Sheetmetal fabrication sometimes seems like magic. Watching a talented tinworker turn a sheet of steel into something like a cool firewall is like watching a magician turn a handkerchief into a dove. It's not really magic-it's a combination of manual skill and mental problem solving.
Hot Rods & Hobbies in Signal Hill, California, is one of the best shops around when it comes to sheetmetal fabrication. We were there to watch Brian Stone build a custom firewall for a '37 Ford Fordor sedan. The stock firewall was still in the car, but a Ford crate engine and 4R70W transmission were ready to be dropped into place and would not fit with the factory firewall (and a new radiator and fan had to fit up front). The new firewall would need to be recessed several inches-and a whole combo of compound curves would present a few more challenges. In addition to fitting right, the new firewall had to look right too.
The buildup was a series of slow steps-measuring, fabricating, remeasuring, fitting, and refitting. The procedures Stone went through were specific to this project, and the level of skill needed to get it done is probably a bit beyond the typical hobbyist, so instead of tracing every step of the build (we'd need a book for that) we're fast forwarding through the job to show you some of the tricks Stone used and some of the tools he fabricated to turn some rectangular pieces of sheetmetal into a work of art. Maybe there are a few tricks you can pick up to improve your own metalwork skills.
The challenge at Hot Rods...
The challenge at Hot Rods & Hobbies was to build a firewall for the '37 sedan that would be deep enough to fit a 430-horse 347ci Ford crate motor-and still keep it looking like a retro piece. The engine isn't perfectly symmetrical; the heads are staggered and the driver side is slightly further back. The engine will also be mounted slightly to the passenger side to not interfere with the pedal assembly and steering.
Obviously, a flat firewall...
Obviously, a flat firewall was not going to work. The width across this part of the body is 37 1/2 inches at the widest point. Stone started with 44 inches of sheetmetal to make sure he'd have enough material after all the reshaping. Bending this piece of 18-gauge cold roll steel on the metal brake was the easy part of the job. Stone and HR&H owner Scott Bonowski agreed that 80-degree bends looked better than right angles. It was determined that the firewall needed to be approximately 2 inches deeper than the original firewall location to fit the engine and trans, allowing a little extra room for removing the valve covers or to get a cherry picker in there to get the engine and transmission out if needed.
The upper corners of this...
The upper corners of this part of the firewall needed to be cut out to fit with the diagonal upper portion of the firewall-which was done after careful measuring.
With the corners cut out,...
With the corners cut out, Stone used a cardboard template as a pattern for the diagonal upper piece he was about to build.
This will also be 18 gaug...
This will also be 18 gauge.
Rolling a 1-inch bead design...
Rolling a 1-inch bead design into this portion of the firewall will make it look better and resemble the stock firewall. Brian had to be careful because this will also shrink and stretch the sheetmetal, changing the dimensions slightly from what he had carefully measured. Before running the piece through the bead roller, he used a planishing hammer to pre-stretch the marked line, which will keep the bead roller from distorting the panel as much. Our lead photo shows him forming the bead. If he looks intense, it's because he knows one goof up and he's back to the beginning.
Stone cut a piece of 1-inch...
Stone cut a piece of 1-inch pipe in half and used it to finish the 1-inch bead.
He rounded a bullnose edge...
He rounded a bullnose edge on this 3/4-inch-thick piece of aluminum, which was used for hammering the lip around the edge of this piece of the firewall. The lip will provide a surface for welding together the upper and lower parts.
For forming the lip around...
For forming the lip around the inside bends, he hammered the piece over a T-dolly, switching back and forth between an oxyacetylene torch and mallet to shape the sheetmetal.
The lip was finished with...
The lip was finished with a planishing hammer.
With the two pieces mocked...
With the two pieces mocked up, Stone scribed a line in Dykem to find exactly where they meet, and trimmed the lower piece along the scribe line for a precise fit.
He then butt-welded the two...
He then butt-welded the two pieces, hammering and grinding each tack individually. Hammering stretches the tack, loosening the panel to keep it from overlapping. If the gap gets too wide, he doesn't hammer the tack. As the metal cools it shrinks and pull together.
Mocking up the firewall with...
Mocking up the firewall with the engine in place, it became clear that it would need to be recessed a few more inches. Note the position of the driver side valve cover.
Using another cardboard template,...
Using another cardboard template, Stone determined where to cut off the lower section of the lower piece, and where to cut an arc for the transmission.
No problem. Just more work....
No problem. Just more work. Stone cut the firewall at the right and left inside bends of the lower firewall and, using some square steel tubing as a dolly, hammered an addition recess (another 2 inches, approximately) into the lower horizontal portion.
The resulting gaps were filled...
The resulting gaps were filled with additional 18-gauge steel.
As a finishing touch, Stone...
As a finishing touch, Stone put this die on the Eckold machine and ran a good-looking bead along the bottom of the firewall, including the arc of the transmission opening.
The final result is an impressive...
The final result is an impressive piece that provides plenty of room for the engine and really looks great.