Best way to go about this job...

[hooblah]

I'm making a removable crossmember for my car. I've currently got the centre chopped out of the original cross member and I will be making the replacement out of box section.

My idea was to use 5mm plate welded to the cut ends of the chassis. Then bolt on 5mm plate to each end with a length of box section spanning the gap.

Ive never welded thick plate to thin sheet before, can anyone offer me any advice when doing this? Is there a better solution?

I've got a Cebora pocket turbo 130 mig using 0.6mm wire BTW, I've also got a CEA Matrix 200 ac/dc tig. Which would be better suited for the job?

 

[Badger1bear]

just out of curiosity....what are you trying to achieve ?

 

[Wallace]

just out of curiosity....what are you trying to achieve ?

Looking at the additional bellhousing clearance my guess is the sump for the bigger engine fouls the pesky crossmember!

 

[hooblah]

Bang on

 

[the snooper]

is your plan going to be strong enough ? are those the track control arms bolted to whats left of the cross member you are going to need to stop any movement of the chassis rails

 

[hooblah]

Those are the lower arms. If done properly it should be strong enough. The wall thickness of the original cross member I'd say was ~1mm. I'll be using 20x20 box section with 2mm wall thickness. I may even double it up for extra strength.

There will also be another crossmember at the ends of the chassis rails. There's no chance of it moving then.

 

[Wallace]

It may be 1mm wall thickness but the shape of the upper & lower pressings will be giving the strength and it's likely to be part of a crumple zone.

 

[hooblah]

True... But I think were way past worrying about crumple zones now lol.

 

[the snooper]

I would say 20 x 20 box would be way too small and even though it may be double thickness the amount of steel / strength will be far less

 

[Wallace]

What V8 is it?

 

[hooblah]

Hmm well if that's the case then I'll consider putting in something a bit more substantial. I'll have to check the clearance when the engines in place.

Straight six turbo diesel

 

[norlander]

when welding fick stuff to fin stuff I always strike up on the thick and walk the puddle over to the thin and back to to the thin and so on.
Arc (stick, mig or tig) can be tricky -tig is my preferred choice for that then mig (but i've only just started using mig).
If feasible I might choose Oxy A-(but you haven't got that- but I have and thought I'd show off).

Think I would consider using mig with 0.6 to spot the plate in place then pulse weld (stop n start) stitched runs (weld 2" then shift to weld another 2" bit away from where you just welded).
Then, I would fit 0.8 if possible and fill in over the first welds and into the thicker stuff to fatten up the fillet.If the original x member is 1mm thick you might be able to run 0.8 wire from the off?

BUT- I have never done any car work like that, have only just got a mig set up and I reckon you should hang on until a more xperienced bloke comes along and comments if you can wait a bit.

Is that your panel beating hammer in the picture?

 

[500e]

Will have to polish the face norlander if he wants a good finish
Look after the motor is in, maybe cut further back & fab a complete new X member.
Have you braced suspension, chassis rails and got a lot of measurements, surprising how floppy it all becomes

 

[the snooper]

i think i would remove a good bit more of that crosmember cap the ends off and weld some angle to that plate above and below where the crossmember will be then simply drop a couple of bolts through if you need it to be removable, but make sure its a decent piece of box for the corssmember or it will flex and eventually crack due to the forces from the track control arms

 

[hooblah]

Thanks for the help guys. It looks like its 2mm thick steel that I'll be welding to.

I've been having a bash at it over the past couple of days and it's proving to be a major pain in the **** to cut the crossmember back so its square. I can't cut too much as those round holes on top are for the engine mounts.

The plan is to cap the ends off and bolt a removable length of 60x40x3 box section in place. I was originally going to use 3mm plate to cap it off but it seems a bit thin now, so I'll be using 5mm instead.

Any suggestions for how to mark and cut the ends so they're square? There's literally nothing I can use for a datum!

 

[Wallace]

Fabricate the crossmember and bolt the end plates on then trim the car to accept the whole assembly. Depending on how much flex you have on the two remaining parts of the original crossmember, I would add a thin shim between each end plate to be removed after welding in place to give some clearance for removal.