In preparation of priming ribs and rear spar parts, I finished scuffing up the last parts.

I also realised I still had to countersink the W707-F reinforcement plate that comes on the outboard side of the spar. These hold flush rivets because the aileron support will sit on top of these.

I started with a lot of courage to countersink all the 8 holes for a #30 hole. The one near the bent flange needs to be done by hand as the countersink cage will not fit. 

No problem... did that before. Just be slow and patient.

On the last hole with the cage, for some reason, the bit went too deep .... grrrrrrrr....
This causes an enlarged hole  of course.

Pretty annoying. In the second picture, I'm holding the AD4 rivet in and you clearly see the enlargement.

This was bad feeling... but it got worse. I decided to do some searching on the forums in the evening and stumbled upon this entry on the forums.

In short... many people are not machine countersinking this plate but are dimpling the rib, the rear spar and the reinforcement plate.

In the wing kit manual in the section of the rear spar work, it clearly states that you should machine countersink it...

But if you take the vans manual section 5. There is a sentence in the countersinking section that says: no countersinking for 1/8 if less then .050.

The reinforcement plate is .040.
This is a contradiction. Who's right ?

If I would have to start now, I would dimple, but it is clearly too late now

I sent a question to Vans support to find out about this and to see if it is better to replace them and dimple.

To be continued...