Pinewood Derby Construction Secrets
The "BSA Kit" instructions provided in the box are adequate for many builders. However, for more creative builders, the District has provided a set of construction limits (see the Official Pinewood Derby Grand Prix Construction Rules page).
First, form your team. The Team usually consist of a cub scout(s) and adult partner. The adult(s) can be a parent, guardian, grandparent or any influencial adult. It is suggested that the adult partner(s) spend quality time assisting the Cub Scout in creating a unique car that will proudly display the combined talents of the your team. Remember, only a hand full of scouts will win a trophy. If you happen to win the race, it's a bonus! However, winnning a trophy is not quite the goal of the Pinewood Derby. The events that lead up to a Pinewood Derby are intended to touch on character development. With that in mind, please do not short-cut the process by borrowing parts from last year's car. Get a fresh start each year with a new Grand Prix pinewood derby kit. You will likely be pleasantly surprised when your Cub remembers the things that may not have gone so smoothly during the construction process last year.
Plan Of Action
The "Team" (adults and cub) should sit down together and discuss the new year's plan. Does the Cub desire to build a fast car or a uniquly designed car?
Try to plan at least 3 or 4 construction sessions over a period of time, well before the Pack race. Many adults choose to divide building sessions into the different categories; Designing, Woodworking & Sanding, Weight Placement, Wheels and Axles, Painting & Acessories and finally testing. Your Pack Unit may have a construction workshop to help each team get started.
The following construction "Tips" are speed oriented suggestions to consider.
Fast Cars- Thin Shape - An aerodynamic designed allows less friction. Tests show that thinly shaped Pinewood Derby cars are faster. Although the wedge design is most common, curved designs can be just as effective.
Add-ons - Some scouts will enjoy placing add-ons to their car. These items are available at the Scout Shop. One word of caution, add-ons generally slow down a car. If you goal is not to make a fast car, then perhaps a very unique design is the thing for you. My son always placed a small windshield on his car with some type of figure that represented a driver. Be creative and have fun, within the limits.
Add-ons are not allowed if they cover any space behind the wheels or if the add-on encloses the car block. Be sure all add-ons are permanently secured to the car body. Remember, all other rules apply.
Weight of Cars - The Pinewood Derby car must weigh no more than 5 oz (142 g). Many successful cars come very close to this maximum weight. While a well made "frictionless" car can sometime outperform a heavier car, the Pinewood Derby car with both these attributes is really fast! To avoid weighing scale discrepancies, shoot for the 4.80 to 4.90 ounce car weight. Lead is the weighting substance of choice because of its high mass and availability. Shops sell lead as rectangular or triangular plates that can be recessed under the car (routed out). Lead tubes can also be inserted in drilled holes. BBs, coins, washer, etc. have been used successfully in the past. However, do not tape or clue these type of weight to the car. All weights that are placed underneath the car must be recessed.
Weight Placement - The placement of weights on a car has always been a big debate. Many recommend placing the weight so that the car will balance approximately 1 inch forward of the rear axle. To find the balance point, temporarily attach the wheels to the car plus anything else that will be affixed to the car, tape your weight(s) in place, and balance the car on an edge of your choice. WEIGH YOUR CAR on a calibrated scale (post office scale, etc.) and keep working with your weights until you reach a weight that is satisfactory. Remember, don't shoot for exactly 5 oz. It is embarrassing to start carving weight from the car to meet the rules.
Friction Is the Enemy - Perhaps the most important step in building a fast car is reducing friction. Any time there are moving parts, there is friction. The axles for Pinewood Derby cars are nails. The shafts of these nails may look smooth, but they are not! Look at one closely with a magnifying glass, especially around the head. You will see all kinds of burrs that could cause friction. Below is a list of helpful hints that may assist you. Remember: ALWAYS WEAR SAFETY GLASSES when using a power tool.
Polish the axles. First with a 400 grit if you have a really bad spot. Then a 600 grit, and then a jewelers rouge. Finish off with a chrome/metal polish.
The head of the axle should be tapered slightly so it rubs against the wheel less.
Some scout spray several coats of furniture polish on the axles. Make sure the polish does not contain a solvent of any sort.
Smooth and Polish Axles
Refining the Wheels - The wheels of a Pinewood Derby car must remain flat. Smoothing the flat wheels will reduce friction. Keep in mind that All BSA Markings on the wheels must be untouched and clearly in view. Below are some hints to consider.
Debur the wheels - Take off the flashing and seam that was produced when the wheel was molded with a 600 grit or better sandpaper. Inside as well as out. Sand any bumps off the wheel the sandpaper. Metal polish will restore the gloss. Be careful lot to break any rules your race has regarding wheel modification. While narrower wheels will have less friction, this is not allowed. The tread must remain flat on the surface. Do not sand too much or you'll create a flat spot. Caution, electric drill sanding may damage the plastic wheel. Some have gone as far as to lath the inside of the wheel hub. This is allowed in some districts as long as the BSA markings are visible.
Use graphite only - Oil damages the paint and collects dust. I'm told that the graphite works better than the new white teflon. You be the judge. Do not bring oily wheels to the race. Break in the wheels by spinning them with lots of graphite. Put a small drop of white glue where the axle goes into the car body and put powdered graphite on it there. That causes less friction if the wheel should rub against the car body. Other than the good polishing of the axles, place the axles and wheels in a ziplock bag with some graphite and shake them. Let stand for a few days prior to the race.
Please remember that the intent of the cosntruction rules is to place most of your participating scouts on the same playing field. Perhaps your Pack can add an Outlaw Race for parents that like extreme racing techniques.
Final Touches - Sand the car for a smooth surface, and put sanding sealer on the car to fill in nicks. Finally, test your car at home.
Sanding & Painting - First use a sandable primer or wood sealer. White is for light colors and grey for dark colors. Some prefer to paint a primer on first to allow last minute touch up of small imperfections that may not have been notice before.
Select a glossy enamel finish for the car. Its worth it. After all that work, this is the final touch. Several light coats work better. After the last coat of paint is dry, at a clear gloss coat to make a bright shine. Some gloss products may be incompatible with the paint.
Water based paints dry quicker (1 hour) than oil based paints (24 Hours).
Cubs love to put decals on the car. The more.....the better.
Making Holes for the Axles - Lay the body in its side. Take a hammer and drive a SPARE axle nail (not one of your polished axles!) into the slot, right at the top of the slot. Be sure to tap the nail in straight. Leave about 1/4" of the nail sticking out. Pull out the axle with a pair of pliers. Do the same thing for the other three axle slots or holes. If you are drilling new holes, then get a drill bit that is the size of the axle. Use a drill press to drill each hole. Then, use a spare nail (axle) to tap in snug. You may need to ream the hole slightly for a good snug fit
Finally! It's Time To Go Straight!
Before you install the wheels and axles, lube the side of the body where the wheel will occasionally rub. Dip your little pinky into some of the powder and rub it around each axle hole or slot. This will reduce wheel to body friction and make the car go faster. Lay the body on its side. Place the wheels on the axles. With a small hammer, gently tap the axles into the axle slot or hole. Leave about 1/8" to 3/32" of clearance between the wheel and the body. Turn the car over. Place it on a small block of wood on your workbench. Gently tap in the other two axles and wheels. If you are using the slots for the axles, glue them in to prevent them from coming out. Epoxy glue is the best, but any good quality white glue will do. Put some glue in the slot before you insert the axle. After the axle is in place, put some more glue on the axle. Be careful not to get any of the glue on the wheel or on the axle where the wheel runs. Wheels glued to axles do not run very fast!
Axles must be in straight front to back - That is, square to the body. Don't trust the slots! If you have one, use a drill press to ensure all axles are straight. One of the front and two of the back should be measured to be the same height. After pressing in the axles, test the car for crooked wheels...roll it on the floor. If the wheels are on straight, the car should roll 8-10 feet in a fairly straight line. Should the car turn left or right, you need to tinker with the axle placement without removing them from the car body, until it rolls straight. Once you match a wheel and axle together with graphite, keep them together. They wear into each other as a matched set.
Informational Web Links - There are several web sites on the internet that offer construction tips. The Pinewood Derby Car events have become an industry in recent years. Many different organizations utilize pinewood derby races for similar child development goals. As a result, construction rules and guidlines vary widely. This is exactly the reason for placing heavy emphasis on the traditional Cub Scout Grand Prix kit and restricted construction rules.
Please remember, every participant in a Cub Scout Pinewood Derby must use the pinewood block, wheels and axles from the BSA Grand Prix kit sold at authorized Scout shops in your area.
One of the best "basic" car building web sites is by PineCar. There are several "How-To" videos on the PineCar web site that can help the novice through the process. Just remember that the basic parts used in these videos are sold by PineCar and not BSA. PineCar pinewood blocks, PineCar wheels and PineCar axles are not allowed. However, most of the tools and car accessories offered by PineCar appear to be acceptable. Other vendors on the Internet have acceptable tools and accessories as well. Always consider the District construction rules before taking a chance on a tool or part that may disqualify your Grand Prix pinewood derby car. PineCar tools and accessories are found in many hobby shops.