I’ve been avoiding countersinking the skin attach holes on the spars, but I couldn’t put it off any longer – I hate drilling/cutting those things. I reviewed Vans’ instructions on countersinking and found out – once again – that their instructions were right. They specify that countersinks which accept dimpled skins should be deep enough so that a test AN426 rivet should sit flush to 0.005″ below the countersunk surface. So, I tweaked up my countersink and did some checking with the depth measurement pin on my calipers just to make sure that everying was set correctly – then fired away. Here’s the beautiful finished product…

Spar-to-skin countersinks

…and here they are primed. I really don’t like to prime in the shop, but in this case I had no choice. I cranked down the air pressure and flow volume on my HVLP detail gun and had no problems.

Spar-to-skin countersinks primed