Home Made 1915 Firewall

[Vrayfoster]

First of all, this fits my car and coil box. I obtained a piece of 3/4" 12 ply Baltic Birch and laid it out in pencil. What I discovered in this process was that coil boxes and firewall mounting arms are slightly different. First I fitted the firewall mounting arms to the firewall base, cutting the wood and sanding until they fit flush to the bottom of the wood. I placed the firewall mounting arms to the frame, bolted them on, slid the firewall in place and then marked the mounting holes including the firewall to body holes. You will be surprised what doesn't line up to my sketch! The hole for the steering column needs to be slightly oval to get it to fit. I cut the hole at the minimum diameter so the one steering column bolt had the most wood available. I used my steering column as a template to determine where the steering mounting holes had to be. I drilled all holes using a drill press with Forstner bits and backed up the plywood so the drill bit wouldn't tear exiting the wood. The taper and radius on the top I used the sanding disc on my table saw and sanded until it fit to the hood former. I only show the bottom steering side of the coil box mount location. When I made mine, I centered the coil box and marked the mounting holes and all 10 larger holes. The larger holes were not symmetrical at all! The carburetor control rod hole drilled at an angle; I measured the angle on the existing firewall for the carburetor control rod them drilled a hardwood block, clamped the block to the firewall as a guide and drilled. My firewall came out 24-1/8" wide. I assume it should have been 24" but that was the size that fit my car and hood former. I included pictures of the final finished firewall and the dimensions I made it to. At best all the dimensions shown are approximate. Verify everything before cutting.

[Allan]

Nice work Victor. I do mine on my drill press. That way I can set the depth of hole so that just the point of the drill bit exits the under side.
Then I flip the item and complete the hole from that side, to prevent any breakout. Did you have to reduce the thickness at the outside edges to get the metal cover to fit? 3/4" is sometimes just a bit too tight.
I was intrigued by your use of twelve ply. I have never heard of plywood having an even number of plies, as that would leave the sheet with grain going in one direction on one face and at right angles on the other.

Allan from down under.

[Vrayfoster]

Allan:
I can't count! it's 13, not 12 ply. 3/4" plywood is about 0.690" thick which is too thick for the hood former so I ran the router around the edge. I don't like drilling from both sides as any misalignment puts in an off centered hole. Thus I just clamped a backing board to it and with Forstner bits I didn't have any break out, chipping, or tearing.