Jewellers lathe?

[Charl]

I saw a 2nd hand jewellers lathe the other day that was at a quite reasonable cost. The thought crossed my mind that it might be just the lathe for stem work. Anybody have experience with them? Or is it better to go with just a normal mini lathe?

[JHowell]

I saw a 2nd hand jewellers lathe the other day that was at a quite reasonable cost. The thought crossed my mind that it might be just the lathe for stem work. Anybody have experience with them? Or is it better to go with just a normal mini lathe?

Hard to say without pictures. If the cost is reasonable enough, I'd probably snag it just to find out what I could do with it, but there's a chance it's too small and too fast. Real jewelers lathes are for tiny stuff, some of the ones I've seen don't even take chucks, just tiny collets and turn between centers. The most valuable attribute a stem lathe can have, in my opinion, is the ability to take rod stock through the spindle. And 5C collets are heaven; you can do lots more work on stems and rings without getting your knuckles whacked by the chuck. But I've also been known to make do with whatever came along if the price was right.

Jack

[Frank]

And 5C collets are heaven; you can do lots more work on stems and rings without getting your knuckles whacked by the chuck.

Jack, I've never used 5C collets before and know very little about them. How does 5C relate to the lathe spindle Morse Taper (mine is MT4)? Are they closed using a draw bar?

[JHowell]

And 5C collets are heaven; you can do lots more work on stems and rings without getting your knuckles whacked by the chuck.

Jack, I've never used 5C collets before and know very little about them. How does 5C relate to the lathe spindle Morse Taper (mine is MT4)? Are they closed using a draw bar?

There are several different collet configurations. 5C is the most common for general use because it goes up to an inch or a little more. I think you need a MT5 spindle nose -- on my Hardinge the collets go right into the spindle with a lever collet closer; the Logans have an adapter that fits in the spindle nose to hold the collets and use a drawbar to close them.

Jack

[Frank]

And 5C collets are heaven; you can do lots more work on stems and rings without getting your knuckles whacked by the chuck.

Jack, I've never used 5C collets before and know very little about them. How does 5C relate to the lathe spindle Morse Taper (mine is MT4)? Are they closed using a draw bar?

There are several different collet configurations. 5C is the most common for general use because it goes up to an inch or a little more. I think you need a MT5 spindle nose -- on my Hardinge the collets go right into the spindle with a lever collet closer; the Logans have an adapter that fits in the spindle nose to hold the collets and use a drawbar to close them.

After some further research on a couple of Machinist sites I realise that for 5C collets MT5 would be the minimum spindle through hole size. However, I think that R8 would work for me.

I can't seem to find an adapter with MT4 OD/R8 ID, so I guess I could make an R8 Collet Closer like the one illustrated here by HotGuns, about 1/2 way down the page: 5C Collet Closer. I figure I could start off with this MT4/MT3 Sleeve, cut it to length and bore out the inside to R8 specs. Should be a fun project.

[JHowell]

That's an interesting possibility, but the adapter ought to be hardened so that you can't machine it. Anything that holds the collet has to be hardened or you'll never get the collet out. Also, the adapter needs a ring or boss around the outside so that a threaded spindle protector can be used -- it not only protects the threads, it allows you to extract the adapter from the spindle.

Jack

[Frank]

That's an interesting possibility, but the adapter ought to be hardened so that you can't machine it. Anything that holds the collet has to be hardened or you'll never get the collet out.

Perhaps if I ask nicely enough (and throw in a bottle of olive oil ) I could persuade Kurt to harden it in his blade heat treat oven after I've machined it to size. That should work, yes?

Also, the adapter needs a ring or boss around the outside so that a threaded spindle protector can be used -- it not only protects the threads, it allows you to extract the adapter from the spindle.

I'm not sure I understand what you mean by "a threaded spindle protector". If you're referring to the spindles on some lathes that are threaded to accept the chuck, then that's not a problem for me, since my lathe spindle isn't threaded. Instead it has an integral face plate onto which the chuck is bolted. Something like this, but all one piece:


As for extracting the adapter, a length of 1" diameter dowel rod or ABS inserted at the other end and given a couple of hammer taps should pop the adapter out. I just have to remember to wrap a cloth around the adapter first.

Admittedly, I could machine the whole adapter from annealed steel rod stock and include the ring/boss/collar and then have it hardened, but I was trying to avoid the hassle of having to machine a MT4 taper. Yep, sometimes I'm a lazy bugger .

[JHowell]

That's an interesting possibility, but the adapter ought to be hardened so that you can't machine it. Anything that holds the collet has to be hardened or you'll never get the collet out.

Perhaps if I ask nicely enough (and throw in a bottle of olive oil ) I could persuade Kurt to harden it in his blade heat treat oven after I've machined it to size. That should work, yes?

No, hardening will make it warp. Maybe not much, but a collet adapter has to be dead on. Hardened parts are precision ground to final dimension. I wouldn't invest a whole bunch of time into trying to get collets to work in a lathe that doesn't have a readily available setup for them. If you have MT4 through the spindle you might be able to find a 3C setup that could be adapted, but otherwise I'd just keep using the chuck until the right lathe comes along. I've got quite a few collets by now, so I use them 95% of the time, but they're a nice to have, not a need to have.

Jack

[Frank]

That's an interesting possibility, but the adapter ought to be hardened so that you can't machine it. Anything that holds the collet has to be hardened or you'll never get the collet out.

Perhaps if I ask nicely enough (and throw in a bottle of olive oil ) I could persuade Kurt to harden it in his blade heat treat oven after I've machined it to size. That should work, yes?

No, hardening will make it warp. Maybe not much, but a collet adapter has to be dead on. Hardened parts are precision ground to final dimension. I wouldn't invest a whole bunch of time into trying to get collets to work in a lathe that doesn't have a readily available setup for them. If you have MT4 through the spindle you might be able to find a 3C setup that could be adapted, but otherwise I'd just keep using the chuck until the right lathe comes along. I've got quite a few collets by now, so I use them 95% of the time, but they're a nice to have, not a need to have.

Jack

Buggrit! Foiled again. Ah well, back to relying on the chuck. Thanks all the same Jack.

[FredS]

BTW - I've seen hundreds of lathes, but I've never seen one that used R8 collets in the spindle. For some reason R8's are used for milling, but not turning.

[KurtHuhn]

[Perhaps if I ask nicely enough (and throw in a bottle of olive oil ) I could persuade Kurt to harden it in his blade heat treat oven after I've machined it to size. That should work, yes?

As Jack said, the problem with hardening most steels is that they want to warp during quench - as you know. This isn't too much of a problem for air hardening steels like A2 or D2, since the quench is fairly gentle and you typically need to heat these in an electric oven to ensure even heat and temperature holding. Done right, properly normalized and pre-heated, you can harden A2, D2, and even O1 without fear of warping. HOWEVER, the part will still change dimensions - not due to warping, but due to the growth of carbides, grain refinement, and the freezing of the carbon and/or chromium into solution, formation of martinsite, and a crapload of stuff I don't yet understand. That's primarily why tooling gets ground to size after heat treat - even parts that are plate quenched can change size by a significant amount (significant in machinist terms anyway). This is actually the basis for the creation of sori on Japanese blades, and the maker tries to control the expansion of steel to meet the end result that he's trying to achieve.

Just a small metallurgy tidbit for Monday morning.

[Frank]

As Jack said, the problem with hardening most steels is that they want to warp during quench - as you know.

Yep, even as I was typing that I was thinking of the warpage factor, but hoped there might be a way around it, like case hardening. Wishful thinking on my part.

BTW - I've seen hundreds of lathes, but I've never seen one that used R8 collets in the spindle. For some reason R8's are used for milling, but not turning.

I came to the same conclusion during my web searches. 3C, 4C and 5C are favoured for lathes because they're non-binding and "quick release". Unfortunately, only R8 and 5C are relatively inexpensive and easy to obtain as opposed to 3C and 4C. I could use a reducer sleeve and MT3 collets, but they're 3 to 4 times the price of R8 and 5C.

[Charl]

Thanks, guys! Think I'll skip this particular jewellers lathe. Like Jack said, this one doesn't even have a chuck, on closer inspection.

[Frank]

Charl, apologies for highjacking your thread.

[Charl]

All part of the learning process, Frank! No problem!