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Cab corner with small rust holes showing.

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Inside left stiffener rusted through.  View after local sandblasting

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Right stiffener removed, holes in outer skin enlarged by sandblasting.  Note that original lip on bottom of corner for pinch weld has rusted away completely.

Rust is evil!  A few small holes showing through the paint don't really say everything about what is underneath.  Once I started sandblasting to clean up the rust, bigger holes opened up.  I cut away the inner stiffener since it was too rotted to save.  There were lots of spot welds to drill out.  At that point I could see the condition of the inside surface of the cab skin.  It was rotted through about three inches up.  The lower 1/2 inch where the pinch welds had been located to join the outer skin and inside stiffener were gone completely.  The corners have compound curves and lots of sharp bends for the pinch weld surfaces.  Since there are no commercially available replacement parts, this was scary stuff!  I had never made parts like this before, and I thought about how to do it for many months while I worked other parts of the truck.  Eventually, there was no more time for procrastination - I had to get the new corners made.

I used a profile tracer to transfer the curves to heavy manila paper (old file folders).  Since I had a bunch of 3/4 inch thick plywood, actually 23/32 thick, I started at the bottom of the corner and drew a pencil line every 23/32 for about 4 inches.   I took the profile at each of five levels and traced those onto the manila paper.   I cut along the lines, then checked that the piece was a good match to the curve of the corner along its line.  Then I used the manila paper patterns to trace the curves onto the plywood.  I cut each piece about 6 by 10 inches with the curve around one corner, then stacked the pieces into the back side of the cab.  After a little tapping and squeezing, I got all of the five pieces in contact with the skin and with each other.  I clamped them temporarily without moving them, then ran a bunch of 3.5 inch deck screws through the stack.  Soon I had a solid wood buck that replicated the shape of the cab corner.  I mounted the buck on a larger plywood piece so I could clamp it to my workbench.

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The five pieces of 3/4 inch plywood cut to shape.

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Lining up the plywood layers.

Since I planned to hammer sheet metal over the edges of the buck, I used 3/8 inch square steel bar for edge reinforcements.  I clamped one end in a vise, then used a MAPP torch to heat and bend the bar to the 5.5 inch radius of the corner curve.  With an inch or so glowing red to orange, all I had to do was keep gentle pressure on the bar to bend it.  I had to make some pieces with a 2 inch radius  where the back of the cab curves up to clear the frame of the truck.  Since I was only eyeballing the curves, I had to do a little banging with a big hammer to get the curves of the bar to match the paper pattern and plywood pieces.  I was amazed that a little heat and patience resulted in some pretty smooth, accurate curves.  When they were good enough, I used a router to mill out some 3/8 by 3/8 slots at the edge of the buck, drilled some holes in the 3/8 bars, and mounted them with some #6 wood screws.  Since I figured that the sheet metal would have to be held tight against the metal edges to get a sharp bend, I also bent up a big clamp out of 1/8 by 1 inch steel, then welded on some stiffeners out of some 3/16 inch scrap plate and U-channel.  A piece of 1/2 inch threaded rod, a short piece of tube, and some nuts allowed the clamp to be tightened against the buck  Finally, I had a buck and clamp for bending and hammering on the metal.

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Studebaker trucks were made out of heavy gauge metal, not like a new car.  The old metal was so rusted, it was tough to tell exactly what the original thickness was, but the choices at the local steel supplier were 24 gauge (.024 inch) and 18 gauge (.048 inch).   Although tougher to cut and form, I chose the 18 gauge because I didn't ever want to do this again.  The heavier stuff is a lot more tolerant of my lousy welding (followed by lots of grinding).  I made a pattern for the metal from a piece of a brown paper grocery bag.  The brown paper is heavy enough to work with, but it can be formed a little by rubbing on it.  It's fairly easy to pick up the edges and bends of the old parts just by running a finger over the brown paper a few times.  I enhanced the marks with a pencil line, then cut it out.  It's always good to check for fit after cutting the paper pattern, since it is much easier to adjust the pattern than the sheet steel.  Since I needed to bend the steel in many directions and don't have stretcher or shrinker (see Eastwood catalog), I cut the edges of the paper pattern into tabs about every 3/4 inch to allow for compound curves.  Then I traced the paper pattern on to the 18 gauge steel and sawed it out with my little saber saw using a 36 tooth/inch metal cutting blade.  The flat shape was run through a slip roll to make the major 90 degree bend with 5.5 inch radius.  Fortunately, there was one of these 3-roll formers in the machine shop of the company where I work.  The bottom edge of the cab turns in slightly, so the 90 degree bend also had to form a slight cone.  A little adjustment of the rolls produced the right bends and cone shape, which I checked with my original manila paper patterns.

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Paper pattern and 18 gauge steel blank after roll forming.  Tabs for slitting and bending were laid out with a permanent marker after cleaning the oil off the steel.

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A Diacro 3-roll slip roll.  This is a 12 inch wide roll, but 24 and 36 inch versions by Diacro and Pexto are usually for sale on Ebay.  That's where I got the picture of this one.

Once the metal blank had been formed to the basic radius, I cut slits for the tab with a cut-off wheel.  To make a 90 degree bend with a radius 3/8 inch smaller, about 0.6 inch of metal has to disappear.  With a slit width of .060-.090, a dozen slits gave about the right gap to make the bends and allow for welding them back together.  The tabs had to be bent down at 90 degrees, then up again, to get a 3/8 inch spacing between the outer skin and the stiffener.  The tips of the tabs came together when I bent the tabs over the buck.  Then the blank was put on to the buck and clamped in place.  I hammered each tab down, then placed another curved 3/8 inch bar on top and did a reverse bend.  Of course, all of this was helped with the use of screwdrivers, Vise-grips, pry bars, clamps, body hammers, and a good square dolly made a from a 1x3 inch steel bar.  The local steel merchant sold me some short pieces of this bar as scrap for a dollar or two.

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Metal blank with tabs cut.  The clamp holds the sheet metal against the edge of the buck to get a sharp corner.  A little tapping with the body hammer and dolly will get all the tabs to lay flat.  Note the strap clamp at the bottom to hold the other edge against the buck, too.

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Reverse bends made in tabs to form pinch weld edge.  The curved 3/8 inch bar was used to clamp the sheet metal against the buck while the tabs were lifted.  Some tapping against the dolly helped to get square bends and align all of the 19 tabs.

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The sheet metal part after bending.

Now it was time for the MIG welder.  I left the sheet metal part clamped to the buck to hold its shape.  To prevent burning through the 18 gauge steel, I used   Vise-grips to hold a 1/4 inch thick piece of copper bar against the outer surface of the tabs, then started tacking the tabs together on the inside.  When they were tacked, I ran a weld bead along the entire inside joint of the all the tabs to provide a base for the outside welds.  Then I welded the outer surfaces.  A whole lot of grinding and a little finish work with a flap wheel made the welds disappear on the outside surfaces.  I had to grind part of the weld beads on the inside so that the inner face of the lip could mate up with the stiffener and the rest of the cab skin.   Since I don't have a pinch welder, I will drill 1/4 inch holes in the lip later and make plug welds.  When I was finished the first side, I started all over again for the other side - another wood buck, more bending, hammering, welding, and grinding.  Eventually I had a matched pair of new corners.

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Welding was done with the part on the buck so the shape wouldn't change.

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A finished cab corner after grinding and a little polishing.

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The inside of the cab corner.  Some of the 19 welds are visible where the lip bends out.

I cut off the old corners a little shy of 3.5 inches, then welded the new corners in place with a 1/4 inch lap seam.  With the new pieces inside the skin, I welded inside and out, then ground the outer welds down to the level of the skin.   The inside welds will add strength, but they must be sealed carefully to prevent the whole thing from rusting all over again.  Then we'll weld the new stiffeners in place.  It will take only a little body filler to hide the outside weld line.  Any remaining trace of the tab welds will be covered by a little primer and sanding.  Of course, I haven't yet figured out how to weld overhead, so installing both corners meant I had to roll the cab from side to side on its cradle.  Welding down or sideways is OK, but the overhead position just rains hot metal down on me!

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The outside of the corner after welding.

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The inside of the corner after welding.

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The right side cab corner welded in place.  The welds were ground on the outside with a flap wheel, then lightly sandblasted.

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The corner after cleaning things up a little.  A little more filling and grinding was needed to match the lip at the weld.  The lip was made a little wider than the final dimension, but will be ground down after welding the stiffener in place.

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