 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 Construction Rules page of this site).
Ultimately, only a hand full of scouts will win a trophy.
Thus, it is suggested that the adult partner spend quality time with assisting the cub scout in creating a unique car
that will proudly display the combined talents of the your team. If you happen to win the race, it's a bonus!
Please do not short-cut the process by borrowing parts from last year's car. Start with a new pinewood derby kit
each year. "Short-cutting habits" will undermind character development
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 construction categories;
Designing, Woodworking & Sanding, Wheels and Axles, Weight Placement, and Painting. Your Pack Unit may have a construction
workshop to help each team get started.
The following construction
"Tips" are only suggestions to consider.
Fast Cars-Thin
Shape - An
aerodynamic designed provides for less friction. Tests show that thin shaped Pinewood Derby cars are faster. Although
the wedge design is most common, curved designs can be just as effective. Also consider the regulation length and width
of the car in your design. No part of the car must extrude past the regulation length (7 inches). Design the placement
of the weights and wheels with the length limits in mind.
Weight of Cars - The Pinewood Derby car must no 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! However, 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 at the last minute to meet the regulations. Caution:
Do not place weights in a way that adds length beyond the regulation length.
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 may 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.
- Be careful not to over sand the axles. The head (shaft) of the axle can be tapered slightly so it rubs against the wheel
less.
- Wax the axles with furniture polish. Make sure the polish does
not contain a solvent of any sort.
- When you place your car on a flat surface, it is quit possible that only three
wheels will touch the track. This is a natural balancing phenomenon. Just make sure that the fourth wheel's tread
fits flat on the tract. The inspectors are looking for intent to deliberately alter the wheels and axles.
Do not drill axles holes at an angle or bend an axle deliberately. Obviously, there is less friction with 3 wheels rolling
than 4. Be sure to check the contact of the flat surface of the wheel to the track (surface) with a magnifying glass.
The inspectors do.
| NOTICE: |
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| Wheel Tread Is FLAT |
Refining the Wheels
- The wheels of a Pinewood Derby car must remain
flat. Smoothing the flat wheels will reduce friction. Below are some hints to consider.
- First, consider your District's construction rules. In the
NT District, the wheel tread must be present during inspection. With this in mind, one should still "debur" the
wheels. These small blemishes are caused by the molding process. To remove the burs, use 600 grit sandpaper.
Inside as well as out. Sand any bumps off the wheel. Metal polish will restore the gloss. Be careful not to break
any rules regarding wheel modification. Narrower wheels have less friction, but are Not Allowed. The tread
must remain flat with 100% of the tread resting flat on the track. Do not sand away the dotted mold on each
end of the tread. Do not sand too much in one place or you'll create a flat spot. Caution, electric drill
sanding may damage the plastic wheels.
- Use graphite only. Oil damages the paint and collects dust. I'm told that
the graphite works better than the new white teflon.
- Break in the wheels by spinning them with lots of graphite.
- Place a small drop of white glue where the axle enters the car block,
then put powdered graphite on top the glue once it dries. This causes less friction if the wheel should
rub against the car body.
- Other than a good polishing
of the axles, place the axles and wheels in a ziplock bag with some graphite and shake them. Some folks soak
there wheels and axles in graphite several days before a race, daily spinning the wheels on the axles.
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
| Build A Wood Frame |
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| Rest Car On Strings To Paint |
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 or similar tool 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
Caution: The axels(nails) must extrude from the body as
perfectly parrallel as possible so that 100% of the wheel tread touches the surface of the track. This effect
is judged more strictly on cars that have new axle holes. When using the pre-slotted axles holders, try your
best to line the axles appropriately. Axle bending is also not allowed.
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!
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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.
Eight Tips For Pinewood Derby Cars
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