Mick,

As I mentioned above, there is a sheet of lite-ply inside the center of the aileron. You can use a dremel tool with a carbide chew-bit to "chew" through the lite ply center. Just so you know what I ultimately did after that first one, I had wrinkled covering on my ailerons that wouldn't come out, so I peeled the undersides and installed my Robart pins with the dremel tool and epoxy, then recovered them.

Those drill centering tools work good, once you get the hang of them. I used them for the starter hole before going at it with the dremel.

You can add extra balsa for "meat" when they're open, if you wish. No matter what you do, you have to deal with the lite ply plate inside. Most of mine ended up at a slight angle coming through the plate, and the epoxy held it nicely from there. Just make sure it exits the surface at the correct spot for the hinge area.

Hope this helps.

~ Jim ~