Any way to un-warp something?

[David_17]

Hi all, i'm currently in the process of making a kit car.

I tack welded the full chassis, clamped down on a flat board then fully welded it (working front, then back, then front etc).

I then turned the chassis over and welded all the bits i couldn't get to from above.

Now when placed flat on the board (the right way up), the back of the chassis is a few mm off the board.

Is there anything i can do to re-flatten it?? Or will i just have to live with it?

Thanks in advance for anyone who can help.

Cheers

Dave

 

[Chickenjohn]

Hit it with a big hammer! Or heat the welded joints with oxyacetylene flame and bend the bars back to true.

 

[langy]

A board isnt really good enough i'm afraid, should of been done on a steel jig.
But having said that there are a lot of production cars out there that aern't as straight and true as you might expect

 

[Shox Dr]

Hit it with a big hammer! Or heat the welded joints with oxyacetylene flame and bend the bars back to true.

Yeah rite oh




You might be able to heat the convex side welds and quench, that will pull it but with it been a triangulated chassis, I dont know how well it will work

 

[brightspark]

a few mm wont make any odds over that distance on chasis its not that critical

 

[David_17]

I was hoping someone would say that

It's level all the way accross (eg front to back is slightly out, side to side is fine). So the suspension geometery should still be ok.

 

[mike os]

only way you will shift it now is on a jig with hydraulics I would think.... but if its only a few mm as said it should be fine..

do the designers give any tolerances on the drawings?

 

[Shox Dr]

A board isnt really good enough i'm afraid, should of been done on a steel jig.
But having said that there are a lot of production cars out there that aern't as straight and true as you might expect

Very true watched a doc on Prodrive, they would take a chassis off the production line and have to straight it as the Rally drivers would know if it was more than 2mm out, The Production chassis could be upto 5mm and pass

 

[brightspark]

i bent my f2stockcar rails back on one side. half an inch the easy answer cut all the suspension mountings off that side and reweld them back on half inch forward re checked the tracking ect perfect

 

[Chickenjohn]

Yeah rite oh



-snip-

Whats your problem????? heating and hitting should straighten it.

 

[Rudi McAnichal]

Can you incorporate some adjustment into the suspension? Many older cars had shims between the body/chassis and the suspension mountings, making it very easy to change camber, castor angle, etc.

 

[the snooper]

as its arched upwards it might give a little with weight when its built up and has a couple of passengers

 

[Welderpaul]

Bashing frames like the one above with a hammer to try to straighten them doesnt work. They just bounce, you dent the box section, and you get knackered.
I would say it is pretty much past straightening - there is too much ridgidity in the frame to straighten it. Often after carefully examining it, and drinking lots of tea, you will find a couple of crucial members that can be cut which will allow you to bend the frame, then reweld back in position. I think your going to have to live with it.

 

[Drains]

If you can identify the bits that are over-length, you can shorten them. Heat the section to dull red with oxy acet/propane, then quench with water spray from the outside (cool steel), to the bit you've heated. The steel will shrink. It's a VERY effective solution if done properly.

Or as Paul says you can cut the frame in the appropriate places and re-weld, but careful the weld doesn't shrink and you end up back where you started.

Smacking the thing with a hammer will seldom work, as you almost certainly need to either lengthen or shorten bits, not bend them.

 

[R BEADLE]

what you could have though i don't think its necessary is sit on two lengths of heavy level channel , tack the front of the chassis to each channel then cut through what ever welds you think necessary , pull the back end down to the channel and tack it then re weld the cut welds , cut the tacks off holding the chassis to the channel , jobs a goodun . like someone else said , i don't thinks its worth worrying about . they probably flex when on the road anyway .

 

[backpurge]

That will straighten with the application of heat in the correct areas no problem at all, be careful regarding quenching as you could render the material brittle.

 

[Fergus]

Off topic I'm afraid.. is that built from the Ron Champion plans? I've only done a fibreglass kit so far and I've always had a hankering to build from scratch.

First I'll need a garage though..

Just another thought, back on topic. I'm assuming that your flat surface is still flat and the deflection is actually in the chassis?

 

[David_17]

Off topic I'm afraid.. is that built from the Ron Champion plans? I've only done a fibreglass kit so far and I've always had a hankering to build from scratch.

First I'll need a garage though..

Just another thought, back on topic. I'm assuming that your flat surface is still flat and the deflection is actually in the chassis?

It's the chris gibbs version with independent rear suspension and based on a sierra instead of rare mk2 escort.

I don't have a garage either, i hire a 30ft lockup for £65 per month and use a generator for power Much cheaper than hiring a garage.

Found today that the table had dipped slightly in the middle (so that's what's caused the chassis to dip). The middle tube is about 10mm lower than the 2 ends. Should still drive ok, just the side panels will need some modification.

 

[Fergus]

Thanks David, does that make it the Haynes version then? Or have I missed one of the books?

 

[David_17]

Yep it's the haynes roadster