# Drilling and tapping carriage for rear tool post



## kwoodhands (May 15, 2020)

I am making a rear mounted tool post. I will have to bore holes in the carriage for 1/4-20 cap screws. I am wondering if cobalt drills or even HSS drills will work. Also , will HSS endmills work for a counterbore. Only 4 holes are needed. I will start with #6 drill and try to tap the hole. 
 mike


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## BaronJ (May 15, 2020)

Mike, it might be a good idea to tell us what lathe you have and a picture or two of what you are trying to do.

With regard to your question, the saddle is most likely cast iron so HSS drills and end mills will do what you want.  But I would be very careful drilling holes in the saddle, it far too easy to damage a hidden surface.


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## kwoodhands (May 22, 2020)

Grizzly 10x22 lathe. I have drilled and tapped the carriage, it is cast iron and very easy to drill and tap.  I changed from 1/4-20 to 10/24 . This required smaller holes and still plenty strong. I am done and tried the tool post last night. Worked great for parting 3" 6061 aluminum. 
I never had a problem parting off 1" rounds or less. The big stuff was a problem before. Had to hacksaw and then face to dimension. Now I can part off and only face to clean up.
Thanks for your post,mike


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## BaronJ (May 23, 2020)

Hello Mike,

Good to hear that you have achieved what you wanted without causing any damage.  

How about a picture of your work, I would be interested as I'm sure would others, particularly if they are contemplating doing something similar.


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## Shopgeezer (May 23, 2020)

I have never understood the advantage of a rear toolpost for parting. Do you use the parting tool upside down, or run the lathe in reverse?


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## packrat (May 23, 2020)

quote " Do you use the parting tool upside down"    Yes that is right


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## BaronJ (May 23, 2020)

Hi Shopgeezer,

Yes you use the parting tool upside down running the lathe the right way.  

You say you've never understood the advantage of a rear toolpost for parting. 

The advantages are quite a lot, the swarf drops out of the cut, rather than staying on top of the tool with the risk of it going down the side and causing a jam.  

The rigidity is vastly improved because more of the cross slide is above the saddle rather than at the end where there is more wear and less support. 

The bulk of the tool holder will have less overhang, the holder body not over hanging the table edge.

Correctly set up the blade will always be at the right height and dead square to the work in both directions.  Apart from being able to work closer to the chuck, which isn't always possible with a parting blade in a QCTP. 












Here are some pictures of my Norman patent rear tool post.  The tool block is interchangeable with the front one.  So if needed I can swap them around for a particular job.

The parting blade is 2 mm thick by 12 mm wide and 200 mm long. In this picture the blade is new and has not been ground yet.


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## Shopgeezer (May 23, 2020)

So the forces on the tool would be trying to lift the tool up in a reversed parting tool. In the front it would be pushed down. I would think that the upside down position would be less rigid since the whole tool post is being lifted from its mount. In the front it is being forced down.


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## BaronJ (May 23, 2020)

Shopgeezer said:


> So the forces on the tool would be trying to lift the tool up in a reversed parting tool. In the front it would be pushed down. I would think that the upside down position would be less rigid since the whole tool post is being lifted from its mount. In the front it is being forced down.



Yes that is correct, but since there is normally less play and wear at that end the opposite is true, there is also more engagement of the slide.  On a small lathe the spindle would be being pushed down rather than being lifted.


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## RM-MN (May 23, 2020)

When you have the parting too in the normal position any flex in the cross slide as the blade cuts causes the blade to dig in.  With it in the rear the forces are to lift it and move the blade away from the cut.  Even with less rigidity it will cut easier with the blade in the rear.


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## Cogsy (May 23, 2020)

RM-MN said:


> When you have the parting too in the normal position any flex in the cross slide as the blade cuts causes the blade to dig in.  With it in the rear the forces are to lift it and move the blade away from the cut.  Even with less rigidity it will cut easier with the blade in the rear.


Surely this can't be true? If your tool is on centre then it is being deflected in the direction of rotation which has to be away from the material no matter if it is a front or rear post. Same thing if you're above centre and being deflected it's always in the direction of rotation and cut depth will increase (which I believe is why it is sometimes recommended to have parting blades set slightly high on less rigid machines although this would equate to slightly low on a rear parting tool).


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## BaronJ (May 24, 2020)

Cogsy said:


> Surely this can't be true? If your tool is on centre then it is being deflected in the direction of rotation which has to be away from the material no matter if it is a front or rear post. Same thing if you're above centre and being deflected it's always in the direction of rotation and cut depth will increase (which I believe is why it is sometimes recommended to have parting blades set slightly high on less rigid machines although this would equate to slightly low on a rear parting tool).



If you look at the forces when parting from the front, the chuck is forced upwards and will cause the tool to dig in because it is pulling the tool post towards the chuck.

Parting from the back, the reverse is true.  The rotation of the chuck pulls the chuck down against the cutting force of the tool, this is pushing the tool away from the chuck.

I would never advocate having the tool set to anywhere other than accurately on the center line. 

I think that people have a lot of trouble with parting because they simply don't understand the dynamics of rigidity and positional requirements.

Anyway haven't we been this way before recently, when we discussed the parting blade getting trapped when parting aluminum.  Which since I've actually found to be caused by the aluminum being smeared down the side of the blade.  It seems that only the soft gummy types are the culprits.


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## Apprentice707 (May 24, 2020)

I have used a rear-mounted toolpost on my Myford S7 for 25 years without any problems. I use HSS and a Ganze type tool holder with inserts depending on what material I am parting off, both work well. The most important things to watch out for are tool height and keeping tool overhang to a minimum, the cutting edge must be on the exact centre height of the lathe. I seldom machine aluminium, but when I do build up on the tool cutting edge is always a problem frequent cleaning during operation keeps this to a minimum. 
Baronj's pillar toolpost has inspired me to add one to my Chinese made 8 x 12, just wish it had a Tee slotted cross slide like the Myford !!

Happy metal shaping y'all.

B


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## goldstar31 (May 24, 2020)

I've written umpteen times on the topic and the the rear mounted inverted blade goes 

In and out of cut
 whereas as front mounted parting tool

Goes into cut and can 

DIG IN---*BANG*
Sorry Cogsy but it is not getting through.

I have had a Geo Thomas one which is angled down wards at 7 degrees, has the top cutting edge ground with a 140 degree female 'top' and a male vee of 140 degrees and the normal cutting edge is 7 degrees in hss and will cut 2" mild steel.

But the nice thing is that there are 2 blades and when cutting,  the swarf is 'narrowed' into nice little curly rolls and doesn't seize and the little curlies simply drop down.

Heminngwaykits sells castings but mine came from the scrap box.

If my memory is correct, Ian Bradley on of the Duplex tean withDr Nrman Hallows made the first one and  Thomas made one- the horizontal variety and then did the present design which- if we think about it only requires the front of the tool refreshed. Usually only a touch on the grinder!

I hope that this helps

Norman


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## kwoodhands (May 24, 2020)

Shopgeezer said:


> I have never understood the advantage of a rear toolpost for parting. Do you use the parting tool upside down, or run the lathe in reverse?


Upside down and the chuck runs in reverse.


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## goldstar31 (May 24, 2020)

Nope!  Mine runs  properly. 

Read the manual or something like that


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## Rodney Brown (May 24, 2020)

Actually with a rear toolpost, the tool can be run upside-down and the chuck in the normal direction (or vice-versa -- tool normal, chuck reverse).

I have an AXA toolpost on the compound, and a BXA toolpost mounted directly to the saddle... easy to do with my Nardini since it has T-slots in the saddle for a rear-mounted attachments. I built some blocks so that I can index it to exactly the same position whenever it is mounted. This gives me fixed tool offsets for tool holders where I want them to be dead-on the centerline (BXA-mounted drill chucks, MT3 tool holders, etc.). A DRO for storing those offsets is my next big investment in this lathe! The primary advantage to me is that my rear tool post is mounted solid to the saddle, not on a compound. This makes it about 10x more rigid for parting, T/P grinding, etc.).

Already said, but something to watch out for... the saddle is designed for cutting forces into the lathe, not lifting the saddle from the lathe (regardless of the direction the chuck is running). Parting with an upside down tool is my preferred method, but if the tool catches it pulls the saddle up from the ways. A bad catch can tear a saddle off the machine.


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## Cogsy (May 24, 2020)

BaronJ said:


> If you look at the forces when parting from the front, the chuck is forced upwards and will cause the tool to dig in because it is pulling the tool post towards the chuck.
> 
> Parting from the back, the reverse is true.  The rotation of the chuck pulls the chuck down against the cutting force of the tool, this is pushing the tool away from the chuck.



Let's assume the tool is exactly on centreline of the work and is making a shallow cut into the workpiece. If we now deflect the toolpost in the direction of rotation (as we get from cutting forces), it will be towards the saddle from the front, or towards the ceiling in the rear. In both cases the distance from the tool tip to the workpiece will increase and depth of cut will reduce as in both cases the tooltip is rotating around a pivotpoint (the tool holder) and describing an arc. Also in both cases, the toolpost is now effectively a spring and will be trying to restore the toolpost back to straight - as we continue to feed, possibly as we reduce our feedrate, the spring in the toolpost brings the tool tip back down, depth of cut increases and we can have a dig in.

If we think the chuck itself is deflecting instead, it's essentially the same result as above but removes the toolpost deflection completely so there is zero difference between a front or rear post in terms of the deflection.

Rear parting holders undoubtedly work but it's my opinion that it's more about gravity assisting with chip clearance. If anything, for a similar rigidity front vs rear toolpost I would expect any looseness in the saddle gibs would mean an upside down parting tool would end up further off centreline than the front.



BaronJ said:


> I would never advocate having the tool set to anywhere other than accurately on the center line.
> 
> I think that people have a lot of trouble with parting because they simply don't understand the dynamics of rigidity and positional requirements.



I have seen it in writing from reputable sources (once on the Sandvik website even) although I do set mine as bang-on as I can. Too much away from the centreline against the rotation direction is obviously bad for dig-in and too much in the direction of rotation can lead to the work 'climbing over' the tool. I believe the recommendations I've seen that advocate for 'slightly high' (for a front toolpost) such that the deflection in the toolpost and the tool itself result in the cutting being done exactly on centre. Probably easy to refine in batches of hundreds on a CNC machine but not easy to do at home.


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## Cogsy (May 25, 2020)

goldstar31 said:


> I've written umpteen times on the topic and the the rear mounted inverted blade goes
> 
> In and out of cut
> whereas as front mounted parting tool
> ...



Any parting tool can dig in - set your rear tool too low and try it out and you'll get yourself a dig in. If I have a dig-in then I'd much prefer the force to be being applied down through the saddle onto the ways than up which would try and rip the saddle off the bed. 

You've written ad nauseam about having a rear parting tool but to my knowledge you have never been able to explain why it is "better" so I don't see what isn't "getting through".



goldstar31 said:


> I have had a Geo Thomas one which is angled down wards at 7 degrees, has the top cutting edge ground with a 140 degree female 'top' and a male vee of 140 degrees and the normal cutting edge is 7 degrees in hss and will cut 2" mild steel.



I can, and do, cut more than 2" mild steel also. I assume virtually everyone here does although maybe I've overestimated the ability or size of the Myfords? (I've never used one myself).



goldstar31 said:


> But the nice thing is that there are 2 blades and when cutting,  the swarf is 'narrowed' into nice little curly rolls and doesn't seize and the little curlies simply drop down.



Gravity is certainly assisting with the 'curlies' dropping down but I don't like making 'curlies' with my parting tool as they can jam in the groove. I prefer actual chips which get flung out (annoyingly into my face sometimes). I also like nice thin parting blades so I don't waste much material for example when parting off piston rings, or when using a narrow, bifurcated cutter to shape crankshaft journals and the like. Actually this is the main reason I have never bothered with a rear parting setup - I use my parting tool for far more than just parting off so I want it to be at the front where I can see it and control it better.




goldstar31 said:


> If my memory is correct, Ian Bradley on of the Duplex tean withDr Nrman Hallows made the first one and  Thomas made one- the horizontal variety and then did the present design which- if we think about it only requires the front of the tool refreshed. Usually only a touch on the grinder!



My toolholder (purchased, probably Chinese) takes standard blades, has built-in angles and only requires the front of the tool to be ground as well. Nothing new here.


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## BaronJ (May 25, 2020)

Hi Kwoodhands,


kwoodhands said:


> Upside down and the chuck runs in reverse.



NO the chuck runs in the normal direction, anti clockwise !
The parting blade is upside down.


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## goldstar31 (May 25, 2020)

Deleted


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## GEARS (May 25, 2020)

Gentlemen, I think the bigger problem has not been mentioned. That is “forgetting  it’s there” especially on small lathes. I have seen nearly finished work like crank shafts with multiple journals ruined in a split second.


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## goldstar31 (May 25, 2020)

Deleted


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## awake (May 25, 2020)

Cogsy said:


> <regarding setting the parting tool on center-line>
> I have seen it in writing from reputable sources (once on the Sandvik website even) although I do set mine as bang-on as I can. Too much away from the centreline against the rotation direction is obviously bad for dig-in and too much in the direction of rotation can lead to the work 'climbing over' the tool. I believe the recommendations I've seen that advocate for 'slightly high' (for a front toolpost) such that the deflection in the toolpost and the tool itself result in the cutting being done exactly on centre. Probably easy to refine in batches of hundreds on a CNC machine but not easy to do at home.



I have a parting tool that not only has a "T" shape to allow additional clearance, but also has a "U" shape along the top surface, which helps to curl the chip inward so that it is less likely to catch. However, the "U" shape means that it is a bit hard to determine where the actual cutting edge is, or should be set - at the bottom of the U? Or at the top? I find I have to set it with the top of the U a bit above center, so that the bottom of the U is on center.

Not sure if that made sense trying to describe it in words ... if needed, I'll go take a picture!


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## Shopgeezer (May 26, 2020)

I have seen that U shape in parting tools but how on Earth would you sharpen it?


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## ShopShoe (May 26, 2020)

FWIW,

What I will say is not very "scientific," and I think science is a good thing, in general.

It took me awhile to figure out parting, but I can say I've got there at this point. 

My parting blades are like you describe above in post #24. I have a mini-lathe, so they are small and do small work. I set the blade with the  trick of putting a 6-inch scale (ruler) between the work and the point of the cutter and making sure the tool height is adjusted so the scale sits vertically, or* very* slightly away from vertical toward the operator. What this does, in my opinion, is even out all the variables to create the best situation for me, in my shop, on my lathe, with my cutting tool. An old trick, but works for me and is simple to do.

In addition, I pay special attention to keeping the tool sharp. In parting a dull blade will dig or climb with the greatest of ease.

--ShopShoe


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## BaronJ (May 26, 2020)

Hi Guys,

Shopgeezer: The blade has a flat face so that is the only bit to sharpen.

Shopshoe: That is a very old trick and one worth remembering.  Being lazy, I commonly use it to center a drill over a round surface !


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## awake (May 26, 2020)

Right, for a U-shaped blade, you only sharpen the front face; don't touch the top. Shopshoe, I used the ruler trick all the time to set / check blade height (and once in a while to center a drill on a round surface!), but at least on my lathe, if I set my U-shaped blade that way, it does not perform well - I have to set it higher than I would normally set a blade so that the bottom of the U is closer to the center line. It took me quite a while (lots of failed experiments, shall we say) to determine that that was what worked best on my lathe. As always, though mileage varies!


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## Shopgeezer (May 26, 2020)

Struggling a bit with the U shape. If the front face is flat, where is the U?  Along the top edge?  Seems that it would have two sharp points at the apex of each arm of the U. That would suggest digging in to the work. Sorry to be thick on this but I have never seen or heard of that shape.


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## awake (May 26, 2020)

Shopgeezer said:


> Struggling a bit with the U shape. If the front face is flat, where is the U?  Along the top edge?



I'm not surprised, since I was confusing myself trying to explain it! But you've got the idea. Here are a couple of pictures that should help. First, here is a close-up of the business end of the parting tool:






And here is a closeup of the chip that it produces:





Notice that the chip is curled up not just like a spiral (well, normally it would look like a "flat spiral," but this got pulled out of shape when I was extracting it from other chips in the chip bin), but also from side to side, if that makes sense. To say it another way, the chip is curled up like a spiral around the axis and is curled into a slight u-shape across the axis. The idea is that the latter curl makes the chip slightly narrower than the width of the parting cut, helping to keep the chip from jamming.



Shopgeezer said:


> Seems that it would have two sharp points at the apex of each arm of the U. That would suggest digging in to the work.



Yes, it seems like it would. I'm guessing the reason it doesn't dig in has to do with three things: 1) The advantage of the curled chip as described above; 2) the fact that the U is fairly shallow; and 3) the "horns" are sharp and small, so rather than digging in, they easily slice through the steel. Please note that I don't know any of these for sure - just my guesses!


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## BaronJ (May 26, 2020)

Hi Guys,

Shopgeezer: If you have a close look at carbide insert parting blades, the carbide insert has a spoon shaped front edge.  Apart from chip breaker action it causes the chip to fold away from the sides of the cut.

Andy:  I've experimented with making a groove like you show, using a Dremal tool with a cutting disc.  Admittedly without too much success. I found that as long as the blade was dead square and truly vertical, getting it on center height cured most problems.  It was only after I went to a rear toolpost that the minor issues went away.  Having said that plenty of cutting fluid particularly with aluminum is a must.

I went through a spell of blade jamming when parting aluminum, and later found out that if the aluminum smeared on the sides of the parting blade I would get jams.  I now use a squirt bottle and diesel fuel for lubrication.  It works better than WD40 in this application. Particularly if the aluminum is a bit gummy.


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## fcheslop (May 26, 2020)

Another fan of the U shaped parting blades,Used them for many years in a rear tool post the cantilever version that over hangs the cross slide to give more room between the tooling


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## goldstar31 (May 27, 2020)

Most. of us 'oldies' who are both very old, live alone and are ill in this virus which actually started in February at the Chinese  New Year. My health people will not visit, are loathe to telephone and a raft of ' ot is not my thing' On the Home Front( I lived through a 6 year war) and then into uniform.
Now things are breaking down and cannot be replaced.
Sheer and utter frustration reigns and Heaven help those who 'start interfering'
So whilst I am in a good mood, might I add a few hopefully pertinent things?
Initially, there is little difference between a Myford and a Sieg. I have both- and for the SiegC4 I've been sensible enough to buy a mill drill attachment for the price that I paid for the second hand lathe itself.
Tooling, if you know what you are doing, will happily swop. 
My new second hand Myford is just running. The split phase motor is now OK and I bust one of the Tufnol cluster gears because the spindle belt was streched, oul soaked and frankly- bloody iseless. Some oone had added a no slip concoction to make matters worse and I changed it all for link belting and had to invnt a special tool to aid my arthritic fingers. 
So it's all ready to take the rear parting tool which has lived and performed adequately on 'all sorts of lathes'. It is one of those tools which reached the end of sensible modifications and that is that.
If someone wants to add a new dimension of tungsten carbide tooling to do the same job but at greater expensem that is up to them.

All that I have to do with my aged contraption is to 'give it a lick' on the grinder. fit it and apply an even older dollop of lard oil- and heigh ho, what's the problem.
This U or vee thing os nothing new, I bought a cheap box of assorted hss tools unseen at a show and found then all with chipbreakers- ready ground.  These will go on my homemade ratchet 4 position tool holder to face the rear one. If I can be minded, I can make a bit for the rear tool holder which will accept a conventional tool- and sort of work as  crude capstan lathe. Whether it is stuck on  either lathe is immaterial.  
What is important in ALL machining is 'that little bit' at the end of each tool.  
I tried a couple of very expensive dedicated inserts in the commissioning( fiddly about) stage- and the words in my lonely little workshop were-- What a load of bloody crap?'


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## Apprentice707 (May 27, 2020)

Well done everyone, we seem to have made a banquet out of a box of crackers. In the end, if we have achieved what we set out to do in the time scale we set without loss of limb or life and no damage to property we have done well.

Cut metal and be happy

B


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## David Shealey (May 27, 2020)

kwoodhands said:


> Upside down and the chuck runs in reverse.


Blade upside down, OR Chuck runs in reverse. Has to be one, or the other, not both.


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## kwoodhands (May 28, 2020)

David Shealey said:


> Blade upside down, OR Chuck runs in reverse. Has to be one, or the other, not both.



I stand corrected, the blade was upside down, chuck ran in forward.
mike


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## SmithDoor (May 31, 2020)

The only time I use rear tool post was on long runs on turret lathes and screw machines
On engine lathe I use a quike change tool post for short runs
The rear tool post just would get in the way

Dave



kwoodhands said:


> I am making a rear mounted tool post. I will have to bore holes in the carriage for 1/4-20 cap screws. I am wondering if cobalt drills or even HSS drills will work. Also , will HSS endmills work for a counterbore. Only 4 holes are needed. I will start with #6 drill and try to tap the hole.
> mike


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