Re: [CAD_CAM_EDM_DRO] jacobs chuck question

blueveil@... wrote:

> My jacobs chuck just popped out of my mill. (ruining a part of
> course). I can see that it looks like a tapered press fit. Is this
> normal? How can I prevent it from falling out again. does anyone
> have any experience with these?
> Thanks in advance.

Are you milling with the jacob's chuck? It will always work loose.
The only way I know to deal with this is to drill a hole in the back of the chuck
(if it is not open already) and drill and tap a small hole in the arbor. Then,
you use a screw (a flat head may work best) to keep tension between
the arbor and chuck. This actually works, but a Jacob's chuck is not a
very good way to hold a milling tool. Collets and end mill holders are much
better.

If the chuck popped off while drilling, it may be that the drill is not sharpened
evenly, and was exerting side pressure. Anyway, you should clean both
the chuck's socket and the arbor with solvent, and then wring the two together
until it locks. Drilling pressure should tighten the fit until it is very hard to get
off. If it will not sieze this way, then put magic marker on the arbor and lightly
wring the chuck onto it. If the magic marker is wiped off only in a ring around
the arbor, the tapers don't match well, and it will not grip properly. Either the
chuck or the arbor will need to be replaced. If it is a spotty pattern, then there
is a ding or bit of grit there that is preventing all-around contact, again preventing
a god grip. You may be able to detect the defect and fix it, otherwise again you
need to replace the offending part.

Jon