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Author: Subject: Chassis tension

posted on 26/11/12 at 02:08 PM Reply With Quote
Chassis tension

Hello, the chassis is starting to take shape. After making the mistake of fully welding the base and a few uprights before I continued I am now left with a slight problem. Now that I am tac each section together to form the complete chassis before welding it all the few uprights I had in place already fully welded need some minor adjustment (2-3mm). Do I need to cut them lose and start again or can I persuade them into persition using ratchet straps and then tac in the correct place when fully aligned? If I do this will the tension cause an issue or will it be fine when fully welded?

If u suggest removing is a simple cut through the weld with a cutting disk ok to allow adjustment then re weld over or should the section be fully removed and ground clean before replacing?

As always thanks for the help.

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posted on 26/11/12 at 02:21 PM Reply With Quote
I *think* the result will be the same either way. had you tacked it all together before fully welding, the heat input will have tried to move everything anyway, but stopped by the rest of the tubes being fitted. I suspect if you use ratchet straps to straighten everything out, and fit the rest of the tubes (tacking everything up first) then the same tension will be there, as if you'd tacked up befroe welding.

i suspect if you take any chassis and cut a few major tubes out it'll twist a bit, but all the tubes rely on being fitted to every other tube to hold it al straight

just my thoughts anyway


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posted on 26/11/12 at 02:27 PM Reply With Quote
Just get a 1mm cutting disc and take the ones that are not correct out, with careful cutting you "may" be able to re-use them. I personaly would not be at all happy dragging them back into place as you are just adding twist, you may of course just be able to cut the welds on three sides of the offending upright, then you could bend them to the correct position. IMHO Ray

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mark chandler

posted on 26/11/12 at 06:05 PM Reply With Quote
I would cut flush with a hacksaw on the three offending sides and stand straight then weld.

Make sure you do one flat then move across to the other side of the frame and attack one there to minimise heat distortion.

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posted on 26/11/12 at 07:11 PM Reply With Quote
I'm with Mark on this one. Treat it like you would a cylinder head etc. i.e. don't do all one end then attack the other, spread the heat distortion from side-to-side/end-to-end. Worked for me when I made my chassis

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posted on 26/11/12 at 08:22 PM Reply With Quote
Thanks guys will give it a bash at the weekend. It's so annoying I went straight in with fully welding the bottom rails rather than tacs. Was just too eager to crack on. Valuable lesson learnt
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posted on 28/11/12 at 11:00 PM Reply With Quote
1 last question. As i have most of next week off work, i plan to really hit the chassis hard and get most of the welding completed.

When tac'd up my chassis seems to be 2-3mm too short from the nose to the seat uprights. Is this being picky or should i release some welds and spread out?

Everyone is telling me that 2-3mm over 2.2m is nothing but i am still a little concerned. What do you think.

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Talon Motorsport

posted on 29/11/12 at 09:18 AM Reply With Quote
2-3mm short over all is nothing to worry about if your diagonal measurements match, as long as the chassis is straight the length of it does'nt realy matter . Tack the front frame and the seat back in place and brace it to keep them there, then tack the uprights in place and see where the top tubes come in relation to them.
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posted on 1/12/12 at 09:40 AM Reply With Quote
What tolerances are acceptable on the diagonals. I don't think there will be a problem as it was fabricated in a jig and whilst it was my home made jig it was fully marked out and double checked so should be good
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