The terms “Spot welds” and “Rosette welds” are often interchanged in the DIY automotive world but they are two different things. A true spot weld is when two panels are pinched together and joined through an electrical current to fuse them together. A rosette or plug weld is when you drill a hole in the top layer, pinch the two panels together, and fill the hole; joining the two panels together. True resistance/spot welders tend to be large and are difficult to tune in. If you have a home shop and aren’t looking to invest the money or floor space you probably won’t have a need for a spot welder. These days most areas where a spot weld would be needed hobbyists are rosette or plug welding the panels together. This process is fairly simple, but there are a few tools and tips that help you get really nice welds that closely resemble and original spot weld. Below we show you the process for making a “spot weld” with your MIG welder.
Start by marking out even spacing of where you want your spot or plug welds on the metal. I like to try and center the weld in the flange or weld seam. You can than take a drill or a metal punch to make holes in the top layer of the metal. Don’t forget to mark the panel before disassembling the seam so it all fits back together correctly.
With the holes punched or drilled you can clamp the panel back together and take a set of spot weld pliers and clamp the seam or flange together tightly. You can the panels to be pressed together quite tightly so that you get a strong weld between them.
Next spin off the gas nozzle on your MIG torch and spin on the Spot Weld Nozzle. This nozzle fits most any MIG welder that uses tweco torch consumables. With the nozzle mounted you can next set the length of your welding wire. You want the wire to sit just below the standoffs on the nozzle. This allows you to get perfectly centered over the plug weld hole.
Remember that you need turn the heat/voltage up on your MIG welder as the thickness of the material is double now that you’re welding two pieces of sheet metal together. I like to run the welder hotter than the suggested settings so I can get a nice, flush weld. Make sure you practice on some similar thickness metal to get your timing and settings just right. A lot of the process is listening to your welder and watching the puddle as it forms. As soon as you see the puddle begin to fill up the hole you should be letting off of the trigger. I’ve found that the split second between thinking about letting off the trigger and actually doing it is all the time you need to perfectly fill the hole. If you’re having problems with burning through the bottom layer you can try putting a copper backer on the behind the bottom layer. A set of plug weld pliers also have the backer built in and may help.
As you plug weld each hole you can move your clamps along the panel. Make sure that you clamp the layers tightly together as once you weld them you can’t force the layers back together.
Hopefully that quick tutorial helped with your future spot welds on panels. You can see all of the welding accessories Eastwood offers by visiting our welding catalog HERE.