapered' as the further in the drill the more difficult it is to withdraw. Heat is without doubt a major factor. The heat generated can be easily seen increasing as any oil/lubricant soon begins to smoke!


I'm not sure what the reason is but suspect that it's a combination of the tip of the drill expanding and the hole size decreasing because of thermal expansion, the hole would normally get larger but my experience is that if the part's significantly larger than the hole it decreases in size. If you're quick and careful sometimes you can get a little farther by getting more coolant in the hole but once the hole shrinks again the drill won't bring it back to size either, at least with extrusion cast aluminum bronze. I've not had much luck using oil for this.


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## Ken I (Nov 30, 2020)

The problem with aluminium bronze (amongst other materials) is work hardening - if you don't have the power or rigidity to keep cutting "under" the hardened skin you are generating - especially drilling - then the cutting edge goes real quick, followed by the corners, then the flute lands and you end up trying to drill with what has become a tapered drill in short order.
The odd length lip grind does help. I wouldn't "dob" the edge on AllyBronze.
Regards, Ken


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## goldstar31 (Dec 1, 2020)

deleted

Nornan


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## goldstar31 (Dec 1, 2020)

Deleted

Norman


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## Steamchick (Dec 1, 2020)

Charles Lamont said:


> If you heat drawn phosphor bronze up to dull red and let it cool it will alter the grain structure to something more similar to a cast bronze. I have found it much easier to drill after this treatment. It also improves its bearing properties. It is a while since I needed to do this and I can't remember if I quenched it or not. Heating to red is highly unscientific anyway, it probably anneals at a lower temperature, but I have never bothered to find out.


I agree Charles. Copper and alloys change state at around (or just below) a "dull red heat" - NO quenching required. Actually, as the "colour" is directly related to temperature, especially tempering colours, it isn't that unscientific, just a "large tolerance" of judgment. And it works and is simple... Technology that has been around since... Hmmmm, maybe the Bronze age, isn't that unreliable so should still work today.

Ken 1, Cheval, Peter T, 'n all - Thanks for all the advice - I had never given it much thought myself, but have learned a lot from this discussion. I have experienced the "binding" when drilling bronze... so I'll try "home hand-ground" drills in future instead of "Factory new" precision-ground drills! Maybe my drill-sharpening imperfections are the same as the off-set ground drills? Gudonya!
K2


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## teeleevs (Dec 1, 2020)

Thanks for all the explanations on this post, I picked up some chunks of brassy looking 2 inch bar, about 30 years ago, probably boat prop shaft, it will take front and sides off a parting blade.


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## L98fiero (Dec 1, 2020)

teeleevs said:


> Thanks for all the explanations on this post, I picked up some chunks of brassy looking 2 inch bar, about 30 years ago, probably boat prop shaft, it will take front and sides off a parting blade.


If it is propeller shaft it's probably C46400 naval bronze/Tobin bronze, machinability rating is 30% of free machining brass. Turn it slow, use a sharp tool with no more than 5% top rake and don't let it rub or it will work harden. One cutting edge longer than the other for deep holes and don't dub drill cutting edges, that's for free machining brass.


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## Steamchick (Dec 2, 2020)

Fascinating.... But Gentlemen, one needs a good grounding in Jargon to appreciate this one. The use of different names is confusing me a bit...? But I am an amateur, so please correct me where I am wrong?
I understand a "slot drill" to be a type of milling cutter - not a drill at all - probably 2 flute, without any end cutting face? And I thought it has sharp corners for making a sharp-cornered bottom to the slot? Or is this a "Side cutter"? A "more normal" twist drill maximises the swarf-clearance space, and uses the self-centring of the cutting tapered-end (118 degrees or whatever) to ensure only end thrust on the drill - effectively supported from bending by the material around the hole. Drills are notoriously bendy so should never be used for any side thrust - Or so I was taught? But the "slot drill" or "side cutting Mill" (correct jargon please?) minimises this side relief, as the swarf clears away on the non-cutting side of the cutting motion. The centre metal of a slot-drill is as large as practical for stiffness to overcome the bending of side thrust, with minimal swarf relief slots. The end face is simply relieved as it effectively never cuts with the side-motion (perpendicular to the axis of rotation) from the traverse of the metal past the tool. I have some with helical side cutting edges and some with straight cutting edges. Please can to help me by explaining "which" one is used "when"?
End mills, as earlier explained by a few of you, can make flat-bottomed holes - as I (and many other amateurs?) will have used them, but we all will have learned that they can wander unless introduced into a previously drilled starter hole. And they do clog easily as the swarf relief is not as large as a twist drill. I understand that end-mills should be used to make blind-ended slots, where you need the end-milling face to cut fresh metal before the side motion can be used to make the slot. Please teach me the correct application - as "self-taught is worth naught!" There seems to be some differences of opinion in the thread, that conflict with some contributors' ideas? But here (this thread) we amateurs (like me) need a clear advice on "when to use what" from experts. And not having a Tool and Cutter grinder, some of us buy second-hand or cheaper tools for the odd-job as most of our models are "one-offs" anyway. (Most of my tools are "hand-me-downs" and second-hand). Where we have a choice of tool, or want to buy the "correct one for purpose", we need to understand what the correct tool should be.
Thanks for your advice, we know it is all well intended,
K2


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## jack620 (Dec 2, 2020)

Steamchick said:


> I understand a "slot drill" to be a type of milling cutter - not a drill at all - probably 2 flute, without any end cutting face?



I posted a picture of a slot drill earlier. The box is labelled “slotdrill”. It was made in the UK, so the terminology is native to your country. Yes, it is a two-flute milling cutter. It DOES have an end cutting face, so it can be plunged into the workpiece.

Can we put this to bed now?


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## Ramon (Dec 2, 2020)

K2, Hi

I began as an amateur in 1972 but trained and earnt a living by machining from 1980 so have seen both sides and understand your concern.

Today with the advent of CNC and absolutely incredible machining centres machining has moved on a pace since my day not only in the machines but in the tooling too.

However - fundementally you can only cut on a mill with two basic types of cutter - a face mill or vertical tooling such as an end mill. What they are made of and whether they feature inserts is secondary - the function is the same.

I can't speak for outside of the UK but there are (were) two basic types of 'vertical' cutter  - a Slot Drill and an End Mill. Usually, though not always, the slot drill has two flutes and can cut on it's end face across the full diameter. As has already been explained one flute is ground to the centre point to enable this to happen. As designed, technically,  it can be plunged into the metal as deep as the flutes allow and can then cut on the side to create a slot. If a cutter was to be used like this ie to it's full depth, then the slot would be roughed out in steps with a smaller one first  - the size cutter being used to finish.

An End Mill - despite its terminology is not designed to cut on its end! The flutes - usually four or more have their centre reileved on the end face. Any attempt to cut on the end quickly fills this relief with swarf so preventing any further penetration into the workpiece. An end mill is designed to cut on it's side and bottom edge but not for plunging.

Since the advent of CNC there are many variations of cutters now with multiple flutes and multiple purposes. Many 'endmills' of varying flutes are now ground to enable plunge cutting. I guess the real culprits are people like myself who still use old terminology as opposed to say "use a three flute end cutting mill" etc.

So to sum up - you can, within the limits of it's length, clean up the corners of a predrilled blind hole with the same size end mill but can't deepen the hole by any degree.

You can do the same using a slot drill but this can be used to deepen the hole from solid.

Like many things there's a specific tool for the job but most times at home and sometimes in the working environment you have to compromise and get by using a tool not quite for it's intended purpose.

Hope that helps some

Tug


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## Ramon (Dec 2, 2020)

jack620 said:


> Can we put this to bed now?



Why? If someone isn't sure why not help them. Sorry Jack but that seems a bit dismissive to me.

It's a true old cliche - no question is stupid if you don't know the answer even if you can't see it the first time. 

Tug


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## Steamchick (Dec 2, 2020)

Thanks Jack620, and Tug, a whole page of discussion was hidden by the software so I missed a lot.
I just found Ken1 's pictures and explanation that were "hidden text" by the thread software... - so that answers some of my queries. See attached: 
So I now understand the "SLOT DRILL" to be an end mill that will drill because the cutting edges cross the centre of rotation. That means the "SIDE MILL" is the tool that I have without any end cutting faces. and "END MILL" is a tool that has some end milling faces, but no centre so cannot "DRILL" satisfactorily. 
Is that correct?
On Drills, in a factory where I was a Design Engineer (so "Knew nowt abaht owt" according to the shop floor) they hand-ground all the drills in the "heavy" machine shop (drills over 1/2") and the centre was always ground to a sharp point - 2-sided - like a wood-working bit centre. I understood this was so they could accurately position the large drilling machine over the centre pop for starting the hole, and because the centre core metal of the drill was so large they were actually grinding a small tapered drill in the centre to clear that metal before the main cutting edge with the swarf relief slots. - Similar principle to a bullet ended drill? Has anyone else experienced these? (Sorry to detract from Milling).
I do understand the difference between drilling and milling, as drilling is working ONLY on the end face = axial forces only, whereas Milling is essentially repeated scraping of a surface with the side of a rotating tool - thus applying severe bending forces to the mill, if not supported at both ends. Therefore the strength of the tool to resist bending is paramount with Mills, whereas the swarf clearance path is a dominant factor in grinding away most of the core of drills. 
I think Ramon summed-up my confusion with his explanation:  "An End Mill - despite its terminology is not designed to cut on its end!  "
I'll say no more and just read more of this discussion.
K2


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## ALEX1952 (Dec 2, 2020)

In respect of drilling holes in bronze etc that tend to grab, it is entirely possible that the drill is at fault, if for arguments sake the drill is used mainly on steel or worse cast iron the cutting edge Dia. can be smaller than the flutes through wear, therefor exacerbating the problem of grab. I agree with comment 3 pages ago learn to flat bottom a drill, it will stay size as the previously drilled hole will act as a drill guide, it is also very cost effective.This method was, and maybe still is widely used in industry. a fixture with a bush to support the drill which if large would have a thinned point, followed by a flat bottom drill. You realy do need this skill otherwise how will you produce a falt bottom on a very deep hole, without special and very expensive tooling. I'll shut up now as I tend to waffle on.


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## Ramon (Dec 2, 2020)

Alex, this is a phemomena of the material - most definitely not the drill. Whilst I agree that a dull or poorly ground drill will not be ideal to say the least and really lead to difficulties anyone familiar with this material would always sharpen the drill before using - such is it's properties. I know for some sharpening a drill (by hand) is a skill they may not possess but it's one that anyone with an interest in model engineering should try to acquire. Just this afternoon I broke and resharpened a brand new 1.05 mm drill by hand. Was not as good as bought but it did continue to cut and get the job done.

This is definitely the one time a person can blame the material and not the tool   

Regards - Tug


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## ALEX1952 (Dec 3, 2020)

i WASN'T SAYING THE DRILL WAS BLUNT OR THE CHARACTERISTICS OF THE MATERIAL WAS NOT A FACTOR, THE POINT I WAS TRYING TO MAKE WAS THAT IT IS ENTIRELY POSSIBLE THAT THE DRILL DIA CAN BE SMALLER AT THE END THAN UP THE FLUTES, THEREFORE EXAGGERATING THE KNOWN CHARACTERISTIC OF THE MATERIAL BINDING,
Please excuse caps didn't realise untill the read through of my comment.


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## Engineeringtech (Dec 3, 2020)

I've been machining for a living here in the USA for 21 years, and haven't encountered the terminology "slot drill".  The cutting tool suppliers sell "endmills" and "center cutting endmills".  You use the latter if you're plunge cutting unless you're following a pilot hole.  And if you're expecting a fairly accurately sized hole or slot, you use a three or two flute cutter, and plenty of coolant or cold air else the chips don't  evacuated fast enough.  They pile up, prevent the removal of heat, and the hole is oversized.  I've never had any exposure to bronzes except phospher bronze springs which didn't require machining,  but I suspect plunging a center cutting endmill or slot drill at the correct rate to prevent work hardening and using plenty of coolant would help.


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## Steamchick (Dec 3, 2020)

Thanks Engtech... I think that has explained why 2-flutes or more flutes. 2=  Better swarf clearance? More flutes = more accurate diameter? ("Hole-following"... or stiffer?) -  but less swarf clearance? - Please correct me if I mis-understand this. 
Can you explain when to use helical flutes and when to use straight flutes? Thanks,
K2


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## Ramon (Dec 3, 2020)

Engtech ,K2 

Here is a link to Tracy Tools in the UK please note they list in the left hand menu 'Slot Drills' and 'EndMills' as two separate items. Tracy Tools
A visit to either will confirm the visual difference. If you refer to my post #58 - I do say this terminology is correct for the UK and explain how they are used.

I guess after a long time of workshop machining with these two distinctly differing cutters maybe I need to start referring to them as 'centre cutting endmills' so that it makes sense to every one else.  Crescent and Monkey wrenches mean little over here though but a shifter and a pair of Stilsons certainly do  

Next thing someone is going to ask what HSS is - I put in slot drill in 'Google' and nothing but carbide comes up. Yep I'm a dynasaw all right but hanging on in there in true fashion 

Regards - Tug


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## Steamchick (Dec 3, 2020)

I never get tired of these discussions. But my car has tyred wheels.
Rainwater is collected in my butt, and traditionally, butter is churned in a butt. I could sit on one, but it isn't part of my body. The bottom of a hole is not the same as the hole in my bottom. If the bottom of a hole is not blind, is it a bottom hole? 
 I shall go and wash-up the pots and pans in the kitchen, before this is mis-understood. 
K2


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## Steamchick (Dec 3, 2020)

Sorry - mis-typed. Should have read... "if the bottom of a hole is not blind, is it a bottomless hole?"
K2


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## Ramon (Dec 3, 2020)

Well I'm pleased to hear you know your 'bottom' from your 'bottom'  K2

Keep smiling  

Tug


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## Steamchick (Dec 4, 2020)

Ramon said:


> Well I'm pleased to hear you know your 'bottom' from your 'bottom'  K2
> 
> Keep smiling
> 
> Tug


Sorry, I seem to have hit the "Bottom of the Butt" - or "Barrel" if you prefer - with these puns... No-one was meant to be the butt of my jokes. I am smiling, even if others are not. Life is too short to miss every happy moment or thought! My Grandfather was especially amused by puns, as I am. So happy thoughts abound. Sorry if you find it sad Norman, though you have seen and been in some situations that you may prefer not to remember, I guess. and have experienced a lot my life than I have - yet.
I'll go back in my corner and chuckle happily to myself.
K2


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## nealeb (Dec 4, 2020)

I gave up about the time I discovered that on one side of the pond you pay a bill with a cheque and on the other side, a check with a bill. 

I suspect that even in the UK these days, the term "slot drill" is used more amongst model engineers than industrial users, certainly going by the online tool suppliers and model engineering magazines (which is where a lot of model engineers learn and so tradition lives on). My understanding is that they are used for slotting as they have less tendency to cut oversize. With two flutes, as one edge is entering cut, the other is leaving and the sideways forces are balanced, so the cutter stays central to the slot. With four flutes ("end mill" in old speak) two opposite edges are doing that, but the "leading" cutting edge is moving sideways across the cut, thereby deflecting the cutter sideways and leading to an oversize slot. And a three-flute cutter? Search me!


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## Steamchick (Dec 4, 2020)

Hi Nealeb. What a concise explanation. Very clear to me. Can you explain why I have some helical cut end mills and slot-drills, and some straight cut? - Seems to me the straight cut may be to avoid any axial thrust that would occur with the helical cut - that could draw the cutter deeper than intended if there is any play in the Quill or column? (Depth of cut "Not locked")? I am just learning when to use which tool (where I have a choice in my limited collection). Also, I was taught to use an undersize tool, then finish to size (Gauge) where possible - as tools "never give a true size"... But I agree that "within tolerance" and for mass production to cut once with a true sized cutter is preferable.
Thanks.
K2


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## goldstar31 (Dec 4, 2020)

Well folks, as you will see-- I gave up literally in disgust at what was heading for pedantry and my suggestions of how to deal with 'holes of one form of metal another left me cold.  I was never an engineer and consequently never had the confines of having to earn a crust in front of a machine or whatever people here do.
As I explained I was sufficiently bright enough to retire at 55- whatever that I was doing and again sufficiently able to retire for longer than I ever worked.  For the last part of my so called working life, I made more money in my brief lunch break having found a slot that others didn't know how to fill.
This is what it is all about.  IAs Model engineering is only a hobby for me, it matters not whether I buy a milling cutter or buy a new one or regrind one- or simply go and say 'Bugger it, it is +3C outside and it is pissing down'  I've had9 illegally) a wonderful morning drinking coffee and tonight, like last Friday, another millionaire friend( Oh Yes) another millionaire friend that filled a slot or niche will start on a bottle of malt and how far down the bottle is a matter of pure conjecture.
OK, I'm an honest broker and suggested that for a very modest £10( a fraction of what we will sink tonight) and a heap of scrap, one could quite simply make a cutter grinder which would 'Do' drills of whatever one fancied-- and the whole thing was met with a  devastating lous silence.
So, quite frankly, my beliefs are such that I should also help mankind as well as family and friends- and in this case that I in what I regard a shortlife time feel that if help is ignore d, I don't want to wate my time or  theirs.

Looking at the topic, it has been dealt with with by people who sadly have had to continue to work.
Clearly, they have missed the slot that is actually available to all- if they can stop to see it. 
Somehow, I doubt that slots of whatever source here are the answer.
My thoughts before I go and enjoy what is left of my life. 
As you will perceive, I'm rather annoyed having wasted what I offered- freely and  for nothing.


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## L98fiero (Dec 4, 2020)

Steamchick said:


> Can you explain when to use helical flutes and when to use straight flutes?


About the only place to use a straight flute end mill is in reinforced plastic to prevent fraying.
As for drills, straight flute carbide drills are typically used for drilling hardened steel and chilled cast iron but they are also be used for a variety of non-ferrous materials including wood and laminates to produce clean walled holes without pulling through and to prevent 'grabbing' in brass. They're obviously not good at deep holes unless using high pressure coolant through the drill.
I've used a 3/32" HSS single flute, straight flute to drill 1" deep in aluminum. It was used as a gun drill so the hole would be accurately positioned on the far side and because of the straight flute they had to be started with a stub drill and then use 0.03 pecks with complete pull out each peck and lots of coolant.


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## Ramon (Dec 4, 2020)

Well we are all entitled to an opinion but I can't say I share yours Goldstar

Someone without the knowledge came on here to ask a basic question. As did some others I replied specifically to that question based on personal experience of being shown the technique some 40 years ago and in order to help that person. That lead as forum topics usually do to further discussion

To me that is what a forum is about - helping others where you can and accepting help from others when you need it. Disagreement is not about being disagreeble - well certainly not in my book.

I don't have millionare friends to share malt with but I do have malt to share - maybe we should take a closer look and consider the reason we're here - Home Model Engine Machining. Some will not have even made a wobbler - others will have just finished a radial - most will be somewhere in between.

Some will have no engineering skills or knowledge but are so very keen to acquire them - others will have more than enough of both, though, it has to be said, not always willing to share them. Those that do however - if their reason is the same as mine - is to help someone whenever they ask - if that's a crime then I apologise.

I too ceased working early and have enjoyed every day of it since. I approach 76 spending best part of the day most of the week in my shed working, believe it, or not on an actual engine (theres that reason again) and loving every minute of it. I'm quite happy to share some part of the day with others in a friendly exchange of views to further this outlook but not, it also has to be said, not if it promotes such churlishness 

Now, I'm off to the shed to work on that engine - with luck it will be finished in a week or so.

Stay safe and keep on smilin'   

Regards - Tug


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## Cogsy (Dec 4, 2020)

Steamchick said:


> I never get tired of these discussions. But my car has tyred wheels.
> Rainwater is collected in my butt, and traditionally, butter is churned in a butt. I could sit on one, but it isn't part of my body. The bottom of a hole is not the same as the hole in my bottom. If the bottom of a hole is not blind, is it a bottom hole?
> I shall go and wash-up the pots and pans in the kitchen, before this is mis-understood.
> K2



Well if you want to get really technical (and speak in the language of true geometry) a hole cannot have a 'bottom'. A drinking straw has only one hole and a drinking cup has none. If we drill or bore into a piece of material we don't make a hole unless we go all the way through. Language is weird...


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## goldstar31 (Dec 4, 2020)

There is an ld and accurate saying'Never look a gift horse in the mouth'. Studiously it is insulting not to acknowledge help from whatever source- and it hasn't happened. It costs little to say Thank you or indeed 'I don't agree or don't understand.

Over the years, and check my llikes, I have noted the horrendous number of number of people who have asked and left the site and worse still the valuable contributors who are no longer here anty more. 

It would seem that my point is borne out  by the loss of free help.

I recall the note that the late Don Ashton -author of valve gear definitive works on valve gear which he actually published at his own expense remarking somewhat bitterly that people were asking the same silly questions-- and getting the same silly answers. 
Don died recently and it took weeks for someone to acknowledge his contribution to model engineering though NOT an engineer . He repaired musical instruments and wrote music.
He wrote music for my wife also sadly missed but Don and I were friends. Don was an unassuming  World Authority on many things. He would have wholly agreed but saddened by the fact that he got so little recognition from this forum.


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## Steamchick (Dec 4, 2020)

L98fiero said:


> About the only place to use a straight flute end mill is in reinforced plastic to prevent fraying.
> As for drills, straight flute carbide drills are typically used for drilling hardened steel and chilled cast iron but they are also be used for a variety of non-ferrous materials including wood and laminates to produce clean walled holes without pulling through and to prevent 'grabbing' in brass. They're obviously not good at deep holes unless using high pressure coolant through the drill.
> I've used a 3/32" HSS single flute, straight flute to drill 1" deep in aluminum. It was used as a gun drill so the hole would be accurately positioned on the far side and because of the straight flute they had to be started with a stub drill and then use 0.03 pecks with complete pull out each peck and lots of coolant.


Thanks Fiero for explaining that one.
K2


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## Steamchick (Dec 4, 2020)

Goldstar: I humbly apologise if I have offended you with my lack of knowledge, or daft comments, but having a lot of hand-me-down tools and second-hand tools when that was all I could afford, (re-ground under-size by the tool-maker who owned the shop), I have a variety of patterns of milling cutters without the knowledge to know when to use which type. This thread has helped greatly - including your contribution. For that I thank you all.
K2


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## goldstar31 (Dec 4, 2020)

Ken,

Beware of even well intentioned information. Many thousand engraving machines have been produced in England, in gernany and China as clones to make 'flat engraving cutters'  Amongst my assorted miscellany,  I have a 'Chinese'. It may well be capable of grinding lathe tools to a high degree of precision and can alter fluted tool blanks to twist drills, end drills, mill drills and whatever- in essence that is what it is-- and the original Deckels and Alexanders are or were astronomically priced, the Chines ones are only slightly less breathtaking. Reminds me that I could utilise a lot more 5C collets for mine.
thinks it is possible to buy a se t of plans  for an adequate  tool and cutter grinder using the scrap box for less than ONE 5C collet

best Wishes

Norman


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## Steamchick (Dec 5, 2020)

goldstar31 said:


> Ken,
> 
> Beware of even well intentioned information. Many thousand engraving machines have been produced in England, in gernany and China as clones to make 'flat engraving cutters'  Amongst my assorted miscellany,  I have a 'Chinese'. It may well be capable of grinding lathe tools to a high degree of precision and can alter fluted tool blanks to twist drills, end drills, mill drills and whatever- in essence that is what it is-- and the original Deckels and Alexanders are or were astronomically priced, the Chines ones are only slightly less breathtaking. Reminds me that I could utilise a lot more 5C collets for mine.
> thinks it is possible to buy a se t of plans  for an adequate  tool and cutter grinder using the scrap box for less than ONE 5C collet
> ...


Thanks Norman. Maybe I'll stick to my hand expertise for lathe tools and drills for now. - I don't bother re-sharpening drills below 35p each - Packs of 10 x 0.5mm "jobber drills" for a £1 last about 5 to 7 years.... and the sub- "half-mil" sizes I buy for drilling jets are too femur to touch, so at less than 35p each I buy a pack of 10 from China every few years.
I don't do a lot of milling - haven't bought a new tool in a decade or so - or sharpened one ever! I just like to learn how to select and use them properly, rather than just "having a go". Hence my interest in this thread.
Look after yourself. 
Ken


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## goldstar31 (Dec 5, 2020)

following yesterday's 'Thundersnow' and a lot of surprises, I got a update from the Quorn Owners' group.  some body has actually demonstrated how  to 'round off the corners of a lathe tool- but on na Quorn and then mechanically and with fine precision  Standing astride the two camps, I must caution that Quorns come in as kits of well over £600 to which must be added additional tool holding of an ER32 collet holder and a box of collets. All this requires additional cost and a lot of time to make the desirable jigs if not already in the builder's possession. Totting it all up requires a deep breath.
 Even then  I doubt that it will re=sharpen your little Chinese drills.  Well the Quorn designer could make 1/10th diameter drills but couldn't re-sharpen them. 
Whatever way one thinks, ending up with a Quorn is an expensive time consuming labour of love- or worse.
So for a tenner or so and a cheap Aldi/Lidl grinder or so and scrap steel, and sayb a week's work , people can have remarkable precision. Not only cheap precision but going through a learning pattern and having cheap hss tools to the configuration  to suit the builder's way of working.

It's all a lead balloon and perhaps red rags to Andalusian bulls!. 
Whilst 'pricing'  the tool and cutter  costs, I espied a New thingy from Hemmingwaykits n a saddle mounted pillar to take a small versatile dividing head. It suggests  the ability to own an amazing bit of kit.  I saw the principle decades ago- and next week - deliveries etc  helping,  I should have the prototype. What is odd is that Hemmingwaykits has the drawings and mould as well.
Meantime, it is all worth future planning.

So best wishes for the future

norman


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## willray (Dec 5, 2020)

nealeb said:


> ... With two flutes, as one edge is entering cut, the other is leaving and the sideways forces are balanced, so the cutter stays central to the slot.



My apologies - people keep saying this, but I seem to be too dense to completely understand.

It would seem to me, that with a 2-flute (well, 2 cutting edge) cutter, you get constantly oscillating sideways forces.   When the cutting edges are "across" the slot - one entering the material and one leaving - you have net zero sideways force on the cutter.  When the cutting edges are "along" the slot - one at the leading edge of the slot cutting, the other in free air in the already cleared slot - you have a significant sideways force applied to the cutter.

With a 4-flute cutter, you constantly have at least one cutting edge engaged in the material, producing a more-constant side thrust.

Since many have said that the 2-flute cutters cut more true to width, I have to believe that this works in practice, but I'm failing to understand how constantly oscillating side forces produce a more-accurate cut than constantly-present forces.

Thanks for any illumination shed into my darkness!
Will


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## Ramon (Dec 5, 2020)

Will, 

The forces at play are just as you describe. Although it may seem unlikely it is a fact that slot drills do cut a more accurate slot (and very close to the cutter's diameter). If a four flute endmill is used to 'size' a slot to the cutter's diameter, even if roughed out beforehand, it will produce a slightly wider slot than expected.

If a _very_ accurate slot width is required it is best to be done with a slightly undersize cutter, moving each side to establish the width.

Regards - Tug


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## chrsbrbnk (Dec 5, 2020)

The core web tends to be more robust on a four flute  than a  2flute or 3flute   but at the sacrifice of chip clearance.  and it is possible to do an angled plunge feed or spiral plunge feed with a   non center cutting endmill if the feed angle is slight enough  everyone's done it.  with really rigid machines like big cnc's there doesn't seem to be much of an advantage if any in using 2 flute cutters over 4 flute as far as cutter cut size accuracy , actually recall anyone going for a two flute for sizing  reasons.  most often it was use a 2 flute for the rough plunge than shift to 4 flute  for finish and size accuracy.    the results of people getting more accurate size with a 2 flute may have more to do with their particular  machines resonances and stiffness from cutter load. other wise as far as accurate size cut comparisons on equally sharp cutters in comparison with the cutters actual size  the stiffer cutter will win  and that relates to the web thickness  and that usually means shallower flutes  .   more flutes do mean more cutter pressure from all the engaged cut surfaces  so the stiffness of the machine  starts to really matter, but there is a benefit from the more constant pressure of multi flute cutters and hence less vibration


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## William May (Dec 5, 2020)

If you are having trouble machining bronze, take heart!
I just finished reading "Ford Methods and The Ford Shops" which goes into extreme detail on the procedures Ford used in producing cars.
It was written in 1914/1915, just as Ford was converting to a moving assembly line. (Not just for car assembly, but for ALL the parts they made.)
One of the things they cover is the broaches they used for bronze bushing manufacture. THEY NEEDED SHARPENING EVERY 100 PIECES. The floor hands kept between 16 and 24 reserve cutters at the machine tool, and switched them out as needed.


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## Badhippie (Dec 5, 2020)

I happened to cut or broach keyways in shafts and hubs on a daily base. In metals such as Titanium and Zirconium and Stainless and Hastelloy. And use 2 flute or keyway cutters they are made for cutting keyways to very close tolerance they are square cut. One thing everyone forgets is the more flutes a cutter has the weaker the cutter becomes so in turn the more flex you have. Now you can counter that and say why do you get a better finish with a higher flute count if it has more flex. Well that’s a direct result of the amount of cutting edges peeling away the metal. But above all of this it comes down to something so simple. And that is speed vs feed vs doc and picking the right size cutter and the right cutter material and coating. 
remember you can polish a turd all day long and at the end of the day you’ll have a turd

Tom


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## Richard Carlstedt (Dec 5, 2020)

Fascinating thread here, a mixture of experiences , theory, humor and personal feelings. I will not address them all except to say that having a smile on one's face is better than a grimace and real experience is better than theory and most important for all is sharing information !. With over 62 years of machine shop experience , let me add a bit of information not discussed.
Yes, two flutes are better than four for slots because they allow chips to freely evacuate, but  I personally prefer three flute cutters as they give good chip flow and are stouter than  a two flute.  ALL  endmills....1, 2,3,4,5 flute  will deflect when pushed in a straight line. The harder you push (Feedrate and DOC) the more you will deflect.
Making a precision slot with a undersized endmill is all well and good, just make sure the size is sufficiently smaller to account for this deflection.
Another comment about straight flute versus helical flutes. Straight flutes do not exert   any axial forces , while positive  helix angles cause the cutter to be pulled out of the spindle. This may be fine on a CNC machine with stout tool holders and good bearings, but can mess up a home shop job that uses collets for holding the cutter .
"If" the cutter does not pull out, be assured that it is attempting to pull your work piece out of the vise !

Rich


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## Ramon (Dec 5, 2020)

Well I did say I was a dynasaw   

I'm speaking from a home workshop point of view based on working experience with non CNC machines. With the advent of CNC which after all from a production point of view is a relatively recent but incredible advance in machining techniques and particularly so in some home workshops.  I would agree that from that perspective things are mightily different but it's surprising how easy it is for some to forget about pre CNC and how short a time that was ago.

Machine rigidity is another matter altogether - if you've only worked modern machines it may be difficult to visualise how less sturdy machines can cope. Even the all encompassing Bridgeport has it's limits.

I programmed and worked a twenty tool Haas machining centre for my last three years or so (1999-2002) - if a slot had had to be done then it would not have been done with a single sized cutter but a tool path created to mill it to size, radius and all if it were a closed slot. Ramping using a conventionally ground end mill is a perfectly feasible action - very easy to accomplish on CNC and not that difficult on conventional machines either. That's a different process  however from direct plunging

Most, though not all of course, home workshop equipment is of a much lower 'grade' than that found in an average machine shop and even conventional kit in them is  (has?) dissapearing at a phenomenal rate. The last jobbing shop I worked at (which bought the Haas) had all conventional turret mills and lathes when I left - now there is nothing that isn't CNC.

I mentioned the fact that a Google search produced virtually all solid carbide cutters - having used them I am aware of the rigidity required in the machine and the tooling to use them to advantage but though I will turn to them to get over something hard if required I know the tooling that has done sterling service for many years on HSS would have a hard job being efficient.

All this is long way from my old Linley mill - still sound and accurate but made around 1940-1950 and using tooling that was readily available when I purchased it in the 1970s - I've never given it a thought before but I've just realised that I've been using that for longer than it was old when I bought it 

So, no I don't disagree but I do stand by my views that a slot drill is a slot drill and an end mill is another cutter all together but it's aimed firmly at those using, and sometimes learning to use, pretty basic kit in order to enjoy our hobby.

Regards to all - Tug


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## Charles Lamont (Dec 5, 2020)

willray said:


> It would seem to me, that with a 2-flute (well, 2 cutting edge) cutter, you get constantly oscillating sideways forces.   When the cutting edges are "across" the slot - one entering the material and one leaving - you have net zero sideways force on the cutter.  When the cutting edges are "along" the slot - one at the leading edge of the slot cutting, the other in free air in the already cleared slot - you have a significant sideways force applied to the cutter.
> 
> Thanks for any illumination shed into my darkness!


Will, you are right so far, but you seem to be missing the point that while one edge is cutting at the 'front' and is subject to lateral deflection, with a two lip cutter, there is no edge in a position be cutting into the side.


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## willray (Dec 5, 2020)

Charles Lamont said:


> Will, you are right so far, but you seem to be missing the point that while one edge is cutting at the 'front' and is subject to lateral deflection, with a two lip cutter, there is no edge in a position be cutting into the side.



ahhh - that may indeed be the lightbulb I am missing!  Thank You!
Will


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## BobsModels (Dec 5, 2020)

Just happened by this thread and thought I would share this with everyone.   Before I start, this narrative is going to show that we all may just over think some problems.   My 18 year old granddaughter (21 now) was building a Stirling engine.  She was in the shop making some parts and came over to me and asked if she could chop off a 3” piece of .500 6061 Al for a displacer piston.  I was busy on the Bridgeport and told yes that would work fine.   She was working on a Clausing 5904, with a DRO on it.   An hour later she brought the displacer piston over to me and asked how she could hold it so she could square off the cutoff pip on the end.   With a wall thickness of .010 she was concerned about crushing it if she put it in a 3 Jaw.    The displacer dimension is 1.122 long with an OD of .380.  It had a .360 ID hole 1.070 deep.  The drawing showed a flat bottom hole.  I looked at the part and asked - how did you do that?   Just for your general information she had been machining since she was 8 years old.  In teaching her and her sister I never ever told them something was difficult to machine, when they started out I would give them suggestions and  I just let them have at it.  Here is what she told me.  She faced off the end, turned the OD to .380, center drilled it with 118 degree spot drill I have, and drilled it out to 9/32 (I think) because she said she was going to use my .187 carbide boring bar  leaving some amount so she could flattened the bottom.  Then she took a .250 endmill and flattened the drilled bottom.   Next she took the boring bar and finished the ID.   She then moved the boring bar to the center and took a couple of cuts across the bottom until it was flat.  She zeroed the DRO, backed the boring bar out, and machined off the entrance until she was at 1.070.  I asked why she was so careful about the bottom being flat as it really did not need to be.  She told me the drawing showed it flat and I told her to always do what the drawings showed - so she made it flat!  I have no idea how she came up with that sequence, and after showing her how to cut off the pip the part was done.

To me the lesson *I learned from her was *– just make the part and move on.  Living 2 hours away she had a limited amount of time at grandpa’s house  (2 or 3 times a year) so she made the most of it when she was here.  See photo for more parts.

Bob

Displacer piston being epoxied to end cap and rod
using a arbor spacer to hold it upright






Other parts


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