Re: [CAD_CAM_EDM_DRO] not stiff enough!

> .132 deflection? What material is that shaft made from, what is the shaft
> geometry? I can suspend a four foot bar on 2 "knife" edges, place 25 # in
> the middle and wouldn't get that much deflection.
>
> Smoke

Read the post again. :^)

Yes, geometry and materials matter a lot with deflection.

Round shaft deflection can be a bit counter intuitive. Most of
the material is close to the neutral axis where it cannot contribute to
stiffness.

For example if a round shaft is twice the diameter it will have
only one sixteenth the deflection simply supported and center loaded.

If you go from 3/4" diameter to 7/8" diameter deflection will be almost
halved.

So if you tried it with only a slight change in diameter you would get very
different results.

It is so critical and sensitive to rotating machine performance
one needs to:

1) do the calculus

2) check for mistakes with experiment

Solid circular cross sections make very poor beams. It has
always amazed me over many years that a 3/4" diameter
steel shaft is about the same order of stiffness in bending as
a common wooden 2"x4". It is sometimes less depending on the wood.

That is why linear shafting meant to hold significant loads is
drilled for support bolts every few inches or so.

My example in the previous post was just to illustrate the four
to one advantage of fixed vs simple support regardless of diameter.

Just trying to find a way for the guy not to have to rebuild his
machine. Or to try to weld case 60 shaft which would turn it
into instant junk.

Oh that reminds me.... you can drill a hole in the middle of hardened case60
shaft with a carbide spade drill. I do it
a good bit. One support bolt in the center hooking the shaft
to a stiff support will reduce deflection four times. Combine
that with fixed end support and I think the system stiffness
will be very satisfactory.

Leslie Watts
L M Watts Furniture
Tiger, Georgia USA
http://www.rabun.net/~leswatts/wattsfurniturewp.html