Re: ATM bearing size - fork mounts

[Kurt Hillig <khillig@umich.edu>]

On Wed, 3 Sep 1997, Gary McKenzie wrote:

> I am considering building a fork mount to hold a 12" f5 newt. I have some
> brand new 50mm self aligning pillow blocks. Would this size ra shaft in
> either steel or aluminium be sufficient? If not what are your
> experiences/opinions of what size would be sufficient?

Here in the states, we'd call that a 2-inch shaft (with a slightly small
value of two ;-).  This is larger than the axle on my 2.5-ton tractor, and
should be plenty stiff enough (whether steel or aluminum)!  Remember,
stiffness scales as the third power of the moment of inertia; a 50mm (2")
shaft has four times the moment of a 25mm (1") shaft, and thus is 64
times stiffer.

I'd sugggest, if you can find or make it (or have it made at a reasonable
price) use thick-wall tubing rather than solid rod.  This can provide a
lot of strength while saving a lot of weight.

Sorry, I don't remember the math to put together a table of weight and
stiffness versus wall thickness - books are at home, I'm not!  But if I
get a chance tonight, I'll put one together and post it here....

                            Dr. Kurt Hillig
  UMNet Administration     I always tell the    fax (313)763-2180
 University of Michigan     absolute truth     phone (313)647-8778
Ann Arbor, MI  48109-3297    as I see it.    X.500 khillig@umich.edu

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