I have a knurled-sleeve Jacobs No. 1 Super Chuck which came to my hands among tooling for a lathe. The chuck has a small slotted screw in back end, near the outer perimeter, roughly parallel to the shank.
Anybody have an idea what it's for? I don't think any Jacobs chucks used screws from the factory. First thought was maybe a rotation stop to prevent putting a wildly-wrong drill in a production setup, but the chuck adjusts full range.
The question is mostly a matter of curiosity. The chuck looks rather beat up, though it's not seized and the jaw surfaces aren't obviously mangled. I'm not likely to use it soon....
I have a knurled-sleeve Jacobs No. 1 Super Chuck ...
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Does it have diamond knurling? I have a very old Jacobs that does, but no extra screw in the back. Perhaps it was added to attach a work stop for production?
Yes, it's diamond knurling. I took the screw out and looked inside, the screw hole runs into the annular passage where the tails of the jaws reside. No moving parts visible at all. The screw is very neatly set so it doesn't alter the outline of the chuck significantly. Not at all a hack job.
Could it have been to connect some kind of purge line, to keep debris from getting into the chuck?
The whole chuck looks battered, as if it was used in an extremely rough environment like a mine or quarry, or maybe a heavy blacksmith shop. It moves freely when more than half open, closing it all the way takes a key and some effort but no other tools.
The oddest artifact is three marks between the key pivot holes. It looks as if the chuck was placed in a larger three jaw chuck and squeezed until the larger jaws left impressions between the pivot holes. Must have taken considerable force..
Yes, it's diamond knurling. I took the screw out and looked inside, the screw hole runs into the annular passage where the tails of the jaws reside. No moving parts visible at all. The screw is very neatly set so it doesn't alter the outline of the chuck significantly. Not at all a hack job.
Could it have been to connect some kind of purge line, to keep debris from getting into the chuck?
[Perhaps, or for oil feed for deep drilling. If so it likely would have had small pipe threads]
The whole chuck looks battered, as if it was used in an extremely rough environment like a mine or quarry, or maybe a heavy blacksmith shop. It moves freely when more than half open, closing it all the way takes a key and some effort but no other tools.
The oddest artifact is three marks between the key pivot holes. It looks as if the chuck was placed in a larger three jaw chuck and squeezed until the larger jaws left impressions between the pivot holes. Must have taken considerable force..
Thanks for writing,
bob prohaska
----------------------------------------------------- I've seen a machinist leave his largest and heaviest lathe chuck on permanently and grab smaller, more easily handled chucks in it. A chuck with replaceable top jaws could have a set cut away to grab the Jacobs body, or bolt shanks while clearing the head. I have a Jacobs that mounts on a
1-1/2 - 8 lathe spindle and holds small drills or work for hand filing or polishing near the jaws. It also fits the spindle thread of a BS-0 indexer.
On a Multicraft at least the body is made from easily machined steel and not hardened. I converted one into a collet closer spider to keep thin rods from whipping, and chucked it by the nose while opening up the mounting end.
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