When drilling the holes through the drag blocks [it gets tedious typing drag / anti drag wire, so from hereto, drag blocks means the same thing], the holes have to line up with the opposite drag block, if the holes are drilled by sight, there is a VERY good chance that the 2 holes will not be in alignment. The fed-thru drag wire then will still seemingly work thru a mis-aligned hole, but this is only due to the flexibility of the wires. When the wires are then tramelled, there is apparantly a good chance that the wing will warp. So, the best way to make an accurate hole is with a drill jig.
I have seen a few really good drill jigs made out of steel. However, my steel skills are poor at present. I have however in the past worked often with copper / soldering etc. So I decided to attempt to make a jig out of this material, utilizing brass fittings.
The main cross member of the jig is 3/4 copper tube, reduced down to 1/2 for the T-pieces. Brass fittings were then used to reduce from 1/2 to 1/4, the 1/4 holes were then reamed out to fit 5/16 x .028 steel tubing. These tubes of course house the 1/4 drill bit. I decided to leave the tube to rotate freely in the brass fittings - hopefully this will minimize wear from the drill bit.
To line up each end of the jig, I inserted a 4ft 1/4 steel bar through the whole setup before soldering the copper joints.
To accommodate the 3/16 wires for the other bays, I will insert a 1/4 x .028 inside the 5/16 tube to reduce down to 3/16.
I will be setting up a couple of mock spars to see if all works out. Fingers crossed..
Update: the jig did its job well.
Almost Gotcha: You really have to take your time [and retract the bit frequently] drilling with the long 12" bits, otherwise there is a chance of 'drill wander'...this happened on my first test piece....I drill too quickly, and in one motion.