Okay, I feel really stupid: I am trying to drill a series of holes in a PVC pipe to make a drain line and my drill press will bore one or two holes, then it drops the bit. I reset the bit, really tighten the chuck, and it happens all over again. Help!
I have had that happen to corded and cordless drill/drivers, as well as the drill press, too. If there is any non-linear stress on the bit, it gets transferred to the chuck. If the chuck is lubricated or dusty it will vibrate the bit loose.
I recommend blowing out any collected material from the chuck. Old wood chips, dust, etc. will work as a lubricant.
Thanks Bubba, it decided to work for me - I suspect it was a lubrication problem; the chuck was a bit rusty so I wiped it down with a little oil. The PVC definitely grabbed the bit slightly once the hole was complete.