Help boring soft jaws in 6 jaw chuck

I've bored many soft jaws in 3 jaw chucks using a plate with 3 socket head cap screw that fit into the cap screw holes in the jaws. However the basic problem with 6 jaw chuck is the fact 3 sets of jaws are 180° opposite so that as soon as one pair is tight the other 2 pair are still loose. Precision ground shaft will be held but an out of roundness results in gripping by only 2 jaws. Checking the cap screw hole in the jaws with a hex head cap screw I find that the diameters are not all exactly the same. How do I support the jaws to bore them? I did try by putting 1/32" thick plastic strips between the jaws since the jaws are almost completely closed but ground shaft put in jaws has .003" change in TIR when moved 1-1/2" left/right.

Does anyone have a suggestion on how to bore 6 jaw chuck soft jaws? I'm thinking of trying 2 ways. One make a plate from UHMW since I have quite a bit of it thinking that being soft it will flex enough to allow all jaws to have tension and being in the center of the jaw direct pressure in the center of each jaw. Or put the needed diameter in the bored as mentioned soft jaws then remove the soft jaws and measure the diameter of the bottom half being the soft jaws extend about 1/8" more. Seems that putting plastic strips between the soft jaws resulted in the part being gripped at a slight angle. Run out is not a problem since the chuck is the set true type and I can adjust for run out. My first attempt only required the removal of slightly less than .050", .025"/side. Larges cut taken was .010" or .020 from diameter. Each addition cut was less until final few were only .001" so as to avoid any boring bar flex.

Given the choice I’d rather use a collet than a 6jaw. Is your part too big for a collet?

L7

I would make a ring with 6 thru holes radial thru it, then tap holes in the OD of each jaw. Set the chuck to the diameter you want, put the ring over the jaws and run a cap screw into each jaw to pull it outward. This is how I used to bore softjaws on a 3 jaw power chuck I had at home where I didn't have a full set of setting rings, much easier to stock a handful of different cap screws than a whole set of rings.

I'm chucking 39/64" drills, reducing the shank size to .500. Collets do not work due to spiral of flutes. Rubber flex is better not great! I did use the chuck to cut 5/8" drills that had soft jaws bored buy someone else. The size was not right but good enough to work. Used set true to 0 run out. I thought I could bore the jaws so as to hold 39/64" but now I screwed-up what might have worked! If it were one or 2 drills I could use 4 jaw chuck with a bushing or something but I'm doing over 30 drills, then regrind the point on new made in USA drills.
I'm not sure how tapping the jaws will work. I do have a Jig Borer but how do I locate the holes in the jaws? I can make the plate in the Jig Borer. In a 3 jaw chuck it will work since a 3 jaw will grip just about anything like a 3 legged table will not rock no matter how bad the floor is or the legs. I have made a plate that I screwed in socket head cap screws to fit the cap screw holes in the jaws and it works great in a 3 jaw chuck. But 6 jaws is another animal!
I'm sure I can find another way but for future reference how can I bore soft jaws in a 6 jaw chuck or how can I grind hard jaws if required?

I tapped the OD of the soft jaw, here is a crude picture:


Once you get all 6 capscrews in just snug them in pairs and it preloads the jaws out just like clamping something.

I’ve reduced plenty of drills. Now that the OP has said what he’s doing I still wouldn’t suggest bothering with a six jaw. Four jaw and a split bushing. For only 30 drills you’d be way ahead in time vs a set up to re bore 6jaw soft jaws. Cheaper too….

L7

Nmbmxer said:

I tapped the OD of the soft jaw, here is a crude picture:

View attachment 323430
Once you get all 6 capscrews in just snug them in pairs and it preloads the jaws out just like clamping something.

Click to expand...

Oh OK I see!!! I like it! Thanks!!