How to properly design a gusset?

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.
http://images39.fotki.com/v1290/phot...EREINF3-vi.jpg

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.
http://images54.fotki.com/v554/photo...EREINF4-vi.jpg

I will weld the H inside the tube as best I can before assembling the joint for tacking and final welding.
http://images53.fotki.com/v444/photo...EREINF6-vi.jpg
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.
http://images17.fotki.com/v522/photo...MVC003F-vi.jpg
I free handed the side plates on my 14" verticle bandsaw.
http://images44.fotki.com/v1471/phot...MVC005F-vi.jpg
After cutting out all eight pieces I hit them with a grinder to clean up.
http://images54.fotki.com/v554/photo...MVC008F-vi.jpg
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.
http://images47.fotki.com/v1462/phot...MVC015F-vi.jpg
Once the angles were cut I did a quick mockup for welding.
http://images17.fotki.com/v522/photo...MVC024F-vi.jpg
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

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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

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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. :whacked: I use the same thickness material I'm using on the frame. Just my two cents.
Ken

Quote:

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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

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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 :LOL::eek:

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

Quote

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

How true this is! Someone who has welded for many years, still may not be a good welder. It seems nowadays that anyone that owns a welder,suddenly becomes a "welder".
Without understanding the correct procedures when welding, as to not create undercuts in welds,can only lead to problems,like stress cracks. Undercuts are one of the most common failures in mig welding tubing.

The "experienced" part comes into play because when it comes to welding the more you do the better you get........if you are trying to learn. You have to have a grasp of the importance of clean substrates, good penetration, and preparation (clamping your work, etc)

My welds hold fine, but aren't very pretty, so I tack and let someone who knows their craft finish it for me. I know my limitations.

Don

I agree with Don, the basics are where it starts then practice and practice. Almost all of the collages have welding courses. That's an excellent way to learn. If you teach yourself sometimes you miss some important steps.
Ken

I withdraw my ''experienced welder'' comment ...sorry.

Ron

Your right Ken , practice is good, but sometimes a person can pick up some bad habits that are hard to break.
I have to do my CWBS test to keep my 'welding ticket" fresh,every 2 years,(even after 32 years) or I'm not qualified to weld ,and as owner of the shop I also have to keep track of my employees tickets as well. It's a pain, but it keeps ya on your toes!
Brian

So...

Anyone know of a formula for figuring out the proper gusset to use on a joint?:LOL:

Quote:

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Originally Posted by STREETWERKZ

So...

Anyone know of a formula for figuring out the proper gusset to use on a joint?:LOL:

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Bigger the better, just hide it :LOL::LOL:

I can't see how the thing you show would add anything meaningful tothe joint. It might resist some twisting moment but basicly your welding strategy I believe is faulty and you will actually create a joint that is weaker by welding the two tubes to that piece inside with a wide bead, whereas if you used some holes so that you could do a rosette weld you could get some shared shear resistance.

Looking at the drawing of the frame member, you need to analize just what forces apply where---the power will be applied forward along the bottom rail at where ever your lower torque arms attach but they will probably be a couple feet forward of the axle so the joints shouldn't have anything but carry the weight of the rear portion of the body.

Quote:

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Originally Posted by jerry clayton

I can't see how the thing you show would add anything meaningful tothe joint. It might resist some twisting moment but basicly your welding strategy I believe is faulty and you will actually create a joint that is weaker by welding the two tubes to that piece inside with a wide bead, whereas if you used some holes so that you could do a rosette weld you could get some shared shear resistance.

Looking at the drawing of the frame member, you need to analize just what forces apply where---the power will be applied forward along the bottom rail at where ever your lower torque arms attach but they will probably be a couple feet forward of the axle so the joints shouldn't have anything but carry the weight of the rear portion of the body.

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Jerry,
As far as adding anything meaningful, there is no difference between this reinforcement and what you recommend in the rosette welded holes other than, I am welding in a long slot rather than a series of holes. Both tubes will be individually TIG welded (not one big weld) to the inner structure. The long welds will actually provide more shear resistance, over a wider footprint, then three holes. As far as the "H" section goes this is probably not really necessary but I can see it will add a lot of crosscar stability to the joint and probably some shear also. Keeping the joint from "breathing" goes a long way in preventing weld failure.
Thanks for your comments, you are making me think this through and I know the joints will be stout.
Mark

A simple fishplate of material the same thickness as the tube material and 6 inches long on the top and bottom bottom of the rail will supply all the strength you need. The cross weld on the bottom is in tension. It is trying to pull apart when loaded. The top weld is normally under compression. It is being pushed together under static load. It does go to tension under hard acceleration and the bottom goes to compression if the suspension attaches behind the joint. Thus the need for plates both top and bottom. The side welds offer little if any additional strength beyond the original material strength.

Quote:

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Originally Posted by STREETWERKZ

So...

Anyone know of a formula for figuring out the proper gusset to use on a joint?:LOL:

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The real answer would result from a thorough structural analysis using the Finite Element technique. Base upon my 25 years general experience in the field I believe you will find that Don was correct; you do not need any fancy gussets. However if done properly they will add strength and safety factor to the area they are applied, needed or not. And then the frame will yield/fail at some other weaker location depending on the fault load.

Kitz

thank you all, I knew there wasn't a simple answer... for a simple man:D
But I had to ask

To me a gusset goes on the outside, bridging an angle. The over plate across a joint was always referred to as a fish plate on trucks and heavy equipment, you may call it something else. I usually try not to weld a fish plate on the ends as a perpendicular weld will weaken the frame at that point and it may break across the end of the plate where the wled is. I'm no engineer but usually I try to visualize how the stresses will apply and reinforce accordingly. There may not be a set formula. I also don't think the frame in the diagram needs any gussets but a plate on the inside over the joint would be good. On my last frame I opened up the frame on the inside so I could get inside the tube and put a good reinforcement along the other side without it showing. Then I welded a piece back in to close it up and plated over that with a larger piece. Now the outside of my framrail tubing is plated and you can't see it.

I have to agree with Jerry and a couple other guys. You don't even need a gusset. 2 x 4 x 3/16 wall and assuming 16 feet long and 2 pieces , you are into about 200 pounds of steel just for the main rails!! Now you should be able to make a sound weld on 3/16 tube any day of the week with either Mig or Tig. You are not going to break it with 500 hp in any kind of chassis. Don't forget you will have some kind of integrated roll bar/cage that will add emensely to the chassis rigidity, not to mention a pile of weight unless you use moly tubing.

I'm reassembling my hotrod in a racecar shop where they are building a FC with moly tubing according to SFI specs. It won't weigh much over 150 pounds complete and it be fully capable of handling 2500 hp every week end. The mate made over 100 runs last year and not a single broken weld pluss the car is 10+ old and the new car is better built than that one.

My street rod has 2x3x1/4 wall tube chassis and 450 hp at the rear wheels. I put over 1000 hard miles on it last year and nothing broke or bent.

By the way nice Cad models. SolidWorks?? If so why not run Cosmos on it just for fun. I have it but it is tricky to set up the restraints and there are too many unknowns for me to do it.

the cad file I did was done in bob cad, very simple and intuitive.
I have a copy of Solid works, but only know how to start the program lol