Cub Scout Pinewood Derby: Building the Batmobile, Part II

This post is the second in a series on building a Cub Scout Pinewood Derby car that takes style cues from the Batmobile. The first posting in this series can be found here.

We left off our construction with the wooden block shaped and sanded, the fenders and design effects cut out and sanded, the hollow fenders sealed by supergluing plasticard to their backs, and the plasticard backing sanded flush with the fenders.

In between the two posts of this series, I did a bit more research and found some video tutorials on the pinecar.com Web site. While there, I discovered a tutorial on hollowing out the bottom of part of the car to make space for the metal weights; this way, extra weight under the car won’t be visible. It certainly isn’t necessary to do this step, but it’s something the kid and I decided would be cool.

With hindsight being perfect, I’d recommend performing this step before shaping the block, since keeping the shaped chassis level in a drill press was a bit of a challenge.

To properly countersink the weight, it was necessary to begin by doing a bit of measuring. The chassis weights that came with the kit measured 3/4″ wide, 3 1/2″ long,and 1/8″ thick. I decided that I’d like to leave enough room to put in two layers of weights if necessary, so I had to carve out a space of the correct length and width, while tripling the thickness, to allow space for the weights, screw heads and a bit of extra depth in case my drill work wasn’t perfectly even. A little basic math, and I’d arrived at how far in I’d need to measure from the axle grooves and the sides of the chassis to properly center the weight (if you’re using Pine Car weights, you’ll need to measure in 3/8″ toward the center from each axle groove and 1/2″ toward the center from either side, assuming you’re using a regulation Cub Scout block).

I started by marking the drill bit with a piece of tape, leaving the 1/4″ inch I wanted for depth exposed. I then drew a grid of lines to serve as a guide for where I should drill the holes.

After the grid was drawn, I wrapped the chassis in rags to protect it from the vise holding it in place, and put the drill bit into the drill press:

Then the drilling started. Drilling the holes right next to each other creates a router-like effect, as the drill bit bites away at the wood and the tape serves as a guide to make the depth more or less uniform:

Of course, the drill isn’t exactly a fine instrument, so the interior surface of the hollow isn’t very clean, as the next photo indicates. Still, it is large enough and deep enough to accommodate the metal weights.

The next step involves cleaning up the hollow, which I did with an ordinary wood chisel. Owners of some hobby tools, like the Dremel rotary tool, will probably have an easier time of this task.

While clearly not done with mechanical precision, the chisel got the job done. The space within will snugly accommodate up to three layers of Pine Car weights, more than we’ll ever need.

By now, all the gluing and sanding we did on the fenders and other effects are completed, to it is time to use the template to dry fit where we want to place them on the car. Obviously, it’s a good idea to lightly tack the wheels into place at this time, so that we can be sure that the fenders won’t be grinding against the wheels when we’re done:

Once we were pleased with the position of all the pieces, we lightly traced the outlines of the pieces with pencil so we could glue them in the right place. We ended up with this:

 As we waited for the glue to dry, we made use of advice from another dad, who recommended that we use a 3/32″ drill bit to bore out the inside of each of the car’s plastic wheels; sometimes, production flaws result in burrs inside the hole through which the axles pass, and these burrs can slow down the car dramatically.

Another day has dawned, and the superglue has had enough time to cure. The time has come for us to begin priming, and the youngster is pretty excited about using spray primer for the first time. He needed a bit of help to depress the button on the can, but it was great fun, anyway. That second car to the right is a spare vehicle we’re working on (it’s supposed to look like a Trans Am when it’s done), just in case we get a kid who shows up on race day with a car that doesn’t pass inspection or that falls apart or something.

After three coats of primer, the Batmobile starts looking more like a Batmobile.

After sanding the primer with a very fine grade sandpaper, the task of basecoating the black paint begins. Good thing the rain held off long enough for us to get a few coats on the car…

Thus, at the end of our second installment of this tutorial, the Batmobile has a few coats of its signature jet black paint:

While the bulk of the work is now finished, important finishing steps remain, ranging from details like decals and such to the sometimes delicate task of aligning the wheels and balancing the car. We’ll have photos for those steps by next week.