jacobs chuck

[Dave Fritz]

My forstner bits slip inside my jacob's chuck. I have to almost pound on the key to tighten it so it won't slip. This happens with different sized bits and even happens with the extension in the chuck.

Anyone have this problem and know of a solution beside a new chuck?

The chuck's jaws are pointed so the contact is pretty minimual. Do they make chucks with flatter jaws to have more surface area in contact with the bit shaft? I also have bits with flats on the shaft, they work better.

Dave F.

 

[john lucas]

you could put a longer handle on your chuck key but I think your best bet is to get a new chuck. they are pretty inexpensive, $30 to $50 if my memory serves me well.

 

[Steve Worcester]

If the chuck is jammed on a taper, you could replace just the chuck portion. If you are using a chuck designed for smaller bits (which it sounds like you are), then moving to one that has more contact would help.
That and make sure the bits are sharp and don't force the bit, let it cut.

 

[MichaelMouse]

My forstner bits slip inside my jacob's chuck. I have to almost pound on the key to tighten it so it won't slip. This happens with different sized bits and even happens with the extension in the chuck.

The chuck's jaws are pointed so the contact is pretty minimual. Do they make chucks with flatter jaws to have more surface area in contact with the bit shaft? I also have bits with flats on the shaft, they work better.
.

I think you'll find that almost all "jaw" are rounded, so the bit will better center on the high spots. Purely mechanical thing. I'd suggest you snug in one of the three chuck key points, then go to the next, snug, then the third. Truth to tell, it's the way we should do it always, but a good chuck can make it unnecessary.

You may have some metal shavings or dirt inside the cone that compresses the jaws as it's tightened, the jam gives you the illusion that it's tight, then releases easily under stress. Oil and run the chuck through the full range a few times to check for smooth operation.

 

[Tim Hall]

Is the shank on the drill bit that goes into the chuck round? if so, that is the problem, you could try to find some that have flat sides, or you could grind the ones you have flat on 2 sides like i did. This however is tricky as you have to make sure you get the right amount off or your bits wont drill centered holes anymore.

 

[Owen Lowe]

We're all assuming the quality and condition of the chuck in question is comparable to what we own and use...

Dave,

What is the condition of the chuck otherwise? What brand is it? Are the jaws chipped? Do the jaws mate completely when closed? Does the slipping occur with all drills of various sizes?

Let us know this stuff and maybe you'll get specific fixes.

 

[MichaelMouse]

Return to reality, and realize that with a cylindrical bit and curved surfaces to help center on the jaws, there are only 3 lines of contact possible, regardless the size of the bit. I'm not talking about my chuck, but all chucks so constructed. Unless you've got a brace and bit, that's all you get. Even a hex shank has those same lines of contact, but it's geometrically impossible for it to roll around the shank unless it loosens beyond the limit of the shank corners.

So crank in the three places to get full contact, and run the cone to get best operation. If the chuck has manufacturing faults like an asymmetrical cone or inconsistent jaw thickness you'll never fix it. One jaw will always be loose, and that'll usually be enough, on a cylindrical bit.