Chassis out of square

[costlow7]

Hi guys
I have just measured my chassis for squareness and was wondering what sort of tolerance is acceptable, in the real world?? I am just wondering in case of bodywork problems later.

[twinturbo]

you would have to tell us over which dimensions.

TT

[costlow7]

I mean from the back outside top corner both sides of SB2 to inside front frame corner, junction of TR1, TR2 and FF4.

[ozzy1]

Realistically you want it as accurate as possible,but unless you are experienced welder you will always get some distortion.I think if you are within 2-3mm overall thats pretty good.You will be able to conceal this easily whether you make the panels from fibreglass or aluminium as there is excess material in the fibreglass to trim and if you make the panels from aluminium you can add the extra.I do recall reading somewhere that someone measured a chassis from a certain manufacturer and one side was longer than the other by 10mm

[Bonzo]

I would more or less take Ozzy's post as a good guide

Anything built out of tube & has a mulititude of welded joints is going to be subject to a certain amount of distortion.

All depends on how far out of square you are really, is it the seatback area out of square, front frame out of square or a combination of both. ?

From a suspension point of view.

As long as the front frame & dif cage are good and square it should be possible to fit the suspension brackets in the right place.
The correct fixing of the suspension brackets is critical to good suspension & wheel geometery.

From a bodywork point of view.

Depends on the route you are taking.
An alloy rear tub & sides are quite forgiving as they can be tailor made to suit.

GRP will fex a few mm to counter a small amount of out of square.
Seem to remember if the GRP sides & nosecone need to have the chassis/front frame the right height as they may be tricky to fit.

Sorry it's all a bit vauge but unless we know how far out of square you are it's a bit difficult to offer the right advice.

[costlow7]

Thanks for all your replys. I asked for advice about what people consider a workable tolerance given that we are all, or most of us working in a garage enviroment. The book does not really give any clear guide to limits or tolerance, or do I need glasses.

I am what I consider way way out of limits at the moment about 10mm which is in the area I have mentioned in my second post. luckly I have only fully welded the bottom rails, and only tacked the frame from the front frame to the seat back. So I can have change things easily, I think a lot of the error may be from the front frame anyway. I will go have another measure when I get some time. I am new to this welding fabrication art, and dealing with all the distortion issues. I have a mate at work who is a top quailty aerospace approved welder so I have been getting some good advice from him as well.

I am using GRP for everything but I dont think I will be useing it for the side panels. So the chassis has to be as good as I can get it.

Thanks again for the help

[will_08]

As said its never going to be perfect, i would like to know what tolerances are actually achievable?

Cutting errors (length & angles) + Parallax errors (from measuring devices) + lack of truth from timber jigs/build base's + heat distortion etc.....................

just got to get as close as you can.

Although big errors at the beginning, start snowballing down the line. Before you know it you'll have to alter loads of tubes to accommodate one error.

Good luck m8

[robo]

Its probably best to tack up the whole chassis first and leave it on the build table before you start welding anything. There was a thread somewhere on the best way round the welding sequence to minimize distortion. I think it was posted by talon.

Bob

[costlow7]

With the kind help from phil from talon I have found out where my error is. He kindly popped down tonight and found it is a error in my bottom rails. It is 5mm and I just missed it, but it is just adding up as I go further in the build. Anyway as the mx5 based chassis pack was from him he has taken it away and I have asked him to fully weld it up.
I now feal a bit of a failure I wanted to do the whole thing myself, but at least now it will be right. He did say my welding looks good so at least thats something.