Problem tapering 2x4 tube

[201]

I'm tapering some 2x4x.125 tube for a mod A frame. This is the taper at the front end of frame apr. 25plus in. long(I'm making the wheel base 3 in. longer than stock).I pie cut the sides with the straight cut 5/8 in from the edge.I clamped it up on my table( 2x2x.250 tubes on 8 in. centers on two I-beams) with tapered side up.Tacked it every 2 in. side to side.Let it cool, un-did it, turned the rail right side up and BAM!-the far end of tube where the front end will be dove 1/8 in.Cut lose tacks, pre-loaded the tube 1/8 in from taper's end back, re-jiged and clamped it down past the 1/8 in deflection and about 1/16 in more. Tacked it and the 1/8 in. deflection is still there.Any ideas?

[Roothawg]

There's a guy here in OKC that makes frame horns or at least sells em. 30 bux a pair and they are already tapered.

Rich at Elite Street Rods in OKC,OK

[201]

Roothog -this is the tapering of the frame from 4in to 2 11/16 at front axle center line to then add on front frame horns

[DrJ]

You "shrank" the side you welded.
Not wrong, it happens.
You need to "shrink" the top side too.
set it up on your jig so you can see it move and bring the top to red hot and watch it move. It'll move away as it expands, you want to put some push on it then so as it cools so it ends up straight. don't over do it or it'll curl up the other way!

[ELpolacko]

We do this sort of thing all the time. We use a hydraulic press to straighten them back after welding. It does help to skip weld the seam, it keeps the heat down a bit but will not prevent the rail from warping.


Btw, when I worked for The Rod Factory years ago I built about a hundred A frames this way.... I formed the "horn" by hand every time by wraping 1.875 X .300 strap around a buck, weld it, then hand grind the final shape. I got real good at this after a while. Now I cant imagine not using the pre-stamped horns.

[201]

Thanks DrJ and Elpolacko. Ill try the heat on top first just to get "the stick time" and the press if I don't like the my results.Or make another rail and don't tell anybody!
NO, just joking. I want to try to do it up right.Cuz I'll know.