Mismatched chuck jaw challenge

[plataman]

Subject chuck is a new 6 inch three jaw adjust-true. This was a great swap meet find at a fraction of the catalogue price of $1,200. There is no wear or evidence that this was ever used, still in original box with all packaging materials etc. Maybe it was a bargain price because of the following: On two of the three jaws the contact surface of the top jaw does not line up with the master jaw! This became evident the first time I chucked a ground rod to dial in the runout and noticed daylight between the rod and number 1 and 2 jaws. the rod is being held only by the master jaws....I can slide a .002 feeler gage down the number 1 jaw and a .003 down number 2! Ever seen this before??? What is the fix? Since this was a swap meet fine return to the supplier is not an option. Help me save this gorgeous chuck! Thanks! Terry in Texas.

[Hugh Currin]

Terry:

Sounds like this is a two piece jaw chuck, top jaw bolts to master jaw? You may be able to buy top jaws from the manufacturer, or another supplier. That would be the easy solution. Or you could take the one jaw that fits off, carefully measure it, and make a new set. While you're at it make a couple of sets, some steel, some aluminum. Leave them a little longer toward the center. Then you can machine the top jaws true as needed.

Let us know how you solve it and what works for you.

Thanks.

Hugh

[Admiral_dk]

My first thought was that the jaws where put in, in the wrong order, but that would normally give you a much bigger error than a few thou ..... 

Hope that you find the solution.

[b.lindsey]

Terry, could it be that the original owner somehow switched the removable parts of the jaws and reinstalled them on the wrong master jaws?  Swapping them about and rechecking could help since they are only out by two -three thousandths. Are there any markings showing the proper pairing of removable to master jaws??

Bill

[plataman]

Thanks everyone for the suggestions. Master jaws are in their proper slots and have matching serial numbers. Top jaws are paired 1,2,3 with the Masters and also match serial numbers with each other but not with the Masters. Confusing because replacing top jaws due to wear or damage may cause the same issue for all chucks. Hmmmm. I hate to grind the jaws but the logical approach would be dial in the Chuck with the top jaws and grind the masters. Comments?

[kvom]

On my chucks with 2-piece jaws the master jaws do no gripping at all;  i.e., the edge of the top jaw extends past the master.  It seems as if the top jaws in your chuck have been machined.  I would replace the ones that are too small.

[Dan Rowe]

What is the runout if the test stock is clamped by the top jaws only?

Dan

[plataman]

Dan, I have dialed in the top jaws as they have more surface contact than master so run-out is negligible. Kvom just gave me an idea...work with the top jaws and grind the master for clearance. Kind of hate to cut a new $1,200 Chuck but he states none of his master jaws contact the work. The downside is it may promote bell mouth way down the road.

[crueby]

I've never see  the kind of chuck you guys are discussing, anyone have a photo of that type?

[kvom]

You need a big boy lathe Crueby.



An advantage of these is that you can make or buy additional top jaws and bore them  to clamp thin work.  In addition, bored soft jaws center repeatedly as long as the chuck remains mounted, even if the fixed jaws have some runout.

The first set of soft jaws I made myself from aluminum bar, but since then I ordered a set from monsterjaws.com.  The "tongue and groove" dimensions that fit the jaws to the lower jaws are standardized in both American and metric sizes.

[crueby]

You need a big boy lathe Crueby.



An advantage of these is that you can make or buy additional top jaws and bore them  to clamp thin work.  In addition, bored soft jaws center repeatedly as long as the chuck remains mounted, even if the fixed jaws have some runout.

The first set of soft jaws I made myself from aluminum bar, but since then I ordered a set from monsterjaws.com.  The "tongue and groove" dimensions that fit the jaws to the lower jaws are standardized in both American and metric sizes.

Oh my. Yes. Thanks for the picture!

[plataman]

OK, Here is a follow up on the Yuasa Adjust True chuck jaw issue: first I had to make a backing plate to fit this chuck to my Atlas 12 inch  1 1/2-8 spindle. That was a trick turning a 7 1/2 inch diameter chunk of durabar cast iron on this machine!

My solution was to grind the jaws just touching the outside jaws and cutting deeper on the master jaws. It worked. No more daylight visible between the jaws and parts. Since this is an Adjust True I can dial in center so there is no runout. Even though this is a six inch three jaw chuck it does look a bit funky hanging out of the Atlas spindle. Works great and much easier to dial in oddball stock than using a four jaw independent chuck. Also successful in removing bellmouth from my old Atlas three jaw with the same grinder setup. Terry

[b.lindsey]

Happy you got it sorted out Terry. So for a bit of work on your part you have a very nice chuck still for a fraction of the catalogue price   Sounds like a win/win to me!!

Bill