# Let's talk drilling...



## HennieL (Apr 11, 2021)

What is your preferred method of drilling deep holes as accurately as possible using a lathe? I have been thinking about this for many years, trying to decide the "best" way to drill a reasonably large hole (say 16mm diameter...) for a depth of (say) 10 x diameter into steel. In your opinion (for hobbyists, and not using specialised through lubricated gun drills, etc.):

would it be better to drill a small diameter pilot hole (say 4mm dia.) as deep as it can go, and then only drilling once using the final size drill, or 
would it be better to use a succession of increasing sized drills (say 4mm, then 8mm, then 10mm, 12mm, 14mm and finally 16mm
Using the second method one would make chip evacuation easier, and put less strain on the drill (both helping to increase the accuracy of the hole), but each successive drill bit would be "guided" only on the outer rim of it's cutting edges, which would make it easier to go off track. The first method would guide over the drill bit's full cutting edges, thus keeping the drill centered, but would create a much larger amount of chips to be evacuated, which would tend to push the drill off center, thus requiring more "peck drilling"...

I normally use the first method, but would appreciate your comments on this. Also, please feel free to comment on any other method you use, and also on drill bit types, twist rates, using a drill chuck vs using Morse tapered drills mounted directly in the tailstock, etc. etc.

Thanks for your comments
Hennie


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## kwoodhands (Apr 11, 2021)

I use a spotting drill first. More accurate then a center drill. If the part is thin I drill with the largest drill after spotting drill. Thicker parts are bored with 1/4" drill and then the largest drill.
Too many variables to help with best results, depends on the material, hole size,  motor power, lubrication  etc.
I only have three MT shank drills but would use them exclusively if I owned more. I had problems with drills turning in a chuck, marring the shank and the drill sliding into the chuck. I bought a better chuck  and this problem went away. I use mostly wire gauge drills and buy them from McMaster Carr. I think Greenlee is the brand. Fractional drills are from Harbor Freight. I have 4 sets of the 1/16"/1/2" drills.
One set I modified for brass, the others I bought because for $10.00 a set it's hard to go wrong.
I found that these sets are more than adequate for general drilling in most metals.
mike


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## HennieL (Apr 12, 2021)

Thanks for your reply, Mike.


> I use a spotting drill first.


Yes. I omitted to state this, but I always start my drilling in the lathe with a center drill, as we call them, and then move to the small diameter drill (usually a 4mm short spiral "deep hole" drill), before drilling the large diameter hole. I also prefer to use my More taper shank drills, but only have a set ranging from 5mm to 16mm, in 1mm increments - would love to get some 0.5mm increments as well, but that's quite expensive to source in South Africa.

I would still love to hear more opinions on my original question - is it better (i.e. more accurate) to drill only a small pilot hole and then go directly to the final size drill, or is it more accurate to increase the hole size in small increments (of say 2mm per increment)?

Regards
Hennie


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## Vietti (Apr 12, 2021)

I like screw machine drills, have a set that goes 1/16 to 1/2.  They are stiffer than a jobber drill and depending on precision desired can be used without a center drill start.  Irritating that they cost more than jobber length and haven't found a source for good relatively inexpensive ones.

Sometimes I use a center cutting end mill to at least start or finish a hole where any wandering cannot be tolerated, beware they don't cut an exact size hole either.

John


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## kwoodhands (Apr 12, 2021)

HennieL said:


> Thanks for your reply, Mike.
> 
> Yes. I omitted to state this, but I always start my drilling in the lathe with a center drill, as we call them, and then move to the small diameter drill (usually a 4mm short spiral "deep hole" drill), before drilling the large diameter hole. I also prefer to use my More taper shank drills, but only have a set ranging from 5mm to 16mm, in 1mm increments - would love to get some 0.5mm increments as well, but that's quite expensive to source in South Africa.
> 
> ...



I happened to read an article this morning in one of my machining books that addresses this question in a way I have never heard of.  The author said to start with a large drill, then progressively smaller drills til the depth is reached.
Then install the size drill you want to finish with and bore the hole.
He said that this method leaves clearance for each successive drill and is best way to drill deep holes.
I will try this myself when I need to bore a deep hole.
Even though it may seem odd , I think it may be  the way to bore deep holes.
mike


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## clockworkcheval (Apr 13, 2021)

Kwoodhands is right in my opinion to start with a spotting drill rather than a center drill. A center drill prepares a hole for a center, thus has a top angle of 60 degrees and also makes a little top-pocket to protect the sharp point of the center. When you enter such a hole with a 118 degrees top angle drill this drill will hit the hole at the rim rather than in the center. And shapes never being ideal one cutting edge of the drill will hit the rim first and thus act as a temporary center of rotation till the other edge hits and takes over the role of center of rotation. Doing this in thin material nicely shows the resulting typical triangular hole. The small holes started with center drills are also triangular (or multi-angled), only so slight that it is not all that obvious. The spotting drill with a top angle of 120 degrees on the other hand gives a drill with a top angle of 118 degrees a well-centered start.
As you drill the hole the hole will deviate from the centerline by a-symmetric forces. The amount of deviation caused by an a-symmetric force increases with the length of the drill to the third power and decreases with the diameter of the drill to the fourth power. Thus if you compare a drill of diameter 16 mm sticking out 50 mm with a drill of 4 mm sticking out 100 mm the 4 mm drill will deviate (16/4) to the power 4 times (100/50) to the power 3 equalling a whopping 2048 times more.
For a long hole I suggest you start with a 120 degree spotting drill, then a 4 mm diameter drill to a depth of say 15-20 mm. If you now follow  with a 16 mm diameter drill it will nicely start at the center, follow the 4 mm diameter hole for the 15-20 mm pre-bore and further on be guided by its own 16 mm diameter hole. Starting with a short drill and exchanging it with longer drills as you get deeper will give you the best shot at drilling a long concentric hole. You need to retract the drill often to get rid of the chips. In short, a well-centered short pilot hole followed by a full size drill. The variation mentioned by Kwoodhands of using drills of decreasing diameters seems to me to lower the stiffness of the ever longer drills whilst not benefitting from the guidance of its own full size hole. For long holes the way you hold the drill whether by Morse cone or chuck is not relevant for the precision of the position of the tip of the drill - the tip will follow the centerhole first and after that the drill will be guided by its own bore.
Boring of course is the more precise option.


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## Peter Murphy (Apr 13, 2021)

HennieL said:


> Yes. I omitted to state this, but I always start my drilling in the lathe with a center drill, as we call them, and then move to the small diameter drill (usually a 4mm short spiral "deep hole" drill), before drilling the large diameter hole. I also prefer to use my More taper shank drills, but only have a set ranging from 5mm to 16mm, in 1mm increments - would love to get some 0.5mm increments as well, but that's quite expensive to source in South Africa.
> 
> I would still love to hear more opinions on my original question - is it better (i.e. more accurate) to drill only a small pilot hole and then go directly to the final size drill, or is it more accurate to increase the hole size in small increments (of say 2mm per increment)?
> 
> ...


Hi Hennie, a spotting drill is different to a centre drill. A centre drills cutting angle is ground to the correct angle to support a tailstock centre. A spotting drills cutting angle is ground to the correct angle to align a drill bit & will give you greater accuracy. I personally don't interchange them. When to Use a Spot Drill [ 7 Useful Tips and Techniques ] - CNCCookbook: Be A Better CNC'er
I do like that idea of starting with a larger bit (preferably an MT bit) & progressally stepping down in bit diameter as you go deeper, then go up in size & finally bore to finish. This would give you the most accuracy, so long as you have some small diameter long drill bits


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## Peter Murphy (Apr 13, 2021)

Hi Clockworkcheval, Fully agree with you & sorry for sort of repeating your post, we had a blackout here due to high winds & I was on my laptop with no internet. Your post appeared as I was posting when the power & internet came back on. Cheers Peter from OZ


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## ajoeiam (Apr 13, 2021)

Monsieur Clockworkcheval describes a technique that works reasonably and here is another - - - - especially useful when the resulting hole will be tapped. 

I never have had the fortune of using a spotting drill - - - was just one more tool and, well, that would have meant more cost and time for the boss so that didn't just fly very well. So - - - albeit I think using a spotting drill is likely more accurate this technique works well especially for tapped holes. 

1. hit the shaft end with a center drill
2. use a drill that is large enough to provide a divot that is large enough to be say 0.5mm or 1/64" larger in dia than either the thread OD or your finished 
    hole OD 
3. using an accurately sharpened drill start your hole - - - - starting hard and pushing strongly for at least 3 if not 5x D (diameter) 
4. spin that tailstock back and now start using a peck cycle
5. if you're only drilling to 7xD or you have a drill where the flutes are passing chips very well you might get to 10xD then #4 suffices
6. if, on the other hand you're drilling something like a grease hole that might be some 12 or even 20" long (its a bloody long bit!!!) I found using a shuttle kind 
    of drilling worked (with care). 
   This was peck once and maybe twice with a small amount of hand wheel back motion on the tailstock. Then after this very small number of 'pecks' unlock the 
   tailstock and drag the setup away from the piece. Found that moving the setup some 4 to 6 inches would shift the material down the flutes of the drill. Care 
   needs to be taken so that you don't really jam up the chips in the leading part of the drill. You might then need some serious pull to remove the setup. I would 
   think that balled tight enough and you just might have a drill bit welded into the material which will have a tendency to cause the surrounding air to change 
   hue - - - remember it seeming to take about half of forever but it does work. 
   To heavy a push on the drill cycle can cause the drill to wander and that makes hitting the center hole with the cross hole for the grease a bunch trickier. 

HTH


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## HennieL (Apr 14, 2021)

Peter Murphy said:


> Hi Hennie, a spotting drill is different to a centre drill. A centre drills cutting angle is ground to the correct angle to support a tailstock centre. A spotting drills cutting angle is ground to the correct angle to align a drill bit & will give you greater accuracy. I personally don't interchange them. When to Use a Spot Drill [ 7 Useful Tips and Techniques ] - CNCCookbook: Be A Better CNC'er


Thanks Peter - just goes to show again... one is never too old to learn 

Thanks for all the other replies, especially the very informative ones by clockworkcheval and ajoeiam - much appreciated.

I sharpen all my drills (well, all those larger than 4mm...) to a 130° point angle, as I mostly work in harder steel - am I correct in deducing that this would then have a larger influence in forcing the drill to go off-centre, even when starting with a centre drill?
It should be fairly easy (I think, having never tried it...) to re-profile the points of my larger centre drills to 130° and then only drilling the first stage (i.e. up to where the larger angle for cutting the tapered hole starts) - would that make a positive difference?


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## Ken I (Apr 14, 2021)

I once drilled a Ø20 hole through a 600mm length of stainless (on a Graziano SAG14) - The long series drill being made by turning down the drill shank and attaching it to a length of Ø12mm rod by silver soldering.
The idea was to use the drill as standard at the start, add the extension piece and "peck" my way deeper - as the flutes are going to get swarf bound quite rapidly.
On my first attempt, I was a bit slap dash and the drill bit was clearly wandering at the start (not really well centered) - the damn thing came out the side of the Ø40mm bar shortly before it reach full length.
I was shocked - I couldn't believe you could drill "around a corner" that badly.
On my second attempt, I was far more careful about getting the drilling started correctly - I also bored the start up to drill size as accurately as I could - so as to provide initial "guidance" to the drill.
This time it went through perfectly and was only ±0.1 TIR at the breakthrough end.

Lesson: Make sure that you start it as perfectly true as possible and bore the start if possible. Everything must be as perfect as you can do.

Here's a link to a Ø4 x 123.5mm long - that's also over 30 times the diameter.

Six Shooter Elbow Engine

Page down to my Jan 7 entry.

Get the start right and the rest follows.

Postscript: I have had the odd problem on deep drilling where the central grain structure is "corkscrewed" during spin casting or other processing - then the drill tends to follow the corkscrew - it can be a right PITB.

Regards, Ken


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## aRM (Apr 14, 2021)

clockworkcheval said:


> Kwoodhands is right in my opinion to start with a spotting drill rather than a center drill. ................


Hello  there
This is one of the BEST Explanations I've read in a long while on WHY a CENTRE DRILL  will not  lead to a very precise and accurate Drilled Hole.  
Much appreciate the Post
Thanks  again for the input
aRM


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## Richard Hed (Apr 14, 2021)

HennieL said:


> Thanks Peter - just goes to show again... one is never too old to learn
> 
> Thanks for all the other replies, especially the very informative ones by clockworkcheval and ajoeiam - much appreciated.
> 
> ...


Wait a miniute.  I am too old to learn!  But it is always helpful to know about these spotting drills.  I never knew about them till I lookt them up because of all your posts.  I thimpfk I have never owned one of these drill bits.  Maybe I 'll get a couple to test out.  Even so, I am still incapable of learning.


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## L98fiero (Apr 14, 2021)

HennieL said:


> I sharpen all my drills (well, all those larger than 4mm...) to a 130° point angle, as I mostly work in harder steel - am I correct in deducing that this


There are 130° spotting drills as well.


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## tornitore45 (Apr 14, 2021)

Until the final size drill is deep enough to be past the conical tip it is free to wander, drill oversize and veer off.
Once the drill margins are into the hole, the freedom to wander is much limited.
A second consideration is that uneven lips can push the the bit on one side but this is greatly reduced with a pilot hole to clear the web.

I would drill a pilot with the normal size, that is, a bit larger than the web.  Then if the pilot drill can not reach the final hole depth I would change to a larger pilot that can, obviously still smaller that the final size.
Then BORE the first 1/2" or so, to size or to the size for the reamer if one plans to ream, to guarantee that the final size bit is fully guided.
Now you can drill with the reamer size or the final size, knowing the bit is constrained by the short bored hole.
If you have to, ream to size.

It does not really matter if one starts the hole with a spot drill or a center drill since that operation is just to start the pilot hole.


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## clockworkcheval (Apr 15, 2021)

Good to see from the many comments that drilling is still the Mother of Manufacturing, a firm descendant of Stone Age Technology.


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## goldstar31 (Apr 15, 2021)

I recall that in 1973Prof Dennis Chadock  writing on his Mark1 Quormn T&C grinder advocated the use of 4 and 6 facet twist drills.  More recently, our own  BaronJ published is design which appeared in  the GadgetBuilder.com site.


No mention- WHY?


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## Peter Murphy (Apr 15, 2021)

tornitore45 said:


> Until the final size drill is deep enough to be past the conical tip it is free to wander, drill oversize and veer off.
> Once the drill margins are into the hole, the freedom to wander is much limited.
> A second consideration is that uneven lips can push the the bit on one side but this is greatly reduced with a pilot hole to clear the web.
> 
> ...


But if you use a 60deg centre drill & your pilot hole is off because the pilot drill can't go in deep enough to align the pilot drills point with the centre of the divot then everything after that including the reaming will be off. If you use the correct size & point angle spotting drill your pilot drill will be guided to the centre of your spotting drill divot, everything after that has a better chance of being true.


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## jack620 (Apr 15, 2021)

tornitore45 said:


> It does not really matter if one starts the hole with a spot drill or a center drill since that operation is just to start the pilot hole.



I disagree. A spotting drill is designed for drilling starter holes for subsequent drilling. Centre drills are not.


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## clockworkcheval (Apr 15, 2021)

It is my understanding that there are two main methods of grinding drills. The first method is forming a slanted cone for each cutting edge. This cone will have the right cutting angle at the cutting edge and then drop off leaving space for the chips. You can form the cone with a grinding tool or with some exercise holding the drill in your hand and making the cone with a movement of your wrist. The second method starts with forming a small straight flat cutting edge with the correct angle - 2 facets. Being flat this leaves not enough room for the chips to evade so you grind two more flats behind the cutting edge at a steeper slant - 2 more facets. If this is done right the four facets will meet at the point of the drill making the drill more self-centering. You can improve this by cutting away the web towards the point. Finally considering that most wear will occur where the cutting edge meets the outer diameter you can grind two more facets at the cutting corners - 2 more facets. The 6 facet drill with webpoint cutaway is superior in selfcentering and in tool lifetime. The setback is that you need a machine to do it correctly.


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## goldstar31 (Apr 15, 2021)

I disagree - with everything


Alexander Pope and echoing Juvenal much earlier said:-

                                                A little learning is a dangerous thing


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## ajoeiam (Apr 15, 2021)

aRM said:


> Hello  there
> This is one of the BEST Explanations I've read in a long while on WHY a CENTRE DRILL  will not  lead to a very precise and accurate Drilled Hole.
> Much appreciate the Post
> Thanks  again for the input
> aRM



I would disagree with the absolute (will not) would prefer something like 'may not'.

Have drilled enough holes to know that this 'starter hole, if you  will, is only one of more than 2 or 3 variables in the process.


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## ajoeiam (Apr 15, 2021)

goldstar31 said:


> I disagree - with everything
> 
> 
> Alexander Pope and echoing Juvenal much earlier said:-
> ...



My question of you, and them, would be : how much is enough?

(Yes I agree with the sentiment but quoted too often leads too many to not want to learn and that is very negative for the system and its longevity!) 

(the answer that is most likely would be "You can't learn enough" which is also true)


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## goldstar31 (Apr 15, 2021)

ajoeiam said:


> My question of you, and them, would be : how much is enough?
> 
> (Yes I agree with the sentiment but quoted too often leads too many to not want to learn and that is very negative for the system and its longevity!)
> 
> (the answer that is most likely would be "You can't learn enough" which is also true)



The more that one learns, the less one knows.

But on a far less important issue, it is obvious that  Van Royen was never read or perhaps someone had an ear  for such things as Van Gogh. 
I made a Quorn to the design of a Professor of Engineering and who explained in detail of how the 4 and 6 facet grinding should be accomplished. Chaddock actually made the Dore Westbury mill and continued to make( not merely grind) the 1/10th inch diameter drills which he used in making a V6 engine to his own design but obviously to embody RR Practice! Again, he wrote in mModel Engineer' how to make piston rings and ball bearings. 
For a party piece(?) he was on the Atomic Bomb project.
Happily, the Mark 3 has  had its scope - simplified(. ho ho)  but it does  avois the terms in ballet to describe rounding off the cutting edges of lathe tools and the end mills - which are really flat bottomed twist drills( clears throat again).
What has to be recalled is that the Mark 1 suggests a vertical pillar of ONE INCH thread- per inch.
As mentioned at an earlier comment, I have a Potts  one( as well) but Mr Potts also made a drill grinder to the Van Royen  concept.  It appears in Ian Bradley's The Grinding Machine.
I hope that I have written a little to avoid  'putting my foot in my mouth'
Best Wishes

Norman at 90++


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## ajoeiam (Apr 15, 2021)

goldstar31 said:


> The more that one learns, the less one knows.
> 
> Norman at 90++



Dunno for anyone else - - - - but it sure seems like that here!!!!!!!!!!!!!!!!!


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## tornitore45 (Apr 16, 2021)

The OP relate to drilling a deep hole straight.   The initial spot method and tool is immaterial once you accept that the first 1/2" MUST be BORED.   If you are just starting a hole without boring then you are not concerned with accuracy of location roundness and straightness.   At that point you can cut the centering divot with a chisel and be almost as good as with a spotting drill.


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## traction engine (Apr 17, 2021)

Well to each his own.  Maybe it's the equipment but in the 50+ years I've been drilling holes, I've NEVER had a problem with straightness and I've never started a drilled hole by boring. However there may be a variation in methodologies.
 You  are correct, if the starter is off, the drill will follow. My equipment puts the center drill on center so my holes are straight. Fix the problem because poor equipment inevitably gives poor results.


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## goldstar31 (Apr 17, 2021)

Deleted by me


Norman


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## terryd (Apr 18, 2021)

Richard Hed said:


> Wait a miniute.  I am too old to learn!  But it is always helpful to know about these spotting drills.  I never knew about them till I lookt them up because of all your posts.  I thimpfk I have never owned one of these drill bits.  Maybe I 'll get a couple to test out.  Even so, I am still incapable of learning.


Hi Richard,

Amazon sell a niceset of accurate spotting drill, I've been using mine now for quite some time with good results

TerryD


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## BaronJ (Apr 18, 2021)

Hi Guys,

One thing that doesn't seem to have been mentioned is that drills by their very nature, flex !  Even if you have a perfectly symmetrically ground drill, if you cause the drill to bend whilst drilling, It will drill a bent or oversize hole !

Having said that, one little trick worth knowing is if you want a slightly larger hole and you don't have the right size drill, grinding a drill with one cutting lip longer than the other will produce a bigger hole than the drills diameter !  For all the reasons previously mentioned.


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## mcostello (Apr 18, 2021)

That trick is supposed to work well on the harder bronzes which can be a bear to drill. Fortunately making a drill bit cut bigger is one of the raw talents I seem to have in spades.


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## Ken I (Apr 18, 2021)

It's a trick you need to be careful with - it not only drills bigger but continues to drill bigger and bigger the deeper you go.
Years ago I was production drilling Ø7mm holes prior to a 7mm hexagon wobbly broach - we needed to drill Ø7.05 - on one occasion we overdid it and by the end of the 11mm deep hole the bore was so bell-mouthed that the hexagon vanished - the result an expensive warranty return from VW when the hex drives stripped on assembly.
I couldn't believe the Ø7 hole had bell-mouthed to Ø8 in just 11mm - of course the damn thing passed all the Go / No-Go gauges - you could only see the error if you sectioned it.


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## BaronJ (Apr 18, 2021)

Ken I said:


> It's a trick you need to be careful with - it not only drills bigger but continues to drill bigger and bigger the deeper you go.
> Years ago I was production drilling Ø7mm holes prior to a 7mm hexagon wobbly broach - we needed to drill Ø7.05 - on one occasion we overdid it and by the end of the 11mm deep hole the bore was so bell-mouthed that the hexagon vanished - the result an expensive warranty return from VW when the hex drives stripped on assembly.
> I couldn't believe the Ø7 hole had bell-mouthed to Ø8 in just 11mm - of course the damn thing passed all the Go / No-Go gauges - you could only see the error if you sectioned it.



Hi Ken,  Surely you mean a "Bell Bottomed" hole !
But I do take your point, a "D" bit would be the right way to go !


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## awake (Apr 19, 2021)

BaronJ said:


> Hi Ken,  Surely you mean a "Bell Bottomed" hole !
> But I do take your point, a "D" bit would be the right way to go !


I have heard that bell bottomed holes were popular in the 70's, but may be making a comeback ...


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## goldstar31 (Apr 19, 2021)

Hello Sailor!   Rude English ex[ression-- said he waving his wooden leg aloft

On a more even keel( !!!!!), I have just ordered a rahr large order stub drills,  metricated ones in 0.1mm and tool bits to ' part brass rags' with all and sundry.
Boring though it is, Boeing is the thing.

Anyone thought of how Northumbrian Small( bagpipes were drilled? I made a set. 
Any one for A and B flat clarinets?

Regards

Norman


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## Richard Carlstedt (Apr 19, 2021)

Well, it all depends on what accuracy level you want ?
Deep hole drilling has some considerations that rise above normal considerations
Unfortunately, it conflicts with many of the "standards" we have learned in our machining careers or hobby. So let me begin :
Lathe work- First know that that your tailstock , may not perfectly match the C/L of your spindle  OR the writer who mentions he has perfect accuracy  ?   And this measurement must include parallelism of the spindle and tail-stock quills !
Mill work- How much spindle run-out do you have , both in bearings and "tool" holder readings?

I am not being a jerk by mentioning the above , but trying to point out that no two people will achieve great results because the subject of Deep Hole Drilling (DHD) boarders on Art Form and success is based on approach and machine( + tool)  capabilities !

Here are some pointers , at the Die shop I worked in , we did DHD every day and to 25 to 40 x diameter.  So what are normal perimeters you ask ?
For gundrilled work in a gundrill lathe you can achieve .0001"  per inch drift or less
For gundrilled work in a mill , you can achieve .0015" per inch drift or less
For conventional drilling without prep, it is not unusual to see .010 to .020" per inch drift
The difference you see is because having the "work" piece turning will always produce more accurate holes as the lathe's axis redirects the drill bit far more than the drill bits axis does.
So if you want straighter holes, use your lathe.

The single, and most important factor to a straight hole is ...."Hole Prep"!
Center-drills and Starting drills do not cut it !
Small drills or step drilling  do not cut it !   ( more later here)
To start the hole, use a Ball Endmill or bore the hole -finished size... to a depth of 2 x diameter
Few machinists know or realize that a Ball Endmill is one of the most precisely ground tooling they have and the nature of the ball form drives that cutter to a precise round hole.
Then having a hole with 2 diameters depth, the "flutes" of your drill bit will be automatically fully supported ( 360 deg) to give you the best chance for a accurate hole.
Now if your lathe is under powered, you can still do your step drills, but first having the hole prep done properly, when you use the full size drill, your load will be less, but the drill will have support from the prep area and produce a much straighter hole .
For example, a 1/4" drill bit is much stouter than a 1/16" drill and having the 1/16' drill first means greater chance of deflection, and if you want the bigger drill to follow the same path, you cannot expect superior results.

The only problem with Ball Endmills is limited size availability  ( by 1/8 or 1/16"), but even so, use them whenever possible for hole starts.  I never use a center-drill, unless it is on a shaft for tailstock support . For regular drilling I use a starter drill in the mill. And if the hole is a normal hole when in the Lathe , I use my drill bit, (yes ! ) but that should be another posting for that technique is 100 years old and not taught anymore  -but give dead center holes.
Rich


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## Mike Henry (Apr 19, 2021)

Hi Rich,

What are your thoughts on using a spot drill to start holes that don't have sizes common to ball end mills?

Mike


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## TSutrina (Apr 19, 2021)

I have never needed to drill a very deep hole accurately.   The century old method is to gun drill the hole.  Modern gun drills have a hole for oil cooling and removing the chips, however; being centuries old the is an improvement done because we can and it speeds up the process.    A gun drill can be DIY made far easier since the relief is a straight flute, ~ 1/4 of the cylinder.  Gun Drilling & BTA Drilling: Ultimate Deep Hole Drilling   Here is a youtube showing use and sharpening


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## Richard Carlstedt (Apr 19, 2021)

Hi Mike.
yes, a spotting drill or "starter drill " ( same drill) works very well and definitely  use them if a ball endmill is not available.   And get them in carbide if possible due to their rigidity . But when you do, try to go to 2 x diameter so you get the full support *for * the jobber drill that follows. I know that most machinists will only do it to get a conical starting surface, but make it deeper to stabilize the drill bit flutes that follow.  (Assuming that the next drill is the size you want -if smaller, then you don't need the 2 x preparation)

Something that shop guys should do is look at the Helix Angle of their drill bit flutes. 
Doing so means looking at the flute distance for it to make a 180 degree rotation. Lets take a 1/4" drill for example here
Hold a machinists scale parallel and against the drill with the  "0" point-edge of the scale at the cut edge and see where the second flute crosses the scale . This may be anywhere from 3/8" to 1-1/2" depending on the helix angle .   THIS Length is how deep the hole prep should be !
This length means the drill will be fully supported 360 degrees and is makes it more accurate in size and depth and reduces egg shaped or triangular holes  ( which are caused by the drill rattling around in the hole) . The short cut answer I gave was 2 times diameter, but it really is related to the Helix length I mentioned--and which takes precedence over 2 x_ X _for good work 
Rich


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## kop (Apr 19, 2021)

Carbide Spot Drills - Standard Cutting Solutions
					

Buy carbide spot drills from Standard Cutting Solutions at factory direct prices. All products shipped within 48 hours.




					www.standardcutting.com
				




Not meant as an ad but an endorsement. US made. Quality tools. Quality customer service.  I'm very pleased.


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## Mike Henry (Apr 20, 2021)

Thanks Rich - still learning something new every day.  Looks like I'll be picking up some carbide spot drills in larger diameters.


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## goldstar31 (Apr 20, 2021)

Well, today I took delivery of:-


a set of  round drill bits
a couple of boxes of metri drills to cover 1 to 10mm in 0.1 intervals( dear)
a set of stub drills- imperial
a scribing block for marking  work

Then I have  just had a phone call to either lend or sell me a Black and Decker  43000 profesional drill grinder to  grind from 1/8th to 1/2" drills. The thing is 110V and I will need a transformer to drop my 240/250V to 110V AC

For a 90 odd YO. I'm going to be busy--- as I have large gardens as well.

Regards


Norman
NB

 And on the 26th it is time for my next eye jab.


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## jack620 (Apr 20, 2021)

I also use a solid carbide spotting drill. They are excellent- very rigid and will cut just about anything.


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## HennieL (May 8, 2021)

Thanks to everyone who contributed to this - most definitely an excellent "knowledge base". We need more of this type of discussion on other "common" workshop techniques... although we could probably skip the "_how to hammer a nail into a piece of wood_" 
So, who's going to post the next topic?


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## goldstar31 (May 8, 2021)

HennieL said:


> So, who's going to post the next topic?



So moving a little, what about the other boring subject-- bore-ing?


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## HennieL (May 8, 2021)

goldstar31 said:


> So moving a little, what about the other boring subject-- bore-ing?


I like it - especially boring very small diameter holes. My smallest boring cutter is 6mm, and I certainly don't feel comfortable using it... deflection, deflection, deflection... So, Goldstar, are you going to start a new thread, or should I?


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## goldstar31 (May 8, 2021)

HennieL said:


> I like it - especially boring very small diameter holes. My smallest boring cutter is 6mm, and I certainly don't feel comfortable using it... deflection, deflection, deflection... So, Goldstar, are you going to start a new thread, or should I?


So you are unable bore a hole  smaller than 'under 3mm'?  I lost my stuff in a wintr's storm that woukkd  drill perhaps 1.5mm.  
My problem is worsening macular degeneration- as mentioned earlier.
Currently, I'm trying again to read and then make 'small' tools from George Thomas's Model Engineer's Workshop Manual. 
Really, the bits holders of 1/2" square and 1"x1/2" and a few little socket screws.  Plus a pack of little bits of hss round.  
There's a parting tool design  for a 'bit' less than an eighth.
So  this is obviously what can be put on a  7 x 19 lathe.
Best Wishes


Norman


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## BaronJ (May 8, 2021)

HennieL said:


> Thanks to everyone who contributed to this - most definitely an excellent "knowledge base". We need more of this type of discussion on other "common" workshop techniques... although we could probably skip the "_how to hammer a nail into a piece of wood_"
> So, who's going to post the next topic?



Hi Guys, 
Just sticking with drilling for a moment, I can remember drilling 3/32" inch diameter holes through six inch lengths of 1/2" inch diameter Teflon rod on the lathe.  The hole had to remain within a couple of thou of the center of the Teflon rod from one end to the other !

I made around 26 or 27 of these.  Dormer in Sheffield, at the time made me a couple of long drills especially for this job.  The way that I achieved doing this task was to place the Teflon rod into an aluminum block mounted on the lathe cross slide with a 1/2" inch hole bored through it, the Teflon rod was pressed into the block with the tailstock after heating it up.  Teflon is very soft but happily withstands a high temperature, and drills easily.

There were some other constraints but the work was completed satisfactorily.


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## goldstar31 (May 20, 2021)

Well it has happened- or well? sort of
So I found  that for only £15 that I could get THREE diffrent sizes of boring tools with a 90 degree and a 45 degree square tool bit holder at the ends.  With a little bit of  alteration each would fit my boring tool holder which fits the  4 way Myford tool turret.  So it is a selection of boring tools which  can slide and lock with the least overhang.

Cheap, cheep
So after all this discussion about drill grinding, I have a sort of pernent lend of a professional drill grinder which  grinds drills from 1/8th to 1/2" diameters.  110 volt but a transformer  came with it!
So I've always had a  sort of abused 4 jaw independent chuck for my newer Myford. At a price way below the market price, I have one Virtually unused! 
So to end a  succesful afternoon, there was an offer to move the Sieg C4 from the study and have the Myford Super 7 with the power cross feed in and in a much warmer place to work.
We finished with a discussion on the fancy 6 staion Myford 5 station turret bit.

Apart from this- it rained.
More anon- including the rain

Norman


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## SmithDoor (May 20, 2021)

My self in drilling on lathe is.
1) Center drill.
2) drill smaller hole in most cases.
3) larger drill still under size.
4) use a boring bar so hole turn true. 
5) If have a Reamer then ream to size or bore to size. 

Dave 



HennieL said:


> What is your preferred method of drilling deep holes as accurately as possible using a lathe? I have been thinking about this for many years, trying to decide the "best" way to drill a reasonably large hole (say 16mm diameter...) for a depth of (say) 10 x diameter into steel. In your opinion (for hobbyists, and not using specialised through lubricated gun drills, etc.):
> 
> would it be better to drill a small diameter pilot hole (say 4mm dia.) as deep as it can go, and then only drilling once using the final size drill, or
> would it be better to use a succession of increasing sized drills (say 4mm, then 8mm, then 10mm, 12mm, 14mm and finally 16mm
> ...


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## Bill Lawson (May 21, 2021)

SmithDoor is correct. My preference, after the spot or c’drill is to use a drill that is about the diameter of the web thickness of the larger drill 1/2” and larger, then bore to establish center line and ream to size.


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## BaronJ (May 22, 2021)

Bill Lawson said:


> SmithDoor is correct. My preference, after the spot or c’drill is to use a drill that is about the diameter of the web thickness of the larger drill 1/2” and larger, then bore to establish center line and ream to size.



Hi Guys,

I would suggest that its "Horses for Courses" !  You use whatever method that achieves the desired result !


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## goldstar31 (May 22, 2021)

SmithDoor said:


> My self in drilling on lathe is.
> 1) Center drill.
> 2) drill smaller hole in most cases.
> 3) larger drill still under size.
> ...



I can assure you that the recommendation is excellent and I have used it many times - on garden gates.
Geo Thomas writing in his Model Engineers Worhshop Manual takes a mere 46 PAGES and if further reading was made I would gues that my figure in an underestimate. Our worthy BaronJ adds to both what Professor Dennis Chaddock and Thomas mention.  Chaddock merely  wrote a book on the to[pic after he had advised on the Manhattan Prpject as we all know went off in -- a couple of BIG bangs.BaonJ or my friend John  wites on 4 facet drilling - it is good but not so Eath Shattering!.

More recently,  NKirk Burwell and Heningewwaykits  ugrades the Quorn to a Mark3  stus and simplifies* Ye Gods!) how to 'round off edges on drills and cutters and lathe tools. The kit is now VERY exp[ensive  and should really come with a bottle of aspirin and  a turban of damp hot towell.
And All this can be summarised in SIX short lines.

Now there is progress, folks-
 or not


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