February 1, 2015 - Maple Plugs for Bolt Holes

The next step was to drill 1/2" diameter holes in the spar ladders where the spar bolts would go.  These 1/2" holes would be filled with maple dowel rod.  The actual spar bolt holes would be drilled through the maple dowel.  You may be asking yourself why the maple dowel.  I believe it's because maple is a harder wood than spruce and Ron Sands, the designer, wanted the spar bolts to go through the harder wood.

I ordered a bunch of stuff for the next few steps.  Bolts, nutplates, aluminum sheet for the nutplates backing strips.  Not pictured: 1/2" drill bit, 1/4" drill bit and #12 drill bit, a 2" by 3 and 3/4" aluminum block and nine feet of 1"2 diameter maple dowel.  I got everything from Aircraft Spruce except for the 1/2" drill bit which I got from McMaster Carr and the maple dowel which I got from a wood specialty company via Amazon.com.

 
   

I used the 2" by 3 and 3/4" aluminum block to make a drilling fixture per the plans.  Although the plans called for the drilling fixture to be made of steel, I just don't have the tools -- or the desire -- to work with steel so I went with aluminum.

Here, I'm drilling a 1/2" hole through the aluminum block.  I'd cut the block to 3 and 3/4" length after the drilling.
   

The drilling fixture has three sets of holes:  1/2", 1/4" and 3/16".    The 1/2" is for the maple dowel.  1/4" is for the AN4 spar bolts for the inboard cabane struts.  3/16" is for the AN3 spar bolts for the outboard interplane struts.

I attached the side panels to the drilling fixture by tapping holes for some #6 screws.  This worked well.

Here's a close-up of the drilling fixture.  I havn't drilled the 1/4" holes in the drill fixture yet.  They will go on that center line.
   
I found the drilling fixture worked best if I clamped it to the spar ladder before drilling.  I'd drill the first hole, then insert the maple dowel -- or later the bolt -- through the first hole before drilling the second hole.  Here I'm about to drill the first hole hole through the spar ladder.
   
The drilling fixture does a nice job.  The maple dowel fits into the hole tightly; in fact, needs a light sanding first.  I'm about ready to drill the second hole.
   
And all done with this set.
   
Each spar ladder needed four sets of holes.  The lower wing spar ladders get two additional sets -- on the very outboard -- for the wingtip skid mount bolts.
   
Drilling holes in the spar ladder.
   
With the 1/2" holes all drilled, it was time to fit the maple dowel.  I had to lightly sand the dowel so it would fit into the hole.  Then I marked it and cut it to size on the bandsaw.
   
I just left the plugs halfway in the spar ladders so I wouldn't lose them.
   
This spar ladder is done.
   
Now all spar ladders are done and ready to have the maple plugs epoxied in.
   
A lower wing spar ladder with its maple plugs epoxied in.
   
Close up of two maple plugs.  I was pleased with how the maple plugs came out.  I guarantee they are not coming out of the spar ladders.
   
 
 
   
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