"Lloyd E. Sponenburgh" lloydspinsidemindspring.com wrote:

John Doe jdoe usenetlove.invalid fired

http://howto.homedepot.com/videos/wa...l-Trimmer.html

That's my two-stroke 21.2 CC grass trimmer.

I'm replacing the outer shaft and the inner driveshaft
[with a straight shaft].

The outer shaft is easy enough.

The inner driveshaft will probably be either of these two...

Aluminum 6061-T6 Bare Drawn Tube 0.375" x 0.065" x 0.245"

Stainless T-304/304L Seamless Tube 0.375" x 0.065" x 0.245"

If steel should be used, should it be lighter than that?

I'm planning to use bearings in the shaft. The original
flexible driveshaft was contained within a long continuous
(maybe HDPE, or UHMW) bearing along the entire curved shaft.

Let's see, now. It's not a gear-head whacker, it's a curved
shaft job.

My replacement shaft is straight.

Five feet of speedo cable is Half a pound?

Yes. A half a pound is significant in my application. But it needs
to be replaced for other reasons, too. And since it's being
replaced, I'd like it to be light as possible.

You expect ordinary drawn tubing to take a near-30-degree bend
at only about 50x radius/diameter, be bent and re-bent
continually as it rotates in the bearings

No. And the motor probably would not be able to turn it.

and _last_? It'll part company with itself in a few hundred
revolutions.

I probably should have made clear that the new shaft is straight,
and that the reference was mainly about the motor power.

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There's a reason they use flexible shafting in those toy weed whackers.

I think you're nuts, unless you plan to go to a straight shaft, AND plan
on not whacking weeds with it anymore.

LLoyd