Plug welding woes?

[boydy1989]

Am fitting a new sill to my MG midget...

Drilled out all the old spot welds, repaired the inner sill, no bother.

Thought id give plug welding a go, so i drilled holes all along the new sill, but i can't make it stick.

Inner sill is clean and shiny underneath, parts clamped up tight together. Using 6mm holes, 0.6mm wire. Little cebora on the lowest setting, with low wire feed too.

From the back, it looks like they have all penetrated just fine, but the sill just doesn't stick. What am I doing wrong?

 

[Wozzaaah]

Bigger holes will help no end, 6mm is just too small. Around 8mm would be much better.
I'd maybe go up a notch on the power setting too, the bottom one may be too low.

 

[boydy1989]

Ill give that a try... I did try a higher power setting, but it just melted through the back sheet too. Too long on the power maybe?

 

[Wozzaaah]

It's been a long time since I did any plug welding but I seem to recall the best way I found of avoiding blowing through was to start in the middle of the hole then work my way to the edge in a spiral manner.
Holding the torch still and allowing the weld to flow outwards would concentrate the heat in one place too long.

 

[cumbriasteve]

Although I don't normally work on cars, a friend asked me to plug weld for him..not really knowing what I was doing at the time, I did very quick welds on a setting well above the norm for the thickness and probably with more luck than skill they turned out great.

 

[boydy1989]

thanks, ill give it a try. Once i get some more tips... on Tuesday... waste of a weekend cos of no more spare tips.

 

[schnappi]

FWIW, when I changed a sill recently I used 6mm holes and the sill stuck fine. If penetration is OK on the back sheet, are you spiralling out far enough to melt into the top sheet? Sounds like you might be staying in the middle of the hole a little too long and getting a cold weld on the top sheet. With the 6mm hole it might be a case of you're filling the hole before you've really had a chance to spiral out. A bigger hole may help as you'll have more time on each plug weld, or you could try spiralling out just a little bit sooner.

 

[spudmini]

Big holes will help, start on the back plate, with 6mm you will be on the edge of the front plate which will take heat away from the back, causing non penetrating welds on the back plate. make sure you have the two pieces clamped together as they will work apart as heated. i got fed up and brought a spot welder. with minis its a must to get that "factory look". I always go one setting up on the power if plugging, dont know why just feels right.

 

[boydy1989]

more good info - thanks. How much is a spot welder? Its a Midget im working on bt the doris has a mini, im sure ill b welding it at some point.

 

[boydy1989]

ebay tells me that a cheap spot welder 'goes in the arc welder'... are these worth even considering?!

 

[Sean]

Nope

try upping the power to near max and winding the wire speed down, its not like trying to lay a bead its trying to get a small stable puddle with the welder just buzing

s

 

[piman]

Hello Boydy,

having looked at spot welders (too expensive for my use) they all seem to have a high power requirement so I doubt if a small arc welder would do the job. If it seems to be too good to be true it probably is?

Alec

 

[Chickenjohn]

Hello Boydy, from what you have written, it sounds the problem with the plug welds not sticking is not one of machine set up, but technique and prep.

I would also make an 8mm hole for the plug welds- get plenty of light on the job wear a reactive helmet and one way we were taught at college is to start the weld at the edge of the hole where the top and bottom sheets meet, run the weld in a tiny spiral ending up filling the middle of the hole.

That is one way that works. The other is to start the weld in the middle and spiral out, with the spiral where the top and bottom sheets meet. Plug welds are tricky as they require good vision and a steady hand. But with practice I'm sure you will get there.

Please post some pictures, we just love pictures of welding on here! ;-)

 

[boydy1989]

may get some piccs... my welding isnt pretty though im a touch shy!

ill try these tequniques too, the video makes it look so easy... The welds seemed to stick really well to the upper plate, just not the back one, so ill try a bigger hole and see where it goes.

heres a couple of pics...

 

[Chickenjohn]

Those look like overlaps. When restoring a classic you'd be far better off making the repair sections up accurately and butt welding them in. Overlaps trap moisture with bare metal inside the overlap and are rust traps. Your repairs will last far longer if butt welded.

The inner sill looks very pitted in the middle section at the bottom. I would cut that out and butt weld in new steel on the same gauge.

 

[boydy1989]

Thanks for the information! Ill bear it in mind.

Its my first ever restoration, and im fully prepared to strip it down entirely in a few years when I have the money to do it properly. Currently its intended to last a year or 2 of a bit of fun on a student budget.

That and, its a massive learning curve for how (not to?) to do it, on a classic that should be fun but also not that expensive, if it does go wrong.

 

[Paul.]

For an idea of what a sprite or midget restoration will involve have a look at the ones that I rebuilt.
http://www.mig-welding.co.uk/forum/album.php?albumid=743
http://www.mig-welding.co.uk/forum/album.php?albumid=724

 

[boydy1989]

wow... mine looks in very good condition by comparison! That is the kind of rebuild i plan to do in a few years, currently being a student means i don't stay in the same house for more than a year and dont get masses of free time either.

I start work in the real world soon though, so should have time & a touch more pocket money to play with...

 

[Chickenjohn]

Thanks for the information! Ill bear it in mind.

Its my first ever restoration, and im fully prepared to strip it down entirely in a few years when I have the money to do it properly. Currently its intended to last a year or 2 of a bit of fun on a student budget.

That and, its a massive learning curve for how (not to?) to do it, on a classic that should be fun but also not that expensive, if it does go wrong.

Good attitude!

I started doing some overlaps when I started on my Traveller restoration, by the end my welding and fabrication skills were up to doing all the repairs as butt welds. Neater- and you can paint both sides.

 

[chunkolini]

Plug welds? I tend to start i the middle, get a strong arc onto the base metal and spiral out to the edge, my plan is starting in the metal avoids cold lapping where it looks sound but just falls off, and gives a sound at the egde as well. I usually use an 8mm hole.
Try making a few test pieces using the methods discussed and then tear them apart.
Chunko'.