Lathe Setup / Tests

[Dr_GMJNParticipant @dr_gmjn]

Posted by Andrew Johnston on 09/11/2020 21:19:39:

Out of idle curiosity I just tried an experiment with a 1" diameter bar of EN3B sticking 6" out of the chuck. I used the well worn CCMT insert that is on the lathe at the moment. Parameters were 800rpm, depth of cut 5 thou and feedrate 4 thou/rev. Absolutely no problem; no chatter or vibration. The finish is perfectly smooth to the touch.

The problem is unlikely to be resonance. I'd place my bet on the chuck; I was using a Burnerd EC collet with 6 fingers, so the work was held solidly.

Andrew

Thanks Andrew. I'll try again in the 4 jaw chuck tomorrow. I've also got another 3 jaw which looks much newer, but is far worse in terms of runout. They all came with the lathe. For most of my work on the steam engine I used a new collet chuck or the 4-jaw.

I suppose if your lathe is heavier duty than my ML7 that could make a difference. However I'm pretty sure I've seen steel cut on an ML7 for this test on YouTube, with no apparent issue.

[ianjParticipant @ians]

This is a copy of the Myford Inspection sheet

[Dr_GMJNParticipant @dr_gmjn]

Thanks for the Myford test sheets Ian. I might re-check mine over the 6” test rather than the 8” I did, just for a laugh.

Interesting that my maximum deviations from nominal on the bed wear measurements were all well within the specified limits, yet the saddle still locked solid at the tailstock end.

[HopperParticipant @hopper]

Posted by Dr_GMJN on 09/11/2020 22:20:59:

Thanks for the Myford test sheets Ian. I might re-check mine over the 6” test rather than the 8” I did, just for a laugh.

Interesting that my maximum deviations from nominal on the bed wear measurements were all well within the specified limits, yet the saddle still locked solid at the tailstock end.

Well yes. If you have 3 thou of wear and set your gib to one thou clearance at the worn spot, it will not fit over the section that is 3 thou larger. You were expected to adjust your gib to suit. IE set it a bit tighter to fit the worn section most of the time, because you rarely need to move the carriage to the very far right end of the bed. If you were doing an unusually long job you set the gib to fit the less worn section of bed and live with the bit of extra slop on the worn section. You cant achieve perfection on a worn lathe. Its all about compromises and developing the skills to work with them.

[Dr_GMJNParticipant @dr_gmjn]

Posted by Hopper on 10/11/2020 02:29:22:

Posted by Dr_GMJN on 09/11/2020 22:20:59:

Thanks for the Myford test sheets Ian. I might re-check mine over the 6” test rather than the 8” I did, just for a laugh.

Interesting that my maximum deviations from nominal on the bed wear measurements were all well within the specified limits, yet the saddle still locked solid at the tailstock end.

Well yes. If you have 3 thou of wear and set your gib to one thou clearance at the worn spot, it will not fit over the section that is 3 thou larger. You were expected to adjust your gib to suit. IE set it a bit tighter to fit the worn section most of the time, because you rarely need to move the carriage to the very far right end of the bed. If you were doing an unusually long job you set the gib to fit the less worn section of bed and live with the bit of extra slop on the worn section. You cant achieve perfection on a worn lathe. Its all about compromises and developing the skills to work with them.

Yes, luckily I never turned anything long enough to lock the saddle solid.

Still, for the sake of about 3 hours’ work with a file, some shim steel and Loctite, might as well get rid of the main wear, and remove the need to adjust it altogether.

For me, Id rather spend time between models getting the equipment right, so I can concentrate 100% on making parts when the time comes (and not wonder if any errors are mine or the machine – I know they’re mine now!).

[HopperParticipant @hopper]

Yep, that;s the beauty of the Wide Guide conversion, even with the extra touch up you had on your front shear. The return on the little bit of time and money it takes makes it the single best thing you can do for a worn Myford. (Along with setting the shimming on the headstock bearings.)

Don't worry, you'll find other things need fettling as you go along. ITs a bit like riding vintage motorbikes. Each ride something pops up that needs taking care of, Might be minor but always something.

Edited By Hopper on 10/11/2020 08:19:25

[Dr_GMJNParticipant @dr_gmjn]

Posted by Andrew Johnston on 09/11/2020 21:19:39:

Out of idle curiosity I just tried an experiment with a 1" diameter bar of EN3B sticking 6" out of the chuck. I used the well worn CCMT insert that is on the lathe at the moment. Parameters were 800rpm, depth of cut 5 thou and feedrate 4 thou/rev. Absolutely no problem; no chatter or vibration. The finish is perfectly smooth to the touch.

The problem is unlikely to be resonance. I'd place my bet on the chuck; I was using a Burnerd EC collet with 6 fingers, so the work was held solidly.

Andrew

Andrew,

I just did a quick test with the 4 jaw, and it seems to work fine on steel at 6". Looking at the Harold Hall website, he suggests 4" unsupported for the outer boss, so that should be even better.

The odd thing is that I put the aluminium test piece in the 4-jaw, and only got a marginal improvement with the burnished effect on the outer boss. I wonder if it's the lower stiffness of the aluminium that causes it to move more than the steel under a cut?

So on to starting another thread on ML7 chucks…

Cheers.

[Dr_GMJNParticipant @dr_gmjn]

Posted by Hopper on 10/11/2020 08:13:25:

Yep, that;s the beauty of the Wide Guide conversion, even with the extra touch up you had on your front shear. The return on the little bit of time and money it takes makes it the single best thing you can do for a worn Myford. (Along with setting the shimming on the headstock bearings.)

Don't worry, you'll find other things need fettling as you go along. ITs a bit like riding vintage motorbikes. Each ride something pops up that needs taking care of, Might be minor but always something.

Edited By Hopper on 10/11/2020 08:19:25

Agreed.

I think the only comment I'd have on your measurement article would be that IMHO the overall bed width should be a key measurement. IIRC you suggest doing it as a double-check?

If you measure the individual bed widths, and you've assumed wear is predominantly on the inner faces, doing the wide-guide conversion will have negligible effect, and you might be left wondering what went wrong. I know you said mine was the first example of wear on the inside face you'd heard of, but at the end of the day, it was an easy fix either way, and it's a very easy check to do with a DTI on a base run against the un-worn rear bed edge – you don't need a large micrometer to do it if you've not got access to one.

Cheers.

[Martin ConnellyParticipant @martinconnelly55370]

Did you read the thread on vertical shear tooling? It is possible it will take off the fine cuts you are trying to do on the dumbbell.

Martin C

Thread 168702

Thread link added.

Edited By Martin Connelly on 10/11/2020 13:04:52

[Dave HalfordParticipant @davehalford22513]

Rotate a jaw till it's at the top when gripping your bar and put a light behind it see if there's any light coming between jaws and bar where they should be touching.

If there is it might be worth keeping if the outside jaws are OK

[Anonymous]

I did an experiment at lunchtime with a 1" diameter 6082 aluminium bar sticking out 6". I changed the insert to an old CCGT one specifically for aluminium. As before I ran at 800rpm and 4 thou/rev feedrate. A DOC of 10 thou gave a smooth finish although there was a light mottled pattern. With a DOC of 5 thou the pattern had almost disappeared. With a 2 thou DOC there was no pattern, just a smooth finish.

Andrew

[Dr_GMJNParticipant @dr_gmjn]

Posted by Andrew Johnston on 10/11/2020 16:19:40:

I did an experiment at lunchtime with a 1" diameter 6082 aluminium bar sticking out 6". I changed the insert to an old CCGT one specifically for aluminium. As before I ran at 800rpm and 4 thou/rev feedrate. A DOC of 10 thou gave a smooth finish although there was a light mottled pattern. With a DOC of 5 thou the pattern had almost disappeared. With a 2 thou DOC there was no pattern, just a smooth finish.

Andrew

What lathe is it though?

[Anonymous]

Posted by Dr_GMJN on 10/11/2020 17:35:25:

What lathe is it though?

Harrison M300:

Andrew

[Dr_GMJNParticipant @dr_gmjn]

Posted by Andrew Johnston on 10/11/2020 18:56:30:

Posted by Dr_GMJN on 10/11/2020 17:35:25:

What lathe is it though?

Harrison M300:

Andrew

So…probably multiple times stiffer overall than my ML7? I wouldn't expect to have much problem machining a 6" aluminium test piece on that!

[Anonymous]

Correct, my lathe is much heavier and more rigid than an ML7. But we're talking light cuts here. So neither characteristic is significant. I did get a slight pattern on the aluminium at larger DOC. I suspect the issues are how firmly the work is held and the cutting tool itself. It may well be that a slower, or faster, spindle speed will help. Any sort of pattern implies a cyclic variation of some sort; albeit not usually resonance. The natural tendency is to reduce speed/DOC/feedrate, which can help. But counterintuitively increasing the parameters can also help. Experimentation is needed.

Andrew

[Howard LewisParticipant @howardlewis46836]

I notice the reference to "A new insert", suggesting a carbide insert.

Carbide inserts do not universally like being used with small cuts. They were developed to remove metal rapidly., and many years after the ML7 was designed and launched

May I suggest repeating the dumbell test with a sharp HSS tool, carefully set on the centre line?

You may get a better result.

Howard

[Dr_GMJNParticipant @dr_gmjn]

Posted by Howard Lewis on 12/11/2020 18:16:44:

I notice the reference to "A new insert", suggesting a carbide insert.

Carbide inserts do not universally like being used with small cuts. They were developed to remove metal rapidly., and many years after the ML7 was designed and launched

May I suggest repeating the dumbell test with a sharp HSS tool, carefully set on the centre line?

You may get a better result.

Howard

Thanks Howard.

To be honest some people have said you're better of with inserts, some people say you're better off with HSS. So…there you go. I had some Sandvik tool holders and inserts already, and have used them in conjunction with various other types of insert sourced from Cutwel (DCGT, DCMT, cast iron grade, aluminium grade, larger or smaller nose radii etc.) for different applications. I've had no particular issues with them when building a Stuart 10V. I didn't use HSS turning or fly-cutting tools at all.

One reason I didn't use HSS was because I have no experience of grinding tools, and assumed that adding the variable of poorly ground tools into the mix at this stage of the game would only end badly.

Cheers!

[Howard LewisParticipant @howardlewis46836]

Carbide tools are designed to generate heat to soften the material locally. They are not sharp (Except the ground variety. Which most of us do not use )

The ML7 was designed many years ago, and launched in 1947. It is somewhat flexible machine, so not the perfect for carbide inserts, although folk who know what they are about do splendid work with such combinations.

A correctly ground HSS tool has a razor sharp cutting edge and should not rub in the way that a carbide tends to do.

I have just compared a shear tool to a freshly sharpened HSS bit in a tangential tool holder, and am pleased ,with the results of a 0.002" cut with a 0.0023"/rev feed. There is not much difference betweenn the two, whether dry or musing neat cutting oil. Not a ground finish, but pretty good, although I would not run a highly loaded white metal bearing on either.

So sharpen a HSS bit, (as large as possible, for rigidity ) and try the dumbell again.. Do ensure that tghe cutting edge is on the centreline, or it will not cut properly.

It is possible that your problems stem from the lack of clamping and rigidity in the Tool Holder / TopSlide interface, so that is one variable to remove before you start looking for greater precision..

Howard

[Dr_GMJNParticipant @dr_gmjn]

Thanks Howard. Yes, the next job is to sort the toolpost issue.

I thought it was a minor issue, but there are apparently no minor issues with an old lathe!

[Howard LewisParticipant @howardlewis46836]

As Hopper said elsewhere on the forum, owning an older machine and fixing the problems can become a way of life in itself.

My wife says that "Fixing one problem unveils at least three more"

You try to slacken a nut. The stud shears off, flush, so then you have to remove the manifold to drill out the remains. And the Easyout (!!!!!) breaks in the drilling!

And so on.

You fix what appears to be the biggest problem and then work your way down the list of the smaller ones. By the the time that you have eliminated all the problems, the machine has worn some more, so you start again.

Forgive my cynicism! But you are less horrified by events that way

Howard

[Dr_GMJNParticipant @dr_gmjn]

I’ve now put the toolpost back, and tried the unsupported test again.

Its 1” diameter EN1A mild steel, turned down with about 5” between the test bosses.

I used the 4-jaw chuck.

I had to mess about with feeds and speeds a bit, but eventually got very good cuts on both bosses.

Im getting a consistent difference in diameter of 0.0002” (according to my Mitutoyo micrometer).

Should I twist the bed to get it perfect, or leave it? I’m not sure I could get it much closer, but is it worth trying?

The other thing is that I’ve centred the test bar to try a between centres test. I’ve never turned between centres before and the only drive bar I’ve got is too small a diameter to fit over the bar. Are there any tricks to use a makeshift drive bar some other way?

Thanks all.

[BazParticipant @baz89810]

I assume it is two tenths larger at the tailstock end, if this is correct leave it well alone.

[Dr_GMJNParticipant @dr_gmjn]

Ok so I used a nut splitter as a makeshift drive bar.

I'm getting 0.0003" difference in diameter over the same 5" boss distance between centres this time.

It's very similar to the unsupported test (0.0002" )so I'm wondering if they are both due to slight bed twist?

Any thoughts?

Thanks all.

Edited By Dr_GMJN on 15/11/2020 18:26:23

[ianjParticipant @ians]

Looking at the Myford Inspection sheets:

test 16, work held in chuck, permissible error .0000" to .0008"

 

test 17, between centres permissible error 0000" to .0004"

 

So I think you are doing well with your test results.

Edited By ian j on 15/11/2020 19:09:00

[Dr_GMJNParticipant @dr_gmjn]

Posted by ian j on 15/11/2020 19:07:57:

Looking at the Myford Inspection sheets:

test 16, work held in chuck, permissible error .0000" to .0008"

 

test 17, between centres permissible error 0000" to .0004"

 

So I think you are doing well with your test results.

Edited By ian j on 15/11/2020 19:09:00

Thanks Ian, completely missed those on the sheet, I thought it was just DTI limits.

The between centres test lols like it’s over 12”, my test piece is only 5”. So I suppose pro-rata, that limit should be 0.00017”? So I’m about twice that limit?

…or is it half? Hmmm.

 

The “held in chuck” seems OK.

Cheers.

Edited By Dr_GMJN on 15/11/2020 19:30:37

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