ORIGINAL: dbacque
Add the Tip Blocks. Carve tips flush with wing using razor plane (cover sheeting with blue painters tape first). Get tip close to shape of airfoil, then sand everything flush. Mark center line around outside of tip block. Now carve everything to shape.
Dave,
For the wing tip blocks I might also suggest tack-glueing them in place with a couple drops of med CA, carve and rough sand to shape, then pop the tip block off and hollow. (pictures in my build thread)
A good centerline mark is helpfull as you suggested. One thing I've done before is to either, use two blocks, or split the block in half and glue the finished edges together -using the glue line as reference to the centerline. The glue joint also helps protect against hanger rash if the tips are carved to a point.
My old Bridi instructions make mention of in-laying 1/64" ply at the centerline to make the tip more durable. I didn't think that was nessasary since I glassed mine, but if you're using an iron on covering, you may want the hanger rash protection by adding the ply or dripping some thin CA on the tip of the tip block.