Wednesday, October 26, 2016

Deep Jaw Chucks

(I made the mistake of accepting Google's suggestion "deep throat chuck" which had nothing to do with machining but a lot about a relative by marriage.)

The standard Sherline lathe chucks don't have enough grab to hold several inch long acetal workpieces.  Acetal is very slippery.  My shop assistant is taking machining classes, so he is rapidly passing me in knowledge.  We used a 6" 4-jaw chuck that I bought some years ago.  This required adding riser blocks to the motor and tool holder to get clearance off the bed.  I suspect that some one makes either long jaw, or very powerful compression 3-jaw chucks with a 3/4"-16 thread.  Suggestions?

I suppose another solution would be to buy another Sherline chuck and drill a hole through each jaw and then screw a sharp pin through it so it isn't just friction holding it in. It appears that 4-jaw chucks exert more clamping force than 3-jaw chucks: four points of contact, not three.

Core problem: with jaws pointing out, the 3" chuck is supposed to go up to 1 3/8" diameter.  At 1 1/4",  it was marginal.  I reversed the jaws, which is supposed to go from 2 1/4" up. Works as long as I cut slowly.   Sherline suggested wrappimg some sandpaper around the acetal.  Works wonderfully well.

2 comments:

Will said...

In theory they might hold tighter. In reality, not that often. Their main purpose is to allow one to shift the centering of the object, to compensate for offset bore-to-surface dimensions. Or to hold irregular surface objects. Trying to get equal force on 4 jaws without loosing centering takes time and effort that some don't bother to employ.

BTW, there are six-jaw chucks, although I don't know how small they make them.

jon spencer said...

Would a Jacobs Spindle Nose Collet Chuck work?