Need Some MIG Help

Hey All
I need some help with my mig welder. I mostly use Tig welding in the shop. And have 2 stick welders one an engine drive. I just bought a used Millermatic 250 mig welder. I have a structual steel welding job and I wanted to use the mig for that. I have done quite a bit of Innersheild & stick welding but haven't done any bare wire welding in years.

My ?s are.. I tried using argon since I allready have a tank that I use for the tig. Welds look like hell. Don't start well. Using .023 wire. Will probably switch to .035 Do I need to order a 75/25 tank? Will this cure the problems? I also want to use this welder at my farm for maint welding.

The structual job is at my daughters house she wants an open metal staircase built. Thought it would be better to use the bare wire than the innersheild from an apperance standpoint but maybe I'm wrong. Alot of the welding will be out of position. What do y'all say

Thanks
Scott

Nice machine! You should be able to make some very nice welds with it.
Check the following:
1. The gas is on and flowing at around 20 CFH
2. It's not too windy when you're welding
3. Metal you're welding is very clean (no paint, no rust, ...)
4. If could could describe more of the problem I could help more but "doesn't start well" if you mean like it's hard to get an arc going, try cranking up the voltage. If it does a big BANG sort of start and spatters all over, lower the voltage
5. Check arc length, should have around 1/4..3/8 inch of wire out of the nozzle.
6. Argon isn't really right for steel, it's hard to get good heat into the metal and the puddle behaves kind of funny.

How exactly do the welds look bad?

Don't start well? Look at all the ground connections. Some even advocate putting a piece of twisted bare welding lead under the ground clamp to improve the connection to the work.

100% CO2 is the cheapest gas and the bottles last longer.

If a weld looks good--it is good?

1-Argon doesn't work as you now know. Using Argon can't/won't/doesn't
work with MIG, period.

75/25 or hotter 90/10 is okay as well as switch to .035

2-Since this is STRUCTURAL and PEOPLE BEARING work done by novice with no mig
experience..........you should make and cut thru test coupons to simulate the joints
being used---both at the weld start and midway, push and drag.
--looking for full fusion (bantered about as "penetration"), toe wetout, bead shape; at various machine settings.

--you might be surprised at what you see and don't see; as well as 'where' one
has to go with machine setup to qualify the weld process

(On some deals--I have to go to spray due to material thickness/plate size, to get
fusion and wetting. Possibly-you might have to as well. Today, I just did a preliminary run of setup coupons with operator for his first time.)

Running coupons is a waste of time for 'real-pros' and 'experts'---who believe that 'if a weld looks good--it is good'.
That's 'Why?' not one shop in 100 will take time screwing around with
coupon or setup qualification nonsense.
That's also 'Why?' weldments exhibit mundane and sometimes dramatic examples of lack of process/operator qualification.

You need to confirm that the MIG has the polarity set for plain wire and not Flux-core.
I will NEVER buy .023 wire. I tried it once with my Miller 210 and thought I would never finish burning it. No where near the heat or penetration of .035! I can easily weld 16ga. with .035.
What I love about MIG is I could teach a 10 year old girl to MIG weld in 30 minutes or less!!!

Hey Guys,
Thanks for all the tips. Looks like the problem was the wrong gas. Got a bottle of 75/25 and the welds look great using both the .023 and .035.
Looks like problem solved

Thanks
Scott

welds that 'look great'

Scott R said:

Hey Guys,
Thanks for all the tips. Looks like the problem was the wrong gas. Got a bottle of 75/25 and the welds look great using both the .023 and .035.
Looks like problem solved

Thanks
Scott

Click to expand...

".....the welds look great...."

A weld, especially a MIG weld can 'look great', while lacking fusion.
Starts are notorious for being cold. Sometimes looks can be deceiving.

Repeating part of my previous msg.---
Running coupons is a waste of time for 'real-pros' and 'experts'---who believe that 'if a weld looks good--it is good'.
That's 'Why?' not one shop in 100 will take time screwing around with coupon or setup qualification nonsense.
That's also 'Why?' weldments exhibit mundane and sometimes dramatic examples of lack of process/operator qualification.


Setup coupon images below:

http://www.practicalmachinist.com/vb/attachment.php?attachmentid=31439&stc=1&d=1297474868