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SouthernMudSlinger
01-15-2007, 01:38 PM
We just got a mig welder (hobart handler 187), and im practicing welding on sheet metal, and im welding around on the peice to keep it from getting too hot in one spot. When I grind it down, hair line cracks show up along where I welded.....im assuming im getting it too hot? Im using a air angle grinder with about a 3" cut off wheel. Also, do you have to weld the patch peice in completly solid? (leaving no holes along the edges of the patch panel)

Preston Herrick
01-15-2007, 01:50 PM
What appear to be cracks are probably one of two things. Either you're not getting enough penetration and you're grinding all of the weld off - which indeed would leave a "crack" or unwelded seam or you're seeing what appears to be a crack but isn't. Rather, it's the very edge of the puddle where it meets the substrate and you haven't ground quite far enough. Sometimes if you grind a hair more, it goes away. Don't know if I've described it right but I've seen what you describe and sometimes it's an illusion. I'd also trade the cut-off wheel for a 2" Rol-loc abrasive disc (with mandrel). A 36 grit disc will take the weld down quickly and smoothly.

drizler
01-15-2007, 02:38 PM
What appear to be cracks are probably one of two things. Either you're not getting enough penetration and you're grinding all of the weld off - which indeed would leave a "crack" or unwelded seam or you're seeing what appears to be a crack but isn't. Rather, it's the very edge of the puddle where it meets the substrate and you haven't ground quite far enough. Sometimes if you grind a hair more, it goes away. Don't know if I've described it right but I've seen what you describe and sometimes it's an illusion. I'd also trade the cut-off wheel for a 2" Rol-loc abrasive disc (with mandrel). A 36 grit disc will take the weld down quickly and smoothly.

Try getting one of those disks that is made up of little flaps of abrasive shaped like your cuttent wheel. Around $5 last a long time and do a better job of smoothing things and cleaning up rather than cutting in along one tiny spot like a grind wheel. That makes my hillbilly welds look almost purdy.

ZRX61
01-15-2007, 07:50 PM
Could be undercut?

Preston Herrick
01-17-2007, 04:05 AM
Try getting one of those disks that is made up of little flaps of abrasive shaped like your cuttent wheel. Around $5 last a long time and do a better job of smoothing things and cleaning up rather than cutting in along one tiny spot like a grind wheel. That makes my hillbilly welds look almost purdy.

I like flap discs too but personally didn't find them to last as long as I'd like. Seems like you get about half way through the disc and they've had it. Course, when they wear down a ways they don't cut as well and tend to glide over the weld and remove more material from surrounding metal. Since the Rol-locs are smaller they're easier to control and fast. The flaps do finish nice.

SouthernMudSlinger
01-19-2007, 12:49 PM
maybe im not getting enough penatration? I bought some of those Rol-loc disks and they work alot better. How can I get better penatration?

Preston Herrick
01-19-2007, 02:03 PM
maybe im not getting enough penatration? I bought some of those Rol-loc disks and they work alot better. How can I get better penatration?

You could try turning up the juice a little. It's a fine line with sheetmetal. The wrong speed and/or too much juice and you'll blow through. A tiny gap between the two pieces will help.

shawge
01-19-2007, 04:25 PM
Pics of your welds with the cracks would help. What's the thickness of the sheet metal you're working on?

I've found that using a piece of copper or aluminum behind the welding area of the two pieces of sheet metal helps me prevent blow through.

drizler
01-19-2007, 05:29 PM
Try out this web board and see what these guys can do for you. They are a pretty savvy bunch and most are pro welders or at least talented amateurs. Post em a couple pics and they can diagnose you pretty quick I bet. For the most part you just need to experiment. Those recommended settings are just a starting point and putting a piece of crushed copper tubing in back will aid you a lot too. Takes time and practice. I find it harder than arc welding which is contrary to most everyone else.
http://www.hobartwelders.com/mboard/

SouthernMudSlinger
01-19-2007, 10:15 PM
I think I got it all figured out now. I wasn't getting good penatration.....the welds were basically sitting on top and I was grinding just about all of it back off. I turned the wire feed speed up a little, and made sure I got enough weld in one spot so that it penatrated through the thickness of the metal, and it didn't crack in the places I got good penatration in.....I still need to practice getting consistent penatration........Thanks for ya'lls help.

Preston Herrick
01-19-2007, 11:31 PM
Way to go! Glad you got it worked out. Fusing metal can be fun.