Straight and Narrow is the Way
Aligning Your Pinewood Derby Car
By Randy Davis
I really enjoy building pinewood derby cars, and looking at pictures of cars built by other folks. The design options are virtually unlimited, and designers have certainly come up with some wonderful cars. In my interaction with kids and parents, I am continually amazed at the creativity of people. But I guess I shouldn't be. Since God made man in His own image, certainly a little of God's wonderful creativity should have been imparted to us!
However, when it comes to making a car go fast, creativity must make friends with physics and precision craftsmanship. Careful work and some basic principles are the keys to making your car streak down the track at top speed. Some key areas that need to be considered when designing and building the ultimate racing machine are: good aerodynamics, maximum weight, proper weight distribution, reduction of friction, reduction of inertia, and proper wheel alignment. Discussing all of these areas would require a book, so in this article we will focus on one aspect of car building: proper wheel alignment.
Basics of Alignment
Proper wheel alignment basically means that all of the wheels are pointing in exactly the same direction, and sit straight up and down. But of course the wheels do not determine their own direction. Instead, it is the axles that determine whether the wheels will go straight.(1)
With Royal Ranger car kits proper axle positioning comes from three factors:
- Accurate dowel rod slots under the car,
- Accurate screw holes in the dowel rods, and
- Straight screw axles.
Let's look at each of these factors.
Accurate Dowel Rod Slots
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 four 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 Brad Point or Forstner drill bit
- 2 blank blocks
Lay the blank blocks on their sides on the drill press table with the bottoms together. 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 using the drill press fence. 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 against the drill press fence, and drill the two holes. After unclamping the blocks, both blocks will have accurate dowel rod slots.
Accurate Screw Holes
The second factor that affects alignment is the accuracy of the axle screw holes in the dowel rods. All four 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.
Before now, inaccurate axle screw holes could not be easily corrected. However, Maximum Velocity now offers a Pro-Body Tool for dowel rods. The tool is a guide for re-drilling accurate holes (after first plugging the holes with round toothpicks). For more information about the Pro-Body Tool for dowel rods, Click Here.
Straight Screw Axles
The next factor that must be checked is the straightness of the screw axles. A simple way to check whether the screws are straight is to insert a screw into the chuck of a drill (threads first) and lightly tighten the chuck of the drill. Start the drill (slow speed) and observe the screw. The screw should appear to spin straight, without any side-to-side wobble. Any bent screws should be replaced (the screws are a standard hardware store item).
Adjusting the Alignment
If the dowel rod slots, the screw holes, and the screws are all straight and true, then alignment will be greatly simplified. However, other factors (center of gravity of the car, wheels, et al) do have a minor influence on alignment so a slight adjustment will likely be needed. After the car body is completed, attach the wheels with the screws and test the alignment by rolling the car on a smooth and flat surface.
Better yet, get a sheet of 1/8 smooth siding material at a home store, put a strip of tape down the middle, block up one end, and put a pillow at the bottom. Use a 'level' to make sure that the board is not tilted to the left or right (many garages and carports are angled to allow water to run off). Then roll the car down the board using the tape strip as a guide to determine if the car rolls straight.
If the car moves more than 1" in an 8 foot distance, then an alignment adjustment is needed. One way to make an adjustment is to remove a front screw, and EVER-SO-SLIGHTLY bend the screw at the point where it meets the side of the car (clamp the screw in a vise, and LIGHTLY tap the screw with a hammer). Then replace the screw and repeatedly test the alignment and rotate the screw until the car goes straight. If you bend the screw too much, just replace it.
Proper wheel alignment is a critical factor in car performance. Just as we are told that "... strait is the gate, and narrow is the way, which leadeth unto life, and few there be that find it."(2), so also straight and narrow is the way to victory in a pinewood derby race. I encourage you to take the straight and narrow way to find victory in your life, and to find victory in your pinewood race.
About the Author
Randy Davis is the owner of Maximum Velocity a family-owned, web-based supplier of information and unique supplies for pinewood derby racing. He can be contacted at: firstname.lastname@example.org
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1 Wheels do have some effect on alignment. If a wheel is not perfectly round, it will make the car vibrate which will affect the direction of travel. Also, if the wheels are not exactly the same diameter, then the car will not sit straight which also affects the direction of travel. If you want to ensure that all of the wheels are perfectly round and of the same diameter, then a machine lathe can be used to true the wheels. Since most people do not have access to this type of machine, Maximum Velocity has introduced the Pro-Wheel Shaver. The tool is basically an affordable, hand powered lathe for pinewood derby wheels. For more information on the Pro-Wheel Shaver, please Click Here. Then click on the picture of the Pro-Wheel Shaver for more details and photos. Please note that the 1/8" bushing IS REQUIRED for Royal Ranger wheels.
2 Matthew 7:14 KJV