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Q. As always, I love your articles – they are full of useful advice. I have a Lincoln 125 MIG welder (with shielding gas) that I have taught myself to use during the rebuilding of my ’57 Chevy pickup and my ’55 Nomad. The question I have is about the end of the outside shielding cone. Where should the end of the center electrode be?
The position of the contact...
The position of the contact tip, just inside the nozzle of a MIG gun, can have a surprising effect on the quality of a weld.
When I purchased the welder, the end of the cone was proud of the center electrode about 1⁄8 inch. I was having problems seeing what I was welding (welding .035-inch sheetmetal), but pressed ahead and learned to work with it. I was having the biggest problem when trying to weld the inside of a right-angle joint, since the cone keeps the electrode too far away. So I cut the end of a new outer cone off so that the electrode was proud of the cone by about 1⁄8 inch, I can now see what I’m doing a lot better and welding in tight corners is a lot easier.
Over this past weekend I was online viewing some instructional tips on MIG welding and noticed on one, the guy’s welding tip looked to be the same as mine, or even protruding more than 1⁄8 inch. Could I go out to 3⁄16 inch or 1⁄4 inch? Should I adjust the gas pressure higher to compensate for not having the cone as close?
South Yarmouth, Massachusetts
Via the Internet
A. Normally, the contact tip inside a MIG gun is manufactured to be a precise length, but you can buy different length nozzles that will determine whether the contact tip is flush, protrudes or is recessed. Some guns have an adjustable nozzle, so you can “dial in” the settings you want. You have a little leeway with the alignment with the contact tip, but for most folks like us, it may protrude about 1⁄8 inch, be flush, or be slightly recessed.
One of the biggest factors you are dealing with here is the welding wire “stickout,” or the distance between the end of the contact tip and the base metal. The longer the stickout, the more the voltage increases, which in extreme cases can cause excessive spatter, slower travel speeds, and arc wander.
You may be able to get a nozzle with a smaller diameter, which will allow you to get into tighter recesses – check with your local welding distributor for this. I don’t suggest raising the gas flow over what’s recommended (usually no more than 20 CFH) – that can cause turbulence, which may actually draw air into the arc, fouling the weld.
Q. Every time I see a pro or amateur cool a weld with air, water or a wet rag, I just cringe. Aside from the damage this does to perfectly fine metal, it’s guaranteed to lock in extra-hard work removing oil-can dents in sheetmetal.
Patience is a key to good bodywork; let the welds cool on their own. We’ve all been told to space your welds, let them cool and move around over the seam as you weld. Also, keep the amount of heat in the weld area to a minimum. Only when you can rest your hand on the weld is it time to continue welding in that area. The area doesn’t need to be cold, just cool enough to touch. Woodworkers call this patience time “waiting for the glue to dry,” and they use it to do other things. Use the time to visit with the wife or kids, drink a beverage or start another project; just don’t make more unnecessary work for yourself. Your column is still the first thing I read in the mag.
Via the Internet
A. I’m completely onboard with you in the belief that chilling very hot steel with either water or air can lead to problems. I’ve learned that steel, even the low-carbon steel used in classic trucks, will get harder if you cool it too quickly. I agree that it’s best to let all welds cool naturally and to wait until they cool before adding more weld in the same area! I like your reference to how woodworkers allow time to “let the glue dry.” I think this has some great carry-over for builders of cars and trucks! CT