SIP Ideal 150, Argoshield Light, 0.8mm wire, 1mm+1mm plug welds for car sill, 6mm plug holes, weld through primer

[SirDick Diodenob esquire]

I have watched the forum tutorials and a few dozen youtubes making plug mig welding look easy. I am just about ok with arc for thick jobs and good with oxy acetylene car welding and am thinking about giving up on mig and getting my old BOC portapak out and renting the bottles, it seems so much easier than mig but I will persavere a bit longer as even the small oxy and acetyline bottle rentals are now a rip off. I have sprayed the practice pieces with proweldc which I think is a weld through copper based primer. The sill needing replaced is 71cm long and the good bits that are not rotten on the inner sill were originally spot welds so I am hoping that plug welds will be ok for the mot ? The whole length of the outer sill is normally covered with a plastic cover. I have checked the earth connections which are low resistance , setting 2 for the wire speed, worked up to setting 3 for voltage and still no good apart from seeming too high , done about 20 tests none of them penetrating the proweldc, does this stuff work or is it a waste of money, should I clean it off around the weld area, I see some comments by youtubers advising not to weld through it but I was under the impression that is the point of weld through primer.

Edit ; Just measured the drill bit properly, my plug holes are 8mm and not 6mm.

 

[BrokenBiker]

Wire brush will probably solve your issues...

 

[SirDick Diodenob esquire]

Wire brush will probably solve your issues...

Thanks , wired brushed the proweldc completely off then gave it a go with a grinder to make sure it was all off, just done 5 practice plugs and they are much better, I think they will be good enough for the mot provided I can get them as good in the vertical when I do the actual sill, nowhere near as nice on the rear as the forum tutorial photos so the penetration is not perfect but the welds seem strong. Maybe I should up the voltage again when I do the job tommorow as there are three layers, an inner vertical , a middle inner sill and an outer sill, its only the outer sill thats rotted away but still that means having to do the plug through the outer sill then weld through the two inner layers of 1+1 mm, maybe I should be drilling the middle inner sill with a milling bit with a flat end on it ?

I am really ****** off with myself for spending 18 euro on the so called weld through primer which seems to be a bit useless or even counter productive maybe I am just using it wrong, I can still probably use it but seems no better than a cheaper primer maybe like Bondo. I also bought a can of Auto Extreme Rust Proofer which I will squirt inside the sill once its done, this was a bargain price of euro 1.60 for a 400ml can. In the olden times when I was doing sills on Austin 1100s and Morris Marinas I would just weld the new sill over the old one , normally they rotted through again within about three years maximum, it didn't matter much as preformed outer sills cost about £2 and the cars were absolute rot boxes so it was inevitable that something else would crumble away first but the car I am working on today I have had for 6 years and hoping to get another six years out of it.

 

[BrokenBiker]

turn the wire speed down a sniff and hold the weld a little bit longer, will get a bit more heat in to the metal which will help with penetration but gives you a bit more control over melting through compared to turning the voltage up. its all really down to personal preferance though, personally i run way hotter than you would expect but travel a lot faster as well. plug welds for me are more of an on/off than a weld you can look at and evaluate while its happening but i will get full penetration every time.

as for the MOT, most average testers wouldnt be able to tell the difference between a good weld and a blob of body filler

ive spent all day evauating a car that had an mot 3 weeks ago and i can fit my fist through some of the holes ive tapped away with a screwdriver in the sills and boot floor.