I spent a little time this evening fluting the horizontal stabilizer ribs. Fluting is the process of shortening the rib flange from one end to the other by bending a short offset with a specialized pair of pliers (black handles in photos). During manufacturing a bend is formed on a flat piece to produce a flange. When the flange is formed a resulting bow occurs in the rib along the web. Fluting the rib flange pulls the web back into alignment so as not to preload it when riveted into the final part.
Once the web of the rib is flat, the flange is squared so that it will lie flat against the skin. I am accomplishing this with a hand seamer (red handles in photos) and then verifying square with the end of a small ruler against the flat work surface. A flange straightening tool is common-place in many kitplane shops, but I have yet to construct one. It is on the to-do list before tackling the large number of ribs in the wing portion of the build.