I have had a need lately for modifying screws, fasteners, small round stock items with no real length to them, the three and four jaw chucks I own are around the 6 size and the jaws are quite deep, this interferes with work holding for example: if I needed to machine the threaded end of a hex-head bolt the head would be the piece being held in the chuck jaws and this would be unstable to machine.
A solution is to make a set of tool makers mini jaws, they clamp on to the regular jaws of the chuck so they expand and contract as normal. Here they are mounted on my 6 chuck
Sets of these can be made to fit your 4-jaw or 3 jaw chucks skies the limit really.
Here you see a up close shot of a 8=32 brass knurled head thumb tack screw being held tight with the head positioned flush to the jaw face giving a nice perpendicular hold to the piece.
Here on this shot you can really see the advantage of this set up, the head has the clearance through the jaw length to be seated so the opposite end can be machined, you can even draw it up to the inside step to use as a depth stop, or place a depth stop from inside the chuck because now the jaws are opened.
Here you can see what work space you have, I believe the length of this screw is about 1-1/8 long
I decided on this set of mini jaws I wanted a 1/8 Diameter hole put through, I did this by drilling a pilot hole then reaming the hole out to size, (the jaws were fully closed on the chuck and there was no hole in new set of mini jaws to begin with) I am only going to use this set for Ό-20 and below size screws and this diameter is a nice comfortable fit for these size screws.
These are made from stainless steel but any material can be used. If made out of carbon I would suggest hardening them.
Making these is self-evident.
while facing on the jaws to thickness I noted the jaw number and stamped each jaw the same for future location in use.
If a larger radius is needed on mini jaw surface, tighten all three mini jaws down to chuck jaws securely, open the chuck so a 1 diameter washer can be fitted behind the mini jaws and located on the original chuck jaws and tighten up the chuck, now the chuck is tight and the mini jaws are in an open position, with a boring bar bore very softly in taking the edge off and produce a wide round profile on jaw tips.
To install the jaws for the first time, place mini jaws on chuck jaws, slightly tighten up to locate all three, with a mallet while at the same time as turning the jaws apply a slight tap to locate jaws into place the jaws now have been self-centered.
Now seat the side grub-screws leaving the top screw till last, once all three screws are set take a facing cut, then unscrew one side screw on each jaw, then reverse the jaws and tighten up the side screw you just relived, take another facing cut, the jaws are now seated.
punch stamp the jaw number on each.
Removal is release one side screw (the same on each jaw) then release the top screw and take off, install is just a reverse, colouring the grub screw would it easier to remember what one has be released.
Hope you all enjoy.