Jacobs tapers

[Rob Hazard]

I have a question:
Is a Jacobs taper (on a large drill chuck) best assembled dry, or with some sort of lubricant?

One of our resident gorillas managed to pop the chuck off our drill press, and I remembered somebody once recommending a tiny smear of graphite grease to help the taper seat.

[George Roberts]

dry

[Gary E]

If you want it to say put, CLEAN and dry. One the other hand we often used a very slight smear of redlead, which you probably dont have anyway, if you need to remove it from the spindle or MT adapter later.

G

[Dave Fleming]

If you don't have a Jacobs Chuck remover then a 'pickle fork' will do fine. Pickle Fork is slang for a tool used in auto and truck wheel alignment.

Same principle, U shaped with tapered forks to fit between chuck and spindle.

[Bill Perkins]

I had the same problem and couldn't get the piece to stay on .I was told to get every trace of oil off with a strong solvent .I scrubbed both surfaces with acetone and have had no more trouble .

[Joe Dupere]

What a timely post. My chuck fell off a couple of weeks ago. Somebody who (I thought) knows about this stuff, told me to grease it. No go. Tonight I'm going home to clean it up and see if that works.

Thanks, Joe.

[Rob Hazard]

Thanks for your replies. I put it back on and it seems fine.

[Cuyahoga Chuck]

Jacobs tapers are very shallow (about 1½° I believe) to maintin a powerful hold with very little engagement. Anything like grooving fretting or out-of-round to the hole or the plug can render both pieces useless.
Any time these pieces disengage unexpectedly it's usually a sign that bad things have happened. Good tapers only come apart with difficulty. You can stone off high spots on a damaged taper but there is no easy way to replace missing metal.
The smoother the finish on the mating parts the better the fit. No lube is required unless there is a reason for disassembly down the road.
If the mating surfaces are chopped up it may be possible to re-create enough new surface to get a tight fit by lapping the pieces together with some fine grit. But the metal removal can't be severe enough to allow the plug to bottom in the hole. If that happens the plug has to be shortened.
Hope this helps.
Charlie