butt welds

[SPARKY]

Heat is your friend, untill fairly recently the FAA required all aircraft tube be welded with GAS!

[floydjer]

Couldn`t hurt to bevel the tube ends/leave a gap/make a root pass into the splice material.

[jimmy six]

Floyd, your method is correct. Tubing must be beveled for a proper weld. (boiler tubing has tooling for this) All repairs, testing also, is done with an air gap, a tig root pass, and we used "stick" to complete it. Like I've said before all testing  was done by bending a section of the weld 180 degrees to a set radius for the diameter of the tubing without failure. Thats why I used used certfied power plant weldors to do any of the structural welds on my roadster including Z-ing the frame...

[doug odom]

BINGO Floydjer, You just hit on the way to do it. Having built many race cars that went out and tried to knock down walls I have seen what lives and what don't.

[floydjer]

Doug, Jimmy...Must be the A.W.S. certified welder in me. :cheers:Jerry

[Peter Jack]

If you check where I live the weldor / welder controversy is probably caused by the English influence.

Pete

[Rex Schimmer]

I agree with much of what Willie has done on his example, I would only add, as Floydjer has already stated, that the ends of the tubing need to be beveled. I would probably go with a full 45 degree bevel on both tubes and then when assembling the tubes over the inter support tube I would leave the ends approx. 1/16 (.060 inch) apart. The root weld should then be made such that it welds both tubes to the inter tube and also to each other. Let the tube cool and then do a double pass filling weld which would fill the remaining vee notch and give a slight weld fillet that would be above the outer tube surface. I would do each of the passes individually and let the tube cool between each pass. As Peter Jack stated many times welded parts break next to the weld, this it typically caused by the fact that if the weld is done correctly with a proper fillet that is above the surface of the tubing that area has more cross section and is therefore stronger than the base material so the tube fails next to the weld. Other causes are undercutting of the final weld pass which will actually reduce the cross section of the tube next to the weld and cause it to fail in the undercut area. If the material is a steel alloy or higher carbon, typically above .03% (1040, 4140, 4130 etc) the heat affected zone next to the weld can be weakened by the welding process and lack of post heat treatment.

Proper cleaning of the area to be welded is extremely important as mill scale, rust and other impurities typically found on steel will pollute the weld area and cause inclusions that can greatly affect its strength. At a minimum grinding all mill scale, rust and remove any oils before any welding pass and then heavy wire brushing or grinding away any weld slag before any additional weld passes are done.

If you look at the bending  strength of a butt joint using an inter tube and you only insert the tube without welding it to the outer tube then the bending strength is the combined strength of both tubes but if you weld it as Willie has shown now there is a strong shear joint between the tubes and they act as one tube and the bending strength is approx. 16 times as strong as either tube by its self. So the rosette welding of the inter and outer tube together is very important. 


Rex                 

[Rex Schimmer]

Just one more thing regarding tube structures for racing cars. The off road builders are probably the world leaders in the design and fabrication of tube structures. It is interesting to see that they use a method of tube joining called "bulkhead" joints that are a type of butt weld and they uses these in many places that would typically be done by bending a tube. I am attaching a web address to a thread at an off road web site and it is an on going discussion of welded structures being done on some off road trucks being built at the Herbst Brothers shop. The fabrication is really fantastic!!! The thread is long but if you want to see some trully great fabrication you will enjoy it.

Rex


http://www.race-dezert.com/forum/showthread.php?t=31417

[Gwillard]

I agree with almost everything Rex mentioned, especially the emphasis on cleaning. If using wire brush, grinder, sander, etc. it is usually best to use one dedicated to one type of material, i.e. aluminum, stainless, steel & its alloys, etc. Cross contamination can cause big problems, especially iron into aluminum.
The only point I disagree with Rex on is the final strength of a splice of the type in question. At best it will achieve a strength equal to a single tube with the OD of the outside tube and ID of the inside tube. This still puts it far above the strength of the parent tube.
Beveling of the tube ends is good practice when the tube wall is of a thickness that would warrant it. Thinwall tube such as .049, .065, etc. need no bevel, just a slight gap between the ends. Wall thickness on the order of .188, .250, and thicker will virtually always benefit from a nice bevel as Rex described.
Hint: When replacing a tube where splices are needed at both ends, the inner sleeves can be placed inside the repair section, then pieces of MIG wire attached to the sleeves and run out through holes in the parent tube past the repair area are used to pull the sleeves into position.

[johnneilson]

FWIW, the SCCA GCR requires this method of "splicing" tubing in the roll cage construction.

And yes, the Off Road race vehicles are the most impressive uses of tubing construction.
When out on the course, the contest goes for "most impressive use of 100 mph tape and zip ties".
It is really amazing how fast a vehicle can go when you have 30+ inches of wheel travel and 800 hp on a dirt trail.

John

[SPARKY]

big off road race in Parker AZ this weekend

[willieworld]

hay everyone---good to hear from all of you ---i would like to backtrack and say a couple of things ---first i would try not to make a butt weld even with a sleeve in a area with a lot of flex---another thing is the heat affected zone is actually on both sides of the weld so when i make the butt weld i try not to weld  to much into the sleeve that way the sleeve doesnt have a H A Z ---i think that if the rosettes are done properly they should hold all by themselves----now  this is just the way i do things and that doesnt make it right --i think that everyone has to do the research and then decide what is right for them --JD brought up another subject about square tube and zd frames and butt welds after i eat i will post some info on that subject -----again thanks everyone -------------------------willie buchta

[interested bystander]

This horse has been dead so long it's beginning to smell over the ether of the internet.

Even though, no doubt, many of the above posters and their 2 cents worth of knowledge  are above the level of the FAA and the Gov't, how about if we all contact the Government Printing Office and order the "Airframe and Powerplant Mechanic's Handbook" that's specific to airframe repair and see what Uncle Sam says about how to repair tube structures. (Or buy it from Aircraft Spruce).

They've been trying to keep airplanes from falling out of the sky for years and I think the lessons learned and the examples listed would apply to keep motorsports vehicles from crashing also!.

[Gwillard]

This horse has been dead so long it's beginning to smell over the ether of the internet.

Even though, no doubt, many of the above posters and their 2 cents worth of knowledge  are above the level of the FAA and the Gov't, how about if we all contact the Government Printing Office and order the "Airframe and Powerplant Mechanic's Handbook" that's specific to airframe repair and see what Uncle Sam says about how to repair tube structures. (Or buy it from Aircraft Spruce).

They've been trying to keep airplanes from falling out of the sky for years and I think the lessons learned and the examples listed would apply to keep motorsports vehicles from crashing also!.

Already have it. Very informative book, lots of good stuff in there including the procedure Willie outlined.  Wish I had it handy but its half way across the state right now.

[wobblywalrus]

The first Honda Elsinores, MT's, and CR's had frames with weak tubing.  Lots of breaks on the frames and subframes.  I made all sorts of weld repairs and almost always the frame cracked again near the weld.  I made similar repairs to Yamahas and BSA's with no problems.  Finally I gave up welding on the Hondas dirt bike frames.  Does anyone know why these frames could not be fixed?  I used gas.