Learn to Build A Winner (Cont'd)

Woodshop 101 (Continued)

3. Wheel Preparation

The concerns in wheel preparation are to assure that:

When we are done with each wheel, we want its cross section to look much like this picture. (Remember that a "cross section" view is what we would see if we sliced the wheel through its center and looked at the cut side.)

[Fig 11. Wheel cross-section]

There are three approaches with which I am familiar. All involve a process called "turning". "Turning" is rotating the work piece (in this case, the wheel) about its axis and applying a cutter so as to produce radial symmetry. The cutter is slow- moving, and usually moves perpendicular to or parallel to the axis of rotation (center).

Method 1.

This method is described in the paper insert in the Grand Prix Pinewood Derby Kit. It requires an electric drill, a straight nail, some fine sandpaper, and a flat-sided wood block. The nail should be a close fit to the inside of the wheels hub. (You may need to file the shoulders of the nail's point to allow the nail to enter the hubs without cracking them.)

The nail is passed through the hubs of all four wheels and into the chuck of an electric drill. With the drill turned on and held very steady, gently hold the sandpaper against the tread surfaces with the wood block.

[Fig 12. Wheel turning]

Some possible problems:

Method 2.

Each wheel is held in a mandrel, such as the PineCarTM P357, and the mandrel is "chucked" into a drill press. Alignment guides (reference and stop blocks) are clamped onto the table of the drill press. The wheel is passed down across a cutter, which can be sandpaper on a wood block or a bit of sharp-edged metal clamped to a wood block. The alignment guide is set to limit how close the cutter can get to the wheel so that each wheel is the same size. Gradually move the cutter closer to the limit block. With each step, pass the wheel across the cutter.

After the last cut is made, use a small piece of cloth with a bit of jewelers rouge on it to polish the wheel tread. Hold the cloth gently against the turning wheel for a few seconds.

[Fig 13. Wheel turning]

Some possible problems:

Method 3.

Turning on a jeweler's lathe. A jeweler's lathe is a precision machine tool. Each wheel is turned individually. The cutter is fed across the tread parallel to the wheel axis in a series of shallow cuts. If you take this route, work with its owner for details on operation.

After the last cut is made, use a small piece of cloth with a bit of jewelers rouge on it to polish the wheel tread. Hold the cloth gently against the turning wheel for a few seconds.

The possible problems are about the same as with method 2.


Regardless of the method used to dress the wheel tread, gently polish the tread surface. Use jeweler's rouge on a clean cloth. Hold the treated cloth gently against the wheel tread for brief periods as the wheel spins. Be careful! This process can produce enough heat to pucker the tread surface if too much pressure is used or if it is applied for too long.

Hub Shaping:

This step need not be done on a lathe. There are several ways. The objective is to create a narrow band on the inner hub, near the wheel's axis, which will contact the side of the Car. If it were permitted, a short, brass sleeve fixed inside the inner hub could be used to place the contact surface even closer to the axis. Since most rules prohibit this, the next best is to place the contact at the central edge of the hub.

[Fig 14. Hub shaping]

4. Axle Preparation


Our goals in this section are to produce axles which allow your Car's wheels to turn with the least possible resistance and which allow the wheels to be aligned to perfection.


When you first take the nails from the kit, look at one of them carefully. You will see that the underside of the nail head is rather rough. It is also more-or-less flat across.

Next, look at the shaft near the nail head. You will notice some ridges on one side of the shaft. The last set of nails that I inspected had 3 such ridges on each nail, separated by about 0.04 inches.

Finally, look at the point. It looks like the metal of the nail has been cut four times to produce the point. When that was done, it caused the nail to bulge where each two adjacent cuts meet the shaft.


The underside of the nail head needs to be shaped and smoothed, and the bulges near the point need to be removed. When you are done, it should look like this.

[Fig 15. Axle shaping]

Here is one way you can accomplish the changes:

Detect the bulges by rolling the nail shaft on the edge of a smooth hard surface. You should be able to feel the vibration as the nail shaft rolls over each bulge. You may also hear the slight "chattering" as the nail shaft bobs up and down.

A more precise measurement of the bulges involves using a micrometer caliper. With the caliper closed gently on the shaft of the nail, draw the shaft out until the cut end is under the caliper pad, then turn the nail shaft. Notice whether any bulges interfere with the turning of the nail.

Use a small, fine metal file to gently remove the bulges near the point. It is easiest if the nail can lie in a shallow grove in a piece of wood while you are filing it. Repeat the test above to evaluate progress.

[Fig 16. Axle shaping]

Once the bulges are removed, chuck about 3/8" of the nail in the drill press. Check the nail for any wobble as it spins in the drill. (Look at the shaft of the nail, not at the head.) If there is any wobble, try rechucking the nail. It is important that the nail spins on its own axis.

Next, with the nail spinning, hold the metal file gently against the underside of the nail head. Make sure that the teeth of the file will cut into the nail as it spins. Try not to touch the nail shaft with the file. Tilt the outside of the file down about 5 to 10 degrees and allow the spinning nail to cut its head into a slightly conical shape.


The ridges on the shaft may remain. Decide if the rolling wheel is to press on the smooth portion of the nail shaft (ridges up) or on the ridged portion of the nail shaft (ridges down). In either case, polish the portion of the shaft that the wheel may contact. I prefer "ridges up" since the span of the ridges is too narrow (less than 0.08 inches) to adequately control the wheel orientation.

The last step is to polish the nail shaft and underside of the nail head. Rub some more jeweler's rouge into a strip of cloth and hold the cloth against the spinning nail and nail head for a few seconds. Then hold a clean strip of cloth against the spinning nail to remove any jeweler's rouge that may have been left on the nail.

Avoid polishing the outside of the nail head. You want it to be obvious to the judges that nails from the kit are being used!

Some people like to sprinkle some graphite on a cloth and hold that against the spinning nail for a few seconds. The idea is to try to impregnate the metal surface with graphite.

Remove the nail from the chuck. It is best to handle the nail with a clean cloth to prevent finger oils and perspiration from being left on the nail.

Use a felt-tip pen such as a "Sharpie" to mark the outside head of the nail to indicate where the shaft ridges are located.

Set the nail aside in a clean container.


Unless the shaft surface is damaged, I prefer to avoid using sandpaper, emory cloth, etc. because these will reduce the diameter of the nail. Reduced diameter of the shaft hurts performance unless the wheel hub inside diameter is similarly reduced!

One down, three to go!

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