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what is the R8 adapter to use for my Jacobs JKP-130-J2 keyless chuck

Budvar

Plastic
Joined
Oct 22, 2023
This is a used chuck that I picked up at some point am an interested is using it with my Bridgeport which requires an R8 mounting. The drill chuck says Jacobs JKP-130-J2 on the side. Jacobschuck website lists this part number as having a 2JT mount. I assume that is a #2 Jacobs Taper. I ordered an adapter arbor from McMaster to go from R8 to Jacobs Taper number two. The male taper is too small to engage in the drill chuck. The male taper measures to spec' at .56" DIA at the large end.

The drill chuck measures about .61" DIA at the large end of the taper and at about .88 depth it measures about .56" DIA so this seems larger than a Jacobs #2 taper.

Also, when I Google Jacobs JKP-130-J2 I'm finding images that don't look exactly like my drill chuck which is stamped "Spain" and is silver and black. Mine looks more like a llambrich but it says Jacobs in their stylized font right on the side of the drill chuck.

I was tempted to swap the adapter to the next size up Jacobs taper but according to the spec's it'll be way to large. So what adapter/taper do I need?
 
There is a DIN taper for drill chucks that is a European alternative to the Jacobs taper. I have some German, Swiss and Chinese chucks with the DIN tapers. So you cannot be sure you are dealing with a Jacobs taper until you find an arbor with a known taper that fits your chuck.


Larry
 
Put the drill chuck in the lathe chuck, and sweep the bore of the drill chuck front to rear. This'll give you the taper specs that you can look up to find a match.

Or mount it on v block, vise, etc.................. Anything to hold it steady while you sweep the bore.
 
Put the drill chuck in the lathe chuck, and sweep the bore of the drill chuck front to rear. This'll give you the taper specs that you can look up to find a match.

Or mount it on v block, vise, etc.................. Anything to hold it steady while you sweep the bore.
this is a good suggestion. I did calculate that my measurements matched up with a JT33 suggested by matthemuppet. Mine is like a JT33 that is missing the first .120" of the large end. The JT33 Arbor I ordered seems to work! I just used a DIA 1/2" endmill in the chuck to side mill (full cutter length) mill a few thousandths off a block of aluminum and it held so in my mind it should hold up to center drill, drill, tap operations just fine
 
There is a DIN taper for drill chucks that is a European alternative to the Jacobs taper. I have some German, Swiss and Chinese chucks with the DIN tapers. So you cannot be sure you are dealing with a Jacobs taper until you find an arbor with a known taper that fits your chuck.


Larry
this "european alternative", din 238 b6-b22, are sections of a morse taper, btw.
 








 
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