Mini Lathe Ways Lapping

Stripped the carriage of my VM210 mini lathe, re-assembled and shimmed the plates holding the carriage onto the ways. The carriage hits a high spot in the center of the ways, would lapping the ways with grinding paste be an option to level the ways to the carriage and is there a specific technique involved?

Many thanks for your advise.

Russell

If it's just one high spot, lower it with a scraper. You don't need the whole years of practice, tubs of engineers blue, fancy tool made from unicorn horn and 2000spots per inch deal, just a few strokes with whatever you have. I found all three of my tools benefitted from a few minutes of this, once use made such spots obvious.

No

Tony

Is it the top of the ways or the underside? Without the hold down plates is there any evidence of a high spot? You really don't want grinding paste anywhere near the bed and if there is a problem scaping may be a better solution,

+1

The plates holding the carriage on don't (I believe) contribute anything to a lathes accuracy. Cutting forces normally press the carriage down on the bed, so it's this interface that's has to operate smoothly and fit accurately.

Underneath, the plates stop the carriage lifting off when something unusual happens, most likely an accident, or maybe a dig-in whilst parting off in reverse. The underside of the bed may not be machined accurately because the plates don't normally touch it. Reducing friction and allowing space for oil to get under the bearing surfaces are reasons for not clamping a carriage firmly to the bed.

My guess is shimming has brought the holding plates into contact with a bulge in the roughly machined underside. Could be scraped off, but is it worth the bother?

Presumably the shims have been installed because the carriage lifts. In what circumstances does that happen? There's a risk shimming is fixing the wrong problem, and it's whatever that causes the carriage to lift that needs attention.

Dave

Yes, but what about using rear-mounted tools?

The shims under the Myford carriage are there for adjustment to a fit.

Could be except I don't think the VM210 mini-lathe has any way of rear-mounting tools. Unless the owner modifies the saddle himself. It's allowed!

Dave

I always lock down the carriage when parting off, so it is not very likely to be lifting during that operation?

That is no doubt good practice and I must try to remember to do it more often!

By way of contrast to the Myford, my slant bed lathe has the carriage lock at the front right but there is an adjustable keep under the rear (on the latter it is possible to run the lathe in reverse safely).

There is never a good reason to lap in machine ways. It's the exact opposite of what a moving way requires to be properly lubricated. You might (probably will) see an apparent improvement in function in the very short term but once done, wear will be highly accellerated.

It's a pretty good way to ruin a machine in short order.

Thanks for the comments, in order to improve the rigidity of my mini lathe I'm trying to eliminate any play while still having free movement, based on your feedback I have slackened off the bolts holding the plates a tad, there is a small amount of play on the carriage now but the carriage moves freely across the ways.

Russell

I think it’s fair to say that the accumulated wisdom of the posts so far is:

Lapping is not the appropriate technique … But there is no harm in identifying specific ‘high spots’ and reducing them with a scraper.

Proceed gently and you should see some improvement … then quit whilst you’re winning !

MichaelG.

Indeed, scraping is ideal as it leaves a finish that retains oil.

FWIW my particular mini lathe carriage was loose @ headstock end & too tight to move @ tailstock end out the box.

Measuring with a mike induced me to run a 4" file(.minus handle) along the lower ways on the bed towards the tailstock end.( what the saddle plates run on)

It took a while,it's still not perfect, but carriage will traverse it's full movement without any looseness or overly tight spots......

I'd leave the top of the bed well alone, unless i was a lot.lot more knowledgeable.