Updated: Sep 19
As mentioned at the beginning of the Wheels article, wheels and axles are where most of the speed lies in Pinewood Derby® cars. Preparing Pinewood Derby® axles lead to huge speed increases if done correctly or the possibility for significant instability and a decrease in speed if prepared incorrectly.
The axles in BSA Pinewood Derby® kits will need a fair amount of work to reach their full speed potential. Therefore, use stainless steel axles if your rules allow them. They offer many advantages over stock axles. They are straighter, have a larger diameter (therefore more stable), can be polished to a much smoother finish (less friction), and many are grooved to minimize the contact area with the wheel bore. Stainless steel axles are faster than stock axles and, as a result, are the preferred choice of Professional League Racers!
When preparing both types of axles (stock and stainless steel), the goal is to sand/polish the contact surfaces as smooth as possible while minimizing the amount of material removed.
This chapter will focus primarily on the steps needed to prepare stock BSA axles. However, the preparation process for stainless steel axles is similar. The differences in the preparation process are mentioned later in this chapter.
One of the most apparent issues with the stock axles is that many are not straight. There are tools available on the market to straighten the axles. However, purchasing extra stock axles and picking the straightest ones for your car is often more economically feasible and much quicker. To check the axles, insert them in a drill and spin slowly to see if they wobble. Choose the straightest ones!
To maximize axle speed you will need a few supplies and tools:
• Handheld power drill • Microfiber or cotton cloth
• A small file • Bowl of water
• Sand paper, grits from 400 - 5k • Paper towels
• Craft (Popsicle™) sticks • Isopropyl alcohol
• Metal polish • Hacksaw (if rail riding/running)
Optionally there are kits designed explicitly for this purpose and contain nearly everything you need to create professional, league-quality axles!
Let’s take a closer look at the stock axles:
Removing the crimp marks on the axle shaft will significantly reduce the diameter of the axle. Crimp mark removal gives the wheel more room to move on the axle, making it more likely the wheel will vibrate, causing the car to wiggle. An unstable, wiggling car is slow.
STEP 1: If building a rail rider/runner car (discussed in other articles in this series), it is a good idea to cut a slot in the axle head. Once installed in the car, you can turn the axles with a small screwdriver. Slotting the axle head is accomplished by clamping the axle between two pieces of wood (so as not to mar the axle surface) and carefully cutting the slot with a hacksaw. Cutting the slot can be tedious; therefore, a tool is available that makes cutting the axle slot more manageable.
STEP 2: The tip and the sharp edges near the tip of the axle need to be filed and sanded. Otherwise, you risk damage to the wheel bore when inserting an axle. Use the small file to bring these edges down, and then finish with 400 and 800-grit sandpaper. The axle prep kit contains a special tool to insert the axle into a drill. Otherwise, you’ll need to complete this step by hand. There is no need to go with the higher grit papers or the metal polish, as the goal is to remove the sharp edges so they won’t scratch the wheel bore.
PRO RACER TIP FROM Reece Racing: If you are building a rail rider/runner car and have cut slots in the axle head, you will want to polish both the sides of the axle head and the top to eliminate the burs created by cutting the groove. Otherwise, the rough slots will pull pieces of lint from your polish cloth that could later become trapped in the wheel bore, slowing the car.
STEP 3: Insert the axle into the drill. The flashing or burs under the axle head must be removed. Using the drill to hold the axle, use the small file to scrape away the flashing. Do so while the drill is NOT running. You can put the axle head against a table or block of wood and file the burrs off. Inspect the axle head closely (magnification helps a great deal). Take note of the size and direction of the scratch marks left by the file. Next, dip a strip of 400-grit sandpaper in the bowl of water. Using a craft stick as a backing for the paper, run the drill and sand underneath the axle head ONLY. For Race Teams with younger members, place the drill on a table and have them operate while the adult team member sands the axle head. For older Race Teams, you can do the opposite.
Filing the flashing/burs will leave the underside of the axle head quite rough. You’ll want to sand with the 400-grit paper for 1 minute (target 600 RPM). Dip the sandpaper in the water bowl at regular intervals. The water keeps the axle from becoming too hot and washes away loose sandpaper and axle material. If cutting a slot in the top of the axle head for a rail riding/running car, sand the sides and top of the axle head during this process to remove any burrs from cutting the slot (30 seconds should suffice). Next, inspect underneath the axle head. The goal is to remove all the gouges/scratches left by the filing process. After the 400-grit paper, move to the 800-grit paper and repeat the process. Sand the underside of the axle head for 1 minute to remove all the scratches left by the 400-grit paper.
STEP 4: It is time to include the axle shaft in the sanding process. As mentioned before, the goal is to remove as little material as possible, resulting in a smooth axle. On a properly aligned car (see Alignment chapter), the rear wheels are riding against the heads of the axles, so take additional care to sand/polish the underneath of the axle heads until they are extra smooth and shiny!
Keeping the sandpaper wet, utilizing medium pressure, and targeting an RPM of approximately 600, do the following three steps with each grit of sandpaper:
Use the following as a guide:
1000-grit paper, 10-20 seconds on shaft, 60 seconds under axle head, 20 seconds on side and top of axle head
1500-grit paper, 10-20 seconds on shaft, 60 seconds under axle head, 20 seconds on side and top of axle head
2000-grit paper, 20-30 seconds on shaft, 60 seconds under axle head
3000-grit paper, 20-30 seconds on shaft, 60 seconds under axle head
5000-grit paper, 30-40 seconds on shaft, 60 seconds under axle head
Remember, the goal is to remove as little material as possible from the shaft, polish a mirror finish underneath the axle head and remove any burs from cutting the tuning groove on the sides and top of the axle head!
For stainless steel axles, DO NOT sand underneath the axle head with the file, 400 or 800-grit paper. Additionally, skip the 1000 and 1500-grit sandpaper steps as well. Instead, go straight to the 2000-grit steps and proceed from there. However, if you’ve cut a groove in the top of the axle head for rail riding, you will want to sand the top and sides of the axle head with the 400, 800, 1000, and 1500-grit paper to remove the burrs from cutting the groove.
After completing the sanding process, wash off the axles to remove all loose metal and sandpaper grit, and wipe them thoroughly with a cloth or paper towel. Make sure to clean the tuning groove as well.
STEP 5: Insert the axle back into the drill. Apply metal polish to a microfiber or cotton cloth. Polish the shaft and underneath the axle head for 60 seconds each. BE CAREFUL; the cloth can entangle the axle and pull fingers in with it. Cutting the microfiber or cotton cloth into smaller pieces helps prevent this.
Wash the axles thoroughly with water, and wipe with a cloth or cotton towel. Then soak for 5-10 minutes in either isopropyl alcohol or ammonia-free glass cleaner. Inspect them under magnification to ensure there is no residue from the polishing process or lint on the axles. Be careful not to touch the axles’ polished surfaces, wipe them again, and put them away in a clean, safe place.
PRO RACER TIP FROM HurriCrane Racing: Coffee filters are an excellent lint-free option for cleaning/wiping axles!
Optional if using graphite as your lubricant: Lightly spray the axles with Lemon Pledge™ Furniture polish. Allow to dry, and put them away.
Optional if using oil: Lightly spray the axles with Dupont® Chain Saver™ or Jig-a-Loo™ lubricant. Allow to dry, and put them away.
Preparing the axle for rail riding
With a rail riding setup, you will need to either drill the steer into the car body or bend one of the front axles. A drill jig designed for this purpose can be used for drilling steer into the car. A purpose-made drill jig is the method you’ll want to use if your race rules prohibit bending axles.
If going with a bent axle for steer (make sure to bend after polishing), here are three different options for bending the axle:
OPTION 1: The bend point on an axle should be about .325-.375” from the bottom of the axle head. Mark the bend point on the axle and clamp it in a bench vise. Use two blocks of wood to prevent damage to the axle. With the mark barely showing above the blocks, place a thin (.25” or so) piece of wood under the axle head and gently tap with a hammer until the axle is bent to the desired amount.
OPTION 2: Place the axle in a power drill or drill press. With the axle spinning, cut a small slot (known as a bending groove) in the axle at the desired bend point using a rotary tool (Dremel®) cutting disc or hacksaw blade. Place the disc or blade on a block of wood at the correct height and push into the spinning axle to cut the groove. Clamp the axle in a bench vise between two blocks of wood with the groove barely exposed. Place the head of a flat-tipped screwdriver in the groove, and tap with a hammer until the axle is bent the desired amount.
OPTION 3: The preferred method for league racers is to use a tool designed specifically for this purpose.
You will want to bend your front axle a PRECISE AMOUNT for maximum speed, ensuring the car is level front to back when racing. See the article on Alignment for more info!
PRO RACER TIP FROM JBD Racing: Do NOT bend the axles for the rear wheels; it is much better to drill the rear holes at an angle (3 degrees of camber) using a drill jig.
Articles in this series (click to read):