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Elevator spar countersinks

I dd a bit of research regarding the clash between the microstop countersinking tool and the spar flanges that was preventing me from countersinking the holes closest to each flange. I couldn’t really find much info so I had to come up with something myself. I was considering cutting one side of the microstop guard so that I could get aligned with the hole. I wasn’t too keen on the idea as this would also reduce the effectiveness of the guard to keep the drill square if you weren’t careful. So I decided to remove the guard from the microstop tool and use the countersinking bit in my pedestal drill. This would obviously mean that I would have to be very careful as the only thing stopping me from countersinking too far was myself.

As I had already set the depth yesterday I quickly countersunk the two inner holes on each spar. No problems there.

I then unscrewed the guard off the microstop tool and set it up on my pedestal drill. Using some clamps, I carefully aligned the spar so that the pedestal drill lowered the bit into the hole. It took a bit of tweaking as I wanted to make sure the countersink would be centred.
I was VERY careful and VERY slow from this point on. I make very small increases in the countersink depth and checked about 20 times before I finished 1 hole. As I discovered on the second hole I did, it only takes a whisker before the hole is enlarged. Here is a shot of the first hole. Looks good!

Here is a shot of both spars will all holes countersunk. If you look closely, you will notice that the far left hole has been enlarged. It was very easy to do and I was doubly careful for the remaining holes. Fortunately I didn’t enlarge any of the other holes. I’ll address the offending hole by going up to the next rivet size so no big deal.

Build time 1 hr.


About gstrack

Husband and father of 2. Control & Instrumentation Engineer. Flying nut. Gadget geek.


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