How to remove this keyed Jacobs drill chuck

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I have an old Jacobs keyed drill chuck in my box-o-spares, and I need a drill chuck for my hobby lathe. I have a suitable tailstock arbour, but the drill chuck has something already installed, and I can't remove it.

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The label reads: 

JACOBS (r) MULTICRAFT (r) USA

and further around reads

3/8 (10mm) CAP
3/8 24 THD KG

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Here's the shot up through the wide-open jaws. Inside is a large-flanged bolt with a shallow 1/8" hex socket. A 3mm tool spins in the hole, and a 3.5mm tool does not fit. Being a metric country, old imperial/SAE/standard/american sizes are less common. I have exactly one allen key that fits. As per photos, I've managed to pretzel the shaft by using a vice and pliers to apply torque in either direction.

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  • Is the little bolt going to be conventional right-hand thread or backwards left-hand thread? It doesn't move in either direction so far.
  • Will applying heat damage the chuck? If there's thread-lock, heat may loosen it.
  • Which two areas should I be applying torque between? The old arbour, the outer ring, or the hex tool in the small bolt?
  • Is the old arbour threadded or some kind of taper? The Jacobs chuck references like http://www.michiganpneumatic.com/customer/mipnto/extrahtm/jacobsref.htm and http://www.jacobschuck.com/drill-chuck-removal-guide do not show how this model chuck is mounted.
  • LAST RESORT – should I drill out the little bolt ? No idea what kind of steel its made from, but it didn't distort when I put a 90 degree twist into the allen key, so its likely to be hardened.

I do not need to save the old arbor. There's plenty of apprentice marks on it now from my vice.

I hope to mount it on this morse-taper0:threadded arbour from my Sherline lathe. The largest flange is 16.48mm in diameter on the old arbour and the MT0 from the lathe has 15.90mm

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The chuck moves smoothly so I'm happy it will be good. I have not bothered cleaning it yet – unless I can remove the old arbour it will be pointless.

Certainly the usual solution would be to order parts, but given the C19 lockdown, I can't even leave my home, so everything needs to be in-stock already.

Best Answer

I agree with heat if that is a screw but that doesn't look like any screw I have seen on a Jacobs Chuck (and mine were left hand threads) .

Is the model number on the chuck visible? If it has a 3jt or a 4jt it is a Jacobs taper different than Morris taper but to remove will require force. I normally use a mechanics pickle fork for separating ball joints , lock the tail in a vice and a few good wacks and the chuck will come off the tapered shaft if it is tapered or JT3 or 4 . There might be a 2 but I have only worked with 3 & 4.

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