The elevators are built with a solid piece of balsa on the inside to support the control horns. On the plans, the 3 mm outer edge continues all the way to the inner end of the elevator, but I decided to build this whole area out of one solid piece of balsa – this is easier to build and also makes it easier to get a smooth transition from the block to the edge.

I first laminated a piece of balsa out of two 1/4″ thick layers, sanded the perpendicular edges straight, and then I placed it on the elevator to trace the outlines and cut the piece to the right size, including the opening for the control horns:

Then, I sanded the piece to shape. It’s slightly oversized (by 0.5 mm) because I didn’t yet glue it on. I have to build four blocks and this way it’s easier to compare the result and modify them until I have four identical pieces. After gluing them on I will do the final sanding:

It’s a complex shape though, because the thickness should be 3 mm all along the outer edge:

While the inner side runs in a slope from 1/2″ to 1/8″:

I have developed a neat little trick for this, which I often use when sanding the more complex shapes. I just cover all the parts that need to stay untouched in blue tape. The blue tape is less sticky than the white one, it’s easier to bend around curves, and – most important – it creates a nice visible contrast with the color of the balsa wood. This is much easier to see than a pencil line, and you can never sand too far, as the tape prevents you from doing so:

Then I sand it roughly to the right shape with a coarse grit (80) on my simple self made sanding block. I usually prefer to move the piece over the block instead of the other way around, which is more precise and easier to do:

And I end the sanding process with some finer grit sandpaper. Because I need to make four blocks, I keep comparing the result while sanding, to make sure I end up with four identical blocks. The glue line of the lamination is an extra guidance here, because it indicates if the pieces are identical (\the glue line shape should be symmetrical). Here you can see I’m almost there:

And when finished you can unpack your gift and you’re treated with a very clean and straight edge as a result:

Before I will glue them on, I first will test and adjust the control horns, after which my elevators are almost finished!