Unintended asymetric turning

My South Bend certainly chatters if the surface speed is too high. Then I slap it into back gear and watch the work slowly revolve like a cement mixer.

Maybe not. You could turn the outside smooth and indicate on it. When I need to temporarily remove the work I loosen the jaws on either side of the label and then tighten only them to put it back. Usually a cut less than 0.005" deep removes metal all the way around.

[cut & paste] To be fair the guys who preferred their 5" chucks liked them better for general work, pie jaws were not discussed. Surely there must be some difference between the chuck that is thrown in with the machine and something you spend $$$s on?

I really do like that $500 Bison Set-Tru, though. You could think of one as the first installment on a larger lathe.

jsw

Reply to
Jim Wilkins
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The main thing to worry about when using a 3-jaw chuck larger than approximately half the swing of the lathe is that you have to be

*very* careful to always turn the chuck by hand through a full turn after griping something larger. The back end of the jaws can stick out far enough to hit the bed ways -- damaging both the jaws and the ways.

Depends on the size of your lathe. With some sizes, that is beyond dirt cheap. :-)

Wrong term there. The usual spelling of one maker's name for the chuck is "set-tru" which is short for "set true" (*not* through). There is someone else here who frequently uses that wrong term -- though usually spelled "adjust-thru" IIRC.

However, if the chuck has already been threaded, it may be that the jaws have been ground true while mounted in the chuck. The thing that turning your own backplate does is to compensate for errors in the spindle of *your* machine -- and make it less accurate on somebody else's machine. A friend had a 10" lathe with two adjust-tru (another manufacturer's trademarked name for the same feature) chucks, which ran fine -- but every time I tried to adapt something else to it it had lots of runout. It turns out that somewhen in its past, someone had seriously crashed the machine, and the threaded part of the spindle nose was bent -- not enough to see easily, but enough to introduce progressively worse runout as you moved the indicator away from the headstock.

We eventually got a replacement spindle via eBay.

But -- a pre-threaded chuck is a convenient think -- *if* you can trust your spindle nose to be true.

Enjoy, DoN.

Reply to
DoN. Nichols

I thought there was an issue with the bearings and the size of the spindle. Also the biggies take longer to stop. The chatter issue should be alleviated by the soft pie jaws which would be the point of getting a new chuck in the first place.

No. Depends on the size of your bank account.

That is tru.

Also much more expensive. OTOH others tell me that they had problems with some of the back plates.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

I thought that's what the big handle was for. Admittedly coordinating the left hand cranking the spindle and the right hand turning the cross-feed is a bit tricky.

If one is going to go through the hassle of getting a new chuck it may as well be one that is the least hassle in use.

And the larger lathe the first installment on a bigger house...

Michael Koblic, Campbell River, BC

Reply to
mkoblic

If you don't require the precision to make machine parts you might consider an old worn engine lathe, now that you know how they work and what you need. Threaded spindles and leather drive belts are fine for a home shop lathe.

My $100 surface grinder for example is worn beyond usefulness for precision flat grinding, but still serves well to resharpen tools.

The first small lathe I bought had ways that dipped about half a millimeter near the chuck. Nevertheless it was good enough for the small brass and aluminum parts I wanted to make, and could still thread accurately enough at the tailstock end.

jsw

Reply to
Jim Wilkins

A consideration -- especially with a small diameter spindle which is easy to bend. But that is something which either is or is not a problem to be determined once. The jaws hitting the bed are something to be considered every time you use the chuck.

I've got a 10" 4-jaw on my 12x24" Clausing, but only a 6-1/4"

3-jaw.

The chatter might be damped by the greater mass, (and certainly by the pie jaws), but you still have the problem of flexing of a skinny spindle.

Craftsman has sold (in the past) two flavors of 6" lathe. The better one is the one made by Atlas, with (IIRC) a 1"-10 spindle nose thread, while they also had one made by Ann Arbor machine tools which only had a 1/2"-20 spindle nose -- and those were notorious for getting bent the first time you took a heavy cut.

"Dirt cheap" in terms of what is available to fit your lathe. There are lathes which have chucks 40" diameter or larger.

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The pre-threaded ones, or the ones which they had to machine to fit their lathe?

My Clausing came with a 2-1/4x8 spindle nose, and I had to make some backplates to fit (sometimes enlarging the hole in existing backplates which had been used on 1-1/2x8 spindles or the like. Overall, I had no problems with those. The trick for turning the bore to clear the register was to mount the backplate backwards with a spacer ring to hold it far enough out so I could bore the threads off at that end.

Enjoy, DoN.

Reply to
DoN. Nichols

The crank on the spindle is for lathes which don't *have* back gears -- or do have them, but still can't go slow enough. I think that the 9x and 7x import lathes don't have real back gears, and thus can't get really slow enough.

Enjoy, DoN.

Reply to
DoN. Nichols

The pre-threaded, semi-finished back plates. If I remember correctly the threads were cut at an angle to the spindle axis. I understand that it was correctable though.

Michael Koblic, Campbell River, BC

Reply to
mkoblic

Depends on how bad it was -- and how thick the backplate was. You would first have to generate a shoulder on the backplate which is true to the existing threads (unless you want to fill with weld and re-thread). Then thread it onto the spindle nose and turn the outside face perpendicular to the threads. Once you have that, reverse the plate and turn the back side square too. Then, if you have not lost too much thickness from a serious off-angle thread -- you can turn the register for the chuck.

Enjoy, DoN.

Reply to
DoN. Nichols

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