What's the best way to go about welding up rust pinholes? The rust has been sand blasted Iv just put a coat of black paint from a can to work out the highs and lows of the panel

I never really welded before other than mucking around with it when I first got my mig.
Should I use gas or gas less for the pinholes?
What type of welding wire is recommended?
and how can I weld them up without blowing through and making it worse?

 

I removed your duplicate thread. As for repairing this - you're going to have a tough time simply welding the holes closed since the metal is so thin there now. You would be better off cutting out the area and putting some new metal in place - that comes with it's own challenges though!

If you want to try welding the holes up, make sure you use shielding gas, and the thinnest wire you can get (0.025" seems to be the common thin wire I can find here, not sure what that is in metric). Basically you want to build up metal around the edge of the hole - kinda like a dam around the hole, then connect the sides of the dam. It's hard to explain, but basically you need to make the area around the hole thicker before you try filling it in. You'll want to do this in very short bursts, like a split second - a series of tack welds basically. Holding the trigger any longer will create too much heat and surely burn holes in it.

Give it a shot - if you're just blowing more holes into it you can always cut it out and try patching it with new metal later

Hope that helped

 

I would cut out the bad area and welded a new piece in,the rust is probably 3 times the size of what you can actually see on the back side.

 

i don't think it would be hard to weld those closed...definitely use shielding gas and go in small spurts (like tack welding) on each hole to close them. another trick is to use a cooper welding spoon behind it since it looks like u have access to the other side (google this if ur unfamiliar).

 

Thanks 82transam I forgot to put a question mark in the title so I made this thread.
Yea I want to try and avoid cutting it out and welding in a patch as Iv never done it and will probably warp the panel badly, the panel is from a series 1 rx7 stone tray wich the metal is pretty thin to start with.
What type of wire should I use just mild steel?
Looks like I might have to get myself a gas bottle and a regulator(the money spent on this car doesn't stop lol)

So start a bit wider than the hole and work it in till the hole is covered?
Do I "tack" weld then let it cool off before pulling the trigger again?
I know every mig welder is different but what's a good setting to start off with and fine tune from?
Sorry for all the questions.

What about if I used fibreglass mat for the underside and put some body filler on the top to seal it shut?

I might give it a go, there's a few places on the body that need patch panels welded in, so probably no better time to learn how to weld beats paying for someone else to do it
Thanks for the info.

 

Iv sandblasted both sides of the panel, it's solid just has those pinholes but looks to be a bit thin around the holes where it looks like low spots.

 

Me either Iv seen it been done before but never had to do it myself.
Shielding gas and tack welds seem to be the go.

Yea Iv read around about using copper behind the panel, the weld won't stick to it and stops you blowing through the panel I'm pretty sure, I'll google and look into it.
Thanks for the advice.

 

which is panel is this? it may be easier to replace with a better second hand one - or even new one - certain panels are still available new in Australia.

 

It's one of the panels from the stone tray on a series 1 rx7, are these still available new?




The savanna metal one piece stone tray that came with the car needed a bit of work, these are the second hand Aussie delivered ones I bought off vince at just rotaries these were the best pair he had.

Is there a way to find out what's still available new at mazda?

 

I didn't bother trying to weld mine, which were quite a bit more eaten away than those. After killing the rust with electrolysis, and sealing it with POR-15, I fiberglassed the back side of those panels and used body filler to fill in the holes.

 

They are nice and straight! I'd chance welding it since its not really visually important. As already pointed out, use gas, thin wire, short bursts, low amps. And start awy from the edge of the hole. If possible get some copper or alluminium clamped up tight on the back side to draw out heat. Doesnt matter if it doesnt file back %100 mirror smooth. you can finish **** like that with stonegard. Will look magic.

 

You should be good then. I would go to harbor freight and buy a welding spoon,it's made from either copper or brass,weld won't stick to it,and it absorbs some of the heat,hold that behind it when you weld it to help with burning through around the thin metal

 

Yea I was thinking about using fibreglass on the back side then body filler on top. Did you sand the por-15 before you put the fibreglass on?
How long has it been since you have done it, Iv read around the metal and fibreglass don't expand the same in the heat and after a while the fibreglass will seperate From the metal but I'm not sure how tru that is.

 

They were a bit wavey and had a bit of rust but other than that there solid.
Will any copper do? I'll have to go have a look at Bunnings/hardware store for copper when I go get the shielding gas.
But I'm still undecided how I'm going to repair it I don't want to warp the **** out of the panel, but I guess I won't know how it will go till I give it a shot.
If it doesn't file back smooth I might use the stone guard but I'll have to use it all around the bottom of the car otherwise it will stand out.
Thanks for the info.

 

we don't have harbour freight here in australia I wish we did they got some nice tools, I'll have to ring around a few welding shops to get the copper/brass spoon your talking about.
Hopefully I can repair the panels this weekend and get them in primer asap, then it's onto the next part of the project.

 

I looked it up. Its just a piece of copper with a handle on it. You could make one out of whatever. I often use aluminium scrap behind thin and delicate jobs - it works well. Actually, I always thought aluminium had better heat conductivity even than copper.

 

That's even better I'm pretty sure the flat bit of sheet metal that's been laying in my shed for years is aluminium I'll just cut and bend it a bit and bolt a handle onto it or just clamp it behind the job. I'll have a look tomorrow

 

Sometimes I just serve as an example of what NOT to do!

I did not sand the POR-15 before I put the fiberglass on, and already the fiberglass is coming unbonded. BUT, it's on the back side, and I've already done the bondo work on the front, soooo... I consider it a finished product at this point. I can always replace the panel later if I have to with the piece I got through Black Dragon.

Welding it up is definitely the best way to go. Good luck!

 

Haha doesn't matter you gotta learn somehow at least you gave it a go

It's not a half bad idea as fibreglass flexes and won't crack in a hurry.
if you had of scuffed the primer before putting the fibreglass mat down and mixed the resin properly it would last a fair while. You should be right as the por-15 should seal it from rust just keep an eye on the area.

Thanks I've started painting another project this weekend so this will have to wait till probably next week.