The handle is not made of balsa wood. Heck no!
Balsa has its uses and is lightweight and easily worked, but in the dimensions needed it has insufficient tensile strength.
No, he handle itself is made of 3/8" plywood. The extenders are made of 3/16" plywood.
I cut the shape out of the 3/8" and then I removed the inner 3/16" using the table saw. (I just took five minutes and whipped up some diagrams...sorry if they aren't perfect, but you'll get the idea)
After the extra material was removed, I made the extenders out of 3/16" ply. The hole on top attaches to the handle while the groove is the slide to let it open up.
And then I had to cut the handle itself. The holes on each side are for the screws that hold on the extenders. The groove in the middle I made using a router. It is for the dowel peg the holds the handle itself to he riser and allows it to slide up and then into the notch that keeps it from sliding out of position.
I also cut off the very top of the handle (the part that opens and he part that I can grab) and opened it up a bit to allow room for my fairly large fingers.
The screws are, if I recall correctly, 4-62's (#4 screws with 62 threads per inch...sorry it's not all metric, but I am a simple American who is woefully behind the rest of the world as far as metrics are concerned), with nuts on the backsides. I had to grind down the ends of the screws and take a bit off of the nuts as well using a bench-grinder. A dab of super-glue (I couldn't find any of my Loc-Tite) holds the nuts in place now.
A word of warning when using a grinder; I was stupid and careless and accidentally touched one of the nuts immediately after grinding it. Managed to brand the tip of my finger. Not a pleasant feeling, for a pleasant smell. Be careful! I know better, and still managed it!
Anyway, that's the basics of how that was done. The rest of the riser for he handle is made of 1/2" ply sandwiched between 3/16" ply, with the "bread" of the sandwich extending above the 1/2" long enough to fit the handle inside. The handle is held in place with a 1/4" dowel peg that runs through the "bread" and through the groove in the handle.
That's about it. Pretty simple, but effective! My dad watched me do it, and his only comment was, "If only you would use your powers for good..." Then he walked away laughing.