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Working With Needle Axles

Since late 2006, Outlaw style wheels equipped with needle axles
(actually pins) have been available from DerbyWorx (RSN Wheels). When
properly implemented, these needle components have a distinct
advantage over regular Outlaw wheels (RS Wheels). Due to the smaller
bore diameter, the amount of bore to axle contact per revolution is
reduced by approximately 56 percent. This equates to approximately 44
less inches of linear contact on a typical 32 foot track.

Of course this type of wheel is not allowed in most races. But in
races that allow any wheel type, the RSN Wheels can provide some
serious performance. However, RSN wheels are trickier to implement
than RS wheels. In this article, I'll share my experience with RSN
wheels and provide an alternate implementation.

In the spring of 2007, my daughter and I built a car using needle
axles for a parent-sibling race. As I was looking at the pins, I saw
a flashing under the head (just like on nail axles), which I thought
would be very difficult to remove without bending the axle.

Figure 1 - RSN Wheel and Axle

So, I decided to replace the pin heads with the beads from some "ball
head pins". These are pins that have a small plastic bead as a head.
I simply cut off the metal head of each needle axle, pulled the
plastic beads off the pins, and then used a touch of epoxy to attach
the beads to the needle axles.

Figure 2 - 2007 Car with Ball Head Pins

The ball heads worked great. The car was easily the fastest car for
the first two heats. However, on the third and fourth heat the car
ran much slower and ended up in third place. After the race I checked
the car and found that one of the front pin axles had been severely
bent (either due to the abrupt stops or mishandling). I bent the axle
back, reran the car, and found the performance was once again quite

I did not implement another car with needle axles until 2009, but in
the meantime I did accept some custom work to drill cars for needle
axles. After a few of these jobs, I quit offering the service. Why?
Even with the softest wood, and the most careful technique, it is very
difficult to drill such tiny holes with good accuracy. The drill bits
are so flexible that they bend when they hit a hard spot in the wood.
I even increased the drill bit size and used cobalt bits, but still
the reject rate was too high.

So, my experience with needle axles was not the best: burrs, bent
axles, and very difficult drilling. There had to be a better way.

In the spring of 2009, my son wanted to run a car in the parent-
sibling race, and he wanted a car that was "screaming fast". Since
the race did not allow motors or bearings, I knew that we needed to
attempt needle axles again. But this time I took a different tactic.
The result was the "Green Stealth", which easily took first place and
continued to perform run after run.

Figure 3 - 2009 Car: "Green Stealth"

How did we do it? Read on to find out.

Remembering the three issues with needle axles, I determined to
address each one. The burrs under the axle heads were easily
addressed with the ball head beads that we used on the first car. The
second problem, bent axles, could only be solved by using axles of a
much harder material. So, we decided to use #65 drill bits (.035 in
diameter, same size as needle axles). The solution for the third
problem (difficult drilling) required a bushing that was large enough
in diameter to allow for easy drilling, but had a small enough hole to
accept the #65 drill bits. I found a perfect material from K&S: 1/16
x .014 aluminum tubing (KS1008), which was cut into 3/4 inch long
pieces.(1) Figure 4 shows these materials.

Figure 4 - Required Materials

The first step is to pull the heads off the pins. This is easily done
with two pairs of pliers. Then, use a #65 drill bit to ream out the
hole in each bead (this is most easily done with a Pin Vise).

Next, polish the smooth part of four, #65 drill bits. This is most
easily done before the beads are installed. A little metal polish on
a rag works well. Then attach the beads to the drill bits with a touch
of epoxy (I used one of the headless pins to apply a touch of epoxy in
the bead hole). Figure 5 shows the results of these steps.

Figure 5 - Beads Installed on Drill Bits

At this point, the drill bits can be cut to length with a pair of
diagonal cutters (or similar). I cut them to 7/8 inch. Make sure to
wear eye protection as the cut off pieces will go flying!

Now, lubricate the axles with Krytox 100, install the wheels, and
insert the drill bit axles into the aluminum bushings. Leave a small
gap (30 thousandths or so) between the bushing and the wheel. Use a
pair of diagonal cutters to crimp the bushing to lock the axles in
place.(2) If you look carefully in Figure 6, you can see the crimp.

Figure 6 - Axles Installed in Bushings

Now, turn your attention to the car. The axle holes will need to be
drilled with a 1/16 inch drill bit. Since the bit is still a little
small, I recommend using a very soft piece of pine. Drill slowly and
carefully. If desired you can put a slight down angle (1 degree or
so) on the rear holes to keep the wheels off of the car body. We used
these techniques on both the "Green Stealth" and its sister car, the
"White Stealth" (see Figure 7).(3)

Figure 7 - White Stealth

Once the car is painted and weighted, you can install the wheel
assemblies. First, ream out the axle holes with a 1/16 inch drill bit
mounted in a Pin Vise.

The tubing tends to run slightly under 1/16 inch, so the bushings
should install with little effort. If they are a little loose, put
some epoxy in the axle hole before installing the bushings. But don't
glue the front dominant wheel until the alignment is set.

Since the axles cannot be bent, you will need to use one or more shims
of paper to adjust the alignment of the car. On the White Stealth,
the front left wheel is raised, and the front right adjusted for rail-
riding. Two thicknesses of Post-it Note paper placed at the back of
the front right axle set the alignment perfectly.

How did this car perform? Typically, a car with RSN wheels will beat
a similar car with RS wheels by over a car length. On the 32 foot
aluminum Freedom Track in our shop, the White Stealth ran under 2.48,
beating a similar RS wheel car by about 10 inches.

If you have the opportunity to run RSN wheels on a car, go for it.
But consider using the implementation method described here. I found
it to be relatively easy to implement, and it produced top results.

RSN & RS Wheels

Pin Vise

KS1008 Tubing (search for KS1008)

#65 Drill Bits - Hardware store, or available from various on-line

Ball-Head Pins - Any sewing or notion store, such as "Jo-Ann".

(1) Since the tubing tends to crush when it is cut, you will likely
only get two pieces from each tube (one from each end). However, the
KS1008 package has 3 pieces, so you can easily get six bushings from
the package.

(2) If you need to remove the wheel for cleaning and lubing, you can
pull on the bead. Either the bead will come off, or the axle will
come out of the bushing. In either case you can clean, relube, and
reinstall the axles.

(3) We built two cars in order to have a backup. My son preferred
the green ball instead of the white "deflector dish" on this car.

Read More at: Pinewood Derby Times Volume 9, Issue 8

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