Extending lathe spindle

I bought a scrapped lathe's headstock to temporarily clamp onto the ways further down where the leadscrew isn't worn, or to block up for larger diameters.

jsw

jsw

Jim, I was thinking around the same lines. Can one simply relocate the headstock futher down the bed?

Ivan Vegvary

I don't think your worn lathe bed is at the root of your taper problem. On a 2" diameter piece in the lathe, a 1/16"(that's HUGE) drop in the cutting tool would only cause a one thousandths taper (2 thou on the diameter), the end toward the headstock being larger because of it. Dropping a whole 1/8" causes a 3.8 thou taper (7.6 thou on the diameter). Things get worse faster after that, of course. But, since you say the wear is only 4-5 inches long, the effect of any drop would only be about 1/2 anyway, because the saddle would average the error out, To measure this, I constructed the above on my cad program. I think I got it right, but you might want to wait for some more expert folks to reply.

Pete Stanaitis

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Ignoramus27446 wrote:

Pete, the saddle rides on "inverted vee ways", and the inclining parts of the vees are worn. I can see and feel that wear.

It depends on the design of the lathe.

My Clausing (Model 5418 -- 12x24") has the motor and countershaft in the pedestal below the headstock, and there are notches cut in the ways to clear the belts going down from the spindle to the countershaft. This would not accept moving the headstock along the bed, and there is a taper pin to lock the position of the headstock on the bed.

But -- if your lathe has a motor and countershaft hinged off the back of the bed, that is a different matter -- and your only worry would probably be deflection of the ways with no support feet under the headstock. Some of the Clausings of the same basic model -- but made for bench mounting -- are powered in just that way.

Enjoy, DoN.

Extending the spindle will yield a machine that has no rigidity. Chatter will be a constant problem.

Harold

I see, but if the wear is DOWN not sideways, shouldn't these numbers still apply? I'd think you could test this thinking by clamping an 8 or 10 inch long flat plate to the back of some machined bed surface and then putting a dial indicator on your longest boring bar to test for sideways movement of the saddle as you traverse the bad area. If the saddle is moving sideways, then I see the problem. Wait a minute. Mount a known cylindrical bar in the lathe. Make it as long as you can. Run all the way along it with a dial indicator. If the worn ways ARE the problem, then you should have NO taper at the tailstock end. The tapering should only start when the left edge of the saddle gets to the wear area. If this is true, I am wrong and will never bother you again on this issue.

Pete Stanaitis

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actually the math works the other way. A little loose up/down lets the carriage slide way back. IMHO extending the chuck will cause more problems than it solves.

Karl

The wear is on the vees and it lets the carriage move sideways.

I have some other possibilities that I am considering.

So, the wear is on one side only of the vees? Gravity will keep the carriage centered if both sides are worn equally.

You can 'see and feel' microinches of surface finish, too. It would be best to measure the wear and do the calculation before doing an expensive rebuild.

Long term fix is to save up the pennies and have the bed re-ground. In the meantime, practice scraping to the point where you have no qualms about scraping the carriage and tailstock to fit the re-ground bed.

Short term fix. Live with it. Extending the mandrel will introduce you to a world of pain that you don't need.

Mark Rand RTFM

To get .008 runout, the ways would have to deviate from a straightedge enough to get a feeler gage in the gap. Test for that.

The 'other possibilities' should include misalignment of the spindle (it isn't aimed accurately parallel to the ways).

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You did support the test bar with the tailstock, right???

jsw