Gallery, Projects and General > How do I??

split cotter dimensions

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russ57:


 :) :nrocks:

I think you are suggesting that perhaps a cotter of 6061 may clamp better than steel,  against a steel shaft, and that the fit of the shaft against the cotter is important.
Discussions elsewhere suggest even a notch cut in the cotter,  rather than a milled crescent works fine.

More Experiment required!
Thanks,  I'll be back!

Lew_Merrick_PE:

--- Quote from: russ57 on March 28, 2012, 09:13:35 PM ---I think you are suggesting that perhaps a cotter of 6061 may clamp better than steel,  against a steel shaft, and that the fit of the shaft against the cotter is important.
Discussions elsewhere suggest even a notch cut in the cotter,  rather than a milled crescent works fine.
--- End quote ---
Russ,

It is less that I am suggesting using 6061 aluminum than it is that I am suggesting that you think about the variables affecting your work.  It is true that using a higher friction material (such as 606xx aluminum) can work in your favor (though there are drawbacks in co-machining aluminum and steel), but that is not the only variable.

If you make "ramps" (avoiding the general term "notch") in your collet/cotter, you will end up with a wedge-lock device.  This may help you in terms of applying a restraining force against rotation, but it also may for you to "rap" the unit to let it go.  It will self-unlock so long as the effective angle of contact between the face of the wedge and the cylinder being clamped has a tangent value greater than the coefficient of friction between the two materials.  Going from memory (always dangerous at my age), this is generally a wedge angle (with respect to the centerline of the collet/cotter) greater than 18°.

One thing to remember about aluminum on steel contact is that aluminum oxidizes into (gee whiz, what a surprise) aluminum oxide -- a very fine abrasive.  Aluminum oxide will rather quickly abrade non-hardened steel at rates that often surprises people.  One of the, I was a hero (for a day) situations occurred with a company I did work for when I "solved" the problem of their aluminum router "skates" wearing out the CRS sheet "tracks" upon which they slid them.  (A UHMW polyethylene "bearing" was the answer.)

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