Thread: How to properly design a gusset?

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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?

Originally Posted by STREETWERKZ

So...

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

Bigger the better, just hide it

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.

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.

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.

Originally Posted by STREETWERKZ

So...

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

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
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