Re: [CAD_CAM_EDM_DRO] shafting question

> Could anyone point me to a resource telling me how much a certain materia
> l will bend if it is X long and has Y load applied to it? I'm trying to decid
> e if I can get away with using 1/2" dia. end supported shafting on my mill or
> if I'm going to need continuously supported shafting.
> I'm concerned the end-supported may bow too much under load, causing inna
> curacy or leading to things binding up on me. The continuously supported shaf
> ting though is much more expensive.
> Also, has anyone had any experience using frelon bearings?

Unless you are machining something like wax (and probably even if you
are) you need something much heaver in cross section than 1/2" round
for an unsupported span of any meaningfull length - ie, I wouldn't
trust it more than four inches between supports, if that.

The problem is not the static (constant) load of machine components
and the mass of your part sitting on the table, but rather the
pressure you must exert on the tool to make it cut and the much, much
higher dynamic loads from cutting. If you don't build a structure
stiff enough to counteract these, your machine will vibrate horribly.
As a simple test, chuck a length of bar in a lathe and see how far
from the chuck you can take a cut without chatter setting in.

I'd suggest 3/4" rail with supports, possibly unsupported 1" if the
distance isn't too great. Narrow unsupported rails are mostly usefull
for measuring tools which don't have to contend with cutting forces.

To answer your original question, you want something like a basic
mechanical or civil engineering textbook, or perhaps "Machinery's
Handbook".

Chris

-------------------------------------------------
Christopher C. Stratton
Engineer, Instrument Maker, and Horn Player
ccs@... 617 628 1062
http://web.mit.edu/~stratton/www/brassbuild.html