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Bending!! Arggh
Gremlin - 28/10/02 at 08:42 PM

I have just completed stage 1 of the chassis and tack welded it together on top then turned it over and tacked the underside. The chassis now bends slightly from front to back. When the front is down the back is about 1-2mm of the deck. If i turn it over the weight pushes it flat!

Is this a problem?

If i turn it back over so it sits flat then add sections H and J1/J2 will this straighten it out?

Metal Hippy™ - 28/10/02 at 08:45 PM

1-2mm is cack all.

Pretty accurate I'd say.

So long as the suspension is mounted to compensate even a banana of a chassis is fine so long as it's welded strong enough.

Gremlin - 28/10/02 at 09:14 PM

I was wrong i have just measured it and its 4mm. Is this still ok?

Obviously making the chassis by hand is never going to be perfect but how close do i need to be?

Hornet - 28/10/02 at 09:52 PM

Gremlin.. while i admire your efforts.... this car will drive fast when completed. I think after reading ur posts, you would be better to perhaps buy a chassis m8... please don't take offence but, I think you are heading for trouble at a very early stage.

Gremlin - 28/10/02 at 11:10 PM

If that aint good enough not a problem i was just checking. Only need to undo tack welds!

My welding is fine i have had that checked so when i come to fully welding there should be no problems and will have it checked for self confidence.

I take it you are saying the chassis should be perfectly flat at this stage. Not a problem.

Any reason why i shouldnt be able to do it?

Metal Hippy™ - 28/10/02 at 11:24 PM

I shouldn't worry.

Sounds like a prophet of doom to me.

If you've had it checked you have the peace of mind to carry on mate.

stephen_gusterson - 28/10/02 at 11:42 PM

hi mr gremlin

I have been on this list since february, and have been on TOL for two years.

If I had a quid for everytime i have seen a post like yours I would be chucking my job tomorrow!

In my own personal experience, and of others on line, the chassis can bow front to back up to half an inch. So you are not doing too badly.

If you want some comfort, go to TOL

http://groups.yahoo.com/group/locost


search for posts from Ken Walton of earlier this year. He addreses the problem.

Basically Ken is a guy in his late 60s who has raced cars for years and built several. His opinion is chassis bend isnt important. Just make sure that when your suspension brakets are on, they are placed to compensate.

Ken explains this in much better style!


To add to the previous cautionary note : do make sure your welding is fine. Having summat break at speed in a minimalist design like the locost would be bad. I added a fair few extra tubes on my car, inc some 3mm re-enforcement plates to the base of the car where tubes come together, like the lower ones of the engine compartment to the firewall. These add to the structural integrity and make handy jacking points too!

If you build a hose, get the mortar mix wrong and the house is junk - same story with welding.

Dont worry about the banana effect on your chassis - you can reduce it by welding opposite corners of the chassis and oposite sides so as to not do all one side at a time. this will help spread the bending loads.


atb


steve



[Edited on 28/10/02 by stephen_gusterson]

Gremlin - 29/10/02 at 12:08 AM

Many thanks everyone. I will get back to it tomorrow and see how things actually look. I can see where its bends exactly a set of tacks so i will cut out tacks and flatten and retack should be no problem.

Have a friend who is a welder who has given me some tips he is willing to check work nearer completion.

Simon - 29/10/02 at 04:55 PM

Gremlin,

After you've removed warping, make sure you clamp everything down before you start welding properly.

Also, make sure you have no bits of steel etc under any of your tubes.

ATB

Simon

James - 29/10/02 at 07:19 PM

quote:
Originally posted by Hornet
Gremlin.. while i admire your efforts.... this car will drive fast when completed. I think after reading ur posts, you would be better to perhaps buy a chassis m8... please don't take offence but, I think you are heading for trouble at a very early stage.


I was mortified when I found that my (70% finished) chassis was warped (and not even evenly either: ie. it wasn't just banana'd across it's length but appeared worse down one side than the other). So I spent the three months summer holiday when I couldn't get to it convincing myself I was going to have to start again.
When I got back to college I spent awhile with the chassis talking to my new instructor who has a lot of experience building cars.
The first thing he did was get me to set it on a plate- that cured the perceived twisting as it seems the floor I was measuring it on wasn't flat!!! This also allowed us to properly assess the bananaing (sp?) which was (is) about 5mm front to back. I was still a bit concerned but he'd said he'd built cars professionally and they were very often far more out than that!
The moral is: bananaing is a fact of Locost life and don't worry about it!

It also led onto various interesting anecdotes that he told me about this subject- the most impressive being that the Austin Princesses he was involved in building were/are an inch longer down one side than the other!

There's another student there who builds rally cars professionally. He says they jig them fully but often, after welding, some bolt holes don't line up by as much as 2" and it's a case of crowbaring them together and then tapping the bolt into place!

James

Gremlin - 29/10/02 at 08:16 PM

Thanks everyone. After closer inspection it was 1 tack that when cut allowed the chassis to sit back flat. Once flat i clamped it back down and tacked. Perfect!!!

A long way to go yet but at least stage 1 off the chassis is flat now i have to start building upwards. 3D that has to much more difficult than 2D. Oh well we will see what happens.