Chassis tube Dimensions

Hi,
Am going to order some steel soon and was just trying to figure out what would be the ideal tube, dimensions and thickness etc. Originally the 917 used lots of different sizes, 35mm/3mm for main frame, 32mm/2.5mm for main braces and then 30mm,25mm,20mm/1.6mm, all alloy of course. I am going to use CDS steel so obviously wall thicknesses can come down and I only want to order prob 3 different sizes.
So I had thought for the main chassis/susp mount rails/roll hoop etc 35mm/2.64mm
Then for the main braces etc 32mm/2.03mm tube.
All the other little support frames, screen frame etc 19mm/1.62mm
I don`t want it to be too heavy but then it wants to be strong enough for plenty of abuse.
Any ideas boys and girls???
regards Chris
 
Hi Chris

Sounds reasonable to me. I did this drawing in of a spider frame in CAD just to play with the 3 D CAD system. I used pictures and rough dimensions from drawings. I also only used 3 different Tube dimensions.

Have you thought about constructing it in CAD first, exploding the drawing to single tubes with all the notch outs and than have everything lasercut. You could even number the tubes and have the laser engrave it. It would fit perfect , less prone to distortion after welding. The original frame consisted out of app 100 single tubes = 200 notch outs. Cost for lasercutting including prograrmming should be around 1000 Euro for one frame.
As most of the notches are angled , the inner tube curve is another one than the outer one. Usually the tube laser cuters can only cut in two axxis ( circular by turning the tube and longitudenal by moving the laserhead). So to get it correct, both curves need to be cut, so that you arrive at the perfect fit. Of COurse you will have the gap between the joining tubes than on the inside on on the halfcircle with the angle smaller 90° and on the outside on the halfcircle with the angle greater 90°, but i think with the thinwalled tubes this is neglectable, you will weld through anyway.

TOM
 

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Hi Tom,
Thanks for the pointers, I did think the CAD approach maybe a way to go but I am more a "Chalk on steel" type of person and the only thing I know about CAD is how to spell it!!!
It was mainly the tube sizes/wall thickness I was interested in, ie. too thick (heavy) or too thin (weak) and just wondered what sort of sizes everybody else has used.
The thought of a stack of tubes all cut to perfect length with the ends done does sound nice mind but I really enjoy metal fabrication!
regards Chris H
 
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