car rust repairs question

[steveo3002]

ive been doing a few rust patches on my car

so far ive cut out a square so its all clean , then made a patch that fits the hole exactly and welded it in , so its sort of invisible once ground flat

its taking some effort to make these repairs...would it be frowned upon to cut the rust out then weld in a patch thats say 10mm bigger ?

im guessing the overlap will rust and cause more issues

 

[rtbcomp]

It's always best to avoid overlaps for the reason you state and a lap joint isn't as strong as a butt weld. A patch that fits the hole and is butt welded will be a better job.

 

[malcolm]

For car bodywork penetration isn't normally a big issue so I'd not be concerned about strength. If you are struggling with a butt weld on thin stuff you'll likely get a better weld with an overlap just through the extra thickness making the weld easier.

Overlap is OK if the reverse isn't exposed to moisture, or if it can be seam sealed and painted.

 

[steveo3002]

well i do have the odd issue with blowing holes in the edges

the main issue is the time involed to make a plate if its shaped...where if i overlap i can hammer into shape as i go along

yes i would prime ,seal , paint both sides

 

[pedrobedro]

Overlap it and hammer away, it's what everybody else does. Cover the join well and it will be fine.

 

[danelectro]

OR get a joggling tool, then it'll be recessed into the panel. Well that's what I use.

Or alternatively, put your new oversized piece in from behind!

 

[rikrobson]

I Bought a piece of ali 10 x 30 x 300 and use that behind the butt join. This doesn't stick and helps stop the blow through. I also use it to fill in holes small holes in panels. If you do use this idea, the ali gets V hot and stays that way and doesn't show it

 

[MG David]

I have used copper to back a joint while butt welding to stop blow through. Just flatten a bit of 22mm pipe and use that. Yes it does get hot.

 

[Uncle Joe]

I use a different method to weld car bodywork, but I'm not sure if I can explain it properly without the aid of drawings, and havent a clue how to post those.....