3 jaw vs 4 jaw scrolling chucks

That is right in my opinion. There is also more force on the scroll at the maximum.
 
Aaron_W said:
Out of curiosity does diameter play a part? I imagine the closer to maximum capacity with the jaws at their most distant, clamping force is at its weakest.

Just looking at the the typical 1/4-1/2" stock I work with and in my 3.1" 3 jaw chuck there isn't much room between the jaws for the work to slip out of. If I was turning a 2 or 3" piece on the other hand.
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With an independent jaw chuck, no; because the geometry and position of the mechanism that moves the jaws remains constant.

With a scroll chuck (aka, non-independent) theoretically, it should vary because the contact point where the jaw meets the scroll moves along a radius. Whenever a radius is involved with a force, there is a torque so, as the radius changes as the jaws move, so does the torque. The difference would also depend on where the pinion gear (driven by the operator) is positioned on the back of scroll.

Ray
 
No pinion on a Sherline chuck, Ray.

In my view, the strength of the hold depends more on the number of teeth engaged in the scroll. As you go out, you have fewer teeth engaged so theoretically there is less clamping strength. However, there should be enough strength to hold a part out to the max extension of the jaws, just before you hit the ways.
 
Sorry missed these replies.

I was just thinking the surface area in contact with the jaws is greater the smaller the diameter of the part. A 1/4"piece of rod is nearly fully contained by the jaws on a 3 jaw, where a 2" piece of rod would have significantly larger gaps which that 4th (or 6th, 8th whatever) jaw would help close.


I have a long list of needs and wants regarding tooling, the 4 jaw chucks are on there but I'll wait until I find a smoking deal or actually have a need.
 
My lathe came with a beat out three jaw chuck. I worked on it ground the belmouth till flat . Recut the side angles and the gripper slots on the jaws. It's been good ever since . But I found a six jaw with both sets of jaws at cooks , after using that the three jaw sits on the bench. So I wouldn't shy away from the four jaw model even better if one with both independent and scroll came at a good price . On my logan I like the eight inch best .
 
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