what tolerances should i build my chassis to? is 1-2mm accurate enough?

Yes, mines about 5mm out on the diagonal.

that why you have adjustable suspension...

Ned.

As long as the suspension pick ups points, steering rack and wheels are in the correct place it does not really matter about the chassis.

So make your chassis as accurate as possible. If you get it within 5mm (especially on the diagonals) after all your welding then you are doing well.

Then as a last job make and attach your suspension pick ups to as high accuracy as possible. Work from a chassis centre line.

This way you should easily get your suspension pick ups within 5mm and probably within 2mm.

John

ill second JB's comments.

when triangulating the wishbones and rear axle it was 4 mm out, without the panhard rod attached which i can tweak to pull it back 2mm to make it bang on.