how are you guys filling this crap in?

i've been doing a lot of metalwork lately on my 31 cab and was wondering how i could get rid of the undercut the welds seem to produce. it seems like no matter how many times i go back to try and fill my passes in, it cut's into the metal just a little bit.

so is there some sort of metal based filler or would bondo take care of that. my welder settings are spot on, i just find it hard to believe i'm the only person to ever face this problem haha

 

Is it undercut or is it warpage? You're dealing with 19 ga. If it's actually undercut, I'd say you're doing a fair job of blowing a bazillion holes too. Let's see some pics. I do a LOT of sheetmetal work and for me it's all about controlling warpage before it becomes an issue. Hammer and dolly work is essential from start to finish.

 

heres a crappy sideways photo of what im talking about. the piece has already been fully welded in and grinded down, but theres still traces of the work:

 

turn your wire speed down.

 

The picture is pretty blurry so it's pretty difficult to see what going on, but it looks like you have alot of warpage.

 

Clean it real good and do a light cover of solder (lead). It will not stick to "burned" or blued metal nor will plastics. It's gotta be clean. Metalprep and a scotchbrite work well, stainless wire brushes help too. Don't wail on it with a standard carbon steel wire brush in a die grinder or drill either. The wires in the brush will leave deposits and plastic or lead will not bond to it.

 

undercut on sheetmetal?

we need a better explanation of the problem to help.

or a clear picture

 

Yep, need better photo & better explanation, 'cause if you can undercut on sheetmetal, then the undercut itself would actually cut all the way through the sheet metal. I see undercut pretty much everyday, but that's 0.095 & thicker material.....

Usually, undercut is corrected by slowing down the oscillation so that your giving the filler metal enough time to 'fill in' for say......when your going to fast, the arc cuts into the steel & your going to fast to leave a complete deposit of weld. Carl Hagan

 

I think I know what your question is.What you are seeing and feeling is a small under cut on each side of the bead. If you can back off the wire speed a little and the amps alittle too.And Hammer the weld while it is red ,On a dolly ofcourse.You dont have to Kill it just nice easy raps This Keeps it from srinking the bead and warping things. And as said clean it good with stainless wire brush . Then lead or mud it.

 

It is more than likely a result of shrinking due to the welding process which is pulling the bead of your weld down. The only way to correct it is to stretch the area out as mentioned by rtp with on dolly hammering. The tough part is that mig welds are hard and can crack from doing this but it can be done. If you don't want to go down that road then just a skim coat of filler or lead will do the trick.

 

looks to me like its a combo of warpage and not having the panels lined up right before welding. But, like others said, hard to tell in the pic.

 

theres no warpage going on, those are just marks from the gringing wheel. let me try and get a better pic

 

heres two more pics, one with a flash and one without. i also tried to sand out those grinder marks to make it more clear.

i guess what my question is...will plastic filler adhere to this, or will i be creating myself more problems later on

 

The bondo should stick fine. But it looks a lot like the metal is being pulled in by the weld and not under cut at all. You probably need to dolly the section back out, gind, planish, planish some more. Maybe even give it a little heat to get things moving again, but I doubt that it is the weld cutting into the sheet metal.

Make smaller tacks, let it cool down longer between welds. Planish and dolly it while welding it.

Of course it is easier to type it out than it is to do it...

 

with that much weld in one spot your never gonna get the low spots out its gonna crack and crack and crack . whats up with the big spot of weld was it buring through? if so the metal around it is probably thin as hell too . a whole bunch of variables here . if your just gonnna mud it over why do ya care about those spots? the second pic looks like it is warped to hell

 

Yea, looks like you are getting it a little too hot. Do one tack at a time, and don't go back until you can touch it with your bare hand to get the least amount of warping. Also, making sure you have tight, consistent gaps before you start welding will help.

 

i think i see what you are getting at...its not sanded up to a invisible repair

theres the odd low spot around the welds , is that what you are unhappy with? if so id say alot of folk are happy to bondo or lead that up

only the best of the best can do 100% pristine work ...id be happy with what i think i can see in your pics

 

yep.

 

I think we get spoiled by looking at some of these bare metal cars that we see at shows or in the magazines. These are done with tooling, specialized equipment and a lifetime of experience and skills. I want to do work at that level too but I know my limitations and thats why I love bondo. I get that same "undercut" right around the edge of the weld too, I'll have to try some of these things explained on this thread to hopefully get a better weld. I can never get the hammer and dolly on the hot weld right, but I'm still trying to learn. Maybe I should shut off this computer right now and go practice the Divco.

 

IMHO, most body shops would fill that with plastic filler and never think a thing of it. A good tight setup, frequently spaced tack welds and tig/gas welding would be the way to go. Mig welds are brittle, and and dont lend themselves to extensive hammer and dolly work. When i first started welding sheet metal I was miging it. I have experinced similar affects. Personally i feel that the machines ablilty to adjust on a finite level is limited. Wire diameter limits you ability to lower the heat setting to anything that is manageble.

In the past results like that for me have occured when my setup is shitty, and i was using the spot weld method with a mig. I dont know how much of it is you, i think it is the technique more or less.

 

exactly. i was just making sure it'd be ok to fill in. thanks for all the help guys.

one more quicky, what would you recommend for trying to continue that body line that stops at the door. am i SOL because i dont have a bead roller

 

I agree that the mig weld is too hard (brittle) for dolly work- short of tig welding the panel and using a dolly to restore the contour- how about using a torch and rod to weld the panels. Using a filler rod instead of a mig wire might give you the advantage of slowly tacking and welding the panel. This would also allow for the dolly work as the panel is welded. If welding the panels perfectly wasn't extremely difficult we wouldn't be amazed when we saw the work of experts.

 

Looks like everyone else hit the nail on the head.

You're heat shrinking the crap out of that seam. It's not the end of the world though. If only you could remove the interior panels of most of the cars at shows you'd find the same thing. lol

If you get a chance see if you can get a hold of Bob over at Atomic in D town. He's a super nice guy and would probably be willing to let you stop by and possibly lend you some pointers? You'd have to ask. Very nice guy and into the same stuff.

 

I clean all the crap out of the valleys before any filler is applied, a wire brush or a spot sandblaster will do the trick.

 

I like to use a filler called All Metal made by a company called US Chemical to cover welds. If there is any chance that any moisture will get through the weld the bondo wont hold up. The stuff is hard to sand though so I only put enough on to seal the weld. Use bondo of your choice to finish it off. My local Napa carries it.

 

Looking at the pictures I would say there is nothing wrong. You grinded down your welds good. Just feel the panel so see if it is ready for bondo and smooth some on. If it is not ready then dolly it out first.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>