Excellent wheel alignment is a key factor in creating a competitive pinewood derby car, and using drilled axle holes (instead of slots) is a key way to improve wheel alignment. Of course, this assumes that the axle holes are drilled accurately.
Today’s article will share how to drill accurate axle holes (and some inferior techniques that you want to avoid) with either a hand drill/Pin Vise or a drill press. But before drilling axle holes make sure to check your local rules to make sure they are acceptable for your race.
The first question that arises with axle holes is, “What drill bit do I use?”1 Generally, to have a snug fit you want to use a bit that is essentially the same size as the axle. The chart below shows typical bits for common kits:
|BSA||0.086 to 0.087||#44 – 0.086|
|PineCar||0.088||#43 – 0.089|
|Awana||0.092||3/32 – 0.938|
Hand Drill/Pin Vise
To accurately drill axle holes with a hand drill or a Pin Vise you must use a drilling guide. Do not attempt to freehand-drill axle holes – the results will likely be much worse than using the axle slots.
The Pro-Body Tool is a drilling guide designed specifically for drilling axle holes in pinewood derby blocks.
Figure 1 – Pro-Body Tool
It is placed over the bottom of the block, and then clamped into place. The drill bit is then run through the holes in the Pro-Body Tool with a hand drill or a Here, however, here are a few additional tips.
- Keep the drill bit aligned with the hole in the tool. Don’t flex the drill bit – it can break.
- Make sure the Pro-Body Tool fits snuggly on the wood. If it is loose, use paper to shim it; if it is too tight sand the sides of the wood block.
- The Pro-Body Tool is equipped with a separate guide hole for drilling a raised hole for one of the front axle.
The Pro-Body Tool is highly accurate, and in some ways is preferable to a drill press. But for more flexibility in hole placement, and for drilling larger quantities of blocks the drill press is a good option.
The principle employed by the Pro-Body Tool is that all holes are referenced to the bottom of the block. Thus, an out of square block will not affect the accuracy of the axle holes.
This same principal must be employed when using a drill press. Thus, when using a drill press, an accurate, vertical fence must be present. 2 By pressing the bottom of the block to the vertical fence the holes will be referenced to the bottom of the block, eliminating any issues due to an out of square block.
However, most people with a drill press do not use a vertical fence. Instead, they place the left side of the block on the drill press table and drill the right side holes. Then they flip the block over, and drill the left side holes. This is okay if the block is perfectly square. But if not, the resulting holes will not be parallel to each other, leading to poor alignment. This is shown – in an exaggerated fashion – in Figure 2.
Figure 2 – Inaccurate holes due to out of square blocks
Some people attempt to resolve this issue by using a long drill bit to completely drill through the block. However, since the drill bit is narrow and long, it will flex, leading to inaccurate holes. This is especially true for dense pine such as is often found in BSA kits.
Instead, it is best to use a short bit, and drill half way through the block. As mentioned earlier, issues due to non-square blocks can be resolved by using an accurate vertical fence. The key is to make sure the block is clamped firmly to the fence, even if the side of the block is not flush against the drill press table (see Figure 3).
Figure 3 – Vertical fence creates accurate holes regardless of block shape
Axle holes can mean significant improvements in alignment, however, they must be drilled accurately to provide any benefit.3 So use the proper tools and techniques to make your car go as straight as possible.
1Regardless of the size, cobalt split point bits create more accurate holes than any other type of drill bits. For more information, check out: “Drilling Small Holes” from Volume 11, Issue 2.
2Meaning that the side of the fence is perfectly parallel with the drill bit.
3Maximum Velocity offers pine blocks with accurately drilled axle holes. Both standard and extended wheelbase versions are available Here.
From Pinewood Derby Times Volume 12, Issue 9
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