Lathe Threading Inserts

[tautech]

Please some advice on the finer points of threading with carbide inserts.
External only at this time so to be able to learn to crawl before advancing to anything more complex. 

Looking to get some triangle inserts for my ordinary triangle turning insert holders and seeking advice on setting rakes and for which metals might need + or - rakes for threading.

Threading with HSS tooling is no problem and prefer a compound slide plunge as opposed to the single point cross slide technique but looking to venture into carbide and single point threading.

Trouble is, what's all this about shims ?
First mentioned here on P11
http://www.mitsubishicarbide.com/application/files/3815/7587/4149/c009n_g_threading.pdf

Need worry about this stuff in the home workshop or not ?

[Ian.M]

Perhaps this will help: https://www.machiningdoctor.com/glossary/lead-angle/
Whether or not you need to bother shimming under the insert depends on if your thread's lead angle is small enough for acceptable flank clearance on the leading side with the insert flat, and if not, for external threading only, whether your toolholder permits slightly tilting the tool about its axis to put the top of the tool tip normal to the thread helix.

[Benta]

For thread turning, you'd normally use inserts like these:
https://www.hoffmann-group.com/GB/en/houk/Machining/Turning/Thread-turning-tools/c/10-03-03-00-00?tId=867
Simple 60 degrees triangular inserts normally don't have the geometry for thread turning.

[tautech]

For thread turning, you'd normally use inserts like these:
https://www.hoffmann-group.com/GB/en/houk/Machining/Turning/Thread-turning-tools/c/10-03-03-00-00?tId=867
Simple 60 degrees triangular inserts normally don't have the geometry for thread turning.

Thanks, yes of course using proper threading inserts like those was always the plan and from your link I learnt more today, that being inserts are available in Full or Partial profile styles.

That poses a further question, for versatility would a 55 degree partial profile be better so to permit 30^o compound slide use for 60^o threads so to not need to keep 60^o inserts too ?
Actually thinking about that more, using a 55^o insert will require a 32.5^o setting on the compound slide to produce a full 60^o thread form. Hmmm.

Yeah I'm a tightwad.
Thanks guys. 

[jpanhalt]

55° included angle is a Whitworth thread.  My British lathe (circa 1966) has that thread everywhere as did the objectives on microscopes I have used.  It is considerably deeper.  Nominal sizes don't fit together "right" with 60° threads.   You could probably screw around with the PD to make them feel better, but why not go with 60°?

BTW, a strange "American" thread -- namely 1/2"x12 -- seems to be used in Taiwan.  I have had two items from Taiwan that used that thread.  One actually has the 55° profile.  It's an inexpensive horizontal bandsaw from Harbor Freight.  I kept it, as its application in that device seemed reasonable.  The other item was adjusting feet on the vertical poles for a steel wire rack.  I did not check the angle.  I returned it, as getting decent casters for it would be a nightmare and probably impossible.  The casters made in Taiwan and available from the American dealer were not double locking.   

For lathe threading, I use a threading insert holder by Kennametal and appropriate inserts that are not always the partial profile version.

Sorry for the somewhat random musings.

BTW#2:  My oldest grandchild is spending next semester in NZ from the University of Vermont. 

[Benta]

Don't go there.
Stick with standard 60 degrees inserts. Unless you're working with old British cars, odds are you'll never need a 55 degrees type. Should it happen, then grind a HSS cutter for the purpose.

[tautech]

55° included angle is a Whitworth thread.  My British lathe (circa 1966) has that thread everywhere as did the objectives on microscopes I have used.  It is considerably deeper.  Nominal sizes don't fit together "right" with 60° threads.   You could probably screw around with the PD to make them feel better, but why not go with 60°?

IIRC BSPT is 55 too so it would be nice to be able to do those too but not all BSPT I can as some need specialist changewheels to produce the correct threading pitch.
I do have BSPT dies but not under 1/2" where I do occasionally require 3/8 and 1/4 gas as we call them.

BTW, a strange "American" thread -- namely 1/2"x12 -- seems to be used in Taiwan.  I have had two items from Taiwan that used that thread.  One actually has the 55° profile.  It's an inexpensive horizontal bandsaw from Harbor Freight.  I kept it, as its application in that device seemed reasonable.  The other item was adjusting feet on the vertical poles for a steel wire rack.  I did not check the angle.  I returned it, as getting decent casters for it would be a nightmare and probably impossible.  The casters made in Taiwan and available from the American dealer were not double locking. 

Yep for some modern stuff a thread gauge and thread chart are indispensable ! 

For lathe threading, I use a threading insert holder by Kennametal and appropriate inserts that are not always the partial profile version.

Hoping I can get away with just normal triangular insert holders of which I have a few but 16 and 22mm get the most use. Thinking partial will do what I need but I need some more clarity on shimming and if I need also invest in them or just say stuff it and keep grinding HSS for threading. 

Sorry for the somewhat random musings.

BTW#2:  My oldest grandchild is spending next semester in NZ from the University of Vermont.

Where ? Studying ? Subject ?

[tautech]

Don't go there.
Stick with standard 60 degrees inserts. Unless you're working with old British cars, odds are you'll never need a 55 degrees type. Should it happen, then grind a HSS cutter for the purpose.

Yep, starting to get that feeling too. 
BSF and BSW are pretty rare now my Landy is gone. 

[jpanhalt]

Small addition:  Just realized you were asking about using a 55° insert for turning 60°threads.  I have two lathes.  The smaller is apartment size -- an SD300 Prazi -- it's a toy.  For that, I used a 60° insert and advanced the tool holder at an angle to avoid chatter.  It is really not very rigid.  With a rigid lathe, that may not be necessary.

[jpanhalt]

Where ? Studying ? Subject ?

I don't know yet.  He is into environmental science and loves the outdoors.  They (he and family) are visiting at Christmas.  His mom told me today that he finally got his visa.  I had a post-doc student from NZ in the mid-90's.  She shared some pictures with me.  I was struck with the variety you have on an island and its similarity to our Alaska in its grandeur.  I envy my grandson.

[tautech]

Small addition:  Just realized you were asking about using a 55° insert for turning 60°threads.  I have two lathes.  The smaller is apartment size -- an SD300 Prazi -- it's a toy.  For that, I used a 60° insert and advanced the tool holder at an angle to avoid chatter.  It is really not very rigid.  With a rigid lathe, that may not be necessary.

Compound slide feed while fiddly is what I've done for all my lathe threading and feel very comfortable with it whereas single point threading using only the cross slide in new to me but it seems the most common method if using carbide.
Mine's a 3 phase 2sp 3hp Harrison 12, built 1970 with a rare Metric/Imperial change over lever so no fiddling with changewheels required for any of the common threads. 
This beast but they don't even have any images of one with this M/Imp change over lever:
http://www.lathes.co.uk/harrison/page16.html

When I got it a few years back I contacted and sent Lathes UK pictures and invited them to use them online and got a reply saying they'd never seen such a well spec'd one in this model. 
Some pics attached from when I just got and cleaned it.
Change over lever is just above the apron on the gear chest wall.

[jpanhalt]

Wow, I had a choice between a Harrison toolroom lathe in about 10" (500AA?) and the Smart and Brown.  I picked wrongly the Smart and Brown.  It's still a great lathe for what I do.

[Benta]

Nice looking lathe
Just to get the terminology right: what you've been doing with the compound at 30 or 29.5 degrees, whatever, is "single point cutting". It's called that because only one cutting edge of the insert is in action. This prevents chatter.
Going in with the cross-slide only is "direct form/thread cutting" where both cutting adges are active, and needs a really rigid and tight machine, and even then it's difficult. I avoid it if I can, though it's OK for smaller threads.

[tautech]

Wow, I had a choice between a Harrison toolroom lathe in about 10" (500AA?) and the Smart and Brown.  I picked wrongly the Smart and Brown.  It's still a great lathe for what I do.

IIRC the 500's are a quite late model and as such might have some modern features also.

There's a Groups Io site where a few of us Harrison owners hang out:
https://harrisonlathe.groups.io/g/main

Might be some interesting reading for you there but like for any Groups mob you have to request membership before you can contribute.

[tautech]

Nice looking lathe
Just to get the terminology right: what you've been doing with the compound at 30 or 29.5 degrees, whatever, is "single point cutting". It's called that because only one cutting edge of the insert is in action. This prevents chatter.
Going in with the cross-slide only is "direct form/thread cutting" where both cutting adges are active, and needs a really rigid and tight machine, and even then it's difficult. I avoid it if I can, though it's OK for smaller threads.

Thanks.
Yep that's what I've been doing with HSS but would like to graduate to carbide.

Single point threading doesn't use the compound slide at all and leaves it on 0^o and only advances the cross slide for thread depth.
Watch some of this:

[Benta]

I don't even need to watch the video. The miserable surface quality is apparent in the photo. The lathe must have been howling when cutting that.

[tautech]

I don't even need to watch the video. The miserable surface quality is apparent in the photo. The lathe must have been howling when cutting that.

Really ?
There is always something to learn and many mistakes resulting in turning chatter result from not using the tailstock center. Some examples in the video have work full supported and some don't for whatever reason but there are good examples of single point threading where only the cross slide is used, very identifiable from the dual swarf flows from the carbide insert.

[tautech]

Thinking I'll shell out for a turning holder too as this fella seems to have a 2nd screw for geometry adjustment:
https://www.ebay.com/itm/284645720497

To best match the lathe tool post I need 25mm shank tool holders which does unfortunately push into another price bracket. 

This seller offers the holder and threading inserts separately for free shipping but costs work out near the same.
Brought from him before and he will put a package deal together and give you a private listing. 

When flush with coin also thinking about upgrading from a tool post like this https://de.aliexpress.com/item/1005003745694437.html

To something quick change like this:
https://www.machineryhouse.co.nz/l294
However as it's required to accept 1"/25mm shanks, oh the price ! 

[hubi]

I don't do much threading, but I like to use a left hand insert holder upside down and feed left to right. Much less stressful if there is no chance of running the tool into a shoulder. With the carbide inserts, I do not bother to set the compound at 30 degrees but leave it at zero. Works well for me using 4140 steel. Anything under 3/8", I use a threading die.

[tautech]

I don't do much threading, but I like to use a left hand insert holder upside down and feed left to right. Much less stressful if there is no chance of running the tool into a shoulder.

I guess every lathe is different as is operator technique. 

I thread at low speed and always finish into a relief lower than the root of the thread, furthermore my Harrison has a manual hand clutch/brake arrangement and at low threading speeds it stops travel and work rotation in an instant !

Never have I been concerned with this lathe about turning all the way to a shoulder, even in general tuning at high speed stopping under 0.5mm/20 thou from a shoulder is very achievable even when peeling off 1.5mm/60 thou cuts. 

[Ian.M]

@tautech,
Your proposed toolpost upgrade may actually make it more difficult to get a good surface finish.  The higher cutting forces typical of Tungsten carbide insert tooling (due to the higher feeds, speeds, and typically higher depth of cut) demand a lot of rigidity.   A four way (turret) toolpost is typically significantly more rigid than a quick change toolpost of comparable dimensions.  The disadvantage to the amateur of sticking with a four way toolpost is of course the need for shimming, but if your tooling has sufficiently consistent tip height, you wont need to change the shims much.  A production shop also has to consider the setup speed advantages of a quick-change toolpost with enough toolholders, and may compromise on finish to save time.

[tautech]

@tautech,
Your proposed toolpost upgrade may actually make it more difficult to get a good surface finish.  The higher cutting forces typical of Tungsten carbide insert tooling (due to the higher feeds, speeds, and typically higher depth of cut) demand a lot of rigidity.   A four way (turret) toolpost is typically significantly more rigid than a quick change toolpost of comparable dimensions.  The disadvantage to the amateur of sticking with a four way toolpost is of course the need for shimming, but if your tooling has sufficiently consistent tip height, you wont need to change the shims much.  A production shop also has to consider the setup speed advantages of a quick-change toolpost with enough toolholders, and may compromise on finish to save time.

100% 
What you say makes a lot of sense, thanks.

Yes in some ways it makes more sense to invest it tooling with the same tip height for shimming to be very simple and hopefully identical for all tool holders. With the selection of 'all over the place' tooling I use now and with a small selection of shims, shimming does rob some time. A bigger/better set of shims would allow for taping each set to a tool shank.

Earlier today while browsing I stumbled across a nice little tool shank shim set that I can no longer find ! 
It certainly would be a cheaper solution to have all tool shanks the same size and a very closely matched set of tool post shims instead.

I normally just set center height to a tailstock center but I'm instead thinking about turning up a center height tool which would speed changing tooling and setting to height much faster and more precise that carbide certainly requires.

The neverending fun of making tools to make using your tools more enjoyable ! 

[mzzj]

Thinking I'll shell out for a turning holder too as this fella seems to have a 2nd screw for geometry adjustment:
https://www.ebay.com/itm/284645720497

To best match the lathe tool post I need 25mm shank tool holders which does unfortunately push into another price bracket. 

That is not geometry adjustment screw in the pics, just another clamping screw to keep the insert and/or shim firmly in the pocket.

In case it wasn't already clear: Typically you don't need to fool around with the angled shims with any of the standard threads. You need one only if you make something with really high helix angle like super-coarse thread outside of standards or multi-start thread.

You can use compound or cross slide, sort of depends on machine and personal preferences.
Earlier I was using combination of compound and cross slide as it makes math/counting really easy(increase depth of cut only from compound slide and never retract it. And use crosslide to retract the tool at the end of the cut but set it at same position before each cut)
Later on I installed 2-axis DRO and moved to using only cross slide as compound slide didn't have DRO scale and it was easier to work with the DRO numbers alone.

And unless you have huge collection of tooling with 25mm shank you can also use smaller QC toolpost. Just set the toolpost higher with piece of steel disk or plate.  (have to be flat and smooth but since you have lathe you can always turn it flat)
25mm shank tooling is not giving much advantage in home shop use unless you work on really large parts and heavy cuts like turning 1:1 scale steam locomotive axles. 
Good toolpost in >16mm shank sizes is plenty of rigid for threading with carbide. Typically the ridigity problems are somewhere else.

[tautech]

Thinking I'll shell out for a turning holder too as this fella seems to have a 2nd screw for geometry adjustment:
https://www.ebay.com/itm/284645720497

To best match the lathe tool post I need 25mm shank tool holders which does unfortunately push into another price bracket. 

That is not geometry adjustment screw in the pics, just another clamping screw to keep the insert and/or shim firmly in the pocket.

Thanks for this confirmation as I did wonder if it was for additional clamping, something plain turning inserts don't need in my experience...which is somewhat limited.

In case it wasn't already clear: Typically you don't need to fool around with the angled shims with any of the standard threads. You need one only if you make something with really high helix angle like super-coarse thread outside of standards or multi-start thread.

Yes, deeper study of the Hoffman PDF from Benta reveals the charts indicating which pitches you can turn without tapered shims....most normal stuff as you say. 

You can use compound or cross slide, sort of depends on machine and personal preferences.
Earlier I was using combination of compound and cross slide as it makes math/counting really easy(increase depth of cut only from compound slide and never retract it. And use crosslide to retract the tool at the end of the cut but set it at same position before each cut)
Later on I installed 2-axis DRO and moved to using only cross slide as compound slide didn't have DRO scale and it was easier to work with the DRO numbers alone.

All my threading thus far has been increasing cut depth with the compound slide and backing out and in with the cross slide.
Many years back I watched a professional machinist thread stepped bolts to a shoulder and into a relief to stop the lathe with the leadscrew nut engaged, bact the tool out with the cross slide then reverse the lathe and tool along the thread to stop it again, return the cross slide to zero and advance the compound for another pass.

This ^ stuck in my mind for decades until I had I had a lathe capable of threading and finally owning a fish tail threading tool.
When pressure came on to put all this together for rifle barrel threading to fit a suppressor, practice on a scrap of round stock had me get it right right from the get go and no one was amazed as I was that a small and seemingly useless bit of technique had stuck fast in my grey matter all them years !

And unless you have huge collection of tooling with 25mm shank you can also use smaller QC toolpost. Just set the toolpost higher with piece of steel disk or plate.  (have to be flat and smooth but since you have lathe you can always turn it flat)
25mm shank tooling is not giving much advantage in home shop use unless you work on really large parts and heavy cuts like turning 1:1 scale steam locomotive axles. 
Good toolpost in >16mm shank sizes is plenty of rigid for threading with carbide. Typically the ridigity problems are somewhere else.

Current 4 sided tool post in use is a 4" beast which IIRC can take 27mm tooling so 25mm tooling works well with it although I still need shim tools a little.
It replaced the smaller 3" tool post that came with this Harrison lathe which couldn't accept 1" tooling and the 4" beast I like better for a few reasons.
The most shimming I need do is for a small 14mm square shank bar I made to do small boring between 1/2 and 3/4" where my bigger bars take over.

This lathe does show some signs of wear and gib tightness is a compromise but sometimes needs addressing especially for parting where any chatter is a recipe for disaster.

Thanks chaps, really enjoying the feedback. 

[Benta]

I have a collection of small zip-lok plastic bags, each containing one tool and matching shims. That makes shimming fast and easy.