Hi all, My T fenders and body have some hairline cracks. What is a good way of fixing them? I have available a MIG welder and can also braze with oxy-acetylene. I tried brazing today and the results were mixed. Some burn throughs. It doesn't go through and through on the crack. The brazing rig is much more portable than the MIG.
You will get many opinions here, but here's mine:
NEVER Braze body cracks. The braze isn't as strong as the surrounding metal, and the braze pollutes the metal so it can't be welded later. Welding is the proper way to repair cracks. How you weld is up to you, I have one friend who can do miracles with a wire welder and another who can gas weld & hammer dolly it and both repairs are basically invisible when finished. The gas guy claims the wire weld is too brittle to last long--me?? I dunno. Me? I have not depth perception; while I have welded, I don't consider my welding to be of quality, so I have others do the structural welds.
You might want to consider a TIG welder. I have had some good results TIGing sheet metal and thin plate. If you can clean the crack and pull the crack tightly together, you may be able to fuse it together without using any filler metal. I have been able to do so in some cases and the repair is almost undetectable. Good luck with your project. Bill
TIG is really the best for thin sheet metal with the proper machine.
Sounds like you have a MiG so that would work as well. Practice on a scrap..
Having done my fair share of panel beating, panel straightening, and rust repair I agree with some of the points made above.
Listen to Dave, once someone brazes up a panel or solders a seem, I cut the whole area out and start from scratch. I'd rather make a whole panel than try and undo all that mess! Also the flux from the brass or lead never seems to completely get cleaned off and will reject your paint, and rust your tin for years to come.
TIG welding is king in this industry. But not everybody has the skill or access to the machine. Oxy-acetylene welding I would say is a close second to the TIG, and much more available. Both have very similar principles and potentially very similar results. The one advantage to welding with gas is the annealing effect on the weld and base metal. Due to this annealing you can hammer and form your weld with less tendency to crack the weld itself.
With either TIG or gas, you must remember that you can't weld what isn't there! Make sure that your weld joints are tight! Do not try to fill holes and gaps. The excessive amount of heat and filler rod will cause uneven shrinkage and warpage. Not to mention all the extra hammering it takes to undue all this. Just make a patch panel and cut it in... You'll be glad you did. I will usually tack the panels with little to no gap about every 1-2 inches. Hammer all the tack welds to combat shrinkage and confirm shape, then connect the dots with continuous weld. If there are no gaps, and you jump around to spread out the heat, you can achieve a panel repair with very little distortion.
MIG welding has its place, and It not for butt welding light tin. When you see someone do tin work with a MIG welder they are always making a continuous series of tack welds in an effort to control the heat. The rapid, localized heating and cooling of each tack weld causes excessive shrinkage that must be dealt with before you can proceed with the weld. You must now grind off the extra filler material and hammer the weld material and surrounding tin to undo the shrinkage. Of course the MIG weld does create a brittle weld, and in turn will crack when you hammer it. Many times when I see a panel done this way, the weld will not be continuous. The repairman will simply stop welding at about 75%, I assume to prevent further warpage. Then just skin it over and call it good.
I'm pretty picky about how I do my repairs, and some may not agree with me. But I like my repairs to look good before paint, on both sides of the panel.
I'm not an expert, but have done my share of Oxyacetylene welding and I agree with Kevin. If it isn't pretty before the painting, it won't be pretty after the painting.
The biggest problem when welding a 1925 and earlier body would be the wood frame underneath.. Most of the rust and cracks would be right where the wood is = fire hazard, so first a lot of work to remove the sheet metal from the framing, then repairs to the wood and metal and last a lot of work fitting it together again.
Some good advise above. I prefer the oxygen-acetelene process myself. No matter where your crack is located always drill out the end of the crack. You can chase a small crack with any type of welding. Once heat is applied the metal wants to expand and cracks will open up or continue to crack unless drilled out. I also use tie-wire or a metal coat hanger for filler metal. Soft metal and not brittle like some of the welding shop supplies. Just my opinion of course.
I have used my Lincoln flux core welder with reverse polarity to weld cracks and patch panels in Model T sheet metal. I used a copper backing strip installed with steel pop rivets. After I finish welding the panel I welded up the pop rivets and removed the copper backing strip.
Just my 2¢ here... TIG and oxy-acetylene are very similar when it comes to the welding process, but the TIG foot pedal is worth its weight in gold when it comes to thin material. I've blown more than a few holes in sheet metal with oxy-acetylene. With TIG, you can back the heat off once you get a bead going.
TIG vs. MIG? No contest. There's no spatter with TIG, and you control the amount of filler on the fly, also important with thin materials.
Tig is the way to go but if all you can get is a mig, start out with some practice metal before you start on your body. Tim