Is it possible to modify chuck jaws to take bolt on jaws?

[MontanaLon]

My 3 jaw chuck came with only 1 set of jaws so can only be used for holding work 1 way. Is it possible to mill the tops flat and then drill it for replaceable jaws so I can work inside and outside?

The other option would be making new jaws but that is likely exceeding both my current abilities and tooling. Not sure what it would take to cut the scroll engagement at any rate.

 

[darkzero]

Yes it's possible but it's a lot of work. The tongue & groove that you'll need to add to your existing jaws needs to be very accurate if you want any repeatability. The jaws are usually hardened, you'll need to anneal them to do the machining & tap the holes. Reharden, then surface grind to final size.

After you get the top jaws fitted you'll probably need to regrind them to run true. Top jaws are kind of expensive too unless you plan on making your own from scratch. I would rather just search for another chuck. But if you just want to adapt your jaws to use soft jaws & don't care about tongue & groove you can skip some steps.

This video may interest you.

 

[MrWhoopee]

I would rather just search for another chuck.

This^^^^^

An experienced and skilled machinist would hesitate to even attempt what you are suggesting. Find another chuck, don't ruin the one you have. Depending on the size of chuck, the heat treating alone could cost as much or more than an import chuck with removable top jaws.

 

[mikey]

Agree - find a high quality chuck.

 

[Karl_T]

I made my own softjaws with scroll teeth years ago. Did it on two different chucks.

I modeled the center tooth on a jaw as two radii. just used an edge finder to find three points on each surface. I happen to have a CNC so I cut a huge long piece of stock full of teeth. No reason a rotary table could not be used to do the same.

No reason not to do the same as a base for quick change jaws.


I do agree its a lot of work just to save a couple hundred. But its a lot more fun to do it yourself.

here's the gcode from 20 years ago:

;TEETH,ADJUST TRUE SOFT JAWS
;set second jaw back 0.100", third back 0.200"
(*BLEC'*',CMST';',CNDL3,CNDR4,ZRSP0,PDOF0.05,FDOV0*)
%LAPPER = 0
%ZDEPTH = 0.5000
%START:
%COUNTER = 0
%ZDEPTH = %ZDEPTH + 0.025 *;DEPTH OF CUT FOR EACH PASS
%LAPPER = %LAPPER + 1
G92 X 0.00 Y 0.00 Z %ZDEPTH
G90
G00 X 0.000 Y -0.250 Z 0.00

%LOOP:
%COUNTER = %COUNTER + 1
G42 T 02
G01 X 0.008 Y 0.000 F 3.0
G01 X 0.122 Y 0.000
G03 X 0.096 Y 0.750 I -1.304 J 0.330
G01 X 0.000 Y 0.750
G02 X 0.008 Y 0.000 I -3.986 J -0.420
G01 X 0.008 Y -0.125
G01 G 40 X 0.2857 Y -0.25
G92 X 0.000 Y -0.25 Z 0.00
IF (%COUNTER LE 9) GOTO %LOOP
G54
G00 X 0.00 Y 0.00 Z 0.00
IF (%LAPPER LE 5) GOTO %START *;DO ALL TEETH 5 TIMES

 

[MontanaLon]

This^^^^^

An experienced and skilled machinist would hesitate to even attempt what you are suggesting. Find another chuck, don't ruin the one you have. Depending on the size of chuck, the heat treating alone could cost as much or more than an import chuck with removable top jaws.

I've looked for another chuck for months. Very few 1-7/8*8 threaded chucks around. The one I have seen had same issue as my current chuck. Only 1 set of jaws and they were same jaws I have.

Plenty of too big chucks around. I'm having trouble even finding back plates in the right thread to adapt a chuck that would fit. Would like a face plate too, same issue.

 

[cjtoombs]

You can make a back plate a lot easier than you can make those jaws. The ones that you buy are unfinished anyway, basically just a hunk of cast iron with a threaded hole in a boss, rough machined. Get a piece of 1 to 1 1/2" thick steel a bit larger diameter than you nee. You can sometimes find drops on eBay cheap, or order a cut from Speedy Metals. This all assumes you have a 4 jaw you can do that work in.

 

[MrWhoopee]

So, are we looking for a 4 in., 5 in., or 6 in. chuck?

You will have to buy a blank backing plate or one that is threaded small enough to re-thread. I'm finding 1-1/2 - 8 threaded plates which could be re-threaded. Since you don't have the reversed jaws, you may have to enlist someone else (either near you or on this forum) to re-thread it for you.

The joy of being a machinist is being able to make what you need but can't buy.

 

[cjtoombs]

I was also thinking you could make an adapter to hold the next bigger size backplate, I think that's 2.25 - 8. You could hold the stock in your current chuck to do the inside threading then turn it around, screw it to your spindle nose and do the outside. Then you could locktite it into a comercial backplate and finish the backplate on the nose of your lathe, ensuring concentrically. I think Shars had a 6" backplate with the larger threads for around $60.