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This is the third and final post in a series about building a Cub Scout Pinewood Derby car that takes style cues from the Batmobile.

The first post in this series can be found here, while the second can be found by clicking here.

We left off with the chassis structurally complete, sanded, primed and painted black. The next step was to apply the decals that came with the kit; these are pretty standard dry rub decals, and were easily applied with teh blunt end of a clay shaper we had on hand. Of course, almost any blunt object will work for this purpose, ranging from a hobbyist’s burnisher to a humble, dull pencil. The kid was able to put these on with ease.

After the decals are rubbed on, they are still pretty fragile, so the next step is to take a piece of treated paper that came with the decals, and rub that paper over the decals to help prevent them from tearing or being rubbed off during handling.

The next step is applying multiple coats of gloss varnish, for two reasons: first, the varnish will seal and protect the paint and decals, and second, a gloss finish is smoother than paint, so there will be less wind resistance on the car as it travels down the track. Since placing the car on newspaper and then spraying gloss varnish wasn’t an option – the car will end up sticking to the paper, and it’s almost impossible to clean up – we improvised a pretty crude method of suspending the car in the air while we sprayed the varnish. We took a scrap of wood we were using for spraypainting and hammered a few roofing nails into it, so that all of the nail heads were about level. We placed the car on top of it and sprayed away.

After spraying multiple coats – and sanding across the woodgrain between coats  to help reduce the ridges between the woodgrains – we had a fully varnished Batmobile:

We were very pleased with the results thus far, but we did notice that our Batmobile still doesn’t have wheels. Since one of my hobbies is miniature wargaming, I decided to embark on a totally unnecessary but fun task for the wheels while I was waiting for the mutliple coats of varnish to dry. I broke out the highly-pigmented paints formulated for miniatures and the fine brushes I normally use for painting eyeballs and coat buttons on miniature soldiers, did a quick metallic drybrush on the rims to make them appear like brushed aluminum and, using some magnification, painted the raised white letters on the tire walls. While this step won’t make the car go faster, it did make it look cooler.

The next step involves tacking the wheels in place. We used a medium-sized tack hammer for the job, being careful not to mar the paint anywhere.

Now that the wheels are tacked on, it is necessary to align them so that the car will roll in a straight line for 10 feet. If a car pulls to one side or the other when it rolls, it will be grinding along the track guides as it rolls downhill on race day – something we clearly don’t want. fortunately, there is a great how-to video on the Pine Car Web site on this very topic.

One we followed the instructions in the video and had the wheels relatively aligned (we still have a slight pull to the left, but we got to a point where we just had to say it was close enough), the axles were glued in place.

Once the glue was dry, the Batmobile is basically finished. We’ll still need to add weight on race day to get it up to 5 ounces, but the car is done for all practical purposes.

The Derby is next Saturday, Jan. 14; we’ll let everyone know how the Batmobile fared in the race in next week’s posting.

Update, 11 January 2012: in case anyone was wondering, the second car we made as we were working on the Batmobile – the white Trans Am we dubbed “The Screaming Eagle” – turned out pretty well, too:

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.

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.