After riveting the skeleton in place I pulled out the skin and aligned it with the edge of the spar and with the pre-drilled holes against the ribs. Everything looked good until I got to the tip rib: there was a significant gap between it and the holes.
I spent quite a bit of time shimmying the skin and the spar but there was no way to get the tip rib to fall under the holes and get the other ribs in place. I had expected this to be a difficult task but this seemed a lot more difficult than it should, plus it really did look like it should have been fairly easy.
I sent fellow 750 builder Mike a tweet for advice and he offered several good suggestions, one of which led me to the problem. Take a look here at how I attached the tip rib to the spar via the l-shaped bracket. On the right is a picture from the photo manual – can you spot the difference?
In my install I attached the smaller part of the bracket to the spar but in the photo from the manual it is the larger part that gets attached to the spar. By installing this “upside down” I lost a good half centimetre or so off my spar, enough I think to make it line up with the skin.
Next workday I will learn how to drill out a rivet and re-assemble.