The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by TINGLER, Sep 26, 2005.
add the same amount of heat to the other side of the frame rail to shrink it.
Shouldn't be that big a deal to fix. Don't know exactly how your bracket, motor mount was welded on, but go to the opposite side of the tubing and with a cutting torch heat a narrow strip equal to the weld you applied. Heat this strip to just a dull red. You can just let it air cool or to speed things up cool the heated area with a wet rag. This is called "heat shrinking". Don't go gung ho on this or you could end up with a "warp" in the opposite direction you had originally. When heat shrinking it is best to sneak up on the problem, i.e., do a little shrinking, let it cool, check the results, if not enough do another strip about 3/4" to 1" away from the first. It doesn't do any good to reheat the orignal strip; once it is shrunk that's it.
If you've got some scrap tubing it might help to practice. after a little practice you'll be amazed at he results.
In reallity, the minor warpage you described probably isn't that big a deal as the warpage will be about equal on both sides of your frame and will cancel each other out.
You might have set your welder too hot or were welding too slow, or both. If not, did you try and weld all the way to the end? ASME 4.1.4 (I think)doesn't even recommend going all the way to the end if memory serves. That literally blows the parent metal away and people usually go back in to try and fill in, making things worse.
cooling it with a wet rag will harding the metal.
heat it and let it cool slowly or cool it with an air hose.
Cooling mld steel with wayer will not harden the material. You would only need to be concerned with this if you wre using high carbon alloy, very unlikely in tubing used for frame rails.
I'm curious if the frame was checked for straightness prior to welding?
If it's imperciptible leave it be.
Two best way to eliminate or control warpage of any kind.
Use as little heat as possible to do the job and as stated, weld in intermitent
areas. The most effective way if you know a large amount of heat will be used is bracing. Brace the shit out of it. Or use fixtures to hold it in place.
Imperceptible = 1/8" tolerance from spec on any measurable dimension.
Finish welding EVERYTHING before bothering to straighten warps unless a warp is so bad you can't make the next measurement for a bracket placement.
Why do you think cars with seperate frames had body shims from the factory?
overstating the obvious:
you can help avoid this by bracing across and diagonally or clamping to some immovable object, a table or I beam or whatever..
this is a good example of why it's critical to control warpage when welding brackets on your rear axle housing
imagine the strain on an axle bearing in a warped housing, it's almost unbearable
Just to add, it's almost impossible, matter of fact I don't think I've ever welded on a rear axle housing that it hasn't warped some. I've taken old rears just to test, and set them up on the axle jig.....put a dial indicator on the end and welded a small shock tab on it, three 1 1/2" welds, and it pulled it.
Dont overthink shit. Just build.
3 words. BFH
Actually heating and cooling the opposite side as stated above will do it.
I've also used a handyman jack reversed as a spreader to "persuade" the rails back out again. Too cheap to buy a porta power.
Roost, That is exactly the reason that Pete and Jakes ladderbar brackets are 360 degee pieces. If you weld all the way around the tube it will end up straight as you've induced the same amount of pull (shrinkage) into the piece all the way around. If done properly the axle tube will end up straight. When I do complete rearend (narrowing) I mock up the axle under the frame with the ends off, install and weld the axle brackets ( and any other brackets such as shocks), then reinstall (weld) the axle ends on with the axle being held with my narrowing fixture. They always end up with the locating arbor (the bar that goes through the axle ends and the carrier bearing bores prior to welding) free to float on a light coat of oil. The locating arbor has been certified to be straight within .002" over a 4' span. This gives you an axle housing that is straighter than a factory unit.
You could also try a strong back clamped to the frame rail before welding,(I realise it won't help this time but for future reference)
To make a strong back get a piece of angle iron at least 1/4"thick 5/16" would be better,make the piece about a couple of feet long (shorter if you don't have the room will be ok) take a piece of 1/4" metal the same size as the angle iron (eg 3"x3") and weld it to the centre of one side on the angle,then when you want to weld on one side of the box section (tubing) clamp the strong back on the opposite side,pull the clamps up TIGHT and you should see that you have bent the rail towards the out side,then weld on the part,let it cool for a while then when you undo the strong back the rail should have stayed straight.
You might have to practice a bit with the pressure on the clamps to get the right amount of deflection that you need for the amount of heat you are putting in to the job..
This is the way we did it on stainless steel machine guards and it saved a lot of straightening afterwards.
I agree for the most part, I've got a narrowing setup/bar & arbors also. Still with the full circle brackets I've never had the housing ends end up perfect running all the way around them, although they're always closer with the lesser heat of TIG. Every piece of metal expands & contracts at different rates and welding all the way around evenly doesn't gaurantee it pulls right back again. I even made variable RPM power turntable to help duplicate robotic factory welds. I always weld the ends on last or cut & redo them no matter what I weld to the tubes. People sometimes want to skimp & not pay to have all this done after just welding brackets on, but after explaining what can happen & what a bitch it'll be if it goes haywire they understand. Sometimes I just pick up two pieces of scrap and have them hold one piece while I hit with the wire, when they feel it pull over to the side they finally get it.
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