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Tank tunnel widening technique

7083 Views 23 Replies 11 Participants Last post by  mattsway
Hi. I have a CB200 tank to go on my XBR500 build and need to get clearance where my frame rails attach to my top tube. At this location, the tank tunnel is 130mm and if possible needs to become 160mm. Having googled around, I hope to be able to use a plastic mallet. Any advice on weight/shape of mallet and technique - do I strike against the inside face of the tunnel first, or the bottom edge where the wall and bottom of the tank meet? Any prep to help move the metal most effectively? I thought about filling with boiling water, but I could always purge the tank of petrol/gas fumes and use a butane torch. Many thanks.


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If you're referring to the the black circled marks in the pic, all you need is the round side of a ball peen hammer. I assume by plastic mallet you mean a teardrop. A teardrop won't work as well here. I work mostly with a repoussé and a ball peen for work like that.
MIG is fine if you learn how to work with it. I have no TIG, so I do all of my welding with MIG and O/A. In sheet metal, burn out comes from penetration. In welding thinner gauge sheet metal, you want to lower your feed speed and lengthen your stick-out. Longer stick-out = less penetration. Lower feed speed = less amperage. The other thing is voltage. Lower volts = narrower puddle. Higher volts = wider puddle.
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