3 jaw chuck - basic question

[Clem Wixted]

I have a grizzley 3 jaw scroll chuck I bought about 20 years ago. I rarely do any metal work on my older wood/metal Walker Turner lathe. Today is the first time I have needed to turn the jaws around to grip a 5 inch metal disc. When I put the disc between the jaws it was off center. I have tried mounting the jaws in different sequences but can't get it to center.

My question is:

What is the procedure for mounting the jaws of a 3 jaw chuck so that it will center the item being held in the jaws?

Thanks,
Clem

[Rich_Carlstedt]

Clem
On most 3 jaw chucks, the jaws are numbered 1,2,3 and the chuck slots also have the same marks. To "Time" your jaws, put the jaws in the matching number slot, and turn the Tee handle backwards, as if unscrewing the jaws.
You may need another hand, or a rubber band around the 3 jaws to keep them from falling out. as you turn the handle backwards, each jaw will go out and then 'Snap" back. When # 1 jaw snaps, stop and turn the wrench handle the opposite way, making sure you have the jaws squeezed in so they pick up.
This will bring the 3 into proper time.
Hope this helps
Rich

[Clem Wixted]

Rich, Thanks for the reply.

When I do as you instructed the jaws line up correctly when gripping small items. However, when I turn the jaws around to grip larger items they don't center the way the do for small items. I was wondering if they need to be inserted in a different sequence for the larger items?

Clem

[Doug_C]

This must be a 2 piece, top removable jaw and not solid type. You cannot reverse the solid type. There would be another set for gripping large OD parts if that were the case.

If these are hardened top jaws, you should keep the jaw number with the original mating master jaw. If it does not grip on center, the jaws will need to be ground to return them to center. Each step should be ground along with the seating face. That will take a tool post grinder or some other rigid grinder setup to accomplish this task. Soft jaws would work too, since they can be machined with normal lathe cutting tools. Just remember to grip on something in the rear part of the master jaws while doing any cutting on the gripping jaws.

There are several threads in the archives here that go into good detail on regrinding chuck jaws. My concern would be whether your lathe could handle such an operation, since it is wood/metal.

DC

[kapullen]

Doug,
The old unimat chucks were solid and did reverse and center to a fashon.
I am relying on memory.
Have to look at the teeth (for the scroll) in the jaws and see if they are cat pupil shape, or like a banana.
It is hard to make a blanket statement with this little information.
Kap

[joahmon]

kap,
FWIW, you are correct about the unimat 3 jaw.
bob

[clemwixted]

While the chuck is an older Grizzley it is like the unimat as you describe. The threads on the reversable jaws are eliptical (cat pupil shaped).

No matter what sequence I use to mount the jaws they are not concentric. They are off by about an eighth of an inch.

If I mount them in a different slot than their matching number would this work?

Clem

[sallymae99]

Clem
Try putting #3 in first in slot #1
#2 in #2

#1 in slot #3

On my three jaw i look into slot #1 as I back off scrool. You can see last thread just go past opening,drop jaw in and reverse scrool.

[Jacin]

Since your scroll is basically a spirol (or inclined plane if that makes it easier to think about) the jaws can be identified for position by simply lining them up and looking at the grooves. When in order each set ought to be slightly offset (up/down) in comporison to the next jaw - in equal amounts of course. Then it is a matter of simply starting you lined up set in the appropriate jaw slot. Does that make sense????

[clemwixted]

Jacin and George,

You are exactly right. The jaws work (center) correctly for small work. When I reverse the jaws that is when they are off center. I will try reversing the jaws and going 3 - 2 - 1 rather than 1 -2 -3 and see what happens.

Thanks all, for your help.

Clem

[Doug_C]

Thanks Kap,

That is news to me. I don't recall ever seeing this type of scroll chuck!

I guess that would make sense if 1,2 and 3 are in sync in the normal installation. Then installing them 3,2, and 1 in the reverse direction should put things back in order.

DC

[Rich_Carlstedt]

Clem
Jacin has it right.
If you line up the jaws for the inside operation that works, you will notice that the cats eye is closest to the end on #1 and furthest on number 3 (on the ends that touch your round work).
now turn the jaws around and rearrage them in order of the cats eye. the one closest to the end will be the number 1 followed by the middle and then the furthest will be the third one, but they may NOT be marked as such. But this is the order you must follow.