Pinewood Derby Stories and Photos from Maximum Velocity
Royal Ranger/ S&W Kits - Getting Top Speed
In terms of kit sales, the official BSA kit is certainly the leader. The runner up is likely PineCar. But after that there are several manufacturers that produce a huge number of kits.
One of these, S&W Crafts Mfg., has been producing kits since 1957. Many kits are sold to Cub Scout packs that choose to not use the official BSA kit, and to YMCA Y-Guides ('Chule Car' races - Chule means 'pine tree' in the Creek language). Until recently they had the contract for Royal Ranger kits (a boys club sponsored by the Assemblies of God church - see: royalrangers.ag.org).
The new supplier to Royal Rangers, Amenco, is building the kits to the same specification, so Royal Rangers should continue to see the same type of kit. Here is a photo of the kit:
What is special about this kit? Mainly, the kit uses dowel rods as axle supports, screw-type axles, and narrow wheels. These narrow wheels can lead to very fast cars; however, the axle support system can be a challenge. So, this article will provide some tips for overcoming the challenges of this kit and help you achieve top speed.
To accommodate the dowel rod axle supports, the block is equipped with two 3/8" diameter, half-round slots. The slots are located about one inch from the ends of the block, thus the wheelbase is longer than most kits on the market. Make sure to load the ballast weight towards the rear of the car (which can be either end; but if you choose to retain the cutout in your design, note that it is offset towards one end of the block).
The dowel rod slots cut into the bottom of the car determine how the dowel rods will mount on the car. One of the first steps in building a pinewood derby car is to inspect the slots to see if they are square with the block, and are consistently cut to the same depth. The best way to check if the slots are square to the block is to use a tool called a 'Square'.
But if you don't have a square, align the long side of a piece of note book paper with the side of the car and see if each slot aligns with the top of the paper.
The depth of the slot can be measured with a ruler. Check the depth of both slots on the left side and on the right side of the block.
If either slot is not square, or if the slot depth is not the same at all our points then the block needs to be replaced. You can certainly just get a new block, but dowel slots can be created on a blank block if you have access to the following:
- Drill press
- 3/8 inch Brad Point or Forstner drill bit
- 2 blank blocks (or one blank block and the defective kit block)
Lay the blank blocks on their sides on the drill press table with the bottoms together (or the top of the defective kit block). Then carefully clamp the blocks together, making sure that the ends match up. Mark the desired drilling locations with a pencil in the joint between the blocks.
Place a flat board under the clamped blocks, set the drilling depth to go though the blank blocks, then set the drilling location. The drill bit must be positioned such that the tip of the bit aligns exactly with the joint between the blocks.
Now start the drill press, hold the blocks firmly, and drill the two holes. After unclamping the blocks, both blocks will have accurate dowel rod slots.
DOWEL ROD AXLE SUPPORTS
The dowel rod axle supports are essentially 3/8 inch dowel rod pieces, cut to length, and pilot-drilled on the ends.
All four pilot holes should be drilled exactly in the center of the dowel rod, and should be drilled parallel with the side of the dowel rod. Use a ruler to check if the holes are drilled in the center of the dowel rods, then insert a round toothpick (or something else that is the same size as the hole, such as a small nail) into the holes to see if the holes are drilled straight. If the toothpick appears to stick out of the hole at an angle then the holes are not straight.
If the holes are not accurate, then they need to be replaced or corrected. An accurate way to correct the pilot holes is to use a Pro-Body Tool (link), a guide for re-drilling accurate axle holes with a hand drill into dowel rod axle supports.(1)
The wheels on the kit have a dome shape-sidewall which minimizes the contact area with the axle supports. However, slightly beveling the end of the axle support will further minimize contact with the side of the wheel. This bevel can be created with a piece of sandpaper mounted on a piece of wood, and a hand drill.
1. Clamp the drill to a work surface.
2. Insert the axle support into the chuck of the drill.
3. Start the drill and apply the sandpaper to the edge of the dowel rod. Create a bevel, but be careful to not shorten the axle support.
The bevel should be very slight. Do not 'sharpen' the end of the dowel rod like a pencil as it will weaken the support and could cause binding in the wheel bore.
Next, the dowel rod pieces must be glued into the slots on the bottom of the block. When doing so, make sure that the axle supports are centered such that an equal amount of the axle support extends from each side of the block.
The axles in this kit are round-head wood screws. For best performance, mount a screw in the chuck of a drill (which has been clamped to a work surface), and use a small file to remove any burrs under the axle head, and to slightly bevel the head. Avoid creating a significant bevel as it can cause binding in the wheel bore.
Next, polish the non-threaded part of the axle shaft with an axle polishing kit or use your favorite polishing method.
The wheels on the Royal Ranger/S&W kit are narrow and are made of a plastic which is readily shaped. This is good since the wheels are generally not perfectly round, and need to be trued. If you have access to a machine shop, then a lathe can be used to accurately true the wheels. However, since most people do not have access to this type of machine, the Pro-Wheel Shaver does an excellent job of truing these wheels.(2)
Please note that a 1/8" bushing IS REQUIRED for these wheels.
Of course as with any pinewood derby car, good lubrication is essential. Make sure to thoroughly lube the wheel bore, and rub some graphite on the end of the axle supports.
Royal Ranger/S&W kits are a unique kit, and present some fun challenges. I encourage you to rise to the challenge and create a car that reaches Maximum Velocity!