I've been cutting out rust back to solid metal and fitting in pieces like a jig saw puzzle.

Pictures of RR rear wheel house;
Ground down weld is just inside the yellow line here (http://www.chevelles.com/showroom/Dean/temp_patch2.jpg)

I had to weld in 3 pieces thick here at the arrow (http://www.chevelles.com/showroom/Dean/temp_patch1.jpg) and I'll have to weld the back side to the trunk floor pan at the dotted line.

Anyway my question is how much of a gap should I leave between the original metal and the patch for the weld.

On the first one I made the patch fit the hole exactly without any gaps at all but I got to thinking after I grind the weld off, how strong is it going to be and should there be a gap for weld fill.

hope I'm making myself clear smile.gif

Dean I try to leave a small gap between metal. I use welding wire the size of .023, basically I size my gap so that wire fits snugly.
A rule of thumb I was tought was to leave a gap the thickness of the gauge the metal you are welding. Say you are welding 18ga metal, leave a gap the thickness of a scrap piece of 18ga metal.

Without a gap you loose weld peneration and also when you weld the metal shrinks in that area. A gap will allow the metal to come together.

Thanks Eric

Is Dean now spending his evening time in the garage and not on the computor??Will that 70 be ready for CB04? Are you having fun yet?? tongue.gif

graemlins/waving.gif
Rick

zero gap works best for me, if there is no gap there is no room for the metal to move and cause warpage, if you've ever welded a patch in the top of a crowned area with a gap you'll notice the shrinkage will pull some of the crown out of the shape. Look at all the chop work that's been done by the metal masters of the world--they look for a perfect fit with no gaps.

Since it's almost impossible to make a straight cut on a piece of metal with the most commonly used tools (cutoff wheel, jigsaw, etc.), you will end up with gaps between the pieces to be welded anyway. I've always found that these small gaps are adequate for good penetration.