Chuck Options

[bug_hunter]

Hey Guys,

Pretty sure most everyone has run into this sometime. I have an old SB9c used solely as a hobby lathe. It has an old Cushman 5-inch, three jaw. Seems quite a bit out there. I check the lathe alignment and tweaked it a bit, then check the runout of the chuck on a piece of 3/8 drill rod. I got about .006. I pulled the chuck apart, and cleaned it and check the runout of the mating surface of the backplate and got about .003. Took a skim cut, and re-checked and got .0005. Put everything back together and rechecked the drill rod. Now I'm around .010. When tightening the chuck, it does not look like all three jaws are gripping equally. I loaded up the outside jaw set I have and got around .003 runout. I also noticed that the three digit number on the jaws do not match that which is on the chuck.

1. What are my options?
2. Can the jaws be replaced?
3. Has anyone successfully ground their jaws on a SB9?
4. Is it safe to use the outside jaws to grip inside?
5. Should I just live with it?
6. Should I just buy a new chuck?



Thanks a lot for the insight,

Greg

 

[benmychree]

Try regrinding the jaws, there are many posts on this forum as to how to go about it. If that does not resolve the problem, a new chuck is in order.

 

[markba633csi]

The scroll is probably worn so even if you grind the jaws the result may still be disappointing.
But you can try..
Chucks don't last forever

 

[RaisedByWolves]

Hey Guys,

1. What are my options?
2. Can the jaws be replaced?
3. Has anyone successfully ground their jaws on a SB9?
4. Is it safe to use the outside jaws to grip inside?
5. Should I just live with it?
6. Should I just buy a new chuck?

View attachment 461041

Thanks a lot for the insight,

Greg

Stop overthinking it.

A three jaw is really not a precision work holding method, you will have runout regardless.

There is a lot of YT videos and discussion on this topic, but never in my 40 yrs as a toolmaker have i even considered this a problem.

Most of your stock will come oversize just to account for both surface irregularities and chuck runout. Once you start cutting from raw stock your part will run true until removed from the chuck.

Plan out your job as to do as many critical details in one setup as possible, think it through before beginning and the issue of runout really isint an issue anymore.

A collet nose/chuck is what you want/need for jobs where you have to flip the part around and chuck/rechuck the part.

 

[markba633csi]

Yes, definitely look into collets when you want to up your lathe game- some jobs simply can't be done easily without collets

 

[bug_hunter]

Thanks guys.

Like most machining questions, "Never one right answer or one way to do things".

 

[RaisedByWolves]

Thanks guys.

Like most machining questions, "Never one right answer or one way to do things".

Nope, and be skeptical of someone who tells you different.

Honestly if you’re trying to get down under .005 with a chuck a 6 jaw set tru or a 4 jaw is the way to go.

Then again for the cost of that (6jaw)you’re in the price range of a set of collets.

 

[great white]

I pretty much exclusively use an independent 4 jaw now.

Once you get used to it, setup is pretty quick and its easy to get dead on center.

I use it exclusively as a hobbiest, so a few extra ticks to get something set up is not an issue.

 

[ShagDog]

If you buy a used replacement chuck, be careful with the SB9 fit. I have 2 SB9's and the threads on them appear to be tighter so that some of my chucks don't screw on far enough. The same chucks fit fine on my older taiwan lathe. Also, I have no problems with the china backplates. The china backplates seem to fit my SB9's just fine.

 

[bug_hunter]

Thanks again for the insight guys.

My plan is to take a shot at grinding the jaws. Not expecting the runout to vastly improve. Any improvement would be gravy. Looking to improve the work holding grip. When I chuck up a piece of stock, the jaws are so far off, I can see light between the stock and jaw on the front half of the jaw.

If you buy a used replacement chuck, be careful with the SB9 fit. I have 2 SB9's and the threads on them appear to be tighter so that some of my chucks don't screw on far enough.

I've heard/read this elsewhere. Hopefully we won't be going down the "new chuck" path in the immediate future.

I pretty much exclusively use an independent 4 jaw now.

Moving in that direction also. Just so easy to toss a piece of steel and the three-jaw, tighten 'er up, and off you go.

Thanks again!