What do you look for when buying a used 4-jaw chuck?

[Fasttrack]

I always figured 4-jaw chucks to be relatively low risk since each jaw is moved independently. That said, I've never bought a used chuck specifically; they always came with the various lathes I've bought.

Assuming the chuck is on a pallet / shelf and not a machine, what would you look at or measure when evaluating it? My biggest concern on a 4-jaw would be the slop between the jaw and track; the value of the chuck would seem to be inversely proportional to the amount the jaws cock and pull the workpiece away from the body of the chuck as they're tightened. And obviously need to inspect for gross damage: signs of crashes, cracked or sprung body, etc. On that note, I'm also looking for a steel / semi-steel body versus a cast iron body.

How about brands to look for and brands to stay away from? I don't know many chuck manufacturers but the ones I know I break up in the following categories:

Top Tier: Buck, Cushman (the old USA made ones)

Middle Tier: Bison

Bottom Tier: No-names / Asian imports / Cast iron bodied chucks (which tend to be low speed and poorly balanced in my experience, although I think Buck makes a line of CI chucks that are probably decent)


Finally, any thoughts on what you would pay for a small (8"-10") used chuck? How about a medium used chuck (12"-16")? Let's say back plate included.

[kendall]

You pretty much covered everything that I look for in a used chuck.

[boslab]

I try to go with Pratt Bernard myself, there was a policy in work that unknown chucks were washed, cleaned then dye pen tested as a minimum, overspeeding chucks can cause cracks and catastrophic failure, if it was a small one it was much more likely, big ie 18” and such not so likely, I wouldn’t like to see an 18” at 2K revs !
other than that you seem to know what your doing better than many, my chucks got stolen, I found out replacement with new was impossible.
mark

[psomero]

Run each jaw through the full travel and make sure the screws aren't buggered anywhere, check the fit of the jaws wrt/ the slots as you stated, look for obvious drops, dings, and crash marks. If they're reversible, flip and repeat everything in the reverse state.

I bought a little 5in 4-jaw, sold it, then got it back and someone had dropped it at some point and I have one tight slot I need to clean up.

[old mart]

Watch out for cracked screws where the key has been hammered to unscrew a chuck.

Check out the price of a new Vertex, it may be in your budget, they are good.

[Mcgyver]

Rohm or Pratt Burnerd would be my two top picks, although Pratt may have lost their way with the introduction of a bargain basement line. You have to find decent used ones to get price down to only stratospheric levels

[The Metal Butcher]

I don't like the tooth style on Pratt Burnerds personally. Sold a plainback 12" in favor of an Asian 12". The Burnerd had absoluetely no teeth on the ID/Large OD faces of the jaws.

Design wise, I look for the teeth, since parts flying out is no fun. If I had a roughing chuck with teeth, then I'd look for one with smooth teeth and vise versa.

Quality wise:

1. Bellmouthing. Gently clamp a very round, straight object. Wiggle it as the jaws settle in. If it wiggles until the very last second that it tightens up, then they are bellmouthed. If they tighten up and the wiggle linearly decreases to zero, you're probably good. Bring a set of feeler gauges to confirm.
2. Jaw rock: With a DTI on the face of the chuck and the indicator at the highest point, you shouldn't get more than 1 thou of rock. A brand new chuck shouldn't move to the touch at all, but some do (Bison for example). If you are worried about jaw lift, put the indicator on the front face of the jaw near the work and tighten with the workpiece out in the end of the jaws. If you get much lift at all it is junk. You could do these tests for your known good chucks to get a baseline.

10" chucks of good name and condition have been selling for about 300-450 for me (think kitagawa on the high one though), and 12" ones about $400-450.

[Richard P Wilson]

Look out for cracks in the corners of the key sockets in the screws. If there are cracks its a sure sign a previous user has been heavy handed. At worst using a cracked screw can expand the screw and make it impossible to use. The other thing, and its impossible to see without removing the jaws and screws, is if the threads in the jaws show any signs of stripping.

[J Tiers]

Look for :general condition", beat on chucks often have problems that are not fixable. I agree with your general thoughts.

If you look at the jaws, if there is bellmouthing, the jaw faces will be "keystone shaped", trapezoidal in general outline, and not rectangular. Not super easy to see if tiny, but then, neither is a very slight sloppy grip on a rod.

But really, bell mouthing from jaw wear is easy to fix by grinding. It just changes the smallest part that can be clamped. The worse problem is bellmouthing that is due to the jaws wiggling "fore and aft" from sloppy chuck ways.

I tend to as mentioned, go on general condition, with a look at the jaw faces. If doubtful, and high priced. I take a walk. If doubtful, and low priced, I may go for it.

The one thing that is essentially certain is that if any parts are needed , that you cannot make, you are very unlikely to be able to buy them, no matter what ANYONE says, unless they are right there with the needed part in their hand, and a reasonable price. (they will not be).

[Richard P Wilson]

Some Pratt Burnerd spares are available in the UK for their more recent products, but you'd need to sell a few body parts to afford them. Last time I looked I bought a decent TOS chuck (new) for less than the price of a set of PB jaws. If the jaws are bad due to wear, then so will all the other parts. IMHO.

When I talked to the stockist he told me that TOS made the spare PB jaws anyway, so might as well just buy one of their chucks.

[dian]

checking bell mouth with feeler gauges? good luck with that.

usually (often?) tilt has a larger effect than tir at the jaws. 4-jaws dont help with that. thats why i dont use them.

[J Tiers]

.......usually (often?) tilt has a larger effect than tir at the jaws. 4-jaws dont help with that. thats why i dont use them.

That is an odd statement. If you avoid 4 jaw chucks for whatever it is that you call "tilt", you would seem to be "avoiding drinking liquids because they sometimes spill". The 4 jaw chucks are an essential and often used tool, in my opinion. An opinion I would suspect a majority share.

But, whatever floats your watch........

[The Metal Butcher]

checking bell mouth with feeler gauges? good luck with that.

usually (often?) tilt has a larger effect than tir at the jaws. 4-jaws dont help with that. thats why i dont use them.

I don't need luck, it's easy. Sorry your daddy never taught you how to use them.

Also, I'm with JTiers. Lol. Yes with smaller lathes and great chucks, one can go a great deal of time before needing a 4 jaw. Until something rectangular or eccentric comes up. On larger lathes where a 3 jaw never runs true, I don't much use them. Every time I put them on I need to remove them again to be able to dial something in and I don't particularly favor moving them often. Lastly, scroll chucks are not immune to this "tilt" you speak of.

[rklopp]

Look for no cracks in the jaw guides. Don't ask... Ebay special. GRRR. No recourse, as I did not notice until way too late. Someone must have dropped the chuck so it landed on one jaw.

[wierdscience]

Another vote for Vertex, they often thread the price/quality needle.