January 14, 2015 - Make Spar Spacers
The next step is to fashion the spacers that go between the spar ladders.  They are made of 1/4" thick plywood, the same height as the spar ladders:  3 and 3/4".   So the first thing to do was cut 3 and 3/4" tall strips out of the 4'x4' sheet on the tablesaw.
   
I started with the Lower Wing as always.  You get better as you go along, so I figure I'll start with the shortest wing, so my best work is on Upper Wing which is the longest.  It probably doesn't make any difference.
 
Anyways, the wing spar has to be exactly 8" across, the entire length.  The outer edge of the spar ladders is straight, so the 8" equidistance is certainly doable.  However, as you can see, the inside edge of the spar ladder is tapered.  What this means is that each cross spacer has a differnet length; i.e., I would have to measure, cut and fit each spacer individually.  No mass-production.  Initially, I wasn't too happy about having to custom make each one but it turned out not to be too bad.
 
I ensured the 8 inch distance through a combination of clamps and homemade shims.
   

A close-up of one of my homemade shims.   Not very fancy, but they worked well.

You can also see the marks on the spar ladder where a spacer is supposed to be.  Per the plans.
   
OK, the spar ladders are in place, exactly eight inches from outer edge to outer edge.   Time to start cutting spacers.  There will be 20 or so for each wing.
   
First, at the spacer location, I would measure how wide apart the ladders were, add an 1/8" more, and then cut the 3 and 3'4" strip to that length.
   
At first I used to tablesaw for the initial rough cut, but I sooned switched to the bandsaw, which was just as good and much faster.
   
Initially, I thought I would use the belt sander to get the spacer width exactly right.  But that just didn't work -- you just don't have the control on the belt sander -- so I quickly shifted to the bandsaw.   The bandsaw worked well.  I was careful to trim off small increments -- it was OK to not trim off enough, but disaster to trim off too much.  I didn't mind making multiple trips to the bandsaw for each spacer.  In the end I was pleased with the close fit of the spacers I was able to achieve, and it was fun work.
   
About halfway through making the spacers for one of the wings.
   
Almost done with a wing.
   
And done.
   

With the spacers done, the next step was to drill a lightening hole in each.  So I had to sit down with a ruler and pencil and mark the center of the ladder.

Notice how each spacer is labeled.  In the upper right hand cornerm, the "U" stands for Upper Wing.  One through eleven means starting from the left end.  1A through 11A means starting from the right end.
   
Then it was over to the trusty drill press and the old 2 and 1/4" hole-cutting bit.  The 1/4" thick plywood cut fine.
   
Lots of little donut holes.  That's a lot of expensive, high-quality plywood being wasted, unfortunately.
   
The Lower Wing spacers on display.
   
The spacers for all three wings.  I was pleased with how well they came out.
   
 
   
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