Mig or Arc?

Post by **webbnuts** » Mon Sep 14, 2009 2:07 pm

Hi peoples.

I have a rusty hole in my sill and only have access to an Arc welder at the moment. I have a peice of plate - will the Arc welder be ok on the sill metal? If i'm going to have more luck with a Mig then I'll hold off the repair until I can get my hands on one....

One other question, are gasless migs any good?

Thanks for any advice.

Webbnuts.

Post by **bmcecosse** » Mon Sep 14, 2009 4:06 pm

No - an arc machine will be FAR too powerful! It's likely even a MIG will just burn through what is probably well rusted sill metal - but you can try. For small jobs - some of the Mini lads use the gasless wire and say it's fine ! But for the dedicated restorer - only a gas machine will do. Note you can buy machines which can use either (the polarity needs to be reversible) - not all machines can do that.

Post by **Mick_Anik** » Mon Sep 14, 2009 8:58 pm

I'd wait for the MIG - in the meantime, maybe, you can cut out the rust with a grinder, make a nice hole with right angles, and pop-rivet in a temporary plate.
I have used an arc welder on a car - a horrible experience.

Post by **pegasus** » Mon Sep 14, 2009 9:17 pm

Wait until you can get hold of a mig, arc is a bit powerfull for car body. The gasless migs have the advantage of not having to get hold of the gas but the wire is rediculously priced and the wire arcs at a lot higher temperature than gas sheilded mig wlding, so if what you are welding is a bit thin it will still blow holes in it, it is also smokey. If you are looking for a mig try to get one that goes down to as low amps as possible for car bodies 25 - 30 amps is about right. I have a dual gas/gasless mig it is nice to have the option to swap but i have only ever used the spool of gasless that came with the machine and never touched it since i only use the gas shielded.

Post by **bmcecosse** » Mon Sep 14, 2009 9:59 pm

And do remember to disconnect the alternator (if you have one) before doing any electric welding.

Post by **cormorant** » Mon Sep 14, 2009 11:25 pm

Gasless is pretty useful if you have to weld outside like I do - otherwise the gas just blows away and you are left with a poor weld.
Machine Mart (Clarke) welders seem to be pretty good for the money if on a budget. With a mig you always need to cut a bit more out, right back to good solid metal, better to chop a big bit out than spend ages trying to "fill" blown holes in thin steel, this doesn't really work anyway.

Post by **pegasus** » Tue Sep 15, 2009 7:29 pm

The Clarke welders are very good for the price and they come highly recommended on the mig welding forums, (its worth taking a look around this forum). Cormorant makes a very good point about the problem with gas and welding outside, it is something to consider when purchasing.
What ever system you choose good luck with your repairs
Mark

Post by **bmcecosse** » Thu Sep 17, 2009 11:06 pm

Inexpensive arc welder coming up at Aldi! Yes - it's no use for bodywork - but it IS useful for lots of other things!

Post by **webbnuts** » Mon Sep 21, 2009 1:11 pm

Thanks for all your replies. I managed to win a SIP MIG on eBay, so picked it up Saturday. Had a go yesterday and am pretty pleased, but the bead was quite high, which I guess is because I had the wire speed set to high thinking about it?

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Post by **webbnuts** » Mon Sep 21, 2009 1:13 pm

Whist you are here, what should I be using to treat this metal and prevent it from rotting? I was thinking either waxoil under body paint, or red oxide and then a top coat?

Post by **listerjones** » Mon Sep 21, 2009 2:37 pm

All three. Red oxide followed by some primer then top coat, then lots of lovely waxoil.

Post by **bmcecosse** » Mon Sep 21, 2009 5:34 pm

You won't get paint to stick on top of waxoyl! bare metal should be reated with 'rust killer' (usually contains phosphoric acid) then a zinc rich primer - then a good solid top coat. The 'garden gate' black paint in the £ shops is a very good chassis paint! Sryao liberal amounts of waxoyl into the closed cavity after all the painting is finished.

Post by **cormorant** » Mon Sep 21, 2009 9:50 pm

[quote="webbnuts"]Thanks for all your replies. I managed to win a SIP MIG on eBay, so picked it up Saturday. Had a go yesterday and am pretty pleased, but the bead was quite high, which I guess is because I had the wire speed set to high thinking about it?

Could be wire speed too high or welder not on a high enough setting, experiment on a bit of scrap. It's easy to do a Mr Blobby with mig but you do need good penetration for the sake of strength

oh and some people mix engine oil/diesel 50/50 as an alternative to waxoil.