Before I weld on the cowl top piece I am going to fabricate what I need for the windshield wipers. I am using the motor and mechanical wiper unit from the old Mazda pickup truck project. I also have the unit from the F-150 donor which I could use but the Mazda unit is much smaller and appears to be more adaptable to the space I have available under the cowl. I first mock up the unit in a very general way to determine what I have to surgically remove to make the unit fit. Again, the wiper unit could be entirely done later, but it's a bit easier to do some of the fabrication while the cowl is still open on the top.
Photo #1 below shows the Mazda wiper unit with a portion of the mounting bracket removed. I will also have to cut a notch in the upper cross brace to clear the 1x1 center brace that runs from the firewall to the windshield lower cross member. I then marked the cowl top piece where the wiper nodes will extent through the sheet metal and drilled the holes on the drill press. These holes have to be slightly elongated (done with a burr) because the wiper nodes fit through the cowl top at a slight angle.
Photo #2: Here the cowl top piece, with the wipe node holes drilled, has been tack welded in place.
Photo #3: And here is the entire roadster body in its rough form. There is still a lot of sanding, filling, and prepping to do to get everything straight and smooth, but the completion of the rough body is a major milestone in the rat project.
With the drivers side cowl corner and side piece in place I repeated those operations on the passenger side of the car. Once those pieces were completed I was ready to fabricate the cowl top.
Photo #1 below: I carefully measured the distance between the two cowl corner pieces at the windshield cross member and cut a piece of 18 gauge to that length and to a width equal to the cowl itself (windshield to front of firewall hoop) plus about 1 1/2" at the front as "error room". I then slid the rear edge of the piece under the windshield cross member about 1/2" and clamped it in place. From the under side I could then trace the edges of each cowl corner piece and the front of the firewall hoop. I then cut out the piece as shown in this photo.
Photo #2 below: This is a close up of the rear corner of the cowl top. A small notch had to be made so the piece would slide under the windshield cross member and also butt up fairly well with the cowl corner curves.
Photo #3 below: Here the cowl top is being checked for fitment.
With the cowl corner tacked in place I move on to fabricating the cowl side piece. This side piece extends from the front edge of the door (minus a 1/4" gap) to the front of the firewall. It is also crowned to match the crown of the door panel. However, I eliminated the crown at the firewall, so the sheet metal will be flat against the firewall hoop. To support the crown at the door a welded two 1"x1" tabs of 3/16 flat stock on to the door jamb at exactly the position as the apex of the crown in the door. I then cut a piece of 18 gauge to the correct width (door edge less a 1/4" gap to the front of the firewall) and to the height of the door top to the bottom of the body (plus an inch extra to wrap around the bottom edge of the skeleton). I then clamped this piece to the car and from the inside, traced a line along the bottom edge of the corner curve piece which I just installed. This should give me a fairly good butt join between the corner piece and the side piece.
Photo #1 below shows the cut out side piece being clamped in place for welding. The butt joint had to be cleaned up only slightly with a die grinder. To try to improve on my butt joint sheet metal welds I decided to weld a 1" strip of sheet metal behind the butt joint and overlapping the joint by about 1/2" on each side. This small strip of 18 gauge will act as a heat sink and will hopefully prevent blow through while still allowing me to get good penetration on the butt weld.
Photo #2 shows the cowl side piece tack welded in place. You can see the small heat marks directly below the lower butt joint where I tack welded the heat sink on the inside of the joint.
Photo #1 below: I begin to curved the panel by clamping it to the firewall hoop and bending it by hand around the hoop. I then took the panel off the car and continued the basic curve by bending over various sized pipes. I then reinstalled the panel on the car and finalized the bend using a hammer and curved dolly.
Photo #2 below: Here is the corner panel curved and clamped for welding.
Photo #2 below: I then attach the paper templete to the car one final to check the fitment.
Photo #3 below: I then trace the template outline onto 18 gauge and cut it out with my air nippers. Notice that I have once again marked the panel with a line down the center which will be used to center the piece in exactly the same position I made the template.