Here are a couple of pointers from my build log (RV-7). The jig I talk about was basically an "M" type shape formed out of mild steel angle. The spring rod was held in place using hose clamps at each end. There was a hole pre-drilled at the bottom of the "M" as a guide to ensure that the exit point of the drill would be exactly where I needed it to be on the spring rod (I align with this before I place the rod in the jig. Can't find a picture of the jig right now, but it's somewhere in my shop, so I'll get a pic tonight if I can.
"Drilled the tail wheel spring and WD-409 tail wheel spring mount. Began the process by marking on the WD-409 from the pre punched nut access hole on the F-779 skin. I then transferred this hole position to the other side of the WD-409 by using the parallel sheet of paper method (painters tape also works well). The WD-409 was then placed in my self-centering drill jig that I had previously fabricated and leveled using the digital level, and the top side only of WD-409 was then drilled to 1/8?. The WD-409 was then removed and the tail spring was placed in the jig. This was drilled exactly midway in the machined section. The tail spring was then removed, deburred, then slid into the WD-409, where it was aligned, then drilled all the way through the bottom side of the WD-409 that wasn?t drilled earlier. This hole combination was progressively opened up to D drill size (0.246?). Final reaming has not yet occurred because I only have a 0.249 and 0.250? reamers, and measuring the AN4 bolt dimensions, they are 0.247 to 0.2475? in diameter (the specs say from 0.246 to 0.249?). Thus I will not final ream the holes until I have ordered a 0.247 and a 0.248? reamer."
Cheers,
Tom.