Help with MIG question...

[Your Old Dog]

I'm welding up some bandsaw blades today. The brazing didn't go as well as I liked. I did much better with MIG.

The question is, my Miller Matic 135 has the gas bottle with it. I think it's using too much gas. How much are you supposed to use when welding indoors out of drafts? I open the main valve about 1 full turn and the regulator the one metering gauge to the unit is reading 30. It's adjustable with a screw. Is that too much or wastefull on this small unit? What would be a good place to start with for pressure.

My one bandsaw blade came out perfect and strong as rest of the blade. Problem is I lost the little dinky wrench that comes with Harbor Freight 4x6 so having a bear of a time adjusting guieds for thicker blades. It came with .030 blade and new one is .036 Starrett variable pitch 10-14 x 1/2inch

[Mike W]

You should open the cylinder valve all the way. I use 20 cfh. It sounds like you have a flow meter as opposed to a flow guage but that is ok. I have always silver soldered my blades.

[mochinist]

The desirable rate of gas flow depends primarily on weld geometry, speed, current, the type of gas, and the metal transfer mode being utilized. Welding flat surfaces requires higher flow than welding grooved materials, since the gas is dispersed more quickly. Faster welding speeds mean that more gas must be supplied to provide adequate coverage. Additionally, higher current requires greater flow, and generally, more helium is required to provide adequate coverage than argon. Perhaps most importantly, the four primary variations of GMAW have differing shielding gas flow requirements—for the small weld pools of the short circuiting and pulsed spray modes, about 10 L/min (20 ft³/h) is generally suitable, while for globular transfer, around 15 L/min (30 ft³/h) is preferred. The spray transfer variation normally requires more because of its higher heat input and thus larger weld pool; along the lines of 20–25 L/min (40–50 ft³/h).[12]

http://en.wikipedia.org/wiki/Gas_metal_arc_welding

[torker]

20 is plenty. You can actually cause porosity with too much gas flow. The higher velocity sucks bad air in from behind the nozzle. I see this all the time with the young guys who work for me. Instead of cleaning the nozzle or the difuser, they keep upping the gas pressure. "Duh... I got 60 cfh of gas and I'm still getting air bubbles in my weld"
Russ

[Your Old Dog]

You can actually cause porosity with too much gas flow.

Well there you go! That's probably why my weld almost a full ride around the bandsaw before breaking! Actually, I think I failed to reset the roller guides and everything was working pretty hard. I'm sure my weld was flawless !!

a picture of my other welded blade to follow asap.

[loose nut]

Mig welding or any other welding of a bandsaw blade is going to leave the blade brittle. They have to be annealed before use. Silver soldering of the blade is probably the best way, it is tricky, for a home shop that doesn't have a proper blade welder.

[Scishopguy]

Help with MIG question... ANNEALING

I have wondered about mig welding bandsaw blades in the past and figured that it should work as well as induction welding, like the blade welders do it. The thing that you don't have with the mig is an easy and quick way to anneal it. I figure a quick shot of heat from the bernzomatic torch should do the trick. The secret is that you only want to bring it up to "dark cherry" in color. If you heat it to bright red you have messed up and it will be brittle. As soon as I get the old junk bandsaw I rescued fixed up I will have to make up some blades and that should be a good test.