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Posted by bruce in BC [24.207.97.175] on Sunday, November 29, 2009 at 12:22:28 :
In Reply to: Best way to weld sheet metal? posted by David Sherman [216.18.131.199] on Sunday, November 29, 2009 at 03:24:51 :
TIG- for the best results TIG is the only way to go . The molecular structure of the metal is the same as the base metal . For body panels I would use tripple killed rod . The problem with using TIG is it is slow and takes talent . The HAE is larger than MIG and takes some hammer work to control . As you get older you have trouble seeing the micro welds as you work . This is now a issue with me and I have some great welds that have drifted as much as 1/2 an inch from the join . Yes the join line was tight enough that no filler rod was needed . A lot of aircraft parts are welded using TIG no other welding method is legal or meets the structural requirements.
OXY ACET - yep it is second on the list from a structural standpoint . BUT the HAE is huge and you need to hammer weld the joints . A tripple 0 tip (000) and access to both sides of the panel , talent , patience are necessary here . If you are replacing a whole quarter panel that had leaded seams it is possible to use bronze rod NOT brass rod .
MIG - this is the most user friendly . The weld is much harder than the base metal and very difficult to work . You need to grind the weld down . Something that is seldom needed with TIG . A welder that will push 023 wire is one of the better choices and if you can get a spool of the softer grindable wire then your work load is cut down considerably . To get to show quality the back of the welds need to be worked too, this is not the case with TIG . Most of us are not concerned about a little bead on the inside of a panel or door skin but for the high end folks the panel joint must not bee able to be seen - in some cases this standard is required on bare metal . I would recommend MIG to most home builders.
If you are thinking about lapped joints then it is possible to glue your patch panels on . The correct panel adhesive is stronger than the base metal . We have glued a patch in place and then beat on it with a hammer - the panel stretched until a hole was pounded through - no tears is the glue joint .
Welded lap joints in the middle of a skin will show up in hot weather . They expand at a different rate than the base metal , they also act as water traps . Avoid lap welds unless it is close to a corner or where a factory lap weld originally existed .
that is my morning rant
Bruce
We need about 4000 more words just to get started on this subject .
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