Frame Tubing

[JHen]

I'm starting a kart project which I plan to have be all terrain. It will be a shifter powered by a Kawasaki KZ 900 engine I have laying around. I've just started today so I'm in the very beginning of the design stage and was wondering if my idea for frame tubing will be sufficient for the abuse it may endure.

I plan to use, for the main structural parts 1.5" x .095" 4130 DOM tubing. For secondary parts like X beams and such, 1" x .065" 4130 DOM tubing. Then for any part of the frame other than that, going down to .5"x 0.035" 4130 DOM tubing.

In general, would this be strong enough too strong? I don't mind a little over kill, I like to overbuild things so they last a long time, are reliable, and SAFE!

 

[devino246]

Your using DOM tubing? Isnt that stuff expensive as he//

 

[JHen]

Not that bad. There is a place that sells surplus and scrap and other stuff that I frequent to get my metal. Typically pay anywhere from 10% to 50% of what you would anywhere else around here.

The tubing in question is $7.29 a foot for the 1.5", $5.52 a foot for the 1", and $3.41 a foot for the 0.5", at least according to the website.

A guess off the top of my head puts the cost of the frame anywhere from $200-$500. I haven't made a detailed plan yet.

 

[devino246]

I would just get welded seam tubing. Thats way too expensive, at least for me.

 

[Rotore]

1" gas tubing is light and doesnt cost too much

 

[JHen]

I'm not that worried about the cost. I know it's expensive stuff but it is also the best. I'm just wondering if I can shave more thickness off the walls for a cheaper and lighter frame or if this is what is needed, or if I need more thickness.

 

[rgvkid]

Im currently finishing a frame in which i used 1" x .090 mild steel tubing. Its a bit on the heavy side. My next frame is going to be made of DOM 1"x.060 or .075 if its available. If you are a bigger person then I would go with DOM 1.25 x .060 or Better .075-.080 if you can find it.

 

[dpaxson]

that wall thickness is overkill if you're planning on designing a true space frame chassis. large daimeter DOM tubing like 1.5" is already strong without having thick walls. plus 4130 is chromoly iirc which is already very strong. Also i'm pretty sure the strength advantages of using chromoly steel are drastically reduced if you don't stress releave/heat treat the frame. I don't know what kind of equipment you have access to or what kind of budget you're looking at but that could be expensive.

 

[modelengineer]

The whole advantage of chromoly is that you can save weight by using thinner wall material for the same strength.

dpaxson is completely right, you MUST stress relieve the material after welding or it will be no better than mild steel, in fact probably worse because of the thinner material.

 

[JHen]

Yeah, I'm aware of the need to heat treat the welds. This is just my first go at a project such as this and am trying to get a grasp of what is needed in this regard.

What thickness for those OD tubes would you suggest?

And as far as tools go, I have all the tools necessary to do this project, save a tube notcher which is nothing more than a drill press with a hole saw or grinding cylinder and a rotating clamping apparatus.