I'm thinking of attaching the floor by drilling a 5mm hole every 5cm in the floor sheet and welding through it to make a spot weld.

Can anyone think of a reason for not doing this?

I've tested a sample and it's very strong. Also, it shouldn't cause any distortion this way.

Andy,
The main disadvantage I can see is that it won't be as effective as a seal to avoid dirt and water getting in to the seams. You can seal it from the inside obviously as I have done to avoid rain getting into the seam from the inside but I chose to seam weld the bottom of the floor to provide a hard seal against ingress from the outside. Rubberised underseal might be good enough but I didn't want to reply on it.

Cheers,
Craig.

I am planning on doing that myself, anythoughts on an order to perform the welds, I was thinking of spotting all the corners then the centre of tube runs and filling in in that sort of way to try and eliminate distortion

I had a steel floor that went dunk everytime you stood on it. cut it out and replaced it with ali. The scary bit was the rust that formed and this was a car that was stood in the workshop for a year before i bought it see archive

I used 8mm holes, its called plug welding, and used all the time in production cars. Make sure you use weld thru primer.
Rescued attachment Spot Floor1.jpg

... I also used 3m structural to seal the outer edge, there was a little localised burning but nothing to worry about. You will get some distortion though - with steel its unavoidable and expected.
Rescued attachment Spot Floor2.jpg

Mark, iv'e notice before looking at your photos the quality of your build looks 1st class, just though id'e pass my thoughts on to you.

I welded my floor all the way around in order to achieve a complete seal. Following advice on the yahoo site, I stich welded it, allowing it to cool in between. I've had no distortion and no dunk either.

Gee chucks, thanks!

It gets to a point where you are pleased with everthing you have done so far that more time is spent on getting everything just right - the upshot of that is that you take longer doing everything - you just cannot win can you!!

Ian,
Yes I did something similar. I stitch welded the outside edge then stitch welded the inside edge 1 inch for every 6, alternating sides and front to back then seam welded the outside 4 inches at a time, again alternating front-back, side-side until it was a continuous seam. I got some distorsion but certainly nothing worth worrying about.

Hopefully nobody will ever see the bottom of my car other than me and the SVA inspector anyway!!!

Cheers,
Craig.

We used to call it button welding. Turn the power up a notch and make sure your floor is clamped down tight to the tubing. Use an 8mm hole maximum and weld to the tube underneath, not the edge of the top sheet. If you are turning your side alli under it should seal the edges from the outside anyway and you can mastic inside but the paint should seal it. edit:- Grind the burrs off the back of the panel if you drill them. If you can get hold of a joggler/hole punch it will make life easier.

[Edited on 27/8/04 by Peteff]

Mark, are those holes all the way through the floor tubes? or just divits from the initial drilling?. I am pretty sure i will going this route with my floor as well.

Thanks
Dale

I used a spot drill to drill the floor, the marks in the chassis are just the 'spin' marks

Has anyone else thought about bonding the floor in place - fully sealed, quick, no distortion and strong.

Read Murphy's law rule 1.

Thanks for all the feedback!