""Don Foreman" wrote in message
...
On Thu, 30 Oct 2008 05:32:32 -0700 (PDT), wrote:

Hi!

No grand schemes today, nor political commentary, I am OT (On Topic).

I'm building a seat frame suppoort for my MOEPED. It must be 16 inches
OAL (overall length) and the legs are 3 inches long. The existing part
is neatly bent from stainless, but those broad curves mean I can't
mount the underseat lighting. (OSS: overseat steering, means my hands
and legs don't block the beams)

I've used up THREE one-yard lengths of 3/4 inch OD by 1/16 inch wall
mild steel tubing from Home Depot so far. It's time to ask for help.

I've mitered the mating ends at 45 degrees, ground them flat, added
fixturing holes. and proceed to braze: the alignment screws up. Tie
wire stretches during brazing, and a clamp I made still allowed
slipping.

I've notched the tubing deeply leaving a thin tag. When bent closed,
the tag area is still open; the bronze doesn't fill a gap that wide.

I think if I notch the tubing leaving a wider tag then when bent, the
stretch on the far side will close the gap, but HOW DEEPLY? You see,
when bent, the far side gets stretched and the V opens up laterally.

Imagine a tube bent but not notched: it would widen to half-
circumfrence. So there is behavior related to depth of notch

I don't want to trial a whole lot of different bend depths, but I can.
There's scrap to do this with.

Have any of you here got some experience with this?

Is there a magic number for this configuration? Can I compute it
without FEA (finite element analysis)?

Doug Goncz
Replikon Research
Seven Corners, VA 22044-0394

As you've discovered, brazing doesn't fill gaps well. It's also not
suitable for butt joints in thin metal. Welding works a lot better.

If you're determined to braze, you need to make some metal things that
go either inside or outside of the joint to increase the amount of
braze surface area. You might even wind wire around the joint area,
braze it and then smooth it up with an angle grinder or sander.

Steel wire... then its called gas welding. I made tons of things this way
when I was a kid before I learned to weld. None did I trust with my body.

Bob La Londe
www.YumaBassMan.com