Cub Scout Pinewood Derby: Building the Batmobile, Part I

My six-year-old son started Cub Scouting this year, and he’s really taken to the program. One activity in particular that excites him is the annual Pinewood Derby race, in which scouts and their parents create race cars from blocks of wood and compete against vehicles made by other scouts. Fortunately, we were provided with an official Boy Scouts of America (BSA) Cub Scout Pinewood Derby Kit, which includes a regulation size pinewood block, four BSA-approved wheels and nail axles for starting materials; the rest was up to us. After doing some Internet research on common pinewood car design mistakes to avoid, we were ready to go.

Since my son is only in his first year of scouting – a Tiger Cub – and since I’m pretty new to this, too, we decided to purchase a design kit from an area hobby shop: the Batcar. Really, the kit just includes a paper template for shaping the car (which I really needed, not knowing what that should look like), some plastic fenders, metal weights to bring the vehicle up to the maximum 5 oz. allowable under derby rules, and decals for the finished car.

We started with this:

Before doing anything else, make sure that the grooves in the bottom of the block – which will later serve to hold the axles – have been cut square with the sides of the block. If the grooves are not square, your car won’t roll straight. You can check to see if the grooves are square by using a square, but anything with a machine-squared edge (even a piece of notebook paper) will do in a pinch.

Now that we know our grooves are square, we need to begin work on shaping the block. Fortunately, the Batcar kit included a cut-out paper template we could trace, so we placed it on the side of the car and traced it.

Now that we have an outline, it was time for a quick trip to the bandsaw to shape the block. We ended up with this:

Of course, this was way too rough to leave as-is. after all, we’ve got to account for wind resistance, and this thing needs to be slicker than Richard Nixon. And so the long, laborious process of sanding the rough saw cuts down began, and my eager, young Cub Scout set to the task in earnest.

The next step involves cutting the fenders and other effects out of the plastic sheet they were cast into, which requires some pretty careful work with an X-Acto knife – this one had to be a daddy step.

While cutting these effects out of the plastic, the manufacturer cautions that a small amount of excess plastic should be left around the edges of the pieces; the excess plastic needs to be sanded away until each piece is level. Cutting too closely can result in large sections of the piece being cut away if the knife slips, so it’s safer to sand them into shape, even if it is a lot more time-consuming.

While the effects for the sides and hood of the car are now ready to go as they are, the fenders will present a problem when glued to the chassis. Gluing the fenders where the template indicates will result in the backs of the fenders projecting above the top surface of the car; since these fenders are hollow, the open backs of the fenders could catch air and slow the car down. Fortunately, the manufacturer anticipated this issue, and included an optional sheet of plasticard that a modeler can glue to the backs of the fenders, closing them off. We ended our first evening of car-building with gluing the hollow fenders to the plasticard with super glue; we’ll cut them out and sand them level in the morning.

We’ll have our next post in this series no later than next week. Best wishes until then.