When attempting to rivet the piano hinge and ribs to the ruddervator skins, I noticed the ruddervators were warped, especially the trailing edges. This was due to the fact that I did not firmly clamp the skins to a flat surface prior to drilling the holes for the piano hinges. I simply measured down the correct amount all along the leading edge and drilled it. This was a very costly mistake both in terms of time and money. I have to reorder the skins and start over. This is rather frustrating since I am now 2 for 2 on rebuilding parts. The learning curve is very steep and expensive.