Here's a quick way to route out the air channel for your toneboards if you don't have a router table. I use a "handscrew clamp", a pair of Bessey clamps, and a Laminate trimmer with a straight bit (size of your choice).
You will also need a way to hold your toneboard. I use an old metal toneboard jig. One can easily be made out of wood.
The jig here is only used for securing the toneboard.
First bore out the delrin rod with the bit of your choice. I use BigB's method of constructing my toneboards. Shaping the radius on a disc sander.
After establishing the basic shape, I chuck the shaped toneboard in the jig backwards, and upside down. Next I clamp the fixture between the jaws of the handscrew clamp. I keep the metal block flush with the top of the handscrew. The beauty of this set up is that the block holding the toneboard can be tilted to change the cutting angle in the final set up if desired.
Next I use the Bessey Clamps to clamp the handscrew clamp to the edge of the table. But at the same time I use the side of the clamps to act as a fence to guide the router.
Just make sure the router and bit are centered along the toneboard. And be aware of where the router bit is in relation to any metal parts. You don't want to hit the jig, or the metal rods of the clamps.
I mark a line along the back of the metal jig, up to which I will slide the router base, and then stop. Adjustments can be made quickly in regards to depth of cut, etc. Hope this helps.
HuntnCarve
Dave