RE: [CAD_CAM_EDM_DRO] Re: sourcing motion control parts - steel vs aluminum

On 10/25/04 6:23 PM, Leslie Watts wrote:

>Aluminum and steel are virtually identical in specific stiffness.

I don't think that's true. The modulus of elasticity for steel is
29,700,000 psi and it's 10,000,000 psi for aluminum (this will vary
based on type and temper, but it's the best info I can find). For
example, a 2" square steel tube with a 1/8" wall would deflect 0.11"
with 100# load in the middle of an 8' run. For aluminum, it would
deflect 0.33".

This info is from the cheesy calculator I hacked together at
<http://metalgeek.com/static/deflection.php>.

If you want to quarrel with my conclusions, I've posted my sources
there. I am NOT an expert on this, although I do bend a lot of metal.
And my limited testing seems to support the accuracy of the calculator.
But I'm certainly open to other ideas.

And one note about 8020. I've used it, although I wouldn't recommend it
for framing (for a hobbyist). Unless you're going to be reconfiguring
it later, it's awfully pricy. However, they do sell a slick little
sliding dohickey for it that seems like it would work fine for a plasma
Y axis.

Hal Eckhart - Casa Forge - Minneapolis MN - <http://www.casaforge.com>