Tube welding question

[agent4573]

So I have two tubes that intersect at a 90 degree angle. They don't intersect through each other though, as one sits on top of the other. I was just going to make some quarter-round gussets to connect the two together, but are there any better options or standard practices to use? It is a load bearing part, but not a critical junction.


*EDIT* In the picture I added, you can see the two long tubes sticking out the back go under the rear crossbar tube. Just looking for the best way to weld up that intersection.

[Rambozo]

So I have two tubes that intersect at a 90 degree angle. They don't intersect through each other though, as one sits on top of the other. I was just going to make some quarter-round gussets to connect the two together, but are there any better options or standard practices to use? It is a load bearing part, but not a critical junction.


*EDIT* In the picture I added, you can see the two long tubes sticking out the back go under the rear crossbar tube. Just looking for the best way to weld up that intersection.

For full strength you will need to use brackets that allow a long enough weld area and apply the forces to the whole tube.
Not sure of the loads involved and your overall design. Any special reason why weren't they made an integral part of the chassis?

[agent4573]

If I ran them through the cross tube it would place the transmission too high. By running them at an angle from the tubes towards the front, it also gives the skid plate a perfect place to mount without there being a stepped edge on the under side of the buggie. Most of the fore/aft load will be carried by the front tubes where they are notched and fully welded. Most of the up/down loads will be carried by additional bars tied into the upper roll cage and additional bars yet to be added around the engine section. So they are techincally a structural weld, but they are not the primary load carrying weld for the section. I just need a way to join them so they can take a decent amount of vibration and some shock loads without cracking apart or rattling against each other.


Your description of the brackets kind of fits any bracket for any use. Can you describe what I should be looking for in this specific case? Fanciest I can think of is to go get a piece of 1.75x.125 wall tube and cut it in half length wise. Weld a peice of 3/16" plate to the back of it and grind the plate with a 1.5" radius. This will allow me to get about a decent weld on the cross tube and the larger 1.75" tube will fit over the tranny mount tube and allow me to do long welds around the edges.

[Rambozo]

There are a ton of different ways to make that connection. The fact that they are touching does make it harder. A couple of plates with holes for one tube and flat welded to the other are typically used around rear end housings for link points that meet the axle tube perpendicular. Aircraft often use small saddles to attach crossing tubes either bolted or welded. You could use gussets as you mentioned before. There are a lot of ways to skin that cat.

"Structural Engineering is the Art of moulding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." - Dr. A. R. Dykes

[Rectified]

Interesting stuff. Would either of you be nice enough to divulge where I can learn more on the topic of chassis design? Maybe a favorite book or youtuber etc...

[Rambozo]

Interesting stuff. Would either of you be nice enough to divulge where I can learn more on the topic of chassis design? Maybe a favorite book or youtuber etc...

One place I would check is the SAE bookstore. You can find almost everything automotive there, and of course a lot of that can apply to other industries. Not cheap, but you can score many used copies on ebay for a fraction of list price. They have more than a few books on chassis design for both racing and production cars.

http://books.sae.org/

If you are building for a particular sanctioning body, be sure to go over their technical rulebook. A lot can be gleaned from the requirements for car building. I'm only really familiar with the ones from NHRA, but I would imagine that every sanctioning body has something like that, and you want to make sure that what you build meets the requirements.

And of course a bible of airframe design and formulas for materials and stress is: "Airframe Structural Design: Practical Design Information and Data on Aircraft Structures"
New editions are all over, but the old version is available as a pdf HERE No idea what has been updated because I still have my dog-eared copy from the 80s.

Last but not least you have to own some version of Machinery's Handbook. It's just packed with info on materials, parts, standards, and formulas for just about everything.

[agent4573]

Rambozo is right on. Most of the books you'll find on this subject are in "textbook" form, so don't expect easy reading on it, but SAE books are a great source to go learn. Once you get past chassis design, if you read "Racecar Vehicle Dynamics", it is extremely detailed in all aspects of designing and setting up the suspension. If you can understand a decent chassis textbook and the vehicle dynamics book, you can do basic designs of almost any type of vehicle.

[Big Paulie]

you obviously have a tubing notcher, based on the other joints. I would notch one end of a short length of tube, and using a die grinder, create a matching notch 90 degrees rotated on the other end. You cannot fit a piece this short in the notcher, so that is why you can only notch one end, then need the grinder for the other. If you handle it carefully, the body of the piece can be as little as 1/4" offset from one tube to another. Just want to leave enough room to fit the two opposing beads. I've use this technique to join a tubing horizontally to a flat surface, but using one end notched, the other cut square.

[everlastsupport]

"Structural Engineering is the Art of molding materials we do not wholly understand into shapes we cannot precisely analyse, so as to withstand forces we cannot really assess, in such a way that the community at large has no reason to suspect the extent of our ignorance." - Dr. A. R. Dykes

Not to be off topic. But I love this quote. The truth is out. More metal and more passes..

The gusset idea should be OK (way I would have went) and Big Paulie's info sounds good as well. (tried and true he mentioned)