material tubing thickness

[bak189]

At this years BUB event, we had a lot of new racers to the salt with a lot of "new builds".
Many of the frames were MIG welded.........and ground down to "look good"......................for 2009
a ground down welded frame will not be allowed to race...............so all you new builders keep this in mind.................in fact for 2009 a close look at
all the welds of frames and chassis will be the order................................................................................

[doug odom]

As far as I can remember back 15 - 20 years the rule book has always said " grinding of welds on the roll cage structure is not permitted."
As far as MIG vs. TIG.  I have both and its the Indian not the arrow that makes a good weld.

[saltfever]

I get a lot of sh*t because I bad mouth MIG welding (mud guns) but when you TIG something you can see the weld puddle and and you can see the penetration and make it right!

Well, if you can't see the weld puddle you have no business welding in the first place! I don't care if it is oxi-acetylene, TIG, MIG, or stick. Seeing the action of the puddle, and knowing how to compensate is what welding is all about. VISION, is one of the most important attributes of good welding. Knowledge and motor-skill respond to what you see! In the case of MIG a good welder is looking at the erosion (or lack of) at the edges of the puddle, looking at both the front and rear of the puddle to see its action, can see the preheated glow in front of the direction of travel, can see penetration, repeat . . .can see penetration (as determined by the meniscus (or lack of), the flatness or sinking of the puddle, etc. In MIG you use different patterns like crescent, zigzag, oscillating to accomplish your objective. If you can't see the puddle then change the filter or get glasses. I agree there are a lot of ignorant MIG welders but that shouldn't condemn the process universally. There is no "one technology fits all". You certainly wouldn't TIG a 1" thick, beveled, 1030, butt joint, when the strength of the weld is mostly determined by the mass of filler material laid down. Submerged arc, or stick, would be used in that case. All welding techniques in the hands of the ignorant or inexperienced is suspect!

[Cajun Kid]

Dodge, I was going to learn to weld over the winter (even buy a Miller MIG)...Now I guess I will just have to re think that !!!!...

Charles

[sheribuchta]

listen everyone---welding is something that can be learned by most anyone--but like a lot of things that we all do only a few can do it well---if you plan on doing a chassis then there are times that you will have to weld left handed if you are right handed---upside down and plenty of strange positions--with the tig you have to do 3 things at the same time and you should be able to do it left or right handed---i know of no test to see if you are going to be a good welder or not ---i have taught many people to weld and my best pupil was a tattoo artist---some people no matter what just dont get it ---i remember i was having trouble with some welding i was doing so i went down to the local welding school and talked to the instructor there and for 20 dollars he gave me a 1 hour lesson  --the best 20 dollars i ever spent--i would suggest if you are new to welding before you fire up that new welder go by the welding school or at the very least have a good welder get you started--but even if you find that you arnt a very good welder you can still fabricate things and tack them together and pay someone just to weld everything together---it will be much cheaper   just some thoughts  willie buchta

[Peter Jack]

I tend to agree Sum. I watch a MIG puddle really closely to ensure that it's getting both legs I also tend to use a little manipulation to help encourage the process. The problem is that until you've got a few hours in and the process slows down to the point where you can analyse as you weld the welds you make may or may not be structurally sound.

Pete

[Dean Los Angeles]

Willie is absolutely right. Welding is something that you understand how it works and have the knack, or you struggle. Americas Funniest Videos could have an entire show on the weird positions you end up trying to get a decent weld in some odd place.

If you are going to weld a frame, then take some of the scrap pieces, or cut some test pieces and weld them up. Then band saw the weld and see what kind of penetration you get. If the test piece isn't perfect then keep cutting test pieces and welding until it is perfect.

If you don't have a 220 welder then go get one and stop playing.

If your welding looks like the second picture then you need serious help. If you pray some day that your weld will look like the first picture, then practice, practice, practice.

[Loose Goose-Terry#1]

  A few pages back Geo posted a pdf of a roll cage showing the intersection of the mitered tubes where they didn't quite line up. I have attached his pdf marked up where the high stressed going would be located on his tube. If this is a really big concern, why not just put a diagonal brace there to distribute the stresses? 

Terry 

[Geo]

Terry is correct about the place the tube will bend.  I have another side of the “funny car cage” that should take care of that.     The point being discussed is the importance of having the center lines of the tubes meet to eliminate the weak area.  One side thought is that I plan to not have any tube meeting point aimed at my body!  Terry, I would worry about creating other weak points by removing the meeting point with the addition of a short diagonal as the one tube is only off by 3/8 inch or so.  And remember my pdf is on the side with the bar not meeting being the horizontal bar and the three upright vertical bars meeting.  Willie, any thoughts on gussets?   

You must also think about creating a shear area where only one bar is located in the middle of a tube.  Remember a triangle has intersections of the rays at the corner not up a little from the end allowing a “tail or leg” to stick out as a support.  The place where the tube will bend, or worse shear off, is just up the leg where the rays meet so when you move the meeting point to the end of the tube the sheer is also moved to a stronger location or past the end of the tube.  I will post another pic after the next weekend of the diagonal tube meeting the floor and upright tube.

A side intrusion bar or a shoulder harness bar does not need to meet another tube at the center of the angle, vertex, where the angle ray lines meet because these tubes are not part of the support structure.  However, you can use part of the support structure for a side intrusion bar or a shoulder harness bar and then meeting the vertex of the angle is important.  Hmmm, head spinning yet?   

Another consideration is where to place bracing and have it add needed strength rather than add weight and moving stress from a strong vertex to a weak area.  I drew the cage and then checked for triangles.  And then thought about what stresses the car will have in the event of not being on wheels.  I did change a tube from my first sketch.  This varies from Bonneville to sled pulling to Maxton to track days to drag racing to…  Most salt cars end up on their top and do not strike an immovable barrier like a concrete wall or get hit by another high speed mass (fellow racer) so plan accordingly.  McRat needs a slightly different cage in his truck than I do with added protection for the additional impact types that may occur in his different events. 

Follow the rule book first and then add if needed.  The cage specified in the rule book has been empirically tested and is good for what we are doing.

I am fortunate enough to have a certified welder in our team and I am still reading welding books as we work on the car.  The comments posted are good about the different types of welding.  Roll bar welding is near the max for tig and middle for mig, depending on machine so all comments can be correct.

My reading about welding brings up temperature being important and 90 degrees best with weakening at 55 degrees and below, gas choice, good quality wire from a major vendor creating a stronger weld than cheap wire, etc.   Another point is how to weld tube intersections to eliminate warpage using tips found in ”Welders Handbook” by Richard Finch, page 38 and “Modern Welding Instructor’s Manual“ by William Bowditch, page 218.

I think this thread is going to result in better cages for all.  Charles,  join me in learning, again after a 25 year break, how to weld.  I just got a setup for aluminum.

Geo

[manta22]

Nobody has brought this up yet so I will-- it seems to me that one of the problems associated with structures built with bent tubing is that those bends then create a "pre- buckled" tube. A straight tube has higher compressive strength than one that is bent, all things being equal. I've never seen a roll cage fabricated with all straight tube members but it would seem to be stronger than bent tube hoops if the welds were all good quality.

Comments?

Regards, Neil  Tucson, AZ

[willieworld]

neil   i think that the arch is the strongest---i think a long tube as in a roll cage in a door car is very weak in the middle of the tube and the arch in a roll cage in a streamliner is 10 times as strong --if you are building a door car do yourself a favor and also do a funny car style cage --then you have a cage in a cage --if you still dont feel safe switch to a motorcycle doesnt get any safer than that ---think about it like this---i do a lot of street riding and i feel like a duck in a shooting gallery most of the time --when i get to bonneville or el mirage i have the track all to myself and my only worry in the world is if i can break the record --doesnt get any better than that    willie buchta

[Seldom Seen Slim]

Willie, it sounds like you're trying to lure Franklin - and his rider-wear-a-parachute concept --- back to us. 

I agree with you -- While there are certainly risks when riding a bike, I sure do feel comfortable riding on the racde track.  I mean, not only is the riding area as good as you can get - no traffic or road obstacles, etc -- but I'm wearing the best safety garb I can afford and have safety and security workers all helping me have a safe ride.  And as Jason (unfortunately) showed -- even a high-speed getoff is relatively safe under thewse conditions.  I'd go on about bike safety, but I don't want to hijack the thread.  Back to building a cage...

[saltfever]

Neil  i think that the arch is the strongest---i think a long tube as in a roll cage in a door car is very weak in the middle of the tube and the arch in a roll cage in a streamliner is 10 times as strong

I think you are missing Neil's point. There are two kinds of material deformation. (1) Elastic. The tube does not reach its yield point and therefore springs back without loss of strength and (2) Plastic. The tube has been deformed past its ultimate yield and takes a "set" or does not return to its original shape. There are no exceptions. Plastically deformed materials are always weaker than their parent condition! 

When you bend a tube you have plastically deformed and weakened it. The question is; by adding in struts or other geometry have you increased the strength of the structure to equal or exceed the loss of strength due to the bending? In most cases the answer is yes. If you don't know you are a test pilot. 

[panic]

The arch, as an architectural shape, has good load bearing capacity in compression only. The curve transfers the bending load above the opening to compression of the vertical legs.
It's an improvement in this respect over the lintel (end-supported horizontal beam), but not over a simple triangle ending at mid-span of the opening - but it does give far more "open" area.
It has little resistance to side-thrust, and becomes a trapezoid-oid (sorry!) much like a rectangle, by morphing the arch radius into a partial ellipse when pushed sideways.

[saltfever]

Welcome back Mr. panic