There seems to be two different opinions in this post on welding CM tubing. One implies it must be Tig welded, the other implies it can be Mig welded. Never tried Mig welding CM but was wondering if it was acceptable in the welding of smaller, lighter duty brackets. Not trying to hi-jack this thread, but hope someone might clear this up. Seems like an important issue here. Bill
Not sure whose information you are seeing, but as far as NHRA and SFI are concerned - ANY weld on CM to CM joints or that affect a CM chassis structure part, i.e. welding a mild steel tube, tab, etc onto a CM tube, must be done with the TIG process. Period.
There may be other places, or industries where MIG on 4130 is acceptable. Pipelines, etc., with a person trained and skilled doing it. But NOT on a piece of .083 tubing where heat needs to be tightly controlled.
Mild steel is not all the same. DOM, ERW, 1010, 1020, etc.
DOM - Drawn Over Mandrel is much more accurate thickness wise than ERW - electric welded seam. This is why kits and tubing made from ERW need to be .134" wall to ensure it passes a .118" sonic check for cert. This obviously adds 10% to the weight of it. DOM will pass and is typically within .0005". I've seen .120 ERW as thin as .113-.114. Years ago, when chassis certs became a thing, a lot of cars that guys had been racing for years and built from kits using .120 welded seam material, became junk. Cut it off at the frame rails and start over.
DOM is typically 1020 where ERW is usually 1010. This indicates the amount of carbon in the alloy which affects the hardness among other things. The difference is easily seen by running an 1/8" drill through pieces of 1010 and 1020 material of similar thickness. CM is 4130. The last 2 digits indicate the percentage of carbon. The price difference between DOM and 4130 is minimal. ERW is cheap s***. It may be okay for a cheap 8 point in an 11 - high 10 second car. I won't use it.
