Square tubing...

[margo]

I am looking at building a stretched out lowrider style chopper. My question is regarding wall thickness and hardness of tubing. I am thinking something in the .035-.060 thickness range(?) and overall size of 2" square tubing. My wheelbase is in the 60" range, with a cantilever style design. Is this thickness going to be strong enought to hold that long a bike up(?) should I get it in an annealed version and heat treat it after welding(?) or is regular drawn steel tubing enough(?) any help is greatly appreciated. I will throw up a sketch once I get it finished and scanned.

Sam

 

[necessaryevil]

Square tubing would look cool, but it is soo weak compared to round tubing that you will have to use really thick .60+ on a frame that long. It's going to be heavy and the frame is going to make kreaking noises when you ride it. A company by the name of Hawk made aluminum square tubed BMX frames in the 90's. Needless to say they were garbage. I think it would be a lot of work on your part and you would'nt be happy with the results, but good luck if you go with the square theme.

 

[2manybikes]

Another option is to use rectangular tubing and orient the long side vertically.
There a whole bunch of mtb frame builders that used ovalized and rectangular tubes successfully.

 

[margo]

I will be indexing the tube at 45 deg. so as to get a diamond shape out of it, and my thinking is this should make it a bit stiffer as well. My tube size has changed from 2" to 1.25"-1.50" based on rotating it which makes the overall profile much larger. sounds like .060 will be the way to go...gonna be a ton o' fun (literally) guess I have to update to a 3 speed version so I can get up hills

 

[margo]

Here is a VERY rough sketch of the design.


My final choice of mat'ls looks like:

1.25" square steel, .080 wall for the front "triangle" section
0.75" square steel, .080 wall for the seatstay (wishbone), chainstay (wishbone), and cantilever
1.00" square steel, .080 wall for the seatpost "loop"

Based on mat'l weights and my aprox. lengths, I am looking at about a 25lb. frame...not sure how that stacks up with similar sized bikes, but hopefully it will work out.

 

[C.S.]

Sounds good enough to me with that design.