degmwilliams
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| posted on 2/6/12 at 11:45 PM |
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When you buy a chassis, what are the tolerances in mm?
When buying a chassis from a kitcar manufacture what would you say is a fair tolerance when measuring there build? Or are there set guide lines in
which they must follow. Any feed back would be good!
Building a tiger Avon st170 (slowly)
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snapper
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| posted on 3/6/12 at 05:02 AM |
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There are no laws stating tolerance for kit builds and as such no standards.
The main issue would be the resultant suspension geometry and there is generaly plenty of room for adjustment
If you are looking for engineering levels of accuracy I fear you will be disappointed.
I would however question the need, as long as the chassis is square and the suspention is adjustable what needs to be that accurate?
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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Talon Motorsport
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| posted on 3/6/12 at 07:50 AM |
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What problem(s) are you having and what does'nt fit?
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jossey
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| posted on 3/6/12 at 08:24 AM |
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Go with the theory that mclaren measure the chassis and reject if more than 1mm wrong but my mondeo I had when measured up was around 22mm out on left
rear corner.
With rose joint wise bones and moving the spacers or moving the wishbone brackets to get all 4 corners to line up.
Thanks
David Johnson
Building my tiger avon slowly but surely.
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degmwilliams
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| posted on 3/6/12 at 08:25 AM |
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I was going to build my own chassis cause I know it would of been to every measurement in the dimensions. I'm a self employed engineer and due
to being so busy with work it was never going to happen. In two years all I got done was fab at build table and cut all my steel out. And sit on the
computer buying parts at night. So I decided to buy a chassis and thought if it was built in a jig it would be perfect. I cant see the sense, if your
building chassis to sell I would have to make sure the jig was spot on to the mm. Since buying one and measuring it for squareness I'm not
impressed. Is it the same with all manufactures or doesn't any one care about there products?
Building a tiger Avon st170 (slowly)
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TimC
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| posted on 3/6/12 at 08:36 AM |
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In my experience its pretty common. There are some very careful chassis manufacturers out there but even some of the 'big names' can have
very disappointing levels of accuracy.
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snakebelly
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| posted on 3/6/12 at 08:41 AM |
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i see from your tag line thats its an Avon you are building so no real surprises on the lack of tolerances there then! having built and rebuilt a few
Avons now i can safely say that measuring tolerances in mm is hopeful! actually thats not really fair, most Avons i have measured have had tolerances
below 10mm some only just.
As has already been said with the nature of these cars most suspension can be brought back into line.
If you think the chassis is out of tolerance and you have a have a body of 12 months or older for gods sake dont take a ruler to it you'll
stroke out!
I would susepct that most buidget sevens have similar issues though and unfortuantely i think its a case of you get what you pay for.
Just as an aside my Caterham series 2 was not spot on in places either.
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MakeEverything
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| posted on 3/6/12 at 08:48 AM |
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When i built my own chassis, it was +/- 2 degrees, purely because thats the tolerance of the tools i was using.
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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gottabedone
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| posted on 3/6/12 at 09:04 AM |
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Which over a 10 foot length is just over 10mm Richard which for a home build is pretty damned good 
Steve
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Talon Motorsport
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| posted on 3/6/12 at 09:10 AM |
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quote:
Originally posted by degmwilliams
I was going to build my own chassis cause I know it would of been to every measurement in the dimensions. I'm a self employed engineer and due
to being so busy with work it was never going to happen. In two years all I got done was fab at build table and cut all my steel out. And sit on the
computer buying parts at night. So I decided to buy a chassis and thought if it was built in a jig it would be perfect. I cant see the sense, if your
building chassis to sell I would have to make sure the jig was spot on to the mm. Since buying one and measuring it for squareness I'm not
impressed. Is it the same with all manufactures or doesn't any one care about there products?
One of the problems with making things in jigs is that people tend to stop measuring what they are making and trust that the jig is correct, with
repeated use through heating and cooling even the best made jig warps over time. It's not untill all the parts are offered up to each other or
measured against what they are ment to be that the problem gets noticed by the manufacturer by which time 10-20 customers have all ready found out.
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MakeEverything
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| posted on 3/6/12 at 09:29 AM |
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quote:
Originally posted by gottabedone
Which over a 10 foot length is just over 10mm Richard which for a home build is pretty damned good
Steve
Thanks! Better than a Mondeo too, seemingly!!
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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PSpirine
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| posted on 3/6/12 at 10:40 AM |
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It may surprise you but a lot of production car bodies will be out by 10mm. You don't notice it much because all the tools are tuned to provide
correct gaps etc. even though one side of the car may be longer than the other! (BMW 7 series had this problem at some point). 
Note however that this doesn't mean that one body to the next will vary by +/- 10mm, it means the body varies from the original specification by
10mm. The actual production tolerance in OEM's is much tighter - the "wonk" is introduced during the tooling/stamping process.
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Minicooper
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| posted on 3/6/12 at 10:47 AM |
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I would be amazed if anyone could produce a lotus 7 alike chassis any better than + or - 5mm, even if the jig is perfect which it won't be, the
stresses of heat and welding will see it move no matter what. Even a small part like a wishbone it will spring as you take it out of the jig
Cheers
David
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iank
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| posted on 3/6/12 at 10:58 AM |
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Bronze welded chassis are, or at least can be, much more accurate as the heat distortion is minimal.
So chassis produced by Arch motors would likely to be best.
Another problem with jigs is they tend to be made around the first chassis, so they repeatably reproduce any errors from that.
You'd have to hope a Procomp chassis would be best of the 7 clones given their posts on this subject.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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degmwilliams
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| posted on 3/6/12 at 11:46 AM |
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I know that erw distorts with the heat from welding. Which then can put a chassis out of square but there are sequences in which you can weld to
reduce distortion. Wish bone jigs can be made to allow for spring. On my chassis some of the steel is cut at different lengths and welded up too 6mm
higher on one end than the other.
[Edited on 3-6-2012 by degmwilliams]
Building a tiger Avon st170 (slowly)
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muntieiow
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| posted on 3/6/12 at 02:34 PM |
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I`ve just started building my own chassis, as you say ERW does pull around alot when welded, but as long as all the joints and mitres are nice and
tight, and you keep moving from side to side when tacking it up there isn`t to much of a problem. You just have to keep checking the measurments and
that it is square over and over again.
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907
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| posted on 3/6/12 at 03:26 PM |
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I think 2 deg over 10ft is a little more than 10mm.
May be a typo with the decimal point.
Paul G
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Andybarbet
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| posted on 3/6/12 at 05:52 PM |
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My sister inlaws other half has a Robinhood Zero chassis, its was about 30mm out so being a welder by trade, he set about cutting & rewelding it,
managed to get it under 10mm.
I seem to remember when we measured my Luego chassis it was less than 5mm, might have to double check this weekend just out of curiosity 
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degmwilliams
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| posted on 3/6/12 at 06:22 PM |
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Well I think 5 mm is unacceptable let alone 30mm. I wouldn't want any of these so called fabricators working for me. And if your having to cut
and reweld your chassis yourself I don't think they should be building them.
Building a tiger Avon st170 (slowly)
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MakeEverything
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| posted on 4/6/12 at 10:40 AM |
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quote:
Originally posted by 907
I think 2 deg over 10ft is a little more than 10mm.
May be a typo with the decimal point.
Paul G
Youre right, over 2m its 69.81mm, but it wasnt that far out!!
I think i measured about 10-15mm variance, but i cant remember now. The +/- 2 degrees was the tool tolerance, but now i look at that, its quite a
lot!!
ETA: youre right, ive just checked and the decimal was in the wrong place!! its +/- 0.2!!
[Edited on 4-6-12 by MakeEverything]
Kindest Regards,
Richard.
...You can make it foolProof, but youll never make it Idiot Proof!...
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Neville Jones
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| posted on 4/6/12 at 12:32 PM |
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My chassis jig is 100x100x5mm shs. It just doesn't move. It's checked before each build, and has been found to maintain its geometry for
the last 25 years. Work off a set of permanent datums, set up with a lot of care and time, and all will go well.
Accuracy is only as good as the care put into the build. With the jig as above, I can confidently say that each chassis I've built is accurate
to +/- 1.5mm. Some will scoff, but you are welcome to run a tape over one if you get near to one. A recent chassis, built 12 months ago was recently
checked, and found to drop straight back onto the jig.
Same goes for wishbones and any other parts jig built. The major design goes into the jigging. Moreso than the parts to come off the jig. If you
build substantial and accurate jigs, what comes off those jigs will be accurate and repeatable.
A chassis or wishbone jig which has to absorb enough heat that it moves, is wrongly designed to start with.
A piece of 1" mdf will never be suitable for making accurate parts, whether steel, ...or wood.
I also use Class A tapes and measuring gear, it helps to know you are staring with the right tools.
Cheers,
Nev.
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gottabedone
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| posted on 4/6/12 at 01:45 PM |
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oops!
That's what happens when you do maths in a rush
Richard - you still deserve the bow though
Steve
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Slimy38
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| posted on 4/6/12 at 02:56 PM |
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What is meant by the term 'tolerance' in this context? What is being compared? Or more importantly, what would I measure in order to see
how good my welding will be?
Neville, A quick question if I may? I get the impression that the loss of accuracy can come from heat distortion during welding. When you're
working with your jig, do you just tack weld or do you fully weld on the jig? If you do tack weld, what do you do to avoid any later distortion?
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degmwilliams
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| posted on 4/6/12 at 06:51 PM |
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Tolerance when fabricating steelwork is usually written on the drawings or plans of the of what ever is being made. If you were to build some steel
frames for a builder on the drawings it might say tolerance +/- 2mm which means you take any measurement off the drawing and either be up to 2mm under
or 2mm over the dimension.
The more welding you do the better you get at knowing which weld to do next or which is the best place to tack to avoid it pulling when welding up.
Building a tiger Avon st170 (slowly)
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coozer
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| posted on 4/6/12 at 07:43 PM |
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A few years ago as a supplier engineer to Toyota I used to go to the factory.. A LOT!
They used to moan on about +/-0.01mm tolerance on our parts but then I'd wander over and see the big fellas 'making' the rear hatch
fit...
Whats that all about then? I asked.
Oh, theres a 'discrepancy' in the tooling thats too costly to fix so the guys twist the hatch to make it fit. "They very good at
it" he said, proudly!
Then off to Turkey for the same bashing where they built the Verso.. body was even worse!
1972 V8 Jago
1980 Z750
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