I bandsawed mine to rough shape. Cut it close to the line and go slowly. Be careful! Then I used a Vixen file (I prefer the fine-tooth side) to smooth it. That leaves a pretty good surface, but a fine mill file did the rest.
This general process works an a lot of RV-3B parts.
A belt sander with a 100 grit or a fine-grit blade will do if a Vixen file isn't available, but the Vixen is the tool to have. I use mine a lot. If you don't have a band saw you can use a cut-off wheel but it'll take longer and might overheat the bar. I'd regard the band saw, Vixen file and fine mill file as the tools of choice.
Dave Paule
RV-3B, now skinning the fuselage