Q.I have a 1934 Chevrolet Standard coupe with a good trunk lid. The problem is the lid has no inner sheetmetal panel. I do not know if it was removed or if it just never had one. I assume it never had one because the inner perimeter of the lid has wood all around it and it has wood-arched braces in the center. I know these bodies came from the factory with a lot of wood for support. I have seen photos of some 1933 and 1934 Chevrolets with inner panels in the trunk lids. I want to make the inner panel and I have a good idea of how to do it. I know I can bend the radius of the inner lid by hand. I can have wheels made for my Pexto 620 to do the outer flange that will connect to the outer trunk lip.
I want to put some large holes in the panel like the factory did for weight reduction and access to the inside of the panel. I know that the factory panels had the edges of these holes radiused, or flanged slightly. How is this done, and at what point in the process should I do the rounding of the edges? If I radius the edges after I have curved the panel to match the trunk lid radius, I will not be working with a flat panel.
As always, your information is most valuable and greatly appreciated. George Persinger Via the Internet
A.George, it seems like you have a pretty good idea about how to proceed with making the inner panel. Actually, flanging the holes isn't too big of a problem; it can easily be done with a hammerform.
It is easier to flange the holes while the panel is still flat, but the reinforced edges of the holes will prevent the panel from being curved evenly. For this reason, I'd suggest flanging the holes after the panel is curved.
Hammerforms are usually made from materials that come in flat sheets, like plywood, medium density fiberboard (MDF), or aluminum. The form and the clamping block must match the curve of the panel for a hammerform to work on a curved panel.
I think MDF is sufficiently strong for this application. You'll need to glue up a block several layers thick, perhaps 3 inches (total) wider than the hole to be flanged. Next, cut a hole in the block the size of the finished, flanged hole you want in the trunk inner panel. Now comes the tricky part: contouring the block to match the curve of your panel. I'd make a template that follows the contour of the inner panel and use this template to draw a curved line on two opposite sides of your hammerform. Now, you can slowly start carving away the top surface of the form using a handheld disc sander, working the surface down evenly from right to left, getting closer to your guidelines on each pass. You should be able to get a fairly accurate curve this way if you work slowly, use great care, and check your progress frequently with a straightedge.
I'd plan on doing 95 percent of the shaping with a power sander, and then use a sanding board for the last 5 percent, which will allow you to fine-tune the shape with great accuracy. If you should sand too deep in one spot, all is not lost, since you can use plastic autobody filler to repair any low spots.
With the top surface of your block properly contoured, you can now radius the edge of the hole in the hammerform. The easiest way to do this is by using a rounding-over bit in a handheld router. I presume a small radius, perhaps 1/8-inch, would match the stock holes best. The router base will need an attachment for this, since the standard round base will not allow the router to follow the concave surface of the hammerform evenly. I'd suggest screwing on a temporary base made from a wooden 1x2, with a hole in the center for the router bit to pass through. This should be about 12 inches wide, and in use, you would keep the long axis of the 1x2 oriented so it makes full contact with the hammerform as you are cutting. It will create a gap if you angle the 1x2, pulling the cutter away from the form slightly. If this isn't quite clear now, you'll see what I mean when you start cutting.