I have just finished welding my lower frame and whilst it was done in a jig and clamped down there seems to be a bit of deflection. This is mainly towards the front of the frame where there were some larger welds causing the most heat. It has resulted in the front (engine bay to nose cone) section curling up somewhat.

When the frame is sat on a flat surface and weight applied it sits flat. Will this all rectify itself when the rest of the frame is fabricated and the loads of the engine etc applied or should it be dealt with now. If so what is the best way to go about it?

When I built my chassis the bottom had a bit of a bend in it after welding so I turned it over, rested the front on some 4x2 and strategically jumped up and down on it. It worked fine

Thanks. That is exactly what I was planning for the weekend!

If your jig is steel, and you have an oxy/propane set, then i would tightly clamp your chassis back in the jig to pull it back straight, then warm up the areas that have pulled with an oxy/propane set, then let it cool down naturally

Jig is wood so not an option. I was thinking of heating up the back of the bent areas and then letting them cool. Would this pull it out?

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Originally posted by Padstar
Jig is wood so not an option. I was thinking of heating up the back of the bent areas and then letting them cool. Would this pull it out?

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Would putting some more triangulation in the frame sort it out.

Brad.

With it just being the lower rails I am hoping a bit of heat and/or gentle persuation will straighten it out. From then on the welds are far smaller and so I should be fine. All of the brace sections will then also be installed so it should all hold together as planned. Just wanted a level base to work from.

Shouldnt be too much of a problem, just clamp the frame to the jig so that it is held flat, and so it cannot move. Then build up the remainder of the chassis, just tacking the sections in place. When you come to doing the final welding make sure that you do a little on each side at a time, so that you dont do the same thing again. If done in this manner you should end up with a nice straight frame. HTH Ray

To what extent should I tac the chasis together? Should I not be welding each section as it comes?

Had assumed eAch drawing got welded as its own little masterpiece?

The chassis should be tacked together first as chippy said, so that it forms a rigid structure, then weld one joint at a time, moving diagonally around the chassis. This will minimise distortion. Good idea is to mark the joints as you weld them, to make it easier to spot any you may have missed.

Yes exactly as stated above, when I built mine I tacked the whole thing with just a blob of weld to hold it all together. Then get your tape measure out and check the whole thing is nice and straight and square, if not this gives you the chance to put it right. Only then as said weld one join at a time alternating across the frame to minimise distortion, and mark with some chalk each one you have done so that you dont miss any, very easy to do. HTH Ray

All good. Heated up the area with most deflection and then gave it a little helping hand. There is now a max of 1mm deflection to one area which i believe will fall out as the rest is fabricated. For the rest i will tac untill complete then weld up as suggested.