Two questions about Bugeye floor panel weld drilling

[BillyBud]

Drilling out old rusted floor panels, I intend to MIG weld in new panels. Will have to drill out a billion spot welds. I have cobalt spot weld drill bits, 6mm and 8mm.

1. Which side is preferable to drill from, top or bottom?
2. 6mm or 8mm bit? Both seem to work equally well so far on test metal.

Thank for your experienced advice.

 

[BillyBud]

 

[Jim_Gruber]

I used a Spot Weld Cutter rather than a straight drill bit. Seemed to work fine just keep it lubricated, Cuts out the top layer but leaves the one below intact.

 

[BillyBud]

Can you answer question #1?

 

[DavidApp]

I think you need to drill from the underside so you remove the floor material leaving the structural members intact.
This info was gleaned from watching you tube videos. I have not got to that part myself. That will be coming up in the future as I have holes in my floor.

David

 

[Bayless]

I think you need to drill from the underside so you remove the floor material leaving the structural members intact.
This info was gleaned from watching you tube videos. I have not got to that part myself. That will be coming up in the future as I have holes in my floor.

David

I did not have to do that but based on my memory of the bottom side, I would tend to agree with David.

 

[apbos]

I only needed to do the boot. I rolled the tub on its’ side on some tires and an old mattress. A plasma cutter or grinder with a cutting wheel will give you a thin strip that will help you peal the metal after removing the spot welds.
Regards
Paul

 

[BillyBud]

Thanks all. I have some front end scrap that I have practiced on to remove the welds. Now I think I should also practice welding the metal back like I will have to do with the new floorboards to see what works best. Below is a photo of my practice, but...I am inclined to change my method and drill from the top because when I have to weld the new steel on I would not be able to do that from the bottom through the new steel floor pans without knowing what was above. I'd be welding blind unless I drilled holes, another complicated step to get right. Think about it and I think you'll come to the same conclusion. I just have to practice welding through the top hole so I make the least mess possible.

 

[Rut]

Thanks all. I have some front end scrap that I have practiced on to remove the welds. Now I think I should also practice welding the metal back like I will have to do with the new floorboards to see what works best. Below is a photo of my practice, but...I am inclined to change my method and drill from the top because when I have to weld the new steel on I would not be able to do that from the bottom through the new steel floor pans without knowing what was above. I'd be welding blind unless I drilled holes, another complicated step to get right. Think about it and I think you'll come to the same conclusion. I just have to practice welding through the top hole so I make the least mess possible.
View attachment 73017

I like to drill all the way thru with at least a 1/4” drill and then weld the floor thru those holes. I also use self tapping screws to hold everything tight while I weld. Also cut the vent out to weld to the new floor pan or make a new one.

Rut

 

[apbos]

I like to drill all the way thru with at least a 1/4” drill and then weld the floor thru those holes. I also use self tapping screws to hold everything tight while I weld. Also cut the vent out to weld to the new floor pan or make a new one.View attachment 73019
Rut

The late great Tony B even suggested auto body panel adhesive might even be used if everything could be made to align. I’ve always wondered if a combination would be the ultimate way to bond and seal everything together.

 

[Rut]

The late great Tony B even suggested auto body panel adhesive might even be used if everything could be made to align. I’ve always wondered if a combination would be the ultimate way to bond and seal everything together.

I used the same painter as Tony and we had some discussion while he was working on the Bugeye, but everything ended up being welded. I’ll be putting a drivers side floor pan in a TR4a this winter and I’ll probably use adhesive along with spot welds spaced much further apart. I’ve tried to pull glued sections apart on a Miata and it’s just as tough as welds.
Rut

 

[BillyBud]

Great practical advice Rut, thank you. I am not familiar with "body panel adhesive", didn't know there was such a thing. Can you provide a link or reference? Thanks again.

 

[Rut]

Great practical advice Rut, thank you. I am not familiar with "body panel adhesive", didn't know there was such a thing. Can you provide a link or reference? Thanks again.

There are several good brands…check out YouTube videos to get an idea of when and where to use them.
Rut

 

[JPSmit]

more and more modern manufacturers ues them in structural panels including BMW

 

[BillyBud]

I have noticed that the factory panels have some kind of tar substance I guess to seal them or perhaps limit vibrations. Perhaps this could replace that on the new floorboards to some degree, filling gaps, etc.

 

[BillyBud]

Thanks Rut and Apbos, I am finding that a plain old 1/4" drill bit seems to work as well as any specialized weld remover bit, although cobalt is probably the best choice for longevity. I think if I cut away the majority of the old floor and just leave the welded strips I will find that they push away if you can start from one detached end of metal. As soon as you go through the top layer the bottom releases and bends away, so no need for chiseling or anything else, and a minimum of drilling. This is another test panel to illustrate. The big holes are 8mm and small ones are either 6mm or 1/4", indistinguishable from each other. 1/4" seems sufficient to remove spot welds, I don't think anything bigger is needed.

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