January 7, 2006 - Countersinking Forward Longerons
I knew this was coming and now here it was.  The countersinking of all the longerons and stiffeners.  Because they are aluminum angle too thick to dimple, they must be countersunk.  I started with the short lower longerons, aux longerons, and stiffeners. 
The stiffeners were too thick to dimple, but too thin to countersink without something underneath to fix the countersinking bit.  Without the backing, I was getting a lot of chattering.  It was no big deal to make a little backing angle;  it just made the countersinking take longer, because I had to move clecos and the angle. 
When countersinking a hole that will accept a dimple, the main question is always how deep and wide to countersink.  I made these little gauges using aluminum sheet the same thickness as the skins.  One is for 3/32" and one is for 1/8".  I used the engraver to label them.  Sharpie markings quickly get worn off. 
All done with the short longerons and stiffeners.  Countersinking isn't one of my favorite things.  Just got to persevere and work through them.
This is a little pile of aluminum shavings.  I had to sweep up the shavings often so that they wouldn't get tracked upstairs in the house. 
 
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