Drilling Holes for Camber and Toe
with Computation Aid
by Stan Pope
This page describes methods for drilling axle insertion holes in pinewood derby car bodies at angles to accomplish predetermined camber and/or toe angles. Coupled with straight axles, this process allows running the car with minimal alignment tuning. The process can also be used with "bent axles" where the target camber and/or toe angle is the sum of the drilled camber and the axle bend angle.
Subsequent tuning can be accomplished using shims as originally described the author's online textbook, Learn to Build a Winner, and subsequently copied by other "authors", or by using "slightly bent axles".
The process assumes that the user has a well aligned and stable drill press and the ability to drill true holes in pine. Proving those assumptions may be accomplished using the techniques described in Drilling quality axle holes, adjusting the drill press table.
Quality cambered axle holes (with negative camber) may also be drilled using a ProBody Tool by inserting the designated spacer between the bottom of the car body and the opposite end of the ProBody Tool. In some cases, the fit between the car body and the ProBody Tool is so tight that the car body must be trimmed or sanded to allow the car body to be offset in the tool to make room for the spacer.
Camber and toe axle angle can also be accomplished using the procedure described by Jay Wiles here and here. Jay's description is worthwhile reading, whether you use the details of his procedure or not. In Jay's procedure, camber and toe angles are entirely derived from bent axles and, while true axle holes are best, small errors in them are well tolerated. (To my knowledge, Jay was the first to openly document a process for guiding a pinewood derby car by using a lightly loaded wheel that is steered against the guide rail. Veiled comments which I overheard in the 1980's indicate that the practice of rail guiding or, Jay's term, "RailRiding", existed as a "closely guarded secret" much earlier.)
- Camber - displacement of a wheel from vertical. In positive camber the top of the wheel is farther from the car's center plane than the bottom of the wheel. Often camber is described in terms of the angle of the axle. When the camber is positive, the outer end of the axle is lower than the inner end.
- Toe - displacement of a wheel from the car's center plane. In positive toe, the rearmost part of the wheel is farther from the car's center plane than the frontmost part of the wheel. Often toe is described in terms of the angle of the axle. When toe is positive, the outer end of the axle is more forward than the inner end.
- Fence - a device fastened to the drill press table to provide a vertical reference plane for positioning parts on the drill press table. The fence should be as close to perpendicular to the table as possible, since any error is included in the drilled holes. (For instance, a 1 degree error in the fence may add to the camber, changing a 2.5 degree camber to 1.5 degrees or 3.5 degrees!)
- Spacer - a calibrated device (or collection of devices) to hold portions of two solids a fixed distance apart.
- Drill press
- 2" Fence
- #44 Drill
- Drill sets: Numbered (#30 to 60) or Fractional Drill (1/16" to 9/64", in 1/64" increments)
- The fence should be as close to perpendicular to the table as possible, since any error is included in the drilled camber holes. (For instance, a 1 degree error in the fence may add to the camber, changing a 2.5 degree camber to 1.5 degrees or 3.5 degrees!)
- The process requires that the sides of the car be parallel. Any deviation from parallel shows as twice that much difference in the toe angles.
- The algorith used for computing the camber angle is a very close approximation when the camber angle is small.
- Since the surface being drilled is not perpendicular to the drill, special care is necessary to prevent the drill from wandering.
Drilling for negative camber
To drill an axle hole with negative camber, the car body is positioned on its side with its bottom side leaning against the fence. The off side is held away from the fence by a spacer that is touching the fence, table and car body. The body width and the spacer size determine the camber angle. For pinewood derby cars, the standard width is 1.75" and that size is assumed in the Spacer Size Table.
If the car body is thin, then the body can flex if it is pressed too hard against the fence. This can be avoided by either by holding the car body only at the top and bottom areas or by pressing the body using a firm flat board that presses evenly across the body.
If you are the happy owner of a set of gage pins in the range or if you have a different width car body, you can use this computer:
Spacer Size Table
Drilling for positive toe
To drill an axle hole with positive toe. i.e. toe-in (or negative toe if you have an application for it), the car body is positioned on its side with its bottom side against the fence. The off side is held away from the table by a pair of unequal diameter spacers that are separated by an amount that is computed to tip body the desired amount.
Note that the difference between the sizes of the two spacers is more important than their absolute sizes. The spacers must be big enough to keep the tail of the body off the table while the pressure from the drill projects between the spacers. For instance, if the spacers need to have a diameter difference of 5/64" and be 3 inches apart to get the desired toe angle, then the smaller spacer should be at least 3/32" in diameter. If a 3/32" (6/64") spacer is selected for spacer2, then the larger spacer, spacer1, would be 11/64"!
The computer below will attempt to provide the largest separation possible. The toe angle produced by a 1/64" spacer diameter difference separated by 1.5 inches can also be produced by a 1/32" (2/64") difference separated by 3 inches or a 1/16" (4/64") difference separated by 6 inches!
This computer will calculate the separation needed to get a specified toe angle.
Copyright 2010 © by Stan Pope. All rights reserved.