Strange acting Jacobs Chuck

I have this nice 25 yr old Jet 1/2" drill press--has a nicely machined Jacobs style chuck-(16mm)--a couple of years ago, it started slipping
while tightening it up. you get it fairly tight with the key,, and then you can just keep on turning the key--w/o it getting any tighter---although you have to turn the chuck key further than "normal" to loosen the chuck.. Inspecting the innards doesn't reveal any obvious defects..Do I need to clean one area & lube another???
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You have probably sprung the jaws. They are replaceable.
JC
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More likely the ring gear is slipping on the body.
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I think you mean the ring-gear sleeve is slipping on the nut.
--
Regards,

Chas.

(To email me, replace "xxx" with letters tango papa golf.)
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Exactly. I don't see how it could be in the jaws. However, when I have a chuck act up in the slightest...it gets replaced. All my production machines have Jacobs chucks and we used to repair them but it just isn't worth it anymore.
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[regarding a nontightenable Jacobs type chuck; the ring-gear sleeve is slipping on the nut]

But, for the edification of the original poster, it IS instructive to disassemble and admire the internal construction. Lightly knurling the inside surface of the geared sleeve would solve the problem, and a freshly lubed worn-in Jacobs chuck is SO smooth in operation after a rebuild, it's worth the effort. Unless, of course, you have paying customers waiting.
Jacobs offers takeapart instructions
<http://www.jacobschuck.com/drill-chuck-repair.asp
Reassembly is easier if you heat the sleeve on a hot plate.
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I've seen many a chuck where the operator chucked the tool improperly in order to get an extra quarter inch of extension rather than use the proper tool. The jaws end up a mess and the chuck doesn't tighten properly until you rebuild it.
With todays modern drilling technology, I avoid Jacobs like the plague in favor of collet chucks. Through the tool coolant is becoming a defacto standard configuration and tools like M.A. Fords Twister XD series have ground shanks, are solid carbide and coated so that you can run feeds and speeds that have been unheard of until recently. This sort of drilling technology is also expensive. A .421 5X drill will drill two inches deep in A286 without pecking at 30 inches per minute and give you thousands of holes but the drill is $186.00 - or was six months ago. You won't do that with a Jacobs or even an Albrecht but it's easy with an ER32.
JC
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Ah, I see where you are going with the jaws!
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Jaws are HSS technology. We have progressed.
Wes
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Many Thanks for all tyhe helpful answers--I think I can fix it or fling it after reading all the possible malfunctions
Spl thanks for the chuck teardown url
Jerry
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Loctite between the nut and gear sleeve might be a solution to your problem. You will need to ensure it does not migrate to other areas.
--
Regards,

Chas.

(To email me, replace "xxx" with letters tango papa golf.)
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