Sunday, November 9, 2008

Dealing With Surface Height Changes

Last week I spent more time planning than executing. That's not a bad thing. When I was in high school I built my own sail boat, and one of the many lessons I learned was measure twice, cut once. I lofted the hull full size on the garage floor and must have walked a hundred miles just walking across the floor to check it.

The upshot of all this is that today I realized that the height change I talked about last time had an impact I had not counted on in the area by the tail light. The good news is that I started the day planning rather than cutting, so I figured out what was wrong before it became a problem. The solution was to use a two layer patch. The last patch was supposed to be at surface level. In fact it is one layer down.

My basic plan for welded patches-not that I have done very many-is to use a picture frame backplate that supports a surface level patch. In the area I am working in now, that plan is inadequate due to the lack of structural integrity around the opening. For this reason I went with a solid patch.

First I made the surface level patch. Not hard even though none of the sides are square. I just held a piece of cardboard against the opening and marked it, then cut it and trimmed here and there. When the pattern fit I transfered it to steel.

The backing plate was even easier. It needed to be 1/2 in. wider and 1/4 in. higher. I had just enough time to weld on the backplate. I finished by covering all the exposed surfaces with POR-15 Metal Prep.

No comments: