I've been doing some initial research on replacing quarter panels due to rust.Several opinions on butt welding or lap welding, however no definitive answers. . If either way is correct, that's fine, I'm just trying to sort it out. Can someone point me in the right direction.

When butt welding, many body men recommend placing a strip of metal on the back the joint to help prevent burn throughs. You cut a strip of metal from a donor fender so the alloy content of the metal will be similar. So a proper butt weld will be very similar to a lap joint weld when completed. A lap joint is easier to weld and is easier to prevent burning through. I think the strength of the joints would be about the same.

If you would use brass for the strip on the back which Randy is talking about, you will achieve the same, but you will still be able to remove the strip afterwards. I learned this from a professional welder. Perhaps it will help you too.

Rusty, Isn't it COPPER you are thinking about? Brass has a very low melting point, copper is the metal that is used for backing welds.

------------------
1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T

Or buy a tool that crimps an offset into the metal (look like modified vise-grips) and you can create a neat lap joint that is flush on the surface. Available at Eastwood and others
Look for "panel flangers" at http://www.eastwoodcompany.com/

------------------
Make it the way you like it, forget what the other guys say!
http://homepages.studentcenter.org/64elcamino/HOME.html

I keep pieces of 1/8" brass on my welding cart and use it all the time to back up welds. You can fill a large hole easily. Keep a bucket of water handy to dence it often and keep it cool. A professional welder showed me that trick a year ago or so.

It depends on how good a weld you want. A butt weld can look good from both sides and is easier to keep from rusting because you do not have the overlap to contend with.

If you are fixing a somewhat rough car for driving, just do a lap weld with as little overlap as you can get. That lap weld is much easier and therefor quicker to do.

Peter

This is what i do, I learned it from a GM training video for sectioning.Cut off the last three inches or so from your repair panel,trim it,so that you can slide it under your original panel,leaving half of it under the old panel and the other half out.tack it every inch or so.Then butt up you new panel,leave about a quarter of an inch gap,and then stitch it an inch or so at a time,jumping from end to end so you dont distort it until its welded all the way across. of course if you have a full quarter it would just be easier to crimp it with a crimping tool,but this works good on patch panel ect.

------------------
70 chevelle,400cid turbo400.blue with silver stripes.http://members.spree.com/entertainment/ochrisl/

A really neat way of butt welding,is to use a carbon block, they come in all sizes and shapes. Any pro-welding shop sells them. They also cut way down on heat transfer to your panels. You can use them over&over again. Great for backing up when air-arching