A while ago I bought three new Jacobs keyless chucks with a new lathe. First one lasted about 6 months then jammed up tight, undoing it with a strap wrench caused it the shatter internally. Next two went within a few months after that, all the same symptoms, looks as if the heat treatment was too severe as these were too brittle. It could have been that they used an inferior grade of cracker dough because they had the same tenancies as when I try to spread butter prior to putting the cheese on.
Bought a couple of 13mm keyless from Osama Bin Swali at Arceurotrade as a stop gap measure and these have been good, in fact I have changed both spindles on the double headed pillar drill and the CVA lathe to keyless.
I still have some Jacobs keyed chucks that work but they don't have the holding power of the keyless, only drawback is you may have to give it an extra squirt if you are power tapping on the lathe but most times they do allow you to back out. It's really nice not having to search for a chuck key. Been using an old air drill today and it must have added 1/2 hour onto the day keep searching for the damn key then having to nip it up again. I reckon the drill manufactures must pay Jacobs to keep spinning drill and shagging the shanks up. I have a nice set of stub drill I bought in China last year that have
3 lobed shanks ground as standard, these NEVER spin, need to get the rest of the drill in the same type sets.
.John S.