Jet Dedicated Mortiser Machine Adjustment

[ken gibbs]

I have a four year odl Jet mortiser and something amazing just happeded. I started to cut a 1/4" mortise and the four sided chisel started to spin along with the bit. So I tightened the chisel setting and it still turned. so I used a different set screw and I can not make the chisel stop rotating. Something has to be blocking the set screw but the set screw will not screw in all of the way to grip the chisel. Nothing that I can see is blocking the bore hole that the threaded bolt runs inside of. Its like the set screw (1/4" bolt with national course threads) has developed a taper. I do not want to break off the set screw (bolt) but I can't get it any tighter without shearing the bolt. Any suggestiions?

[Will Overton]

Did you remove the chisel and bit to make sure they were not bound. If the bit jambed in the chisel (not uncommon) and the chisel started spinning, it may have created a groove where the set screw is supposed to hold it.

[Stephen Cherry]

sounds like the bushing that reduces the diameter, which has a hole in it to allow the bolt to pass through, has rotated

http://www.sawmillcreek.org/showthread.php?t=142826

[ken gibbs]

The bshing looks like it was pressed fit into its socket. I can feel the opening inside of the bushing with my little finger and it feels lilke it is in the correct place. The last time I used this mortiser, it locked down tight. The set bolt does not look like it has warped and shows no damage. I think that will try to bore out the threads and then I may have to cut new threads for a slightly larger set bolt to hold the chisel where it belongs. I can't see any foreign object damage inside of the bore hole.