I Ruined a Spar

 The bottom of the holes, where the drill bit comes out, has some wood fiber burrs, even with a sharp drill bit.  The factory ignored it.  I'm to nutty to ignore it.  A 30 degree break-away knife works great to clean up the holes.  I normally just use a backup board to prevent this but I couldn't get it as flat and square as just using the table.

 The first spar I drilled got ruined because I started drilling a hole in the wrong place for the strut/brace wire fitting.  I had the template upside down, tall wire end pointing at the tip instead of the root.  It was the result of how I made the templates for the fittings and not checking the fitting outline I drew on the spar.  Fortunately Aircraft Spruce hadn't shipped the other spar material so they were good about adding another spar blank to that order.

This all started because of how I made the templates.  I made the holes for the 1/4" hole and the .377" hole using the Whitney punch.  It doesn't make holes as big as 3/8".  I could have made the holes actual size because I have 3/8" and 1/4" duplicating punches.  I like the shorter centering nib on the Whitney punches, rather than the duplicating punches, because you don't need as thick a spacer under the template to get the punch to set completely in the template hole.  This all worked perfect for making the fittings.

 I could have used the actual fittings to locate the holes in the spars but they're all welded and painted and a tight fit to the spars.  So I used the original templates.  After ruining the first spar I decided I needed a better process so this didn't happen again.  I also wanted to use the original templates for better accuracy.

I start by drilling the 3/8" hole first.  I bought a bag of small bushings at Oshkosh some years back and regularly find uses for them.  This one is 3/8" O.D and 1/4" I.D.  It allows me to use a 1/4" bolt in the original template hole to position the template for the next hole.

 For the 1/4" hole I aligned the 3/16" drill bit in the template hole.  While holding the spar so it didn't move, I changed to the 1/4" bit and drilled the hole.

I made a bushing for the 1/4" hole from a piece of 1/4" aluminum tubing.  It allowed me to use a 3/16" bolt for this hole in the template.

 With the first 2 bolts in the 3/16" bit was aligned to one of the holes, the template removed and the hole drilled.

The same was done for the 4th hole.

 A truly tortured process, but it worked very well.  All 4 bolts fit perfectly.  Because the table is so square, they also fit perfectly on the backside of the 1 1/4" thick spar.  Not bad.