Welding overlapping joints on a chassis

[Daniel Rogers]

Our chassis is completely assembled and tac-welded. I was wondering if it is best to take apart over-lapping joints to fully weld joints that are later covered up with another piece OR just weld around all visible joints after being fully assembled. Thanks

[Owen Thomas]

Depends. Is the joint structural? Do you want to risk compliance there? Will you feel safe driving the thing if it is just "cover welded"? I would at least make sure the hidden joint can't be broken with a medium-sized mallet hit, but hey I'm not a welder. This is a judgement call that you need to make, but there are some rough calculations you can do to get a strength estimate of the welded joint with and without the extra weld.

One word of caution: welding the hidden joints will change thier shape, and your pretty coped tubes will probably not fit quite right anymore. Something to keep in mind, as it can cause problems around suspension nodes.

[Racer-X]

You don't need to weld under the joints because you are "always" able to weld 360* around any tube no matter how the joint is set up. The only way I can see this being an issue is if the surrounding tubes weren't designed with this in mind and deformed due to how they were loaded/too thin of a wall thickness.

When the chassis was designed what was the plan? How was it tested?

[Pete Marsh]

What you're referring to is called an "open node" and is covered in structural engineering, usually with reference RHS tube trusses.

Consider lattice crane booms and the like.

The difference in performance is considerable. Look it up.

Pete

[Daniel Rogers]

The Chassis was designed to distribute loads through the joints, but, being a new to chassis design, I did not think about the overlapping joints until I came about them during assembly. I talked with a welder and reiterated what Racer-X said about still being able to get a 360 weld. I have a picture, can you post pictures to this forum?

[Ben K]

Originally posted by Daniel Rogers:
The Chassis was designed to distribute loads through the joints, but, being a new to chassis design, I did not think about the overlapping joints until I came about them during assembly. I talked with a welder and reiterated what Racer-X said about still being able to get a 360 weld. I have a picture, can you post pictures to this forum?

Just use imgur and 'space out' the link (like www. imgur .com) so that it doesn't get caught by the filter

Ben

[Drew Price]

I always welded complex nodes in one tube at a time, and trimmed the corners as needed to clear the weld fillets. It doesn't take much extra time and is easily done with a belt sander or grinding wheel.


Something like this:

https://lh4.googleusercontent.com/-dhvW11axnRU/TDbFNFtNmeI/AAAAAAAAGUg/JWJED-Ul62I/s512/99_Cage_Build%2520049.jpg

https://lh4.googleusercontent.com/-qy1ZR8u0MMM/TDbFLjzr9oI/AAAAAAAAGUI/TvqC7fATNfU/s640/99_Cage_Build%2520040.jpg

https://lh4.googleusercontent.com/-dVKoOHsSfks/TDbFfHuhz3I/AAAAAAAAGXw/KcEG9Phwigg/s640/99_Cage_Build%2520134.jpg

https://lh4.googleusercontent.com/-4du5jp64bD8/TDbFlbCky_I/AAAAAAAAGZA/NvsFv_2Hx34/s640/99_Cage_Build%2520165.jpg

http://sphotos-a.xx.fbcdn.net/hphotos-snc7/2790_614060101495_839356_n.jpg

http://sphotos-b.xx.fbcdn.net/hphotos-ash4/2790_614060096505_2123980_n.jpg

http://sphotos-b.xx.fbcdn.net/hphotos-ash4/2790_614911699885_8045349_n.jpg

[jd74914]

Drew's pictures above show the "correct" way for constructing complex multi-tube nodes. Welding the internal tubes first produces a stronger joint because it is absent of the open nodes Pete cites. Construction this way really doesn't take much extra time.

Since you have already tacked everything in I would probably go ahead and weld it. If you tack [in multiple planes] like I do, it is going to be a ton of work to cut everything apart. In the grand scheme having a few open nodes is really not a big deal.

Live and learn.

[Drew Price]

I'm with Jim. This far in the season that time wasted could well be of benefit other places.