Question for guys using tweco mig guns

[TubularFab]

I recently acquired a Miller XMT 300 CC/CV welder and separately an older Miller 115v wire feeder (an S52 if I remember right). Anyway, I finally got around to hooking it all up an playing with it some. The wire feeder came from Ebay and came with a Tweco 400 amp gun and 10 or 11 foot lead. I installed new drive wheels and a new contact tip prior to trying it out. It came with a .045 contact tip in it and some .045 flux core wire, but I am running .035 mig wire.

Anyway, the wire feed seems to be very irractic. It'll weld good for a couple of seconds then start burning back, then go back to working well again. When you're not welding the feed seems very smooth and consistent. The only thing I find a little odd is you can easily move the end of the mig wire in/out about 1/4" - 3/8" at the tip without it moving at the drive rollers. I first figured I needed a different liner for the smaller diameter wire, but according to Tweco's website it's the same liner for both wire sizes. Is the liner just shot? I've usually only had liner trouble from them getting junk in them and bind up on the wire - not the opposite.

Also, can soomeone give a good explanation of inductance in mig welding? All I've found while searching is that more inductance = wetter puddle. What is the benefit of being able to adjust it? I've tried it in several settings from 0 to 100 on the knob but the other issue has kept me from getting any definitive results...

Thank you,
Jason

[ZTFab]

Inductance controls the rate of rise up to peak current during dip transfer.

Without the correct setting it will cause globules to explode out of the arc resulting in excessive spatter.

Too slow of a current rise will result in stubbing or starting problems.

The higher the inductance the lower the speed at which the short-circuiting current builds up.

A low inductance setting will give higher short circuiting frequency and a relatively cold weld.

High inductance will give lower short circuiting frequency and a relatively hot weld due to longer arcing periods between short circuits.

I pulled this from "EngineeringTalk.com"...hope it helps.

[TubularFab]

Yep - that is a good bit more detail than "higher inductance = wetter puddle"! Of all the MIG welders I've had access to over the last 16 years (around 25 if I'm remembering them all) this is the first that's had an adjustable inductance.

[ZTFab]

I never dealt with it myself. Let me know how it works for you when you get it going.

- Paul

[chopper5]

are the drive wheels for .035 wire? and what about the liner did you put in a new one? or blow out the old one

[TubularFab]

Ok, figured out the problem. Since the feeder came with the lead and gun installed and .045 threaded through it not to mention about 25 .045 tips and 50 .035 tips I jumped to the conclusion it had a .035 - .045 liner which is the smallest one tweco lists on the 400 amp gun. Turns out it had a brand new 1/16" liner - as in .065! No wonder the .035 wire was sloppy in there! With the right liner it now welds great.

[halbritt]

Oddly enough, I don't think the "inductance" setting on an inverter is actually inductance at all, but it has the same effect. I believe the control software actually drives the frequency of the inverter differently based on the setting. The net effect is that it will give a wetter puddle, but the thing to watch out for is that it can have a serious effect on the total amount of heat into a weld, so if you're running hot, you might end up getting too hot.