Tube Fabrication Question - Help!

jcarius

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Ok, SO I'm sure this is obvious to someone, but I'll be durned if I can figure out the best way ...

I need to add a diagonal to an existing rectangle made up of round tube ... when building up from scratch I can just fishmouth the tube per usual and fit everything up before welding - but when you go to insert the diagonal piece in a existing structure, there isn't space for the tube ends pass into and yet fit tightly in the corners ...

I'm missing something I'm sure - Help!

Thanks,

Jim
 

atomicjoe23

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I haven't found myself in that pickle before so I don't know what the pro's would do or whether my suggestion would be legal for tech inspection (so please chime in if it isn't or there's a better way), but you could use a tube clampe and have a two-piece diagonal.
 

Zambo

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Cut one corner of a fishmouth off so you can get the tube in and then weld that piece back in place.
 

rocofab

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you can do it like zambo said, or you can join the diagonal to the two main tubes rather than in the centere of the node, once its within 100mm center to center of the nodes.
a very basic windows paint drawing of what i mean, lol
2dpdnd.jpg


this is within FIA regs here in ireland but im not 100% sure if it would be suitable for your motorsport so id double check with scruitiny. plus which tubes are the main supporting tubes would depend on the vehicle or application.
 

Andrew

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notch both ends as best you can, then use a mallet and pound one end in :D

I'm building a race truck right now and I've run into that problem several times. Also, on the end you will be pounding in, notch the back of the tube more than the front... there will be a gap on one side when the tube is snug in there, but good welding can fix that

Good luck!
 

Giant Geoff

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After fitting the diagonal tube, pull out the vertical tube to put in the diagonal.

I always slide in the vertical tubes last if ther are diagonals on each side.
 

giannini

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i agree 100% with Zambo. Cut one side if the notch off, fit the tube in place and then weld the cut off piece back in. I learned this trick from a highly respected member of this forum.:) I would also use a band saw or a very thin cut off wheel to make the cut so the least amount of material is removed.
 

RyanWiW

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How about an i.d. sleeve. Notch your diagonal as needed, then cut it in half. Insert an inner diameter sleeve. If your using 1 3/4" .120 wall, then the i.d. sleeve would be 1 1/2" .120 wall. Then drill two 1/2" holes in each side of the main diagonal that can be used for rosette welds. If you do it right, you will have about a 1/8" to 1/4" gap between the two main diagonal halfs. Then you can put the piece in place, weld the rosettes and the 1/8" to 1/4" gap. Completely score legal as far as i know.
 

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atomicjoe23

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How about an i.d. sleeve. Notch your diagonal as needed, then cut it in half. Insert an inner diameter sleeve. If your using 1 3/4" .120 wall, then the i.d. sleeve would be 1 1/2" .120 wall. Then drill two 1/2" holes in each side of the main diagonal that can be used for rosette welds. If you do it right, you will have about a 1/8" to 1/4" gap between the two main diagonal halfs. Then you can put the piece in place, weld the rosettes and the 1/8" to 1/4" gap. Completely score legal as far as i know.

This is the best route proposed so far. . .I know it probably works, but I would personally be leery of cutting part of a notch off and then re-welding the notch. . .not a good place to be cutting and welding. . .sure the weld will be strong, but it will be stronger than the surrounding area and that's an area where your tube will be stressed. In my opinion, that will be the first place your cage will fail.
 

goofballracer

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im pretty sure dump did thos and what ever he sys and does i would do in a heartbeat
 

Zambo

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im pretty sure dump did thos and what ever he sys and does i would do in a heartbeat
Yes, the sentence I typed at the top of my post is a link to that thread.

The thing with putting the tubes all together and then welding is that you cant weld the horizontal and verticle tubes underneath where the diagonal tube notches into the corner. So while cutting an ear off of the notch to insert the diagonal may not be as strong as possible, it is damn sure going to be stronger than leaving the joint underneath the diagonal notch unwelded.
 

jcarius

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Well, it's good to see that it wasn't as dumb a question as I feared ... thanks all. Now if I could just make my welds look like those ...

Jim
 

atomicjoe23

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Yes, the sentence I typed at the top of my post is a link to that thread..

Dump has a good design philosophy and outlines it pretty well in that post. . .

The thing with putting the tubes all together and then welding is that you cant weld the horizontal and verticle tubes underneath where the diagonal tube notches into the corner. So while cutting an ear off of the notch to insert the diagonal may not be as strong as possible, it is damn sure going to be stronger than leaving the joint underneath the diagonal notch unwelded.

I think this sums up it up very well. . .although cutting the notch may not be desirable it is more desirable than not welding a tube all the way around. . .you have to pick the lesser of two evils; every build has compromise made somewhere and this is just one example of where compromise has to be made.
 
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