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But welds, gap or no gap?

A gas welding technique question: Most textbooks tell you to butt thin sheetmetal together then tack and weld. When I was taught gas welding at a coommunity college, the instructor insisted that all metal 1/8" or less should have a gap of the metal thickness between them. Then you tack and weld. He claimed much reduced distortion as a result. If my acetylene tank weren't empty I'd go try both to satisfy myself but it is and the welding supply shop isn't open till Tuesday.

Any opinions out there?

Reply to
Ken C
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might depend on how tight the "other end" of where you're welding is. welding up 18g cones with no gap left no distortion. figure it like the denser/more weld bead that is deposited hot, the more it will shrink when cold...

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Reply to
dogalone

Are you sure that it wasn't the other way round?? Often thicknesses under

1/8th is a zero gap. Leaving a gap when gas welding will ensure you can maintain a keyhole as you go around giving you full penetration. that might be the reason for the instructor's guideline. Distortion is dependent on several factors. Generally it is not a great problem with straight on pipe connections. The weld will shrink evenly around the pipe pulling the pipe axially. There is some shrinkage on the circumference but on heavy pipe it can be ignored. In the case of thin-wall tubing such as six inch and 1/8th wall it can reduce the diameter at the weld. I should mention that welding up one side of a tube first can pull the pipe leaving a crooked connection. Randy

Reply to
Randy Zimmerman

No, definitely below 1/8". We were welding 1/16" sheetmetal plate and were told in no uncertain terms to tack with a gap to reduce shrinkage. CErtainly it is no problem at all to fill the gap on 1/16" steel, once I get my acetylene tank filled I'll have a go with 20gu - where of course the gap will be smaller - and see how it fares. He indicated it was to reduce distortion (*not* to improve the chances of full penetration as it might be for thicker steel)

Ken

Reply to
Ken C

Reply to
Randy Zimmerman

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