Lathe Setup / Tests

All, I've just been doing a light re-furb on the ML7. I've eliminated most of the wear on the slides, converted to "wide guide", and the saddle is now adjusted to move freely along the entire length.

I've also replaced the saddle and cross-slide gibs, and fitted the Arc needle bearing sets to the cross and top slides, both of which now work very smoothly with no apparent play (at least when moved by hand).

The only test I've done so far is running a finger gauge across a faceplate, using the cross slide. I'm getting about 0.0005" reading from O/D to centre, which reduces to something negligible over the kinds of diameters I'm working on.

I'll do the bed twist check using the dumbell machining test on a 1" diameter x 4" long bar next. The bed was levelled previously using using a DTI against a bar in the chuck and tightenting down while getting zero movement.

I put two centres in the spindle and tailstock, and brought them together with some 0.005" shim material between them, and it didn't move significantly,

I then tried attaching a finger gauge to a magnetic base on the faceplate, with the lever positioned on the inside of the tailstock taper; I'm getting about a 0.010" runout there when the faceplate is turned. Does this indicate that the tailstock needs adjusting - if so, what's the best method?

Any other checks/adjustments I could do?

Thanks all.

Try again with a steel ruler. Shim might be too flexible.

Best way to set tailstock is by turning a test piece between centres and measuring for taper over a 4 to 6 inch length.

With wear on the inner vertical bed surfaces you can get variation in different positions though. So for critical long jobs check for taper before getting close to final cut and adjust to suit.

Dial indicator readings can suffer from flex in the mounting and stand when rotated so turning test is more definitive.

This is a poor method of testing. The self-weight of the assembly will cause the reading to change as you turn the faceplate. 10 thou is about the expected amount of sag so your tailstock could well be spot on but the dial moves because it's the stem of the DTI stand that's bending.

Thanks both.

All, When looking through some previous forum posts, I found and saved a check sheet from a Boxford lathe that someone posted a while ago. I apologise to whoever posted it because I can't find the thread now. Anyway, I've done some further checks on my ML7 with a Myford test bar, based on the sheet, and the results are in purple ink:



It sould be noted that my test bar is only 8" long, as opposed to the 12" specified on the sheet. I was using a 0.0005" graduated finger gauge to do the initial tests, repeated with a 0.001" dial gauge as a sanity check.

It seems like the "between centres" horizontal measurents are pretty good, as are most other things apart from those assocated with the test bar being secured in one or other of the morse tapers. I did post here:

**LINK**

- about potentially cleaning my tapers, and made some tools for the job. However, despite a thorough cleaning, the results are what the are.

Any comments on what, if anything, I could do to improve these figures?

Thanks very much.

Ok now you are ready to start some small projects and see how things go. Many great pieces have been made on lathes much worse than yours.

Maybe revisit the Morse taper if it proves to be a problem.

Do not try for perfection you will be running round in circles forever.

regards

Your results don't say +ve or -ve for 7 &11, could be nose up or down.

Does holding a bar in the 3 jaw (a newish one) give a similar result

Dave, in both cases, the free end of the bar is pointing up. I made an error in noting #11, it should read 0.001” not 0.011”

I’m assuming #9, #10, #11 & #12 mean move the dial gauge with the saddle along the item - the previous tests indicate the required movement with arrows.

I’ve only got a very old 3 jaw chuck.

Thanks.

Thanks,

Actually I just completed my first M.E. Project, and obviously I‘ve learned a lot about practical use of the lathe and mill. I wanted to take the opportunity before my second project to get my equipment the best I can get it. The ML7 is old, and obviously a bit worn. I’ve corrected the most annoying thing (bed wear), and am now trying to establish where I am with it, and adjusting it to be as smooth as possible while retaining accuracy.

As a double check does trapping a 12" rule vertically between the two centres give a lean toward the tailstock?

Then try machining a point on scrap rod sticking out as much as you can in the three jaw and try the test again.

With regard to the Faceplate, IF absolute accuracy bis essential for the job in hand, it can be skimmed to clean up all the way across.

It should be satisfactory for subsequent jobs, assuming that the Faceplate locates in exactly the same place again (Depends on the accuracy on the fit between the Faceplate register and that on the Mandrel, and the torque applied to the Faceplate when fitting.

After that you are into micron chasing territory.

Bear in mind that commercially produced parts are machined to be within a tolerance, so may not all be exactly the same, but sufficiently accurate for one part to be able to replace another without making the assembly unfit for purpose.

Exceptionjs to this are lapped fits, such as Fuel Injection Pump Plungers and their Rotors, or Injector Needles and Bodies. But here, we are dealing with pressures of upto 1500 bar, and the need to minimise leakage of a low viscosity fluid.

Horses for Courses! (Especially if you are doing sub contract work for NASA! )

Howard

Dave, the 12” ruler test doesn’t deflect either way. I don’t want to tighten it too much, or else I could damage the points.

Howard, Unfortunately the faceplate cross-face test consistently gives 0.0005” error - convex. But this is over the full 3.5” radius. I’m only dealing with things at the most a couple of inches in diameter for facing in the lathe - this equates to about 0.00014” or 3.5 microns of dome, so I doubt it’s worth trying to correct for a model steam engine.

Are you suggesting I skim the faceplates on the lathe? If so I suppose I’d be making them domed too? I think I mentioned that was was like a farmers welly, the other fairly good.

Thanks both.

You rmeasurements show 15 thou slope in both 1 and 7, you can see that with the naked eye if you put the points together, the rule should make that even more obvious. It doesn't take much pressure (like you would finger tighten a nut) and the points are harder than the rule.

If there really is no movement in the rule then that 15thou is a lie so look to the other end, what you mounted the dial gauge on must be dropping.

Dave, All,

Apologies, I just re-did the test and it turns out I've posted the wrong figures, it should be 0.0015" rather than 0.015" in both cases I noted them down at the time of the test, and then put them on the sheet, those two got lost in translation:

Test bar between centres - 0.0015" difference along the top:



End of test bar in spindle taper, 0.0015" difference along top:



Centres, point-to-point (tailstock looks lower, yet the bar rises left to right. Could be something to do with the bed?



Corrected Sheet:



Sorry for the confusion.

Nothing at all to worry about. See my post on the other thread on alignment you posted on.

Thanks, understood, but please see my reply on the other thread, ie for a beginner, with an old lathe, its natural to doubt its accuracy due to wear, and unknown history, and to want to get it as good as it can be. That's all I'm trying to do here. I'm fine with it - after all its capabilities undoubtedly exceed mine, but I want it to be as good as I can get it. I think I'm there with it now.

BTW I really appreciate your knowledge and advice - after the improvements you outlined on the forum and in your articles, my ML7 has been improved massively in terms of feel and useability. I would never have contemplated modifying a lathe in such away without some guidance and encouragement.

You're welcome. Glad you are getting there. It's a learning experience thats for sure.

The above misalignment looks odd, although I prefer putting a razor blade or thin ruler in there rather than purely visual.

But it could possibly be a poorly made centre or centres. Try rotating each centre half a turn, one a time, and see how alignment changes or remains same.

Also make sure tailstock clamp lever and the barrel lock lever also are firmly applied before making the test.

Could be bed wear althoough the couple thou you had should not make a huge visible difference like that. Check the tailstock barrel is sitting level to the bed by mounting a dial gauge on the carriage and running it along the top of the extended, and locked, tailstock barrel.  If not, first suspect would be swarf or burrs on the tailstock base or the horizontal adjustment faces there in.

Edited By Hopper on 09/11/2020 05:32:25

Thanks Hopper.

I re-did the point-to-point test with hardened centres (both brand new) and got a different result:



This is a 6" steel rule clamped with just enough force to stop it dropping:



I also re-did test #9 on the sheet, which I assume is running a gauge along the fully extended and locked tailstock spindle, using the saddle to move the gauge. Again I got 0.0005":



You're going to ask me up or down, and I forgot to note it. I think that wichever way it was, I won't be making an attempt to get rid of such a small error!

Now to move onto the turning tests, and that should be it.

Cheers.

So on to the next, and hopefully last issue.

In the past, I've tried the dumbell test-piece where you turn off half a thou or so off a boss near the chuck, and off another about 6" away. To ascertain bed twist:



It's never worked, becasue I've got severe chatter, and a swirl pattern on the surface of the free-end boss. Having now completely stripped the saddle and slides, converted to wide-guide, and adjusted the gibs, I tried again, expecting to have cured whatever looseness there might have been. Result: exactly the same. There's no way I can machine even half a thou off an unsupported 1" steel boss, 6" from the chuck.

So I tried 1" aluminium, and although better, still got the same issue:

chuck boss:



6" from chuck boss:



This happens on the high and medium speeds on the ML7. Life's too short to try it on the slowest (non-back-gear) speed.

Final cut was approx. 0.0005", very slow feedrate, new tool insert. Tool was set as close to the post as possible, top slide locked by the gib strip lock screws I installed.

The measured diameters were within 0.0001" (tenth of a thou) of each other, but I'm concerned that there's an inherent looseness somewhere causing this chatter. While the bar was in the chuck, I set the mag base on the front slide, and a DTI against the spindle collar, and gave it a pull - there was negligible movement, certianly no rattle or noticeable play. Any ideas?

Thanks.

Motor / belt resonance ?. as you are that close I wouldn't look for perfection, If I was machining something that far out from the chuck I would definately be supporting with live centre in tail stock. IIRC usual recommendation for stick out from chuck, unsupported, is 2 - 3 x stock diameter max.

George.