Run out for lathe with speed reducer

[mikec182]

I have a 1992 Mark V 510, I'm working on making pepper mills for family Christmas gifts. The problem I'm having is making sure the billet is centered on the drive and live centers. Have been using a speed reducer (555428) and checking run out on a 1/2 inch centering pin chucked in the drill chuck my dial indicator reads about .012 run out with the speed reducer and about .007 on the main head stock with the same setup. Can there be this much run out and still give me workable centering? Any tips on centering spindles and any comments will be appreciated.
Thanks
Mike

[BuckeyeDennis]

That’s a lot of runout. I’m wondering if the drill chuck might be the source, rather than the headstock and speed reducer. How much runout do you measure directly on their spindles, with the chuck removed?

[mikec182]

Thanks Buckeye Dennis for your response, I checked the bare shaft on the head stock and have about .004 run out and with the speed reducer the run out is .006. I wonder if the drill chuck is getting thrown off by a few thousands when the set screw is cinched down.
I've come to the conclusion I'm going to have to build a steady rest to compensate for the run out.
Any thoughts?
Thanks Mikec182

[BuckeyeDennis]

I’m not sure what the allowable runout spec is for a Mark V spindle, but I expect that it varies with the particular spindle type — double-bearing quills generally being better. IIRC, a 10ER with original-quality bearings typically have around 0.001” TIR, which is considered exceptional for a woodworking machine.

A little runout doesn’t mean that you can’t turn a nice round part, it just means that the OD might not be perfectly concentric with an internal bore. What features are you turning that require better than 0.010” of accuracy, to pick a number?

[mikec182]

I'm currently making ceramic crush grind pepper mills I picked up from WOODCRAFT. One can see an illustration on their website Woodcraft.com #77C14 When I part off the housing from the body on the practice piece. The two pieces won't turn concentrically when put back together about 1/16th off.
I need to run more practice pieces and see if
Thanks Mikec182

[BuckeyeDennis]

I think I found the mill in qestion on the Woodcraft site. Item #146927, and instruction-sheet #77C14, correct?

Drilling the center hole is not likely to give you perfectly centered bore, even on a perfect lathe. Drills tend to wander a little. Especially if mounted on a Shopsmith tailstock, which is not terribly rigid. In general, if you need to make a well-centered hole, you have to first drill it undersized, and then bore it out to final size with a single-point cutting tool.

But if you follow the Woodcraft instructions, you don’t need to make a perfectly centered bore. That’s because they drill the bore first, and then rechuck each workpiece using the bore itself as the chucking feature. Only then do they turn the OD to final size, and that trues up the OD to be concentric with the bore.

NOW, your spindle runout could come into play, by offsetting the workpiece OD from the bore centerline (by an amount equal to the spindle runout). We’re talking just a few thousandths here, based on your runout measurements. BUT, if you follow the Woodcraft instructions exactly, you’ll also eliminate any error from spindle runout. That’s because you’ll turn the jam chuck on the same spindle, and thus its chucking surface will be perfectly concentric with the actual spindle axis of rotation (not just its OD).

So unless I’m misunderstanding something, simply changing your order of operations should solve the problem.

BTW, the speed reducer is a good idea when drilling out the ID, but probably not needed after that. For best results, just be sure to turn the jam chuck on whichever spindle you’ll be using it on.

[everettdavis]

I would use a Nova Chuck and a quality forstner bit to bore the hole if I could. I rely on my 10ER for most turning and have speed changer. What you describe is as others have noted, likely in the drill Chuck. I have had a live center with a lot of radial play due to a worn bearing throw off some work as well.

Please post a follow-up on what you find. I don't have a speed reducer to measure but yours sounds OK.

[everettdavis]

Not knowing your experience with chucks I apologize if you already knew this, but one of the first things I learned in metal working was to tighten the drill chuck progressively in all the holes until stock or bit was secure.

Tightening only one side will introduce its own measure of run-out as the stock is canted in the chuck ever so slightly if you only tighten one side. It will not run true.

Everett

[mikec182]

Thanks for your input, I've been out of the loop for a couple days now I'm back at it and I see how you figured this one out for me I'll follow your suggestion and let you know how it comes out.
Thanks
Mikec182

[mikec182]

Thanks for your comments, The chuck I'm using is from PSI # CUG3418CC 4 jaw utility grip. I've been using this for quite awhile with no issues. I do believe the run out problem is caused by the tail stock which runs out of round when boring even when attempting to hold it steady. I don't know if there is a way to make the this more stable The collars are tight on the tail stock post and the lock bar is secure but I still get some movement when applying spindle pressure to the forstner bit.
The response I received from Buckeye Dennis enlightened me to the issues with concentricity. I'll follow up on his observation and yours to see I can get this right on my practice pieces.
Thanks
Mikec182