Theoretical Considerations By John Zabrieski 1995
Practical Considerations By Mark Stonich 1995
From: Carey Chen
List-Id: Human Powered Vehicles Mailing List <hpv.ihpva.org>
A few months ago on the lowracer list, there was a discussion as to which tube is more resistant to twisting forces. It was the opinion of the engineer types that the square tube was better. Using square tubing does have several advantages other than being stiffer. You can get more material in to a smaller space than that required by a round tube. This is a particular problem on lowracers because there is only so much room between your legs to put the drive train. Earlier Rans bikes also had square tubing which probably were quite stiff. Where square tubing loses to round tubing is on asthetics, it doesn't look right, it looks primitive. Square tubing is also not readily available in different sizes and even less so in larger sizes in chro-moly. With the renewed interest in FWD. I may have to build another one.
Mailing-List:
ListBot mailing list contact lowracer-help@listbot.com From: Bill Volk
Subject: Brazing square tubing
Date: Mon, 14 Aug 2000
Marc asks:
I've switched to square tubing for my initial design experiments but I'm unsure how best to join the segments for my mono-tube SWB frame. Unlike round tubing there's not much of a "fish-mouth" to work with and the sides are flat so building up a fillet is problematic.....
If the angle isn't extreme ... less than 15 degrees for example ... I suggest cutting a "pie slice" in the tube (cutting 3 sides) and flexing it into position (thank you Jack Baker of S&B for suggesting that to me) ... clamping it ... and then doing a tack-braze on the opposite side....
Then just cut plates to form a "lug" on both sides of the tube. This worked great on Heavy Metal and it's held up well for 14006 miles. I also suggest covering the "tack" with a third curved plate ... I didn't do that .... and the tack will eventually crack ... not that it matters a heck of a lot with the plates and the uncut top...
See: http://uworkit.com/GIFFrame.cgi?KwD0ceX1yxDys+kB82OsmA.gif
If I had to do extreme angles I'd put in a plate between the tubes with a overlap of maybe 1/4" all around and do a fillet braze on both sides. That would be an incredably strong joint and you could even do a 90 degree angle this way.
The ZOX is TIG welded and what Sergio does is to add sections of tubing to the joints. Sort of like this:
http://uworkit.com/GIFFrame.cgi?tb8HiU5dm5pWUqL4bN2oQQ.gif