On 2008-03-11, Tim Wescott wrote:
More design questions:

I need a stick-like thing, about 30 inches long, to go from a pivot
point to a little electric motor. It needs to be moderately rigid,
light and inexpensive in lots of 50 each or so. It would also be quite
nice if it's moderately attractive -- mill finish aluminum without too
many scuff marks is just fine for this. Prettier is better.

Hmm ... does it need to be more rigid in one direction of
rotation than the other (e.g. more load with clockwise rotation than
with counter-clockwise?) If so, then either carbon fiber or fiberglass,
laid with the right fiber orientation would probably be stronger. (Note
that this is presuming that you are transferring torque through the tube
from the motor's shaft.

If you need it stronger in compression or tension, then other
choices might be better -- though tension would do well with either
fiberglass or carbon fiber.

I'm thinking that thin-wall aluminum* tube of about 5/8" diameter will
work well, and I'm getting ready to be shocked once again by how much
things cost these days. While I'm waiting for quotes, I thought I'd
solicit the group for suggestions.

Thin wall? Is it being used for torque (as I suggested above)
or just to hold a motor tensioned against the belt or gears?

Fiberglass? Carbon fiber? Phenolic? Other plastics? Titanium**?
Extra thin-wall steel? Balsa wood comes to mind, but while it is low
tech I suspect it'll cost more than aluminum. Cooked spaghetti is too
limp, and uncooked is too brittle.

Define how you are planning to use it, and perhaps we can come
up with better selections.

Anyone have suggestions? Do you have supplier names to go with your
suggestions?

* Alloy isn't terribly important. Even dead soft would work, although
harder would be better.

** OK, maybe it's more expensive than aluminum.

Especially if it needs any working to make it the right shape.

Enjoy,
DoN.

--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---