The four holes in the main gear axle must be parallel to one another and drilled perfectly through the center of the round pipe. With a little planning this was easier than I anticipated.
To ensure the holes are centered on the axle I clamped two aluminum angles to my drill pres to hold the axle centered on the drill bit.
Using a small rod in the chuck I measured between the angle and the rod. When the measurement was the same on both sides I tightened the clamps.
Drilled one of the outer holes first. Moved the axle to the next hole. In the first hole I placed a drill bit into it. Now I can rotate the axle until the bit in the first hole lines up with the bit in the drill press.
When drilling the holes I first drilled a small hole then drilled out to the property size. Both times I verified that the rotation was correct.
One of the center holes is off about 0.010″ close enough for this bird.