welding lap or weld

[zippy500]

I have been looking at various patch panel welding such as floor pans, inner wing and boot area on you tube. I see that professionally body shops are just lap welding panels in (after cutting out the rust), doesn't this have an exposed edge on one side ?

I suppose it does the job. I thought that butt welding was the best way to weld a section in.

Just think for when I start cutting rust sections out.

What are peoples view on this

[///mChris]

What do you mean by exposed? Certainly you'll need to use some filler. The metal needs to be cleaned to bare metal, so you have to figure out how to paint it afterwards.

What I've done is use my handy flange tool

http://www.harborfreight.com/air-punch-flange-tool-1110.html

You make a flange around the hole on the car. This insets it a tad. Then use the hole puncher to cut the holes for plug welds.

Alternatively, I made up something similar to this for butt welds:

http://www.eastwood.com/butt-weld-clamps-and-backers-kit.html

[jerry]

i've disassembled a couple cars and as far as i can recall, all the OEM joints were lap joints using a spot welder. there are a few Mig welds here and there as well. However, unless you are replacing an entire panel, i would opt for butt joints as they can be made invisible when properly executed. it takes alot of preparation and PRACTICE. their use is a matter of your personal desire to minimize the appearance of repairs.

i've been doing a major rustoration on a 72tii since january and i can tell you from personal experience, your welding skills WILL improve with time. there are a few patches i'd like to do over. where it becomes really important is the outer skin repairs. do your lap joints in discrete areas and save the obvious locations for later, hopefully, as your ability improves. that's my strategy.

[ThatGuy]

I feel that the proper way to repair rusted out panels is to butt weld the patch in place. I choose not to lap weld any patch that I do. That being said, you have to ask yourself what you want the car to be.

Lap welding patch panels makes it a little easier to get your patch to line up and makes it easier to weld but lapping panels is not always the best way. Easier but not always better.

If you want it to last and you live somewhere with a lot of humidity, rain and/or snow, a lap weld will rust again if not properly sealed/painted/treated after welding. You are correct about the exposed edges on one side of the patch. If the patch is somewhere that you cannot access the backside of the patch to treat it, it will rust again. It may last for years without showing signs of rust but bare metal will rust.

Even a butt weld needs to be treated properly or it will rust again. If the back of the welded area is inaccessible it should be painted with a weld through primer before welding to help mitigate the chances of it rusting again soon.

Any time you weld metal, it burns off any and all coatings, oil or protection and you are left with bare metal at the weld area.

I'm not going to say too much about those "professional" shops that you said are lap welding patch panels.

[TobyB]

oooo, this one has no right answer!

Depends on what your primary concerns are! A butt weld will be anywhere from

slightly to a LOT weaker than the original panel. It may or may not

seal perfectly.

It's also possible to make a nearly- invisible repair this way IF you are

pretty good.

A lap weld is pretty easy to do, easy to seal, and can be as strong or stronger

than the original panel. And is often faster, though not always.

Which you want to use is up to you. I do more butt welding in visible

body panels, and more lap welding in non- visible structure, but there

are no hard- and- fast rules.

There's a non- answer for you!

t