Welding steel under tension?????
 

Im having issue with the chassis installation in my Falcon. I tacked the rails into the car and was very happy with the geometry. I then welded in a rear cross member only to notice that due to a lack of bracing the rail moved about 1/2" at the top of the wheel arch. I grabbed the bottle jack out of my engine crane and can very easily push the rail back to its correct position. However my question is should you weld when the steel is under tension or compression?? Will this reduce the strength of the weld/chassis by welding it when it when the steel is not in a neutral position? Any advice would be appreciated!!!!
Thanks
Dallas

you can overbend it so it returns closer to where you want it to be.. but in all honesty it wont change a thing.. the moment of inertia (stiffness) is not dependent on the internal stress, but on geometry, and as you subject the chassis to vibration it will relax the tension anyway.. so considder this a lesson in welding distortion.. and finish the chassis, and enjoy the car

Lesson learnt, thanks for the advice. I guess nothing that i do would compare to the stress that the chassis rails go through in the first place to be bent into shape!!!

exactly

This is why if you were welding a "T" -- you'd do a bit on one side - and then a bit on the other side --- because the leg is going to pull one way or the other with the heat/cool cycle.

You want to SEE the distortion -- lay two steel straps -- side by side for a butt weld - then tack once at the very end - watch the gap at the other end open up.

I'm no expert but I can tell you that I've learned a thing or two about clamping! And about tacking - and the "order of tacking" - because it does make a difference! I always laugh at my buddies that have just gotten a new MIG machine -- and they stick some metal together - and then "think" they're "welders"..... :rofl:

Touche Greg!:D