Threading - 29.5/30 vs 90

[VicHobbyGuy]

Some parting tool issues I've heard about that subsequently became resolved ended up being machine issues, not tool issues. Same general idea, if the machine components are not fully supported as they should be or have the ability for undesirable play, those factors can result in similar issues or even cause kind of a feedback loop.

Exactly - Parting became a lot quieter and less 'exciting' for me after I replaced the compound with a solid block (a.k.a. plinth) and at about the same time switched to a better quality (Warner) thin (P1N .040") tool. So, probably machine+tool solution - I didn't 'go back' to figure out which; I was just happy that parting was easier.

 

[DPittman]

Someday soon I will try better carbide inserts for threading than the crap I used previousl

I believe you had mentioned at one time you have/had a Mesa threading and grooving tool holder....did you not get any threading inserts to go with that? If not, you should. They are expensive, but they are sharp and really work nice with that tool holder, you can flip them end to end and then there are also lefthand ones that make upside down threading easier. Yes they can still chip the point off like most carbide (and probably even easier because of the sharp tip.

 

[Susquatch]

For those with smallish lathes (or perhaps any lathe) Clough42 on Youtube just found out why his 400 lb lathe didn't like form tools much, and fixed it. Since threading tools are form tools no matter how you use them, this video might be appropriate form some people.

It highlights the idea that the whole system contributes to chatter, and some times it is fixable...

I have had problems parting............ I will look. You never know.

 

[Susquatch]

I believe you had mentioned at one time you have/had a Mesa threading and grooving tool holder....did you not get any threading inserts to go with that? If not, you should. They are expensive, but they are sharp and really work nice with that tool holder, you can flip them end to end and then there are also lefthand ones that make upside down threading easier. Yes they can still chip the point off like most carbide (and probably even easier because of the sharp tip.

You have a GREAT memory.

Yes, I have the Mesa threading tool and I like it. The point on the bits I have are all chipped though. I should buy replacements. $$$ Ugh. Perhaps I will get enough so I can try grinding the point a bit on one.

 

[Johnwa]

If it weren’t for having to grind tools I would almost always stick witH HSS. With HSS you can shave off a thousandths with a sharp too. I can’t do that with carbide. With my Southbend it either does’t cut or takes off 5 to 10 thou. On my SM it will consistently take off about 5 thou but won’t shave off much less than that. This is all with regular inserts.

 

[Susquatch]

I believe you had mentioned at one time you have/had a Mesa threading and grooving tool holder....did you not get any threading inserts to go with that? If not, you should. They are expensive, but they are sharp and really work nice with that tool holder, you can flip them end to end and then there are also lefthand ones that make upside down threading easier. Yes they can still chip the point off like most carbide (and probably even easier because of the sharp tip.

@DPittman & @PeterT - Here are photos of my existing Mesa Carbide tool inserts. It's easy to see how they failed.

And here is a photo of a cheap kit insert. Basically the same type of failure.

Now compare that with the ARWarner HSS Inserts with maybe 20 or 30 times the number of jobs under their belt. The flat below the tip is original and intentional.

For regular non-precision threading, I just grind some regular HSS tooling. As soon as I get some of the regular carbide threading inserts like Peter recommended, I will try them and post again.

 

[DPittman]

Yes I learned that the inserts did not like to be bumped up against the work surface when fiddling around centering the height or just being uncareful. I would imagine they would not handle interrupted cuts very well either. However i have been pleased with them when I handle them appropriately. I doubt you would be able to regrind an edge on those as sharp and fine as the original.
I've only tried the triangle hss inserts from AR Warner but like them also.

 

[PeterT]

@Susquatch that is classic carbide fracture. I would share your reluctance to use inserts too if that was a consistent outcome. The key question is, how is it happening? Typically its alignment, chatter, interrupted cut, flex, slide or play anywhere in the supporting components from the holder through to the ways. Easy to type, maybe not so easy to diagnose. My gut feel is its a feedback loop. Initial alignment is good, speed & feed are acceptable. But something is allowing it to move in & out of the cut & brittle materials like carbide just don't like that. The HSS may be the identical form & sharpness & subjected to the forces, but just more tolerant. I think if you fix the problem, even the HSS will look better that they were or at least cut more efficiently.

I'm not familiar with the Warner system but I suspect its good. For $20 of disposable R&D & would try an Ali lay down threading tool. Ease into it with fine threads & something nice like 12L14. If it starts chipping & degrading too, then my assumption would be some kind of other machine/setup issue going on. If its good initially but issues arise at certain DOC or material types, then the focus turns back to insert tooling. Not knowing your machine, but if the leadscrew is wearing & locking isn't done, that can have a big impact on threading & parting which are kind of devious cousins.

A an aside I have been tricked before aligning regular carbides on vertical center in what I call lazy man way - lightly trap a ruler between cutter & work, it should hand vertical. This is actually a bad habit taught to me in school that should be removed from cranial RAM IMO. Many inserts have rake geometry where this actually can land you in the wrong vertical position & adversely affect cutting. Secondly, trapping a steel rule, typically pretty hard material, cant be good for carbide. I've chipped them kissing off a chuck jaw for zeroing so I don't do that anymore, or use an aluminum shim as buffer. Its better to take a micro skim off the end of bar until the nub is gone right through center & lock the toolholder there. Remove the tool & repeat, it should be identical & repeatable. I had a toolholder where the stud started floating & rotating which meant the toolholder was going along for the ride even though the stop & nit were tight.

 

[Susquatch]

@Susquatch that is classic carbide fracture. I would share your reluctance to use inserts too if that was a consistent outcome. The key question is, how is it happening? Typically its alignment, chatter, interrupted cut, flex, slide or play anywhere in the supporting components from the holder through to the ways. Easy to type, maybe not so easy to diagnose. My gut feel is its a feedback loop. Initial alignment is good, speed & feed are acceptable. But something is allowing it to move in & out of the cut & brittle materials like carbide just don't like that. The HSS may be the identical form & sharpness & subjected to the forces, but just more tolerant. I think if you fix the problem, even the HSS will look better that they were or at least cut more efficiently.

I'm not familiar with the Warner system but I suspect its good. For $20 of disposable R&D & would try an Ali lay down threading tool. Ease into it with fine threads & something nice like 12L14. If it starts chipping & degrading too, then my assumption would be some kind of other machine/setup issue going on. If its good initially but issues arise at certain DOC or material types, then the focus turns back to insert tooling. Not knowing your machine, but if the leadscrew is wearing & locking isn't done, that can have a big impact on threading & parting which are kind of devious cousins.

A an aside I have been tricked before aligning regular carbides on vertical center in what I call lazy man way - lightly trap a ruler between cutter & work, it should hand vertical. This is actually a bad habit taught to me in school that should be removed from cranial RAM IMO. Many inserts have rake geometry where this actually can land you in the wrong vertical position & adversely affect cutting. Secondly, trapping a steel rule, typically pretty hard material, cant be good for carbide. I've chipped them kissing off a chuck jaw for zeroing so I don't do that anymore, or use an aluminum shim as buffer. Its better to take a micro skim off the end of bar until the nub is gone right through center & lock the toolholder there. Remove the tool & repeat, it should be identical & repeatable. I had a toolholder where the stud started floating & rotating which meant the toolholder was going along for the ride even though the stop & nit were tight.

These are good questions to ask. Since my experience lined up with what I've read elsewhere, I just assumed it is a hss vs carbide thing. But maybe not. I do have a few things that have bothered me at the back of my mind.

Eg, how repeatable is my piston style BXA Tool Holder?

I don't use a ruler to set height. Never did. Made myself a tool height standard when I got my 2nd lathe 10 years ago. I use that to set and check tool heights.

I have not ordered a carbide insert threading tool yet, but when it arrives I'll try what you suggest. I'm still researching alternatives. The kbc discount is calling me.

 

[Bandit]

So I came on to this thread again from the "threading, depth of cuts thread". Interesting, 90 degrees, or 29.5+/- for threading, why one or the other, and why did they come about.
Perhaps the history of the lathe is why. We won't go back to a piece of wood held between two trees, turned by some one, while another someone holds a rock against the turning wood, or what ever they may have used. Take a look the early lathes made of wood and metal, there was no lead screw, no cross slide. A rest of some kind and a cutting tool of some kind, the cutting tool hand held. Like the wood lathe we know. The cutting tool was guided by hand, traveling speed, depth of cut.
The metal lathes were the same, I have read where the operator made punch marks, gauged with a scale in the bar of metal being threaded, and cut free hand from mark to mark while the bar turned, (no VFD), most likely more then one row of punch marks. Bolts and nuts etc. were not inter-useable between makers. Somewhere was made a cutter that had more then a single cutting point, you still had to get it started right!
Who had the brain to put a lead screw on a lathe and a saddle with a cross slide to be moved by the lead screw was a dam smart one.
Now for the oats, you could cut a 90 degree plunge cut thread with this setup. No compound, no 29.5+/- cuts, unless some free hand setup. When did the compound slide come about? No real idea, middle to late 1800's I guess. I do know some lathes sold had no compound slide even in the mid 1920's, I have one, could purchase with or with out a compound slide. For just a few dollars more! Maybe this was the case much later then that.
We take for granted a cross slide, compound slide, power feeds etc. We are pretty lucky.

 

[Susquatch]

This is as good a place as any to put this question because the subject is quite relevant.

But this new question is strictly about carbide inserts for threading.

First of all, I have to apologize to @thestelster who already gave me some advice on this subject, but I've lost it. Can you remind me what holders and what inserts you use for threading Stel?

Over the course of the last 6 months I've been busy reading carbide references and learning about what everything means. I recently made a giant step forward when I realized that all the dimensions are usually imperial but often have metric equivalents.

Thus a metric TNMG160404 is the same as (and interchangeable with) an imperial TNMG331. It's a huge source of confusion lifted off of my back.

Yes, I know that is not universally true and that some inserts are really metric but labelled as imperial. It doesn't seem to matter though. I now understand the interchangeability better than I did and I can actually look at a catalog and have a general sense of what I'm looking at. Until recently it was all just Greek

I have purchased TNMG, WNMG, and CNMG holders with anvils as well as steel, stainless, & aluminium inserts all with 0.4mm / 0.016 / 1/64th tips. I may get a few inserts with bigger tip radiusses for finishing, but I had to start someplace. Maybe I'll use David 's US source to get 3 of those.

Unfortunately, the delay caused by learning insert lingo has caused me to misplace the recommendations @thestelster gave me for holders and inserts for threading. I am anxious to get some and try them.

I'll happily accept advice from others too.

So how does that relate to this thread?

Well, my theory is that carbide usually requires a larger bite to work properly and I am thinking that this requirement might not be compatible with what happens on the 29.5 degree face which is only shaving a wee bit on each pass. In this case, I'm thinking a 90 degree plunge cut might be WAAAY better.

However, now that I know I can sharpen carbide and/or use sharp inserts for aluminium on steel, maybe that isn't true either!

For now, all I can ask of you guys is your advice. As soon as I can get and try a carbide threading holder and inserts, I will try it myself. Doing is believing as they say.

Advice?

 

[Dabbler]

For my single point threading, I use 390 degrees, but now I'm rethinking that assumption. I have bigger machines now. But it is common in Europe to teach 90 degrees - not 29.9/30...

I *love* that there are 500 ways to do a thing, and I really like to sort out why each one was recommended and how it might be applied.... I'm all ears to updates to this thread!

 

[thestelster]

@Susquatch

What inserts do you like and why?

External threading on the lathe, I exclusively use carbide insert tooling. The tool on the left, probably 98% of the time. For internal threading, anything larger than about 3/4" bore, I'll use carbide, and HSS for smaller bores.

canadianhobbymetalworkers.com

 

[thestelster]

Solid Toolpost Turret

What is the part number at MMC? https://www.mcmaster.com/metals/shape~rod-and-disc/oversized-easy-to-machine-gray-cast-iron-rods-and-discs/ If you go to that link above, they have a whole wack of sizes. They offer cast iron in gray cast as well as ductile, but I'm pretty sure that grey cast...

canadianhobbymetalworkers.com

 

[PeterT]

Sharpening carbide is another subject unto itself. Have you ever had a very dull knife & did the step-1 re-profiling with a very coarse stone? Say 80-100# just to put a visual on it. It can actually be quite 'sharp' if we want to use a variation of the word. It will saw through a tomato & cut your finger. So why spend all the extra time progressing up through 3000# stones & maybe even stropping with polish? The key word is saw. Under magnification the step-1 edge is zig zag profile brought about by the exposed stone particles gouging through the steel. The size of the hill & valley zig zags of the blade wont be appreciably different in size than the (coarse) average particle size of the stone +/- variations in dressing direction, feed, pressure etc. But compared to a knife blade with a manicured razor edge, this isn't really an optimal cutting surface because a) the amount of exposed cutting surface is very small and b) they occur at different geometric orientations. So it will dullen quickly & generally be much inefficient. Now when you use this analogy on a lathe cutting tool, the entire cut is dictated by this edge because the orientation stays the same (+/- flex & heating etc).

I view sharpening carbides as much the same. These days its easy to get your hands onto diamond or CBN dressing wheels, plates or whatever. They are much more affordable & sufficiently hard to re-dress carbide tools, after all they were done that way in the factory. I doubt that carbides come out of the molds consumer sharp & ready to use. Most of the home shop guys I've seen who routinely sharpen carbides are doing something more like lapping, at least for the finished edge. Usually is lower dressing speed & finer particle size abrasive, often slurry or paste. I might be wrong but I think its for the reasons outlined. Carbide is very hard & will more readily fracture with higher dressing load or particle size. It may seem sharp but... (see tomato analogy). I want to get into scraping at some point, so dressing carbide tools is going to come up. Fortunately, smarter people have already solved these issues.

Coated carbides are yet another factor. They are very often 'less sharp' compared to HSS when new. That could be the carbide profile or the effect of coating round-over or both. That less sharp profile is a tradeoff the factory has made considering a bunch of other factories in an industrial setting. Yes, those will have to accept deeper feed & are less suitable to hobby machines. But those inserts do not define or typify all carbides as evidenced in their catalogs. I have no information to support this but I think lapping through a coating to expose a better edge or altered geometry is maybe a shorter term fix. I've had inserts where the coating is chipped but remainder of carbide is intact & they cut like crap. So dressing a coated insert might correct the geometry, but now also exposing the coating interface joint which it I doubt was how it was designed to operate. Now maybe it lasts a couple years in a home shop environment & defers the cost of replacement & that's perfectly viable. Maybe that's why results vary. Also, when you see some inserts in cross section, there is a limit to how far you can dress before interfering with other geometry.

Now when it comes to profiled cutters like threading, the advantages of carbides starts to tip the scale IMO. All of the geometric tuning is built into the carbide molds & every insert comes out the same. Can you achieve a simple vee profile in HSS within a degree? Of course. How about at a specific rake angle & still ensuring 60-deg thread cut profile? Probably, but need to be more careful now. How about a buttress or non-vee thread? More work. How about chip flow/control features? Mmm.. maybe with a Dremel? Now the tool eventually becomes dull or unusable. Its a personal choice but for the cost I'd prefer to screw in another & carry on vs start over again with hand working. If its problem material or special circumstances then of course there is no magic solution, we do what we have to do.

Redressing aluminum cutting inserts probably has a few advantages. Out of the box they are typically uncoated so no issues that way. They are also typically very sharp, arguably just as sharp as you can achieve with HSS (or how about HSS after 5 minutes of use which is probably the real criteria). But their rake & cutting geometry & chip breaking is optimized to these alloys, so the flipside is they are not really optimized for steels. Will they still work on steel out of the box? My money says yes, I've done it many times. For lighter cuts & finishing & specific alloys, but you may have to make other speed & feed adjustments & accept tool life. Is it more prone to fracturing under heavy or interrupted cutting, mystery metal? Again yes. o they would be the wrong choice for that criteria. But the margin of potential usability and non-usability within this bookend spectrum is very wide. My own opinion is that there is a lot of perpetuated myth syndrome. Somebody bought some lathe inserts, probably the wrong ones, had nothing but problems & threw the whole carbide enchilada under the bus without delving much further. I'm not here to convince anyone of anything, but even if you knew nothing & just did a visual mental tally of 1000 home shop machining pics on the internet where amateurs are making 'nice stuff'.... there is a lot of carbide being used & its not breaking the bank. We as hobbyists are benefitting by industrial spinoff.

The point is as diamond & CBN prices have come down for dressing tools, so have the inserts. I can buy a box of 10 CCMT for $20 so why sharpen them unless I am after a different profile? that I couldnt buy in another flavor. Yes, bigger tools, bigger cost, I accept that. But also bigger lathe & getting outside the range of typical hobbyist. I just don't buy the HSS is sharper line but just my opinion. I've put this challenge out to people before who might be into bladesmithing & have one of those sharpness scales (generic link below). I would be very interested to see the numerical difference between HSS & out of box aluminum inserts. And then repeat it after X minutes or hours of machining time on the same coupon & cutting conditions. Based on my consumption of Bandaid's, carbide tooling seems pretty sharp LOL

fineedgeknife.com - fineedgeknife Resources and Information.

fineedgeknife.com is your first and best source for all of the information you’re looking for. From general topics to more of what you would expect to find here, fineedgeknife.com has it all. We hope you find what you are searching for!

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[Susquatch]

Redressing aluminum cutting inserts probably has a few advantages. Out of the box they are typically uncoated so no issues that way. They are also typically very sharp, arguably just as sharp as you can achieve with HSS (or how about HSS after 5 minutes of use which is probably the real criteria).

That's a lot to digest Peter.

I think the point you made above is a very valid one.

My experience is that HSS has to be sharpened every few jobs. The edge doesn't last forever. But I can usually do that with a very light touchup on a wet stone and then polishing compound on a leather wheel. I doubt I could do that with Carbide. I'd prolly need new diamond grinding tools - which I don't have yet.

Here is a photo I took a few day ago that shows the edge between carbide for aluminium (with chip breaker), and a HSS insert from Arthur Warner. Neither one has been used yet.

They both LOOK & FEEL VERY SHARP.

I may try to do an edge comparison over time when I get time.

I'll digest the rest of your post later tonight when my mind is a bit clearer. Just thought I'd react to that part while it's fresh in mind.

 

[Susquatch]

I *love* that there are 500 ways to do a thing, and I really like to sort out why each one was recommended and how it might be applied.... I'm all ears to updates to this thread!

Me too on both counts!

In time, the 90 might become standard for me too! But for now, I'm still a fan of 29.5 degree with HSS. I do a lot of threading and that seems to produce the most reliable quality threads.

 

[Raygers]

Me too on both counts!

In time, the 90 might become standard for me too! But for now, I'm still a fan of 29.5 degree with HSS. I do a lot of threading and that seems to produce the most reliable quality threads.

When I was in college I was taught both methods with the advisor that 30-degree method is the accurate method, there is less loading of the part, especially if a small diameter part. 90 degrees can and will dig in but is adequate for most applications. the calculations differ but are available online these days.

 

[johnnielsen]

I was taught a modified version of the 90 degree method using a hand ground tool. Each pass except the first involved plunging say .010 with the cross slide and dialing the compound over half of that (.005). A skim pass was the last where you dialed back the compound .001 to clean up the back side of the thread.

 

[Susquatch]

I was taught a modified version of the 90 degree method using a hand ground tool. Each pass except the first involved plunging say .010 with the cross slide and dialing the compound over half of that (.005). A skim pass was the last where you dialed back the compound .001 to clean up the back side of the thread.

Wow John! I've never heard of that method. It's a cool one to add to my tool box.

Please forgive me for doing a bit of an assessment of your method. My curiosity got the better of me.

From the perspective of the part and the tool, I think it is "almost" the same as the 29.5 degree method, not the 90 degree method. But from the perspective of the operator it is more like the 90.

Without doing the full math, I think that advancing the cross-slide some amount and then the compound half of that is exactly the same as taking a 30 degree cut with the compound.

Your final skim pass has roughly the same effect on the backside as the 29.5 cuts do too. The main difference is that it only does the cleanup once instead of a little each time. In my mind, there is nothing to suggest a little each time is better at all. I think the only reason for it is to avoid a rather more complicated cleanup at the end because the compound is on an angle. Setting the compound to 30 for most of the passes and then to 29.5 for the last introduces other factors that might throw a wrench into the gears. It's easier and less complicated to just leave it at 29.5 throughout the entire threading operation. But we all know that teeny tiny passes can cause their own surface finish issues so doing the cleanup your way all at once might leave a nicer finish than many smaller 1/2 degree passes might leave.

I think the biggest difference is that your way looses the reference baseline provided by a cross-slide that is kept the same for the whole process.

Setting the compound to zero before each cut establishes a baseline that each progression of the compound builds on. This allows the cross slide to be backed out at the end of each pass so the tool can be reversed without damaging the threads and then reset to zero for the next pass with the compound doing all the advancement. For me at least, being able to leave the compound free to simply build the thread while the cross slide acts more like an engagement at a constant location is easier and less complicated. But it is equally easy for me to see why another machinist would hate what I love..

Just one last comment - isn't geometry beautiful!

Thanks for sharing with us John. That's a beautiful method to add to my Toolbox and a nice opportunity to think a little more deeply about what is going on during a threading operation.