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Transforming that Block into the Ultimate Derby Car
After waiting for a whole year, the time has finally arrived to transform a pine block into the ultimate derby car. I know it is tempting to draw a few lines and start cutting. But before that, ask yourself two questions:
1. Where will the weight go? Depending on how much wood you remove, you will likely need to add between 2.5 to 3.5 ounces of weight. Too often car builders don't consider the need to add weight until after the car is shaped and painted. The time to deal with the weight is now, before cutting the block. So, figure out what kind of weight you will be using and where it will go. Speaking of where the weight will go ...
2. Does the design allow the weight to be placed near the rear axle? For best performance most people recommend locating the center of gravity of the car 1 to 1-1/2" in front of the rear axle. So, put about 2/3 of the weight in front of the rear axle, and the rest behind the rear axle (For cars with a light front end, you may need to put 3/4 in front and 1/4 behind).
Sketching - Now that you know where the weight will go, draw the side profile of the car on both sides of the block, and draw the top profile on the bottom of the block. Then draw the location of the pockets/holes for the weight.
Rough Cutting - The weight pockets/holes are much easier to create while the block is rectangular. So, begin the shaping process by creating the weight pockets/holes. Then begin shaping the block by removing the wood from the top of the car (using the drawing on the sides of the car), then remove the wood from the sides of the car (using the drawing on the bottom of the car).
Shaping - Shape the car using a rasp, file, coarse (60-grit) sandpaper, etc. If you have a steady hand, a Dremel tool is handy. If there are any gouges (boo-boos), fill them with wood putty.
Sanding - When the car is shaped as desired, sand the car with medium (150-220 grit) sandpaper, followed by fine (400 grit) sandpaper. If you want a nice finish, make sure that the car is very smooth. There should not be any visible marks on the car (with the possible exception of fine sandpaper marks on the bottom of the car, or on the back of the car where the wood end-grain is visible).
Preparing to Paint - The car is now ready to paint. I recommend inserting a long cabinet screw into the bottom of the car (screw it into a weight pocket if present) as a painting handle. The screw only needs to go deep enough to be firmly in place. Be careful to not run the screw completely through the car! Now locate a place in a dust-free, shaded area where you can hang the car while it dries. In this location hang a short wire between two nails or screws such that the car can be suspended from the wire without touching a wall or other object.
Painting Protection - If you will be using spray paint, put on eye and breathing protection. Then place a plastic bag over the hand that will hold the car and secure the bag with a rubber band around the wrist.
Painting - Paint the car following the recommendations on the paint can. For spray painting, I recommend starting with several coats of primer followed by 2 to 3 coats of acrylic-lacquer paint. For brush painting, acrylic paints work well.
Drying - Hang the car to dry between coats. Use a binder clip or clothespin to attach the screw to the wire. After the paint is dry and before applying the next coat of paint, sand the car very lightly with 600 grit sandpaper and wipe off the paint dust.
Detailing - The car is now ready for numbers, decals, or other decorations. After decorating, you may want to apply a clear coat finish.
Whew! That was a lot of work, but the car body is complete and it looks great. But if you want the car to be fast, your work has only begun ...
From Pinewood Derby Times Volume 1, Issue 3
A feature article is a regular part of the Pinewood Derby Times Newsletter. To subscribe to this free e-newsletter, please visit: www.maximum-velocity.com/subscribe.htm