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Fixing up tin tops - spot or mig welding
garyo - 5/5/10 at 01:33 PM

I know nothing about fixing up tin-tops with panel damage, and have only ever done bespoke fabricating for silly cars using a MIG.

Is it widely accepted that using a spot welder is preferable to using a MIG, since you can get into tighter spots, and 'hide' the weld as an invisible weld pool where two panels touch?

Alternatively, I can see that you could drill out the old pot welds then MIG the hole back up using a form of rose weld.

Cheers

Gary

MikeRJ - 5/5/10 at 01:43 PM

MIG works fine, especially if you have one of the nice joddler tools that incorporates a hole punch. It may need a touch with the linishing disk to be invisible, if it matters.

NS Dev - 5/5/10 at 01:44 PM

I restore cars for a living now and I still don't have a spot welder.

I plug (rose) weld all areas that need to be "spot" welded, and seam weld in any areas that I am butt welding in to repair panels.

There are occasions that a spot welder would be useful, but the mig is much more useful for 99% of work.

BenB - 5/5/10 at 01:54 PM

I've always seam welded with the MIG then skimmed with some filler on my MOT jobs and worked fine for me...

NS Dev - 5/5/10 at 01:58 PM

filler.....a dirty word in my workshop!!

Does a job though!

britishtrident - 5/5/10 at 02:08 PM

You can actually get special shrouds for mig welding plug/rose spot welds.

There was a good page on the net written by a US guy restoring a VW camper van who experimented to find the best way to plug weld with a MIG. ISTR he recommended clamping a stainless steel bar to the reverse side.

skinned knuckles - 5/5/10 at 02:34 PM

personally i prefer TIG for everything. MIG is faster but tig is more controllable and welds ally better.

BenB - 5/5/10 at 02:39 PM

quote:
Originally posted by NS Dev
filler.....a dirty word in my workshop!!

Does a job though!


Only a light skim and because I'm heavy handed with the flap disc on the angry grinder!

RedAvon - 5/5/10 at 02:50 PM

Could you guys recommend a MIG please I'm fed up with trying to do small stuff with a stick welder - need it for all usual DIY car related stuff - thinking of Clarke 150TE (turbo) Machine Mart £293 ?

Thanks

MikeRJ - 5/5/10 at 03:27 PM

The Clarke MIG welders are about the best of the "cheap" far eastern machines. Lots of people on here have them. Avoid the SIP/Cosmo welders, they have a number of flaws that make them a PITA to use.

The 150TE will be more than adequate for anything you'd need to do on a Locost.

[Edited on 5/5/10 by MikeRJ]

garyo - 5/5/10 at 03:45 PM

Thanks for the replies guys.

So when I've drilled out some existing spot welds, should I make new plug welds in a different location, or should I attempt to use the same holes, in which case I guess I need a backing piece - e.g. the stainless steel bar suggested above.

So gravity doesn't make MIG a pain... even if upside down?

Are there any tricks for minimising splatter and spark damage, other than lots and lots of sheets?

Gary

garyo - 5/5/10 at 04:06 PM

quote:

filler.....a dirty word in my workshop!!


Much respect to anyone that can get a paintable finish without filler. MIG tends to be very hard compared to the surrounding steel - how do you get a good finish on this when using mild steel car panels that may contain compound curves? Angle grind it down with a keen eye and lots of skill?

Gary

Mark Allanson - 5/5/10 at 04:09 PM

Using a flap wheel and NOT a grind wheel helps, it keeps the heat down so minimising heat distortion.

MikeRJ - 5/5/10 at 09:02 PM

quote:
Originally posted by garyo
Thanks for the replies guys.

So when I've drilled out some existing spot welds, should I make new plug welds in a different location, or should I attempt to use the same holes, in which case I guess I need a backing piece - e.g. the stainless steel bar suggested above.


Depends which panel you are reusing, if it's the top one (i.e. the one you start drilling into) then you'll want to reuse the holes you've made.

If it's the bottom panel and you've drilled out the spot welds with the proper spot weld cutter, it should have minimal damage to it, you just need to grind the bumps off it and you are good to go

NS Dev - 6/5/10 at 08:22 AM

quote:
Originally posted by garyo
quote:

filler.....a dirty word in my workshop!!


Much respect to anyone that can get a paintable finish without filler. MIG tends to be very hard compared to the surrounding steel - how do you get a good finish on this when using mild steel car panels that may contain compound curves? Angle grind it down with a keen eye and lots of skill?

Gary


LOL we do use some, just not much!

I can get simple stuff good enough that build primer does the trick. More complex joints get lead loaded.

We tend to lead load to waterproof and strengthen though, and then take out any scratches and sanding marks in the lead using filler..........

I just hate using it too much!

On our website, if you look at the pics of the bedford CF van, I did all the engine bay welding well enough that it never needed any filling before paint.

RedAvon - 6/5/10 at 08:46 PM

Thanks for the replies on the MIG - think I will go for the Clarke 150T or 151T.

Cheers
Ian