Tightening a scroll chuck

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curtis cutter
Posts: 559
Joined: Fri May 18, 2012 11:46 pm
Location: Curtis, WA

Tightening a scroll chuck

Post by curtis cutter »

Maybe someone can help me here with an explanation. I see people tightening all three points on a three jaw scroll chuck. Am I missing something with my thought that if you tighten one point it makes no difference if you tighten the other two as it cannot add more clamping force?

Gregg
Gregg
Just let go of it, it will eventually unplug itself.
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Harold_V
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Re: Tightening a scroll chuck

Post by Harold_V »

Due to clearance of the scroll, yeah, tightening all three makes a difference. If you hope to grip very tightly, use all three. As much as it may not make sense, it DOES add more clamping force. You can clearly see that because each change offers a little more tightening, until all slack has been averaged.

Because of the clearance, the scroll shifts each time a different socket is selected. The shift alters the relative position of the jaws, albeit only slightly. Armed with that thought, don't use all three if you hope to achieve consistency. One of the three will generally cause the chuck to grip the item nearer to concentricity with the spindle than the other two. That's the basis of soft jaw machining and use. One always uses the same socket, and is the chief reason why some chucks come with one socket identified, even if it doesn't have master jaws. The socket that provides the best condition is the one marked.

If your question revolves around the types of chucks found on drill motors, there's no getting around the fact that using all three holes will enhance gripping power, and, in this case, how concentric the chucked item runs usually makes little difference, although it can if one is gripping a tap in a mill or drill press spindle, as an example.

H
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curtis cutter
Posts: 559
Joined: Fri May 18, 2012 11:46 pm
Location: Curtis, WA

Re: Tightening a scroll chuck

Post by curtis cutter »

Thanks Harold.

Spending some time cleaning the chuck as it had been greased prior and getting rid of that in favor of the light oil coat.
Gregg
Just let go of it, it will eventually unplug itself.
johnfreese
Posts: 219
Joined: Thu Jan 21, 2016 2:10 am

Re: Tightening a scroll chuck

Post by johnfreese »

I have a 6" Buck adjust-true chuck and an 8" Pratt Burnerd adjudt-true. They only have one pinion so I don't give a crap about which pinion to use. I suspect that where you have 3 pinions to choose from the most important thing is that you be consistent in which pinion or pinions you use when tightening. I also suspect that if you have a little clearance on the scroll that one of the pinions will give better concentricity than the others. If that is the case, always use that pinion when tightening.
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