Last month, we laid the foundation for the front end of the Project Potvin '29 roadster in the form of building a buck over which to shape the track nose. The buck turned out great and it was shipped to Elgin, Illinois, after a little bit of tweaking and fine-tuning, where Sam Waltermire at the Roadster Shop would be handling the aluminum work on the track nose. We met up with the boys at the Roadster Shop and followed along as Sam started to bang out the aluminum nose.
Making a pattern was the first step in transforming the wooden buck into an actual aluminum piece. Using various points on the buck as references, a pattern was made and transferred to a sheet of aluminum. These reference points will tell Sam a number of things. Two points will correspond with two pins located on the buck; these will serve to locate the workpiece as it's being shaped in relation to the buck. A set of lines running perpendicular to the workpiece marks the location where the pattern was folded to conform to the shape of the buck. These lines will communicate to Sam the location and approximate amount of shrinking needed on the workpiece. These few lines will get the shape started and "rough form" the workpiece to the shape of the buck.
Taking a pattern off the wooden...
Taking a pattern off the wooden buck that will be transferred to a sheet of aluminum is the first step to creating the track nose.
Before any forming is done to the aluminum, Sam anneals it to make it easier to work with. Common aluminum is annealed by heating it to its critical temperature, which is near 800 degrees Fahrenheit. The easiest way to anneal aluminum in the garage is to use an oxyacetylene torch. A pure acetylene flame is applied to the surface, coating it with a light layer of soot. Once the entire work surface is covered, a neutral flame is used to burn off the soot. You can also buy temperature-indicating crayons at welding supply stores to more closely monitor the temperature of the metal as it is heated.
The first step in shaping the aluminum workpiece takes place in a Pullmax machine. Though originally designed to shear sheetmetal, numerous additional uses-from punching louvers to forming beads-have been devised for the Pullmax. Since the workpiece for the track nose needs to be shrunk on the edge, a set of thumbnail dies is installed in the jaws of the Pullmax. More commonly used in a power hammer, the Pullmax works great for smaller-scale work like the track-nose pieces. The thumbnail dies work by shrinking in the material from the edge. A tuck or peak is formed when the workpiece is pushed through the dies; the tuck is hammered flat on the way back out, shrinking that area. A common misconception is that the Pullmax and its larger brethren, the power hammer, is beating on the material. While contact is made, it's not beating on it so much as it's working it to the desired effect. Most machines can be adjusted in both the stroke of the plunger unit and the height of the dies, adjusting the amount of severity that the workpiece endures when the dies close. This allows the user total control over how much each stroke affects the workpiece.
The black lines designate...
The black lines designate where the initial shrinking will take place and about how far back to create the front silhouette.
While the Pullmax and a few body hammers work great in shaping the workpiece, the surface finish that results leaves something to be desired. All that shrinking and hammering needs to be smoothed out to a glass-like finish and that's where the air planishing hammer comes in. Using a low-crown set of dies, the planishing hammer gently hammers the workpiece smooth, using a process similar to a typical handheld hammer and dolly process, only much quicker. The finish created by the planishing hammer can be massaged into a finish fit to polish, if the operator so desires.
These three techniques-shrinking in the Pullmax, freehand hammer-forming using a variety of rubber mallets, and air planishing to massage the surface smooth-were used to form the two halves that will be joined to form the track nose of the '29. Both halves were fabricated using the buck as the foundation, resulting in an almost identical pair to form the one-piece nose. Next month, we'll join the two halves and mount the finished nose onto the front of the '29, thus completing the rhinoplasty on the Project Potvin '29.
Lineup marks are made on the...
Lineup marks are made on the pattern and will be transferred to the sheet of aluminum.
These will correspond to two...
These will correspond to two pins installed on the buck that will serve to line up the aluminum material in the same place on the buck every time as the piece is being formed.
The pattern is complete and...
The pattern is complete and ready to be transferred to the sheet of aluminum. The triangular marks at the top represent where the paper was folded to conform to the buck and will be approximately the amount of shrinking to get the aluminum to do the same.
After tracing the pattern...
After tracing the pattern to the aluminum sheet, it's cut out using a sheetmetal nibbler. Notice that all the corresponding marks have been transferred to the aluminum, including the stretch pattern and locating pins.
The aluminum pieces are annealed...
The aluminum pieces are annealed before any of the metalwork begins. A light coat of carbon is applied using a pure acetylene flame.
It's going to take a lot of...
It's going to take a lot of shrinking to get that big compound curve at the front of the nose. That's a job for a Pullmax machine equipped with a set of thumbnail shrinking dies. The shrinking process happens in two steps.
This next step is where the...
This next step is where the material is actually shrunk. Walked back through the jaws in the opposite direction, the jaws hold the peak in place while simultaneously forcing the material into itself, ultimately shrinking it in the process.
After some time on the Pullmax,...
After some time on the Pullmax, the panel is starting to take shape. While the Pullmax offers a lot of control in terms of how fast or slow it gets the job done, it's still important to periodically check the workpiece against the buck.
While the shrinking process...
While the shrinking process is doing a great job of shaping the outer edge, the inner area needed to be massaged using a tear-dropped plastic mallet.
The workpiece is really starting...
The workpiece is really starting to take shape, so it's off to the planishing hammer where the rather rough work from the Pullmax and plastic mallet can be massaged.
After a few minutes on the...
After a few minutes on the planishing hammer, the workpiece is starting to follow the silhouette of the buck much better and all the abrupt curves put into it by the Pullmax have been worked into a consistent compound curve.
The edge is still a little...
The edge is still a little rough, so a hammer and dolly are used to get it nice and straight.
It's impossible to describe...
It's impossible to describe how much time is spent on the planishing hammer-once again, the workpiece goes back in between the jaws of the planishing hammer to then work it smooth after every strike of the hammer.
It became apparent that a...
It became apparent that a few spots on the buck needed to be massaged once the workpiece really started to take shape. As the metal began to form, it was noticed that the natural curve in the silhouette resulted in a high spot at the center of the buck.
With the front side of the...
With the front side of the panel fitting against the buck pretty well, it was time to start fine-tuning the bottom portion. The same process is used here, but on a smaller scale.
Sam uses a flexible steel...
Sam uses a flexible steel ruler and drags it along the surface of the workpiece, effectively marring the surface and revealing any high and low spots in the process.
With the high spots revealed,...
With the high spots revealed, a few light blows with a body hammer can coax them down. This process is commonly done with a file, effectively removing material in the process.
The second half of the track...
The second half of the track nose is made in the same manner as the first, albeit quite a bit quicker since most of the forethought has already been figured out with the first piece.