Main wing spar Issue 2 - missing rib 1 pocket holes

With the rear spar cap removed it is possible to drill the pocket hole (for one of the rib 1 rivets) in the inner layers. As shown in a TAF graphic (from P. Latten's blog) this pocket hole is supposed to pass into one thick, one thin, and one thick layer, and be nominally 6mm diameter. I have verified that the unrestrained expansion of a Gesipa 4mm rivet tail tops out at about 5.5mm so this diameter (6.25mm) is sufficient.

I was keen to ensure that the hole were completely formed in all three of these layers, with no sliver of metal left remaining at the bottom of the hole. I also wanted to avoid removing any material for the layer following this stack of three layers. For this reason it was necessary to flex the layers apart slightly with the use of shims. Given all the AN3 bolts were removed this was easy, with only a solid rivet at some distance away limiting this separation. A gap of 0.8mm could be created with only a little force - no danger to the clamping of this solid rivet was to occur. This gap would allow clearing of any shavings by compressed air.

These shims could be used to separate the various other layers of the spar core to allow any debris to be blown out. Some metal shavings were removed in this way, most probably created by the finishing counterboring of the AN6, AN5, and AN3 holes during manufacture.

For the left spar, only the topmost thick layer was missing the pocket hole, with the thin layer hole present but slightly misaligned, so rectification was easy.

The right spar was harder, both thick layers were missing the hole. I used used the stainless steel shims (marked red) as protection against drilling too far. I then moved the shim away from the hole, and used a 1/4" chuck reamer by hand until the tip penetrated into the air gap, without causing any damage to subsequent layers. Compressed air removed a thin disk of aluminium that came off the end of the reamer.

The job was completed by applying some alodine to the bare metal and painting the interior of the pocket hole with Duralac yellow.

The spar layer surfaces were also Alodined with a pen.