You could yes, but will ruin all the properties of the stainless in the heat affected zone.
Could you not get some stainless box to glue on, with some stainless wire?
Theres nothing stopping you from miging it mate, just bear in mind the stainless will rust in the area close to the mild steel, with either mild or stainless wire.
What size box is it??
Id be inclined to stick with the stainless personally. Youve got this far, and it would be a shame to spoil a top job for the sake of £20!
Any chance of some pics??
Rather than using the brackets that bloke used I was thinking of something more along the lines of this out of short lengths of box section (see attached image)
My only concern with this is that it is going to put a lot of rotational stress on the existing round chassis bars.....
I'm guessing the £70 includes fabrication time. Stainless sheet shouldn't be so much more expensive than mild.
I had a look at Tony's photos. The lower wishbone takes a lot of lateral (sideways) force, and he's got no sideways support. I'd be inclined to put in some cross tubes where the lower wishbones attach. Then the wishbones themselves can be attached by little brackets as Tony has done (should be able to make them from 2mm stainless scrap). There should be very little fore-aft force on them
I'm not sure how much of the structure is on the original chassis and how much has been modified. Post some photos of your chassis and I'll offer some suggestions.
You cant really see whats going on with my chassis because its covered with all the parts still....
these photos show the chassis with the redundant bits cut off
The £70 was just for the stainless box section!!! I would have needed 4 meters of the stuff if i was going to go with plan A which was to put complete lengths of box section across the chassis.
plan B would be cheaper as it requires less material, but will it be strong enough?
I think it would look neater done as in the pics, with the brackets fab'd from 4/5mm stainless.
Nut sure on the diameter of the tube, 38mm? Make the brackets quite wide on the back (25mm ish)so it eliminates the twist and wont peel off.
I would agree with you about the method in the photos looking the smartest.
The tubes are about 40mm with 1.6mm walls...(might be 2.1) I cant measure it! (the material is the stuff they use to make exhausts out of!)
My concern with the method shown in the photos is that; is it possible to get a strong enough joint? (obviously adding gussets and such like would be a must!!)
and will the tubular chassis parts take the stress without giving up?
Oh, and I would deffinately be geting it TIG welded!
I was thinking of something like the drawing in my attachment below (please forgive my lack of effort in drawing).
If the wishbones can reach as far as the chassis then U shaped brackets should secure them OK. A total thickness of 3mm for the brackets should be OK.
My concern was about the load transmitted from the wishbones. They've got lateral, vertical, longitudinal and torsional to choose from. Assuming you have rubber bushes then vertical is next to nothing - push the wheel up and the bushes will twist with no effort - verticals are taken by the damper. Torsionals go away the same way. There is some longitudinal, that's why you need 3mm. But the lateral forces (towards the centre of the car) are very high. Suspension bushes are often specified up to 20,000Nm in that direction to make the car handle. That's a couple of tonnes per millemeter.
My rough drawing has the tubes between the chassis rails which would spread the load between 2 tubes rather than one. Think of puting the chassis on it's side and having an elephant sit on it. The cross tube makes both lower rails take the loads rather than just one.
A diagonal tube up to the upper rail would make 3 tubes take the sideways load. 4 tubes if you have a cross brace somewhere at the top (although the upper wishbones themselves won't take a lot of load so it's not neccessary just for them - a lot of car manufacturers have very light and slender upper wishbones).
MIG vs TIG for this sort of thing: the difference will be how pretty the welds end up. MIG would be fine, but any suspension attachment needs to be done by an experienced welder. Lots of stress and fatigue in these bits, and it's bad when the suspension falls off.
I suspect you have 409 tube rather than 419. 409 is exhaust tubing.
That way makes a lot of sence. I can pick up 409 grade exhaust tubing a lot cheaper than I can get box section. So if I use the tube for the internal cross braces and then sheet for the actual brackets that should work ok.
Do you think the cross chassis bracing has to be directly behind the attachment point or could I get away with say 100mm either side?
(I only ask because there are already some cross chassis tubes but they may not be in the correct location!)
What is the best way of making the brackets?
Do you recon a single piece of sheet bent and then internaly welded along the bend would be strong enough?
If you use a substatial piece, id say 4/5mm would be good, start out with a flat piece, drill each end then bend it up. If you know someone with a press brake or even a fly press it will save you a hot of hassle
Probably a good idea to go to 4mm as Hitachimad suggests.
100mm each side should be fine, the cross tubes are just there to give some lateral support for the wishbone mounts. The bloke in the photos you posted hadn't added any and his car presumably hasn't fallen apart, although if he took it to Lotus Engineering for handling development the cross tubes would be one of the first things they would add.
A single piece of metal should be strong enough. Many specialist chassis are like that. Another alternative is to have a single 2mm U shaped section, and two flat sections at each end. Something half like http://www.vord.net/cars/mgb_mods/rear_susp/upper_arm_mounting.htm although I've used a battery mounting and a reinforcing plate rather than two flat sections.
Getting the thing welded with the liability problems we have these days might be a pain. It does need to be welded well (pigeon **** welding won't be any good for a suspension mounting as they are under large fatigue forces, and the consequences of them breaking at speed are reasonably serious.
I'd try some other fab shops, but don't tell them it's a chassis. Tell them it's garden decoration and you need a really good weld as you are planning to hang some really heavy pot plants off the brackets.
Otherwise trailer it down to Bedford and I'll bung them on so long as you promise not to sue when they fall off again. (I'm a DIY welder without qualifications).
Hi, If you want to do the welding yourself,why dont take a walk down to the local fabrication shop and see if they have any offcuts or lengths they might sell you,might be cheaper than the prices you have been quoted.