TheSamba.com :: View topic - Lap welding with a MIG? Questions and tips?

Wed Sep 28, 2016 1:12 pm

I'm starting in on body work on my bus. The front passenger floor patch where it overlaps with the wheel arch.... There is a lap there. I drilled holes through the patch panel where it over laps to weld into, that I can grind smooth. Not really working well. They don't weld tight together and little less than half don't hold. Should I just run a weld along the edge and forget trying to match to spot welder from the factory? Or am I doing something wrong? I'm painting both inside surfaces before hand then when I drill the hole it exposes bare metal to weld to.

Wed Sep 28, 2016 2:13 pm

screw the two panels together with sheet metal screws then try welding. You can fill the screw holes by plug welding them.

Wed Sep 28, 2016 2:18 pm

Probably getting contamination from the paint. Try using a weldable primer. Make sure the two parts are as tight together as possible.

Wed Sep 28, 2016 2:47 pm

OK I think weldable primer is in order! Nothing else is going to work.
And screwing them together makes sense.

I'm going to seam seal this one from below and move on but thanks.

Wed Sep 28, 2016 2:49 pm

Possibly you need to turn up the heat and maybe turn down the wire feed. It needs to kind of BUZZ sound like bacon frying on a very hot pan.

Wed Sep 28, 2016 2:59 pm

A friend locally said to hit the weld with a big hammer while it's still hot and it will flatten them together tight. Worth a shot!

Wed Sep 28, 2016 3:10 pm

How big of a hole are you drilling?

Wed Sep 28, 2016 3:27 pm

1/4" or so?

Wed Sep 28, 2016 3:37 pm

deltabrent wrote: 1/4" or so?

1/4" is plenty.

Wed Sep 28, 2016 3:39 pm

deltabrent wrote: A friend locally said to hit the weld with a big hammer while it's still hot and it will flatten them together tight. Worth a shot!
Only if there's something heavy behind it to back it up.
1/4" is lots but do make sure you are penetrating the lower layer and not just refilling the upper hole.

Wed Sep 28, 2016 3:55 pm

When I did the sill on my cargo door I did 1/8" and it didn't work at all. I drilled them all out and redid them bigger and had but better results. The front floor hasn't worked as well though.

Wed Sep 28, 2016 4:21 pm

deltabrent wrote: 1/4" or so?

For a beginner you might want to go bigger, maybe to even 3/8". You want to light up the weld on the body first and then weld the hole edge of the sheet metal you are putting on to that lump of weld on the body, all in one motion.

Wed Sep 28, 2016 4:42 pm

Sounds like your welder isn't set up/adjusted right. You likely are not getting penetration with your welds if they are coming loose. Try turning it up a bit. Should be getting a nice crackling sound for a good weld.

Wed Sep 28, 2016 4:47 pm

OK I'm getting convinced to drill these out and do it again! Maybe try turning up the voltage. Thanks.

Wed Sep 28, 2016 7:10 pm

Sounds like it needs more heat. You need shielding gas to get any kind of good results also, otherwise my advice is to not even bother. Also, when doing rosette/plug welds cleanlines, prep and being well clamped together are important as others have stated.

A quick tip, go watch some YouTube videos of panel welding, in particular listen to the sound you hear from other people's welding. Then go practice on some scrap metal that's a similar guage to what your working on. play with your welder settings until you can duplicate a good sound, before you even worry about how the weld looks. Leave the bus alone until you figure out what's going wrong....there are a lot of variables and a lot of damage can be done

Wed Sep 28, 2016 7:13 pm

what kind of welder you got?

Wed Sep 28, 2016 10:46 pm

Practice on two pieces of similar metal not on the bus. You should be able to melt a hole from top to bottom with just the welder without drilling a hole. If you can't do that, not enough power, contamination or wire speed is too much.

(Also hold the nozzle closer to start the weld). Er, I'm just assuming you are using a Mig welder here.

Wed Sep 28, 2016 10:58 pm

If you really want to pull the pieces tightly together then you need these-
http://www.aircraft-tool.com/shop/detail.aspx?PRODUCT_ID=KWN-1%2f8
They are made for riveting, but you can use them to plug/spot weld also. Pricey, but worth it IMHO. I use regular Clecos all the time. These are on wish list.

Thu Sep 29, 2016 3:03 am

I bought one of these a few months back but haven't tried it yet. It looks like it would make doing stuff like that a bit easier and is relatively cheap.
http://www.eastwood.com/spot-weld-kit.html

Thu Sep 29, 2016 8:01 am

Make sure that you're drilling all the way through the upper panel and exposing bare metal underneath. I like to really crank up the welder to rosette weld. I use a 220 V MIG, 175 A, turned up to about half it's power. (C setting on a Lincoln). I snip the wire, then put the wire in the middle of the hole you drilled, holding down the panel with the edge of the copper shielding gas nozzle. This gets the full blast of the shielding gas around the weld. Pull the trigger and don't move the weld too much, just lead it around to the edge of the hole until it fills. If it blows out the bottom, adjust your trigger technique and give it short blasts. The weld should flow out and not be a big mound.

Just an FYI; Weld through primer is somewhat of a misnomer. If you're rosette welding a plug, the paint must be removed if you want a clean, strong weld. I hate using that stuff as it takes so long. But it's easier than replacing the panel again!