My neighbor's son has a Miller MIG welder he will let me use. He's done some repairs for me in the past but I'd like to learn and start with replacing the trunk floor pan. There are 4 settings for aperage/voltage(?). Has anyone used this specific welder or should I practice, practice, practice ( not a bad idea anyway ). My main concern is to get adequate penetration so I don't want to, for example, use setting 1 and have a weld that may look ok but not be solid. I plan on overlapping about 1", do spots at 1 or 2" intervals and then do some stitches between the spot welds. Is this a good approach? This is all leading up to floor pan repair/replacement.

Sheet metal is light gage, i would start off with the lowest setting and go from there. I use the lowest setting on my Lincoln.

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68SS ZZ4, 4sp T-10, 12 bolt, getting painted

78Z28, 330hp vortec, TH350, 10 bolt (just finished)

practice, practice, practice. Thats the best way to find out what the welder settings will do for you. Mine has 4 settings on it also and I use the 2nd from the lowest for sheet metal.

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67 Camaro SS Conv.
70 Challenger R/T Conv.

I'm assuming you are using the Argon/CO2 or just CO2 shielding gas, and not the flux core wire, flux core is not very good.

Keep the gaps between pieces as small as you can, and sand the joints with an abrasive disc.
Migs hate rust and crud, gaps, and wind blowing the shielding gas away. Screw the parts together if you have to.You need good ventilation to breathe, just not too much.

Hook your ground clamp as close to the work as possible. Avoid the current path running through any components like the steering box, differential etc. It can cause arcing inside where the bearings or gears are.

Get a can of weld spatter spray and spray around the area to keep the spatter from sticking. Also use tin foil or someting to protect the area. That stuff goes everywhere! Running a short arc helps reduce spatter. Play with the adjustments till the welder sounds like sizzling bacon, no popping etc.

Spot weld each corner, then between each corner then about every two inches all around, then in between each spot, then in between that, and so on.
Don't let the whole thing heat up. Take your time or take a break. If you see warping, try a hammer and dolly to straighten it out.

Keep a bucket of water handy and a fire extinguisher too. I keep a fire extinguisher on top of my welder.
Keep flamables out of the area.

Try a #9 arc welding lens, the brand with the crome like outer face works very well. The better you can see the better you can weld.
Most welding helmets come with a #10 or #12 shade which is for welding at 200 amps.
Good luck, David

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Check my web page for suspension info:
David's Homepage (http://ourworld.compuserve.com/homepages/David_Pozzi/)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Can Am Vintage Racer

I have a little Lincoln Mig-10 and I use it on the lowest setting with a pretty fast wire speed. To keep heat down, I almost skip weld in a relative fast motion. One problem you will probably find is that the old sheet metal will blow through before the new floor pan metal. If anything penetration will be the least of you worries. The big problem is getting all of the old pitting marks out in the old surface and getting the old edge super clean on both sides. When you hit those tiny rust pit marks that you've thought you had clean with the Mig welder, the sheet metal usually blows a 1/4" hole right through in that location. After a while you become an expert in filling up to a 1/2" hole with your little welder by using a circular fill motion.
I prefer to butt weld instead of overlapping. It takes more cut and fit time and more tedious panel alignment between spot welds, but it eliminates the lap area that will corrode quicker due to welding byproducts.
Another big problem is heat distortion. Even though you have tack welded in say 2" spacing. Even on the lowest setting after about 1" of a weld you can see significant blueing of the metal due to heat. If you are not a skilled welder, a compromise might be to treat the whole project as a spot welding affair. That means making adjoining spot welds rather than continuous beads, and alternating from area to area to keep heat disappating OK. It may seem tedious and unsightly to have 100's of spot welds laid end to end, but you can keep the heat distortion and discoloration down. Also, remember for every minute you spend welding, you will probably have three minutes of finish weld grinding afterwards.
Wait until you take apart the three sections to the seat support and them weld them back in. Boy what a royal pain that is!

All good advise. I just thought I would mention a few more things.

1. If you are just learning to weld stay away from butt welds if possible, they will only make learning more difficult for you.

2. Practice yes, but use a small piece of the new floor (you will more than likely trim it slightly) with a piece of the old floor. This way you will be practicing with the same metals you will be welding in the car.

3. Check the wire size in the welder, I like to use .023 for sheet metal. You will blow more holes using .030 because of the extra heat needed.

4. I like to clean the old metal off with those 3M "hockey pucks" on a die grinder, but beware 3M really like them (about $5.00 each, and they burn up fast!).

Good luck, Austin

THANKS FOR THE INFO!! man i learned alot just from reading this post ,it should be archived ,keep the responses coming,thanks again...

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70camaro(350)ground-up restification,350 slightly modified

The best way to avoid burning through the old metal is to work from the new piece into the old. Davidpozzi likes frying bacon and I like frying eggs....same sounds

Hi there you have gotten some good advice,the only thing I see missing is weld thru primer!3M sells it. USE IT! if you dont as soon as you weld those new panels together they will start to rust. It is the biggest reason for problems with replacing any panel we do hundreds a year and have had no come backs, yet I have seen alot from other shops that don't spend the extra time and money for this cheap insurance. Oh yea Don't forget the eching primer. Also try to duplicate the size, space and style of the factory welds. Good luck.

Chris, Do you use the Weld thru primer before welding the panels - then use the etch? This thread has been helpful since I am gettting around to dealing with my quarter panel in the next month.

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Jeff Bradway - my resto page: http://67camaro.virtualave.net

Weld through primer before you weld. Etching primer after welding is complete, use etching primer only on bare metal spots before priming.
Austin

If you are making just spot welds, or you are plug welding (through a hole in the upper panel to the lower panel that has no hole) you can use much higher heat. You will only be welding for a second and I do this with the highest setting on my welder. It takes MUCH practice but if you have it set on a low setting then you have to keep it there so long to ensure penetration that you create a lot of heat. If you weld these little spots with a lot of heat, the weld penetrates in less than a second and you have much less distortion.

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Fan of anything that moves human beings and is interesting or different

Good info, I just bought a Lincoln Mig Pak 15. Eastwood was running a sale on them a few weeks back. I just got done wiring my garage for 240V, so now all I have to do is start practicing by welding lawn chairs to my buddies' cars.

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Shawn Peterson
1969 Z28, 406SB
http://www.geocities.com/corsican69

Is there any benfit to plug welding vs. spot welding?