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Old 12-30-2016, 10:59 AM
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Getting butt welded sheet metal joints smooth

Guys, I often view this forum when I need help with my fab projects. I decided to finally join. I have a problem that I have been unable to master. This has been going on for years. I can not get butt welded sheet metal panels smooth. I either have low, pits (shrinkage) around the welds as shown in the pics, or I grind too much away, get pin holes in the metal and then burn thru a lot when fixing the holes- showing how thin I've made the parent metal.

The part in these pics is a mini wheel tub that I am expanding further. I cut an aftermarket tub and added a slice to the inner rear section where I thought it became to tight for the tire.

I originally had the tub welded up and welds ground down. I used a flap disk to grind them flush with the parent metal and then used the edge of a 3" cut off wheel on a small die grinder to make the panel look smooth. Finally I finished with a quick go over with and 80 grit 2" sand disc to blend it all together. Then I hit the welded seams with a planishing hammer. There were tons of pin holes in and round the welds. I filled those, ground them flush with the parent metal, and the product at this point is what you see in the pictures.

Again, I have never been able to master this. How do you people get these patches to fit perfectly flush so you can't even see the weld seam? Is this the result of me using too much heat or having too big of gaps between my butt welded pieces.

This tub and projects from the past have always been under my car or hidden. I want to stretch my car's fenders and make wheel flared though, so I will need to know how to make perfect butt welded seams on an exterior body panel. I'm extremely frustrated.

I am not new to welding sheet metal and especially am not new to welding in general. I'm using a lincoln sp-255 220v wire welder with 75/25 and using .030 wire. .023 doesn't work worth a crap in this welder no matter what I do. I realize .023 is best for this type of stuff but I can not get it to function. I do have a miller syncrowave 200 TIG welder and did some of this welding with that (cutting perfect shaped patches to elliminate gap and be able to TIG from there is a whole nother subject and skill I need 2 master 2!!!)), but I had up to 5/16" gap in some places on this tube, so most of it was MIG'ed with the Lincoln. Please help!!!

j





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Old 12-30-2016, 11:36 AM
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Body putty
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Old 12-30-2016, 11:38 AM
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That's 1 cheat I've used in the past, but I know guys do it the right way. I see it on the internet all the time. What extra steps and precautions do I need to take to get the desired effect?

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Old 12-30-2016, 10:44 PM
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Try straight C02 to get the bead to flow out more. You might need a smaller welder as my SP175 on .023 wire is still pretty hard... for me anyway.
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Old 12-31-2016, 03:20 AM
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Quote:
Originally Posted by johnsongrass1 View Post
Try straight C02 to get the bead to flow out more. You might need a smaller welder as my SP175 on .023 wire is still pretty hard... for me anyway.
Thanks a lot for the suggestion. It couldn't come at a better time. My gas is out and I am going to get some this morning.

I would have a very, very hard time justifying getting another welder. If anything I think I will tell myself I need to pony up, start cutting patch panels with MUCH tighter, better gaps, and using my TIG welder. Why is it that these large welders can't do the thin gauges? Voltage and wire feeding settings are finite, actual numbers. These are not arbitrary setttings. In my mind these number should yield the same results when placed on any different machine platform. That doesn't seem to be the case though. Does anyone have any information on this?

I have been watching a few youtube videos on the subject of this thread. I believe the pictures I have posted here are a result of me welding too much in 1 area at a time which is yielding in the extreme shrinkage of the metal near the weld. Am I correct?

On my upcoming patches and panels I will weld much smaller tacks and hop all around the seams to reduce distortion. In the mean time, what is my best course of action to fix this piece without using bondo?

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Old 12-31-2016, 04:59 AM
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You'd be better off with a 70/30 mix than using Co2 without a doubt.
If you do a lot of sheetmetal welding go with .020 wire and tips.
show some pics of the weld before you start grinding and we can be more help. my best guess is your trying to weld too cold. and yes, you cant just run a bead with sheetmetal, its tacked, spaced and tacked again. while your getting the hang of it try using a course hand file to cut down the weld. a good weld tack wont need but a few strokes with a hand file to be flush with the surface.

Last edited by deadbodyman; 12-31-2016 at 05:17 AM.
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Old 12-31-2016, 06:35 AM
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no gap fitup

gaps cause problems as the weld shrinks, and the back side of the metal has to be clean. I have some scraps of copper pipe I hammer and form for a back up . harbor freight also sells back up coppers. A friend teaches the panel fab street rod classes. here;s a link to an exercise he has his studenst do to practice a no gap fitup and minimum filler weld
lazze sells accurate alignment tabs you can use with cleco's to hold the panels so you can scribe, then weld Rod doc also has some good info on zero gap and no filler. It takes a lot of pracatice. My lincoln Square wave 255 tig has a pulser that can help preventing burn thru.
http://www.metalmeet.com/forum/showt...light=mindover

Last edited by timothale; 12-31-2016 at 06:42 AM.
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Old 12-31-2016, 06:42 AM
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Quote:
Originally Posted by deadbodyman View Post
You'd be better off with a 70/30 mix than using Co2 without a doubt.
If you do a lot of sheetmetal welding go with .020 wire and tips.
show some pics of the weld before you start grinding and we can be more help. my best guess is your trying to weld too cold. and yes, you cant just run a bead with sheetmetal, its tacked, spaced and tacked again. while your getting the hang of it try using a course hand file to cut down the weld. a good weld tack wont need but a few strokes with a hand file to be flush with the surface.
I did some research on the internet on using co2 on sheet metal and found that it is not good for sheet metal as it welds hotter. I've always used 75/25 and never even knew they sold 70/30.

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Old 12-31-2016, 06:50 AM
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lazze info

here's a link to a lazze video
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Old 12-31-2016, 06:59 AM
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Thanks for the great videos timothale. Lazze has a lot of great vids. I haven't watched the 1 u posted.

What is the metal meet link u posted in ur 1st post? I can't open it because I'm not a member. I registered but now have to wait for a moderator to approve. What a cumbersome pain the ***** process. That's an old forum practice that metal meets should change if they wanna get more members, but I digress.

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Old 12-31-2016, 07:04 AM
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zero gap tacks

to tack the zero gap panels, extend a sharp tungsten about 1/4 inch then slide the point across the panel with the cup on the panel until you feel the seam with your tungsten , then rock the torch sideways keeping the cup in contact with the panel and a small gap , then just a quick stomp on the pedal. I bought my tig used and it came with a water cooled torch with the thumb amperage control, good for some things but I had to get a new foot pedal for doing some things like these tacks.
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Old 12-31-2016, 07:10 AM
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Alright. I'll try that too.

In response to deadbodyman, I forgot To mention in my 1st reply to u that my welder doesn't work well with small wire. Idk why. Using .023 is not an option. There r a couple posts talking about this where I posed some questions concerning the topic. If u have any suggestions on that let me know.

Someone also mentioned welding too cold. I do NOT believe that to be the issue at all. The pictures may appear to be showing a large build up of material seen when welding cold, but the ground welds are flush with the parent metal. The unground areas around them are the pits and shrinkage in trying to fix. Yes they are extreme. That's why I'm here.


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Old 12-31-2016, 07:18 AM
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GREAT cleco vid by lazze. I'm finally sold on them and ordering now.


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Old 12-31-2016, 07:21 AM
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rod doc info

rod doc lists the various size tungstens and amperages he uses for various gages of sheetmetal. but every welder works a little different. another possibility of welding problems is old dirty or surface rust on your wire. I worked for a metal fab shop on the coast in california and the salt air mist blowing in every afternoon could cause problems. The shop had the ability to custom mix the gas from huge bulk tanks. and I remember one time they even had a small bit of hydrogen mixed in. I have no idea what it was suppose to do but they welded different parts with different alloy content.
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Old 12-31-2016, 07:45 AM
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Hey new here! Will do an introduction later(pressed for time) Here is a thread from another site about butt welds,Its long but great information and explained well by Robert!! Hope this helps! Pete MP&C Shop Projects - The Garage Journal Board
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