Just a few quick thoughts.

From your description, it sounds as if the Tailstock is higher than the Headstock

If you levelled (removed twist ) by machining a "dumbell" you should be able to rule out twist in the bed, which we hope is not badly worn at the Headstock end.

Avoid using chucks when checking alignment. They contain their own errors which you do not want them introducing extra inaccuracies into your measurement.

It is possible that, at some time in the past, a different Tailstock, might have been fitted to your lathe, so that the centre is higher than the Headstock centreline.

I am assuming that you did check / clean the Headstock 2MT, bore and then trim up the centres before carrying out the between centre checks?

IF the Headstock is out of alignment, it means checking that there is no dirt / swarf between the Headstock and the bed proper, before trying to eliminate any error. As you already know, a minute error at the Headstock end will be magnified as you move towards the Tailstock.

Once the Headstock has been disturbed then it will need to be aligned , anyway..

To check the Headstock, for being level, you need to put a 2MT alignment g bar into the clean, undamaged bore of the mandrel. That will tell you if it the Headstock that is pointing up, or whether the Tailstock is high.

Howard

Please note the corrected figures!

With a Myford 8" test bar mounted in the spindle taper, I'm getting a vertical rise of 0.0015" over the cylindrical part of the bar.

With the test bar mounted between centres, I'm getting a similar rise.

However, with the two centres point-to-point, the tailstock point looks lower.

I'm getting a 0.002" runout at the end of the bar, with it mounted in the taper.

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?

Here's the corrected Sheet:

If you want me to re-do any of the checks, just let me know.

Of course those figures are for a larger Boxford lathe I think, and my test bar is only 8" rather than the 12" specified.

Is there an equivalent table for an ML7?

Guys you need to relax and stop chasing perfection on a 50 year old low-cost lathe.

Most lathes of that era were manufactured with the tailstock centre a thou or two higher than the headstock spindle. This was to allow for wear. As the base of the tailstock wore, it came down into perfect alignment before it started to go out.

A small amount of vertical misalignment (And note, the term here is not runout, Runout refers to eccentricity under rotation) will not affect the operation of your lathe by any measurable amount. Adjust the tailstock horizontal offset so a 6" turning test piece between centres turns parallel along its length and be done.

Bed wear will also cause a carriage-mounted dial indicator to read a few thou variation along a ground test bar between centres and add to the confusion. The turning test tells the truth in terms of the end result.

However, if you do have excessive vertical misalignment of the tailstock of more than a few thou, the most common cause is swarf, paint or burrs either on the base of the tailstock or on the two mating surfaces that allow for the horizontal movement for adjustment between the two parts of the body. Easily fixed with a fine flat file.

They ought to ban the sale of those damn ground test bars. They are the cause of more unnecessary angst than they are worth. Adjust your lathe so it turns straight and true under working conditions and carry on lathing.

Edited By Hopper on 08/11/2020 22:53:30

If the error were due to a hollowed bed the test bar would read higher on the dial gauge where the hollow is and lower at the less worn end. It reads like he has the opposite of this.

Well at .0015" rise between centres you are within the ball park, ie it won't affect your lathe's performance. It's not worth trying to machine/remove .0015" off the base of the tailstock for that.

Edited By Hopper on 09/11/2020 05:11:47

Hello Hopper,

Not quite sure if I agree with you re test bars. IF you know what you are doing, then they are very useful. However I do take your point that in the hands of the inexperienced, they can lead the owner a merry dance.

Andrew.

.

This might be a good time to mention Dr Schlesinger’s thoughtful design

See p9 of ‘Testing Machine Tools’ [7th edition] … which is now freely available on t’internet

… So much for the exclusivity of owning an original printed one

MichaelG.