Yes, leave the bit up a 1/16" or so. The reason is that the collet pulls
down as it tightens. If the bit is already at the bottom, the collet may
never tighten even though you screwed it down tight.
"Tim Simmons" wrote in message
...

Also, I read that you should position the bit 1/16" above the base rather
than riding on the bottom. Is that true? If so, why? Does it alleviate
extra vibrations by not touching the bottom?