I'm close to working on my convertible again (yay!!). First up is repairing rust on the inner rocker panels under the carpet. I took an intro to welding class a few years ago at my local community college. I'll be using the opportunity to practice and learn. Most of the work will be done by a buddy who used to weld for Toyota.

I'll be borrowing a coworkers mig welder and using flux core wire. It's a 100 amp Lincoln though I haven't found out yet what kind of duty cycle it has. Is that going to be high enough amps to do the work? I've done a little reading and from what I've found it will depend on the gauge metal on the floor boards.

I was hoping to hear back from some people who have done some welding on our cars. Should I be putting feelers out with friends and coworkers for someone with a different welder...though I want to stick with mig, not tig simply because the buddy doing the work and teaching me prefers mig.

 

100 amps is plenty for sheet metal work. In fact the trick is to use the absolute smallest wire that the welder can run. You can always turn the feed up if you get into thicker sections. I don't have much experience with flux-core but when I have a lot of sheet metal work to do I always use straight argon or at least 75/25 argon / co2. Save some of the scrap you cut out to practice with. Get comfortable with the settings and try different hand-arm positions so the entire length of weld is easy for you to get to and see as you go. Stop and re-position as it gets difficult to reach. That and clean,clean, clean the surface, easier to get consistent results that way.

 

From talking to the coworker loaning out the welder it can be converted to gas but I hasn't been and unless the coworker gets inspired to upgrade his welder it won't be happening. Unless I find another welder to borrow then gas won't be an option.

Through work I can get 26ga sheet metal for free....I think we have some 24ga also, but I imagine those are going to be too thin to use for my patches. What gauge metal should I be getting?

 

Agreed, that's plenty.

Also, run your bead in a C pattern, not a zigzag.

This -> ccccccccccccccccccc

Not this -> vvvvvvvvvvvvvv

 

gas will help with the very fine sheet metal work, with bodywork you'll likely be on very low heat setting anyways so the amps are more than you will need.


with thin stuff you want to do wide arcs and try not to heat up your puddle or keep going over it before it has cooled some. starting the weld is the trickiest part, since most welders immediately want to blow a hole right through thin sheet metal. unfortunately migs have no control over initial amperage like a tig, so you likely will blow a hole through the work to start.

 

Get an auto-darkening helmet from harbor freight.

 

I put in new floors in my Jaguar E-type and switching from .030 to .024 wire was really helpful. I have a Hobart 120v Mig that is perfect for sheet metal (you're probably looking at 20g for the rockers). I got it with a tiny tank from cyberweld.com for about $800 IIRC. The HF auto darkening helm works fine as well.

I would pony up the money for gas if I were you as thanks to your buddy for lending you the welder. Flux core is really messy and apparently much more prone to blow thru. Even pure CO2 is more blow-thru likely than 75/25. And nothing will ruin the experience like blow thru, trust me.

Have you checked with local equipment rental shops to see if they have mig kits? Local welding supply shops may rent complete kits as well. I've never personally used flux core but everything I've read says if you arent in an open windy field you don't want to use it.

I'd also pick up a HF flange tool. While butt welding seems "pure" and "professional", but for interior and support pieces the flange will give you a stronger repair and make blow thru not an automatic given.

Greg's Garage on YouTube has a really good video on mig butts and fixing blow thru. Worth watching.

Another helpful learning I had was the importance of copper or aluminum backing places. Just some smashed lengths of copper water pipe held behind the weld area will dramatically reduce blow thru.

Have I mentioned blow thru blows chunks? Chunks of hot molten metal?

And for any lap welds make sure you use a good weld-thru primer. I really like the SEM copper one.

Good luck. Frankly I've come to enjoy welding in panels but it was ugly for a while there!

Jim

 

Thanks for all the feedback, I've got 10 hours or so on all the different types of welding.. acetylene, stick, mig and tig. I've got all my safety gear stuffed away somewhere. But my friend will be doing most of the welding and I'll be mostly watching and learning on one side and I'll give it a go on the other side of the car.

I may break down and buy a welder after Xmas....though I really want to use that money for a megasquirt (wanna move away from Rtek) I work in HVAC and I may be able to get tradesman pricing. I know at HVAC and electrical supply shops I get tools and equipment cheaper if I'm buying them out of pocket than my employer gets if it's for a job or going on my truck. But that's at supply houses I'm in daily where they know me. Anyway, if I can get lower costs than retail I'd have to consider it.

I may borrow the welder for a weekend and just play around with it. I'm betting I'll need to get something thicker than 26 or even 24 ga metal. I'd like to find out before I need it if I'm going thicker.

If I need to I can hit up a buddy at a shop I used to work for. They do a decent amount of commercial/industrial rooftop units and work in thicker metal. They may have partial sheets of metal they are scraping which are large enough for my purposes.

 

Good points, thanks

 

I had not thought of renting, thanks for the heads up. I'll look into it.

I had def not thought of using backing plates for blowthrough and I have all kinds of copper piping on my work truck, thanks again for the heads up

 

While you can perform sheet metal floor pan repairs with flux core, I'd recommend for your sanity to not do so unless you only have a few small repairs to make.

First, the tinnest flux cored wire you will get is 0.030". That's on the thick side for sheet metal and flux core actually burns hotter than MIG. Great when you need to weld thick metal on a small machine, bad for sheet metal. Another issue is that in order to shield the weld, it really does take a second or so for the flux to form a gas cloud. With short tacks, you are going to get very poor shielding and thus fairly poor welds. Running longer tacks will burn through.

And then there's the splatter. It's unavoidable with flux core and fairly extreme. It will triple the time it takes to clean up the welds, especially combined with the necessity to put down much more metal than is necessary with flux core.

Thirdly, flux core is not really an ideal process for low currents. Most flux core machines don't run well at low wire feed speeds simply because there isn't enough flux being feed into the weld to maintain that shield. They tend to pop and spit, laying the weld on top of the seam which will then go away when you grind.

Fourthly, the higher heat of flux core means a hell of a lot more warpage. Probably less of a concern on a floor pan, however still, you don't want to have to beat the panels to all hell in order to have a flat floor. The warpage also makes it a pain in the butt to grind as the weld sinks, or pops up.

With the gas shield you can go down to 0.023" wire which is going to make your world a far happier place. No splatter to clean up, and you also have options in wire. There are wires specifically for automotive repair that contain large amounts of deoxidisers and are far easier to grind. Anything that decreases grinding time is a necessity.

 

I really don't have a lot of repair work to do on the floor pans. I haven't ground off the rust yet, but from under the car it runs from the inner rocker panel and goes down the length of the rocker panel about 1/2" to 1"wide and ends before the rear wheel well.

 

With really thin stuff that's unsupported and to help with blowing through the material, if it's feasible, I put a piece of brass beneath the material. I bought just a brass length about an inch wide from my local mom & pops hardware store. You can also use soft brass tubing and just hammer it flat. It gives you somewhere to start that's also not as thin as what you'll be welding. This is particularly important as welders tend to have quite a bit higher starting amps than whatever it's set at (assuming it's not scratch or lift start)).

 

They say that rust is like an iceberg... you can only see 10% of what's there.

 

If you haven't ground out the rust, then you definitely don't know that you only have a little repair to do.

 

I'm estimating how much rot is there based on previous experience with my first car a 67' Firebird.

The rust I have is not substantial, I simply want to take care of it while gearing up for rebuild and other body work.

 

If I could comment to add perspective, not that any is needed, I must say that this is all great advice! I made repairs to my 1st gen floors, A-pillars, rockers, B-pillars, spare wheel well area and everywhere in between with a cheap HF flux core welder. Let me say I learned that I should have spent the extra few dollars for a decent Mig welder... Lots of blow throughs, LOTS of splatter, and impossible to butt weld the thin sheet metal. I had the most success with 1/8 to 1/4 inch lap joints. I could roll the weld bead up to the upper overlapping piece and it would consume the lap on the bottom side. The flux core made a mess of the job tho. And that SEM copper weld thru primer is great stuff.


I also learned that, at least on the first gens, that Mazda did not spray the inner coating inside the rocker panels all the way forward to the A-pillar or all the way back to the B-pillar. It stops short about 12 inches or so. That, salty New York roads, and a nice sized mouse nest made for one rotten rocker panel/B-pillar/floor/wheel well area.

I'm not sure if the second gens have the same issue or not, but thought I'd mention that. I hope you have great success with your repairs! Would love to see some pics of the job as it goes along.

 

i used 0.8mm wire and plain co2

 

Good news, today I worked with the coworker who has the welder to loan out. He bought it with gas already setup. I misunderstood him when we first talked about it.

 

Your project just became a lot more pleasant!

 

If its the same spot as mine(going by ur desc, it sounds like it is) ur gonna have some you cant see. I was amazed at the amount of rust my "rust free" car had. Never noticed it untill i took the sound deadening off and then i found the first hole which made me cut it open a little. Ended up chasing it all the way up to the firewall and also found some inside the rocker. The other side is also getting cut open now.

Started as this



Then i cut all of this out and found more









Then i found some more and cut more floor out so i could fix this hole.

 

I've repaired mine with a Flux core wire welder from Harbour freight and used sheet metal from lowes. You'll want to use some seam sealer and paint it afterwords to prevent flash rust and leaks.

 

I decided to change focus. It'll be easier to do this work once the car is mobile and I can move it to a better location.

It's presently sitting outside with a zero compression front rotor. I don't have a garage within "just push it" distance.

Instead of doing this work I'll focus on getting the engine pulled and torn down. I'll start the winter focusing on the engine and electrical issues...see where things stand come spring.

 

Personally, I'd shoot for finding it a home. I know lots of people that used storage garages. They were able to find some pretty cheap ones, I don't know about that market in your area.