Thread: How to properly design a gusset?

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I guess any general info would be nice.
specifically for my model a build, the 2"x4" square tube frame.
I have 2 60 degree miters that will be gusseted on the inside of the tubing side walls.
I would also like to add gussets to the inside of the bend, so my questions would be

1) how is gusset leg length determined?
2) how to determine material thickness for the gusset?
3) how much material is needed for a gusset to werk properly with in its basic triangle shape? meaning I have see gussets with designs, and a radius on the unconnected side, how much material can be sacrificed for "cool"?
4) whatever I didn't think of? lol

thanks

Josh, from your drawing, I don't think any gussets are needed in those spots. You could, but as long as your welds are good and you have mentioned inside gusset plates, I don't really see the need. They might also complicate the build, especially the ones on top.

You say you are using 2 x 4 tubing, I would recommend 3/16 wall. With that you should never have any problems, especially if you tie your crossmembers into the sides well.


Don

yes I made internal gusset plates which I am going to box so I can weld on all four sides.

My brain for whatever reason kicked in to "How, and Why" mode.

Mostly because I realized I have always just taken someones word for it that "this is the gusset you need" or just made what seemed reasonable to me.

here is some good info I have found that answers alot of the questions I have

http://www.dsm.com/en_US/html/dep/gussets.htm

http://weldingdesign.com/processes/news/wdf_10914/

http://cemsig.ct.upt.ro/astratan/did...n_examples.pdf

This is what I aome up with for my frame reinforcements. I am going to fab up these small "H" sections to weld inside the joints.


I will grind a 1/4" relief into each tube section to allow the welds to be below surface to eliminate the need to grind them.


I will weld the H inside the tube as best I can before assembling the joint for tacking and final welding.

Final welding will fill in the "slot" so a little bit of clean-up with a grinder will smooth it off...

Mark

Got out in the shop and made all of the "H" beam pieces.
I used some 3/16 x 2 1/2" scrap I had in the bin.
Laying out the cuts.

I free handed the side plates on my 14" verticle bandsaw.

After cutting out all eight pieces I hit them with a grinder to clean up.

After I got them cleaned up I stacked them together and wrapped them with tape so I could cut all of the angles at once... Much faster that way. I used a milling clamp to hold them in the H/V Bandsaw.

Once the angles were cut I did a quick mockup for welding.

Thanks for looking. I would appreciate any constructive critisizm guys.
Mark S.

Mark, Thats a good idea and good work as well. I have also always welded a support inside of my frames at the butt joint. I cut mine to fit inside of the joint and rosebud weld the piece of reinforcing plate to both frame members. Inside and outside, or two pieces per joint. Certainly nothing wrong with your "H" beam idea and it should serve you very well.

But now remember guys we are not building "Watches", there car frames. Look at any factory frame you will not find a single weld anywhere, those suckers are all riveted together.

RS

I'm with Don on this. If you are a good welder, getting 100% penetration with a 7018 rod or the equivalent, you don't need gussets.---Brian

Originally Posted by Hombre259

Mark, Thats a good idea and good work as well. I have also always welded a support inside of my frames at the butt joint. I cut mine to fit inside of the joint and rosebud weld the piece of reinforcing plate to both frame members. Inside and outside, or two pieces per joint. Certainly nothing wrong with your "H" beam idea and it should serve you very well.

But now remember guys we are not building "Watches", there car frames.

Look at any factory frame you will not find a single weld anywhere, those suckers are all riveted together.

RS

Thank you Hombre, I appreciate the kudos. Good welds or not I have always done this also. For Hi-Performance use it is a simple bit of insurance that goes a long way to strengthening the joints.
And, just to add to your "riveted stock frame" observation, I guess that is why most people box the inners and weld all of the riveted joints.
Mark S.

If your welding skills are marginal, the ''backing'' is a good idea. One thing you want to be sure of using this type of joint is that the ''backing plate is right against the tube. Any gap will cancel the benefits you hope to gain from this system especially if you are going to gring the welds afterwards.

Another alturnitive is to have an experienced welder do the work for you.

Ron

I can weld, I'm not worried about that.
I would like something extra at the miter joints, due to the 500+ hp motor going in it.
Believe me, I don't baby anything, so it needs to be safe.

I like the internal gusset, same as sleeving a tube joint IMO
However I still have this nagging need to understand fully a gussets job, how it werkz, and how to determine the proper application for a gusset, size, material, thickness % etc.

sometimes I have these voices in my head that don't shut up until they get an answer lol

If you go to page 5 in my HOW TO BUILD A '32 SEDAN you can see how I do it. I like to do it internally so you don't see the patches on the outside. You can do this on the inside internally and the inside of the outside. I use the same thickness material I'm using on the frame. Just my two cents.
Ken

Originally Posted by Youngster

If your welding skills are marginal, the ''backing'' is a good idea. One thing you want to be sure of using this type of joint is that the ''backing plate is right against the tube. Any gap will cancel the benefits you hope to gain from this system especially if you are going to gring the welds afterwards.

Another alturnitive is to have an experienced welder do the work for you.

Ron

The "Backing" is a good idea no matter how good a welder you are. A gusseted weld is simply to some a safety factor. I guess the engineers amoung us can decide if its needed or not. It would seem to me that any simple "BUTT" weld would benefit to some degree with a little internal support.

I also don't understand the "Experienced Welder" comment. Would seem like a good welder would be what is needed, plenty of them on here. Some experienced welders may be bad welders. Depends intirely on how they were experienced

RS

Personally ...... I like your "H" inserts ...... I've made a few backhalf repairs with box tube .... I wittled a aluminum buck 6" long that I use as a fixture to make inside box tube inserts. It's basic but works & an acceptable fix. I actually cut a section ob box on the short angles opposite each other. Then clamp it to the aluminum buck. I remove the excess material then weld. It slips inside the box tube perfectly. I usually drill some rosette holes on both sides & presto ...... easy fix. I wish I had the pix of the last one I did.

REGS

Hombre ... I didn't mean to slam anyones welding ablity. That was meant for those with limited welding experience. I have repaired a good many ''hobby welders'' projects in the past. My appologies.

Ron

Hombre,

I love your welding comment! That reminds me of the saying, "Wisdom always comes with age, but sometimes age comes alone."

Generally, the filler rod used in welding is stronger than the base metal. That means that after a full penetration weld is ground down to the exact thickness of the base metal, the connection should not break at the weld. However, there are many factors that can weaken the joint. Any flaws in the weld weaken it such as holes, cracks, or impurities. And the heat and cooling of welding changes the chemistry of the base metal around the weld which often makes it more brittle than it was originally. For these reasons, it is a good idea to add a gusset plate across the weld to reinforce the original weld and to add weld length to the connection. Obviously, if you divide the force acting on the joint by the weld area you calculate the stress on the weld. By adding weld length, the stress goes down.

Mark