Is it axial or radial run out?

Tony

Chris you are quite right .0005" is neither here nor there but the guy asked a question. BTW even NASA & NPL should only use tight tolerances where appropriate.

Tony

and when they do its with very expensive equipment that's regularly calibrated

Could be a hardened old V belt with a tight spot in it. Try testing with belt off the pulley.

"I really am fed up with people calling super 7s flimsy I regularly part off 2 inch 304, maybe its the blunt tools !!!"

Bernard, my remark was not meant as a criticism of the Myford 7 series of lathes. They are wonderful machines and I cherish and value my much modified ML7-R (now a S7 less gear-box in all but name). I too have performed some heavy work, parting-off, cutting multi-start worms etc.on mine with great success, although the fact remains that if you put a clock on a work-piece and adjust the levelling screws or lean on the bed you will see the needle move but so what? The machine performs its allotted tasks admirably, it's just that such a deflection does not occur on my Student which obviously has a much more substantial bed casting.

In terms of performance as a lathe, the Colchester walks all over the Myford but only as a 'lathe'. The little Myford, with all its attachments, both proprietary and shop-made, is a complete machining centre in itself. There is hardly any task, within its capacity, that cannot be performed on the Myford.

Mike, you are not actually measuring the spindle run out but a 'ground spindle held in an ER40 collet chuck, with a backplate screwed onto the spindle.' I suggest you remove the collet back plate & check for run out on the spindle outside register & internal taper, not sure about the ball race rotating at half spindle speed though.

Tony

The way to make a machine tool accurate /precise to the highest degree is to make it rigid, which implies weight and metal where it will do most good.

MANY years ago, in Shrewsbury there was a company making Boring Mills. The slideways were coated with Formica, which apparently when oiled resulted in a very low coefficient of friction.

Needed for a machine that was assembled in a hole in the ground large enough to swallow a house, but containing only the lower half of the machine.

My current lathe weighs 300Kg and replaced a ML7 which did flex, when used for milling..

No doubt this one does, but under a much great load than I have ever applied.

Used sensibly, a 7 Series Myford will do excellent work, but overload it at your peril if you want long life and consistently precise output.

As we regularly say, "Horses for Courses"

It might well be that a new belt, if it has a fat joint, will increase tension sufficiently to change bearing clearances temporarily and result in run out.

And single phase motors are not renowned for producing a consistent angular speed..

If it could be incorporated into the drive, maybe a hefty flywheel would provide some inprovement?

Howard

If you are running it in backgear it could be the meshing of the gears causing runout. Do it with no belt on the pulley, no gears engaged and rotate by hand. With dial indicator directly on the spindle.

A S7 in good condition should do better than that! Ignore comments that it doesn't matter. The thing is built to perform better, and it should. That's what matters.

It's not clear whether this runout appears when the spindle is effectively in isolation, or only when it is being acted upon by the machine's drive train. If you haven't already done so, I suggest that the spindle drive belt is slackened, and the spindle bearing set-up procedure is gone through. Then, begin the hunt starting with the isolated spindle, then add components of the drive train, one by one, measure, rinse and repeat…

Also, I'm not clear whether you're measuring runout, where there's no 'slop', or free movement that appears on alternate rotations. The rear bearing ball set will indeed orbit at half spindle speed.

You have measured runout when back-gear is engaged. Is there a little backlash in the back-gear train? If it's too tight, any eccentricity of a gear may cause radial forces on the spindle. Turn by hand and check.