Last summer, I reported my problems with drill bits slipping in the chuck of my little Delta DP350 bench drill press. At the time, I had a Phase II Keyless (1/32 to 1/2 inch, JT33 taper, about $20) on it. I was forced to tighten this chuck with a hook spanner and sometimes a strap wrench, defeating the whole point of "keyless", and still it sometimes slipped.
I was attracted to the keyed ball-bearing jacobs-type chucks, but none were available in JT33 taper. So, I got a plain-bearing heavy-duty keyed Jacobs chuck, made by Jacobs, for about $84 (MSC 08590093).
This works. Not a hint of slipping, though I had to tap it right smartly with a rawhide-faced hammer to set it on the JT33 taper well enough that the chuck wouldn't pop off when the drill broke through and pulled on the chuck.
I would guess that the key issue is accuracy of machining all those oddly shaped parts within the chuck. This keyed chuck is faster to tighten and untighten than either the original jacobs-style chuck that came with the DP350 or the Phase II keyless.
Joe Gwinn
The original thread is at "Re: VFD recommendations sought; wearing belts; slipping chucks" (18 June 2005).