wandersen
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Tonight I successfully drilled eight perfectly aligned drag/anti-drag wire holes in the upper wing. This post will show some pictures of the jig I built from hardware store angle iron. I'll also describe the drilling technique that is critical for consistent results.
The problem I found when drilling these holes in one step was that the drill would take off in an unwanted direction when the drill tip transitioned the high density maple to the low density spruce. The drill would hit the density transition at the angle. One side of the bit would grab into the hard wood, and dig out the soft wood, causing the drill to take off at an unwanted new angle from what was initially set.
To drill a straight hole, I needed to drill two holes - one from the spruce side and one from the maple side. They needed to meet more or less at the glue line interface between the different woods.
The problem was aligning the holes. We didn't want what my wife calls the "trans continental railroad builders problem". <g
I found brad point drills helped run the holes straight. I started with a 12" drill, but ended cutting it down to about 7" in length to fit in the interior part of the wings between the ribs. I found that running the hand drill at a higher speed and pecking at the wood hole helped keep everything straight. I drill the holes nice and slow with minimal pressure, pecking away. Once both sides were drilled to the wood interface, a chucking reamer in the drill was run through the hole.
The jig is build from hardware store angle iron. This was a good project to practice TIG welding.
The sliders and posts were welded first. A nut was welded to the tubes and a bolt is used to lock the slider in place. I used 3/16" rod on the bolts for easy hand tightening. All the sliders and perpendicular tubing were first welded up. The 3/16" and 1/4" ID tubing was then inserted into appropriate sized holes drilled in the posts. The 3/16" and 1/4" ID tubing was in a single piece through both posts. The tubes were welded into place to both posts. I then reamed the tubing to size and made sure it was straight end to end. Cutting through the the tubing at the midpoint made two independent pieces. These were aligned perfectly when the slider bolt was tightened down.
The end alignment piece was made with 3/16" rod bent at a 90 deg angle, then welded. It was aligned by inserting it into the 3/16" tubing and clamped to the third post. I need to weld up a 1/4" piece on the other side for the 1/4" drag wires. I haven't done that yet.
The final picture shows the alignment I was able to consistently achieve on each drag block hole. The droop is from gravity. held straight, it's almost perfect.
Let me know if you have questions.
Edited by: wandersen