So I really am not good with any of this ......... but the thing I hate/struggle the most with is when I tack weld up a piece - it looks fine ...... quench ..... do in sections ...... BUt then I try and grind the weld back ..... and flatten out like you see fabricators do (fitzee) etc for a smooth finish. I then bang along the weld seem to look for anywhere I've gone too far and thinned out. If it looks "suss" I tack weld there to see if it will hold ... nope EVERYTIME Now I end up having to do a big weld to fix out the blowout ......... a lot of heat, warp ... and time. I dont get it. Im guessing the answer is I'm no fabricator/fitzee ..... and everywhere where I've patched is going to have at best a skim coat and maybe up to 1/4" think of bondo to straighten out and I shouldn't be worried about grinding it back so aggressively. thoughts ? PIC is of me starting to attempt to "patch weld/fix" the spot after blowthrough after griding.
Try using a heavy piece of copper or brass as a backup. Clamp it in place on the backside of your seam. Quenching a weld makes it hard and it won’t bend. Weld slow and let it cool before proceeding to the next part of the seam.
Sorry guys - not really the welding thats the issue Its the grinding back ..... meaning by time I grind the weld back ....... I've cut into the sheet metal and its paper thin.
I use a 3” grinding wheel on my air cut off wheel to grind just the weld down, try not to grind off the weld onto the sheet metal
What type of grinding , grind just the weld , Also while hot , dolly & hammer Looks like mig , To much heat, do small stitches, & brass or cooper on back side if you can get it behind. What wire size , Try .023 if you using .030 or higher Tighter the gaps are better
Lot of good information on here about welding but remember that grinding also generates a lot of heat. On thin material, do a little bit here, a little bit there, let it cool. If the parent metal turns blue, you're staying in one spot too long, keep moving. Start grinding away from you and bring the grinder back to you. If you do this, you won't be as likely to push your grinding wheel into the parent metal and you can actually see when you get close. It took me miles and miles of dressing welds on top of oil storage tanks to learn this. When I started welding, I was taught immediately to not let my welds pile up above the parent metal. You're wasting welding wire and time and you have to grind more off. Practice, practice, practice, you'll figure it out.
I disagree. You’re showing us blow through at a weld seam. Not grind through. Warpage is caused by using too much heat while your welding. Not normally grinding. practice practice.
I think the picture confused people ...... this was AFTER ........ let me walk through steps below. 1) When I butt welded the two pieces together - I had the ENTIRE run done without a single blowthrough. 2) I then grind the weld back with a grinding wheel 3) I then sand it back with a sanding disc to get smooth 4) I tap along the seem hard with a hammer - if I feel a "spongy" bit - I know it might be soft 5) I then tack weld that to "re strengthen it up" --- this is where the pic is taken. Its now paper thin ... I mean paper thin ... I can weld 20 GA without blowing through all day long ..... this is like no longer even as thick as razor blade. I think the answer is to not bother grinding it back so far ..... doesnt have to be smooth since bondo going back on top ? but .... *shrug*
eg would leaving it like this (more on the left) - be ok ..... so I dont risk cutting into base sheet metal
Basically you have ground the metal paper thin. Only grind THE WELD, nothing else. I use the edge of a cut off disc to carefully take down only the weld. And don't quench it. Same both sides. I will often do this after every run of tacks then tune the join with a hammer and dolly. Slowly and carefully. Also, with a mig, the weld will be harder than the surrounding metal. If you use a flat, flexy disc the abrasive will eat into the surrounding metal faster than the weld. So while chasing the weld, you're really losing the sheet metal more.
Read every word that X38 wrote. Then read it again and understand it. Don’t skip a step or try another way. Truth. The only thing I would do differently myself is use a TIG welder, but that can be the next step after you have mastered the MIG. TIG’s have a softer weld that is much easier to grind and smooth.
Use the edge of the wheel, an hard wheel and only grind the weld. The disc/wheel should be 90° to the parent metal, It’s like surgery with skilled steady hands. If the weld has sunk and you can’t grind the weld without touching the base metal anymore then tap the weld up with hammer and dolly and grind a little bit more. Be careful not to get too hot with the grinder. My helper was having a hard time getting it. I painted over the weld and told him to grind the weld and don’t take the paint off the parent metal. It’s not a race, get accurate first. It’s about hand eye coordination, fine motor skills, and patience, then you can pick up speed. Also you CANNOT grind out a low spot, you’ll make a hole. Grinding 1/2 plate is different than grinding 20 ga.
This weld question and answer post has got me wondering.. Can an overly enthusiastic welder, (with a lot of time and mig wire) build a complete '32 Ford coupe body just out of weld, .... weld bead welded upon weld bead until a complete body exist?
You could, when you back up a hole with a copper block, you can "make a panel" using just spots. By the time you finish, there will be no gas left on the planet.
In the 1930's custom body work was gas welded, and any extra weld was filed off. I never understood the MIG welding beads twice the thickness of the sheet metal that have to be ground off. TIG beads are far flatter.
I contend it is your welding. There is no penitration. Where you have ground the weld I can see the original seam. What does the backside look like? If you can see the seam, the metal was not fused together. That is why you have "soft" spots. You just ground off the only metal that was holding it together. Your panel fit looks good enough for a fusion weld with gas or tig with no filler. Get some test panels, set up on the bench and turn the heat up until the welds are fused all the way through.
57 Fargo nailed it! That's exactly how I do it. This way you're grinding the weld only. Get it almost flush with the surrounding metal then finish with a 36g disc on a 5" pneumatic sander. Don't get too aggressive. It doesn't have to be perfect. A skim coat of Rage will make it so.
The Shielded TIG approach is definitely the preferred apparatus but MIG economically fits in many more Hotrod budgets...and that's generally unshielded flux wire as the Shielded gas MIG is more money too. On top of that many are not even 220 volt machines and wielded by learners... ...all my ASSumptions aside once the practise practise practise, read, read, read and do, do, do any combination of these can make a Hotrodder smile but the mastering of the approach is imperative to a good outcome regardless of caliber of equipment INCLUDING the grinding and finishing which is equally challenging... Good thread...as it's part of read, read read and learning by asking questions...
110 machines are fine for welding sheetmetal, though 220 are a much better investment. Flux wire sucks for sheet metal, shielding gas is much easier and neater.
So I was taught how to weld sheet metal tacks on a piece of sheet metal. Not joining two pieces, just spots all over it. When you get a good tack spot, it’ll leave a bit of extra metal on the back side. Once you get the hang of that being repeatable, then start doing some scrap practice pieces. Teaches also how to set your welder up for heat and wire speed. Also how far to keep the wire away from the metal, how much wire to let stick out. I use gas, and with my side cutters I don’t cut the wire after a weld (to get the “ball” off the end flush) I I do the opposite with the cutters so the wire sticks out a bit. I mention the last part because I see the remnants of the wire in the pic, makes me think you may be putting the wire directly on the metal when you pull the trigger. Anyways, I’m no instructor, was given some tips, the told to “practice and burn up a lot of wire”.
Clean, clean, clean. Needs to be what? Clean. That's 1st but guess what, no matter how clean it will find a way to be contaminated. Imported stock is dirty within. Old is just old but it welds cleaner. There's a fine line between burning right thru and that soft and supple puddle when doing MIG. It's best with a helper that can peen or planish each weld while it's still red and cooling. Not always an option. Gentle reheating, sort of the most unscientific method of annealing, can help if you have a fix on that fine line. Can't let it warp. .023 is almost the ONLY choice for sheetmetal welding. If it wasn't so damned expensive now EZ GRIND would be too. Softer yield, for those who need PhD input, nets better finishing results. Can it be done? Yes, and yet I always remain suspect as to longevity. This is all .023 mig, and I too ground thru and had to re-weld in 2 spots, which I backed with a big aluminum block as a heat sink. No mud will be used...
Hold the abrasive wheel at 90 degrees to the weld and cut with the thin edge. More control and much less heat, I did 64 feet of sheet metal welding on my first project and got pretty good after a lot of practice. Also I back up all the welds with a sheet of copper
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