  Pinewood Derby Construction Secrets
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 an influential adult. It is suggested that
the adult partner spend quality time assisting the Cub Scout in creating a unique car that will proudly display
the combined talents of the "Team". Remember, only a hand full of scouts will win a trophy.
If you happen to win the race or are chosen for best design, it's a bonus! Winning a trophy is not the goal
of the Pinewood Derby. It's the events that lead up to a Pinewood Derby that are intended to touch upon character
development. With that in mind, please do not short-cut the process by borrowing parts from last year's car or
purchasing pre-formed wheels, axles or car body. Get a fresh start each year with a new BSA Grand Prix Pinewood
Derby Car kit. You will likely be pleasantly surprised, next year, when your Cub remembers the things that
may not have gone so smoothly during the construction process this year.
Plan Of Action
The "Team" should sit down together and discuss the new year's plan.
Perhaps one of the first questions should be: Does the Cub desire to build a fast car or a uniquely designed car? The
Natchez Trace District offers awards for top speedsters and designs. Speedstars do not qualify for design awards.
Design entries at the district will not race.
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 & Accessories 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 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. Many shops sell lead as rectangular or triangular plate that can be "recessed" under the car.
Lead tubes can also be inserted into the car block by drilling holes. Unfortunately, BBs, coins, washer have
a higher probability of dropping off the car during a race, which is not allowed. Do not tape weights
to the car. All weights that are placed underneath the car
must be recessed into the car body.
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.
Six Points of Friction - Discuss with you son(s) the
6 places friction occurs on a pinewood derby car. Take time to talk about each one. Let them dream up their own
ways to reduce each area of friction
- Between Axles and Wheels
- Between Wheel and Car Side
- Between the Car and the Air
- Between Wheels and Track
- Between Wheels and Track Guide
- Between Car Bottom and Track Guide
Tips - 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 nail 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 sanded or filed slightly to remove molding
marks.
- 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 three
wheels rolling than four. However, many experts say that "three-wheel" cars can cause a natural unbalanced
effect during the race that will slow the car down slightly just before the finishline.
| NOTICE: |
|
| 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 remain flat to the track surface to pass inspection. Burs are small blemishes
on the plastic wheels caused by the molding process. To remove the burs, sand any bumps off the wheel. This
process is easier using a special wheel turning mandrel, sold by Pinecar and other retailers. Do not sand
away the dotted mold on each end of the tread.
- Do not cover your wheels in graphite or other lubricant. Be careful
not to break any rules regarding wheel modification. While narrower wheels have less friction, this is Not Allowed.
The tread must remain flat with 100% of the tread resting flat on the track. Do not sand the wheel tread too
much in one place or you'll create a flat spot. Caution, electric drill sanding can damage the plastic
wheels if used incorrectly.
- 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 in the axle
holes.
- On the car body, some builders place a small drop of white glue where
the axle enters the car block, then powdered graphite is placed 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 in a ziplock bag with some graphite and shake them. Some folks soak their axles
in graphite several days before a race, daily spinning the wheels on the axles. Axles can perform better with use.
- Wheel performance is key to a smoother and faster running car. Radial
and lateral run-out (up and down/side to side movement of the wheel) slows down your project car, causing it to vibrate and
shimmy and constantly changing the car's center of gravity. You can verify each wheel's condition by spinning it on one of
the axles provided in the kit. Be sure the axle is free of burrs and is smooth. If the wheel runs very smoothly and for a
considerable amount of time, mark it and set it aside as a good one. Check all four this way. If you have one or two "wobbly"
wheels, install them on the lightest end of the car. This will reduce their effect. If you have more than that, consider purchasing
a second kit and use the best 4 wheels from both.
Sanding & Painting -
Sand the car for a smooth surface. Sanding sealer helps to fill-in
nicks. Adults should supervise all sanding and painting. Children should never use spray can paints. Always
wear protective gear when painting (eyes, breathing, hands). Never paint in a closed area that does no have ventilation.
| Build A Wood Frame |
|
|
| Rest Car On Strings or WireTo Paint |
Making Holes for the Axles - If you are using the axle slot on the block, 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, obtain the appropriate sized drill
bit. 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. Matching the axle size with the drill size is important for the
process to work.
Another Tip - To improve axle alignment avoid drilling into the
wood grains which can deflect the tiny bit. Begin with an uncut block. Widen and deepen the existing slots to about 1/4" square
with a saw. Fill them with JB Weld epoxy, sand smooth. Using drill press, high rpm and #44 bit(0.086" dia) drill axle holes.
Be careful to layout the hole centers with precision, prick the center to start the bit. Maintain the original wheel base
spacing. Once holes are drilled you can recut the slot using a bandsaw very carefully. The epoxy will drill a much straighter
and consistant hole than natural wood.
Caution: The axles(nails) must extrude from the body as
perfectly parallel 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 axle holes. When using the pre-slotted axles holders, try your
best to line the axles appropriately using an alignment tool, sold at retailers that have PineCar accessories. Axle
bending or wheel tipping 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 holes or
slot. This will reduce wheel to body friction. Or, use the clue tip previously mentioned. 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 from loosening
out. Epoxy glue is the best. Put some glue in the slot before you insert the axle. Be careful not to get any of the glue
on the wheel or on the axle where the wheel rest. Wheels, glue and axles is not a fast alternative!
Axles must aligned in the car body straight, front to back. That is,
square to the body. Don't trust the slots! A wheel alignment tool helps straighten the wheels and axles.
After installing 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
for the car you will race in the current year.
- Finally, made notes about you construction experience. You
most likely figured out how to do a few task more efficiently. These notes will benefit you on the construction
of a new car next year.
Informational Web Links - There
are several web sites on the Internet that offer construction tips. Pinewood Derby Car events have become
an industry in recent years. Many different organizations have pinewood derby races. Therefore,
construction rules and guidelines vary widely. The Natchez Trace District and most other Districts place 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. Extra wheels and axles can also be purchased from an authorized Scout Shop.
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 car building 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, many 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 your District's 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.
PineCar Videos Link
Six Tips For Pinewood Derby Cars
|
