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Flame Straightening has been used for many years for repair and forming.  However it requires a lot of skill in addition to an understanding the basic principles of how it works.  Only a few individuals have mastered it fully.  "Arc Straightening", on the other hand, is not widely reported, is much easier to apply, and the results are much more predictable and repeatable.

The fact is when you are welding you get distortion.  That is thought of as the opposite of straightening. However if you start with a curved piece and put the weld bead on properly it will straighten!
The following is an example used to straighten the roll bar legs fabricated for our Street Rod.
When building the roll bar  for the 1934 Pro Street, Street Rod,  0.093 wall mild steel tubing was ordered.  To allow UPS shipping two pre-bent sections and some straight tubing was purchased.  Some tubing was ordered that slipped inside for a backing ring for the butt joints.  A simple fixture was made to hold the parts in place while tack welding them together.  The distance between the two legs was very critical since the pipe stubs they would slip in were already welded to the car frame.
 It was important to factor in the distortion that welding would cause so as to have the proper final dimension.  That was done, but as expected it wasn't sufficiently accurate!
Ruler in hand, it was off by 3/16 inches!  What to do?  Having recently traveled to Mexico where an earthmoving equipment manufacturer using "arc straightening," that looked like the best alternative since it was predictable and repeatable.

MIG weld beads were placed toward the top of one leg on the side that needed to move out slightly.

Weld beads were placed as shown in the accompanying photo,   With each bead the results were measured and slowly but surely as the weld cooled and shrank, the end of the bar moved. If it was desired to have the bar move in the other plain as well, the beads could be placed further around the bar.  It is not easy to bend a 0.093 wall 1 3/4 inch steel tube but "Arc Straightening" did the job.  It took 5 weld beads and the job was accomplished, the spacing between the bars was exactly that needed.
to achieve the final result the welds were just ground smooth. The finished bar leaves no indication of the weld beads.  For the mild steel tubing the effect on the structural strength was minimal.  Do not use this technique on 4130 tubing, the extra heat-input will lower the strength.  Rapid cooling could also cause cracks to form. 

This process is not widely known or used.  It has the potential to solve some unique problems with less heat input then flame straightening.  It is also much easier to apply and much more predictable.  There may be an application in your shop.


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