In article ,
Ted Edwards wrote:
O.K. How long is "short" compared to the diameter of the
workpiece? If there is more than 4 times the diameter sticking out of
the chuck, you will have deflection -- to an amount dependent on the
cutting forces involved.

Where does this "4 times" rule of thumb come from? I am querying this
because deflection is much more sensitive to diameter than length. e.g.
comparing 1" diameter bar of 4" length to a .5" bar of 2" length, both
loaded with 100 lbs at the free end, the deflection is _twice_ as great
for the smaller bar. This is even worse if the deflection in proportion
to the diameter is considered.

You're assuming a constant loading (100 lbs in this case). I
think that with smaller diameter workpieces, it is normal to take
lighter cuts, so the loading should scale, too.

Enjoy,
DoN.

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