Thread Cutting Tooling

[eldon]

Following on from Bradders post on Turning and Chambering a Barrel

 

Great post!

 

Why did you pick 59.5 degrees?

Metric being 60 and UNF being 60 degrees is there a discrepancy on your machine or some other reason?

 

[MJR]

Its a throw back to threading with HSS tools where the idea is to load the cutting side of the tool face and reduce load/friction on the non cutting side. Not really needed with insert cutting tools which are fine with a straight plunge cut but it does have the advantage of moving the cross slide away from the tailstock for better access.

[Vermincinerator]

Great post!

 

Why did you pick 59.5 degrees?

Metric being 60 and UNF being 60 degrees is there a discrepancy on your machine or some other reason?

When screwcutting using the compound slide to index the tool, it is always set up half a degree short of the actuall thread angle to eliminate cuts on both edges of the tool.

 

Ian.

[eldon]

When screwcutting using the compound slide to index the tool, it is always set up half a degree short of the actuall thread angle to eliminate cuts on both edges of the tool.

 

Ian.

 

I understand that on the old carbide tooling Ian but surely with modern tipped tools the offset isn't necessary is it and a straight plunge is acceptable?

[Vermincinerator]

 

I understand that on the old carbide tooling Ian but surely with modern tipped tools the offset isn't necessary is it and a straight plunge is acceptable?

Yes a straight plunge is acceptable if you are set up on a modern CNC machine that will screwcut at very high cutting speed, modern throw away carbide tips are not designed to be used at normal centrelathe cutting speeds

Plunging the tool straight in whether it be HSS carbide or throw away causes the chip to fold on itself causing tears on the flank of the thread

[MJR]

Sorry but the misconception that insert cutting tools are not suitable for manual centre lathes is simply not true. What you do need to do however is select the correct insert for the machining operation at the speeds you intend to use on the particular material you are using. I am a fan of tipped tooling, you don't need to spend time grinding HSS and ensuring you have all the clearance angles correct just select the correct insert and crack on. Also the theory that suggests setting over the compound to allow a HSS tool tip to only cut on one side is again incorrect. Sure setting the compound over to 29.5 degrees or less does reduce friction on the trailing edge of the tool but the tip is still cutting on both sides whichever way you look at it - draw it out and you will see what I mean.

[Big Al]

Sorry but the misconception that insert cutting tools are not suitable for manual centre lathes is simply not true. What you do need to do however is select the correct insert for the machining operation at the speeds you intend to use on the particular material you are using. I am a fan of tipped tooling, you don't need to spend time grinding HSS and ensuring you have all the clearance angles correct just select the correct insert and crack on. Also the theory that suggests setting over the compound to allow a HSS tool tip to only cut on one side is again incorrect. Sure setting the compound over to 29.5 degrees or less does reduce friction on the trailing edge of the tool but the tip is still cutting on both sides whichever way you look at it - draw it out and you will see what I mean.

 

 

 

Nobody said indexable carbide inserts weren't suitable for manual lathes, Vermincinerator just pointed out the facts of which he is correct. Indexable carbide tips are designed to cut at faster surface speeds and feed rates which we cannot easily achieve when screw cutting on a manual lathe. Of course they can be used but just not optimally. If I have a fine pitched thread I would still much rather use my own HSS or HSS-Co tools as they are far sharper than carbide and cut rather than tear.

 

Feeding from an angled cross slide does ensure the tip cuts on the leading flank only, Ive done it for 30yrs and as recently as this afternoon. Just watch the chip formation of a straight plunge compared to an angled feed, you can see the difference and exactly what edge is cutting very clearly.

[MJR]

Then you've been labouring under a mishaprehension for the last 30 years.......

 

Answer me this. You set the compound over to your 29.5 degrees and advance to dial 0.010". You and I both know the depth of cut isn't .010" but you have increased the depth of thread and material will be removed. The majority of material removed is on the side of the direction of travel but what happens to the material on the opposite side of the cutting tip, do you think it just falls off? No of course not it is cut by the trailing edge of the tool tip. If you don't believe me grind a tool tip so one side is square to the work piece and the side on the direction of travel is 30 degrees, in other words half a normal 60 degree thread tip and cut a thread with it. Have a look what shape the thread profile is.

[Big Al]

Sometimes pictures are easier to understand. Both are examples of flank infeed and chip formation taken from both Sandvik and Seco websites. How much cutting do you see the trailing flank doing?

[Big Al]

Radial infeed shows chip formation from both flanks, when tool is advanced from the cross slide as a plunge cut.

[MJR]

Pay attention Bradders, you'll learn something.

 

Al, I agree with regard to the symmetrical plunge cut but the chip is obscuring what I describe with regard to the compound set over cut.

 

This guy describes it very well, his clips are well worth a watch. https://m.youtube.com/watch?v=PnH_oeOUps4

From around 8.30 onwards.

[Vermincinerator]

Thanks Alan,

Like myself and Braddrrs you were taught the correct way to screw cut on a manual centre lathe, i too prefer to use HSS tools and was also taught how to grind all shapes and profiles as an apprentice, like you said HSS cuts rather then shears and has the advantage of being able to be used at very low speeds with a light cut without the fear of shattering, i like to finnish my precision threads rotating the chuck by hand with a 001" overall cut.

 

Ian

[bradders]

Pay attention Bradders, you'll learn something.

 

Al, I agree with regard to the symmetrical plunge cut but the chip is obscuring what I describe with regard to the compound set over cut.

 

This guy describes it very well, his clips are well worth a watch. https://m.youtube.com/watch?v=PnH_oeOUps4

From around 8.30 onwards.

 

I'm always ready and willing to learn

As for cutting and threading inserts, I used these days mainly for convenience....but they aren't always convenient!

[MJR]

Thats true, they arent always convenient!

[MJR]

Ian. like you I was 'taught' some 30 years ago to set the compound over when screw cuttiing. But techniques and advances in tool technologies mean things move on. I still use HSS sometimes but use inserts more and more. I suppose you could liken it to advances in rifle sights, open v notch sights do the job and in some instances may even be the best option but for precision shooting they cant come close to modern optical sights. Just a question of choosing the correct tool for the job.....

[Big Al]

Ian. like you I was 'taught' some 30 years ago to set the compound over when screw cuttiing. But techniques and advances in tool technologies mean things move on. I still use HSS sometimes but use inserts more and more. I suppose you could liken it to advances in rifle sights, open v notch sights do the job and in some instances may even be the best option but for precision shooting they cant come close to modern optical sights. Just a question of choosing the correct tool for the job.....

 

 

In many things regarding manual center lathes I find that the wheel was round a long time ago and little has changed in the last 50yrs or more. The man who taught me to screw cut in the 80s was himself taught the same method in the early 60s, I would guess he learned it from a man taught in the 40s. The basic method of screw cutting with the tool fed by the compound at half the included angle has been around a long time. In truth it can't be improved upon, the method works as well as it ever needs to on a manual lathe. We are all limited to have fast we can screw simply by our ability to engage the half nut repeatably or stop the machine before we hit the shoulder. 190rpm is my speed for this but these carbide inserts tear at such a slow speed rather than cut, I dont see that as an advancement at all. The only real benefit is it saves time touching a tool up fro time to time or allows someone who isn't confident in their tool grinding to do the job. All that said I do use them myself but more out of laziness than anything else.

 

Carbide has been around a long time and always had its uses but I guess with the advent of indexable tips it made us lazy, for the manual centre lathe in the hands of a competent operator Im not convinced its an advancement but rather more just a convenience. Personally when doing barrel work I dont like the feeling that my machine is about to take off Very rarely do I run it faster than 800rpm which with the right insert and feed is about right for turning tenons, it removes metal quickly with good chip control and a good surface finish.

 

Your analogy about precision with rifle sights doesn't work for me as I dont consider carbide to be as precise as HSS due to it not being as sharp. If I wanted to cut a thou or less off somewhere (in a place where I couldn't polish it easily) I wouldn't be trying to rub it off with an insert, a nice sharp HSS tool would be the most precise.

 

Getting back to that American guy, if he wants to spread the misconception then I wont stand in his way.

[MJR]

Al, why are you threading towards the shoulder? You are indeed limiting yourself by doing so. Thread from a relief groove away from the shoulder and you can increase the speed substantially with no fear of crashing the tip and obtain a beautiful thread form with an insert tool. If you don't/can't engage the half nut correctly then you need to investigate the reason for that. Are you engaging the ghost engagement that's not shown on many dials?

You've been show the detail of the tip load on computer generated program, If you choose to ignore it that's fine, crack on and use what works for you but be aware there is a quicker method that either increase profitability for you or reduces the cost to your customers and significantly reduces the chance of damage to your equipment.

[Big Al]

Al, why are you threading towards the shoulder? You are indeed limiting yourself by doing so. Thread from a relief groove away from the shoulder and you can increase the speed substantially with no fear of crashing the tip and obtain a beautiful thread form with an insert tool. If you don't/can't engage the half nut correctly then you need to investigate the reason for that. Are you engaging the ghost engagement that's not shown on many dials?

You've been show the detail of the tip load on computer generated program, If you choose to ignore it that's fine, crack on and use what works for you but be aware there is a quicker method that either increase profitability for you or reduces the cost to your customers and significantly reduces the chance of damage to your equipment.

 

 

Why do I feel like Im being drawn into a dick slapping contest here with someone who hasn't played the game many times? then again people can learn a lot from Youtube these days. I find it interesting that you are selective regarding the points you pick up on when there is plenty out there. Was screwing away from a shoulder the last Youtube video you had watched?

 

I think I would be genuinely surprised if there was a method of screw cutting I hadn't seen or used sometime in my life be it towards or away from the chuck, or in/out of blind holes etc with the tool mounted in front of the work upside down or behind the work running away from the chuck with the machine in reverse. I would genuinely think Ive done it all ways for one reason or another over the years to suit particular applications. I would expect this to be the case with most people who have used a lathe for various types of thread work over a lot of years.

 

All that said, you seem to miss the point entirely (that I already made in my last post) with regard to rifle work/thread cutting using a manual centre lathe. I cut threads at 190rpm because that is as fast as I can comfortably engage my half nuts, this is the same whether Im working towards or away from the chuck. If you get yourself into that groove you describe and you miss your mark at carbide speeds then your well into the thread and its wrecked. I dont have an Ainjest on my machine so 190rpm is as fast as I want or need to cut threads. Ive seen the guys who work quicker with reactions like a cobra but sooner or later it goes tits up whereas I can't remember the last time I spoiled a thread or crashed a tool in any direction. As for my thread dial, I kind of know how to do it and where all the engagement points are, its quite elementary stuff you are talking about here. Its standard stuff to ride the thread before the nuts engage so Ive no trouble hitting my marks except where I have previously mentioned.

 

I think its silly to talk about increasing profitability or reducing costs when it comes to the thread cutting element on a rifle barrel, the time it takes me plodding away at 190 rpm is minimal in the first place and Im happy that my prices are fair yet profitable based on the time it takes me.

[MJR]

Well you can slap your dick all you want but don't involve me, we have a name for people who do that....

 

I'm just showing you another method which you now claim to have used but seem incapable of now using. First it's HHs only, then it's ' im not comfortable engaging the half nuts'. really? Stop trying to move the goal posts! How long did you say you've been using a lathe?

[Big Al]

Well you can slap your dick all you want but don't involve me, we have a name for people who do that....

 

I'm just showing you another method which you now claim to have used but seem incapable of now using. First it's HHs only, then it's ' im not comfortable engaging the half nuts'. really? Stop trying to move the goal posts! How long did you say you've been using a lathe?

 

 

This is getting more and more silly by the minute MJR, you dont seem to be getting a quite simple but very crucial point in this discussion.

 

Regardless of the orientation that we screw cut everything depends on engaging the half nuts in the appropriate place or places (unless they need to stay in all the time like cutting metric threads with an imperial lead screw or vice versa) very crucially here there is a limit to what spindle speed your average but fully competent operator can do this at. Ive told you what mine is or what I am happy working at, about 190rpm, maybe a bit more at a push. Now if I screw towards or away from the chuck Im still going to be doing it at 190rpm. At that speed I would need to fall asleep to hit the shoulder when Ive got a groove to run into, like I said I really can't remember the last time that happened.

 

So why would I want to use the method you describe?

 

I can't work at any faster speeds for the reasons Ive mentioned and the direction of travel matters little based on that fact.

 

Tell me, do you screw cut on a manual lathe at speeds that your carbide tips were designed to operate using a standard thread dial indicator, if so exactly how fast are you running?

[MJR]

Al, you're moving the goal posts again. You seem to be ignoring the information regarding the stress on a HSS thread cutting tool tip and instead trying to glean information?

If 190 rpm is your limit, fine, go with it.

But yes I do use faster speeds than that on a manual machine and as I said earlier I have experimented and found insert tips that give more than acceptable results using plunge cuts and threading away from shoulders.

[Vermincinerator]

Yes, but screwcutting by advancing the tool with the compound slide gives better then "more then acceptable" results then plunge cuts.

 

Ian.

[Big Al]

Al, you're moving the goal posts again. You seem to be ignoring the information regarding the stress on a HSS thread cutting tool tip and instead trying to glean information?

If 190 rpm is your limit, fine, go with it.

But yes I do use faster speeds than that on a manual machine and as I said earlier I have experimented and found insert tips that give more than acceptable results using plunge cuts and threading away from shoulders.

 

 

With respect MJR I really feel like Im trying to debate with a guy who doesn't really know much about the subject matter, I keep making valid points any experienced turner or machinist would get and you seem to miss them completely or choose to ignore them, as such I dont really know where to go with this but heres a summary of how Ive seen things.

 

Back at the beginning of this debate you made two points which I picked up on.

 

 

Sorry but the misconception that insert cutting tools are not suitable for manual centre lathes is simply not true. What you do need to do however is select the correct insert for the machining operation at the speeds you intend to use on the particular material you are using. I am a fan of tipped tooling, you don't need to spend time grinding HSS and ensuring you have all the clearance angles correct just select the correct insert and crack on. Also the theory that suggests setting over the compound to allow a HSS tool tip to only cut on one side is again incorrect. Sure setting the compound over to 29.5 degrees or less does reduce friction on the trailing edge of the tool but the tip is still cutting on both sides whichever way you look at it - draw it out and you will see what I mean.

 

The first point you made was because you grabbed the wrong end of the stick. Vermincinerator never said indexable carbide inserts were not suitable for use on a manual centre lathe, he said they weren't designed for use at normal centre lathe cutting speeds and that is a perfectly accurate statement. None of us have argued with you that you cannot use them or that they dont provide good results at times but equally there are times when HSS used at normal centre lathe cutting speeds is better. Threading inserts like you and I use are meant to cut at surface speeds way beyond what anyone can achieve on a centre lathe, that is an undeniable fact, yes they can offer a workable compromise if that is all you need.

 

Secondly, you tell us that the flank infeed method is flawed and that there is no need to feed in via the angled compound method, you tell us to draw it out and we will see where the tool cuts.

 

I did exactly that except I used drawings that were provided by Sandvik and Seco in their technical information documents - for those who dont know who they are they are two of the worlds largest makers of thread cutting inserts. When I give you the facts you ignore them or say the images are wrong and instead refer me to a Youtube video of an American guy playing on his computer doing simulations that almost suit your position, even then you changed from the tool cutting on both sides to it cutting on a very small parts of the second side but even that is questionable.

 

These were the points of the discussion, once you didn't want to see or read the truth you moved away from them onto a different subject entirely yet you keep accusing me of moving goalposts? You chose to then pick up on the direction in which to thread and how I should be doing it better/differently. I made reference to cutting towards a shoulder and again you got the wrong end of the stick, you jumped onto the incorrect assumption again that this was the only way I might thread or know how to. From there your now telling me the right way to thread and most efficient profitable route for my business????

 

Something I learned a long time ago from my own very skilled mentors (who proved their skills to me daily at work in real life, not by making Youtube videos) was that there are many ways to do things and to be a good machinist you need to be versatile and adapt to the challenges different jobs offer. I use indexable carbide tooling in my workshop, I also use HSS. I know when to choose which, the advantages and disadvantages of that choice and when a compromise will do and when it wont.

 

With respect, Ive been sucking eggs a long time.

[Big Al]

If you want to use Youtube for information it can be useful if you go to trusted websites, none more so that Sanvik.

 

 

The relevant part is from the beginning until 1m12s

 

Here is a very relevant screenshot from from 1m12s

 

 

Take a look at the last two bullet points and lets look at exactly what they mean in the real world to an experienced machinist.

 

Less heat generation = lower tool wear, greater tool reliability, less chance of tip breakage

 

Less vibration = again better tip reliability but more importantly better surface finish, vibration = chatter = bad.

 

Higher production reliability = less chance of tip breakage and all round reliable performance.

 

First choice for most threading operations = there might be a subtle clue in that one somewhere

 

I could spend all day doing this, finding information from reliable industry sources that support what I and others have tried to tell you. You need to come up with something better than some random American guy making Youtube videos (that almost suit your position) for me to comment any further on this Im afraid. Time to go an cuts some threads

[MJR]

Yep that will be you moving the goal post again....

 

Now you accuse me of knowing nothing of the subject matter, fine, but tell me where you YouTube clip addresses suitability for manual machines? It doesn't? Seems ok for you to refer to a YouTube clip but not me ?

 

I was originally trying to adress the misconception that setting the compound over makes the tool tip cut on one side only - it doesn't. The tip still cuts on both sides as demonstrated by the clip I linked to, the one you choose to dismiss.

 

I don't deny the reference bullet point you use in your last post but your clip also high lights the use of incremental feed and radial feed so really all techniques have their merit and like I said in a much earlier post, you have to choose the tip and techniques suited to the work piece.

 

We are obviously not going to agree so crack on and use what works best for you and good luck.