First I drill the air channel the size and depth I want. Then I drill the exhaust end the size and depth I desire.
No need to drill out the exhaust on an open reed tone board. Just drill the air channel right through. There isn't enough material in the back end of the tone board to affect back pressure.
Once you get drilled through, you can use a wooden dowel with a lengthwise slot cut in it and a piece of sand paper stuck in that slot to clean up the end of the tone board air channel, and round off the edges if you want. This will also open it up some, but again, it is not necessary.
Then I cut the length on the band saw. Then I use the best sander to get the arch.
A belt sander will ruin more tone boards than it will make. Once you get it cut flat, take a file to the very end of the tone board and file the ark in. Don't try to get it perfect, you just want to remove material to get it close to arking downward.
Now here is the trick. Go to Walmart and by the cheapest rubber car mat you can find. It should be rubber, not plastic.
Take it home, and cut it up so that you have a "sanding pad" about 3/4" wide and about 2 inches long.
That car mat will last you for years. Start with 120 grit sand paper and sand the rest of your ark in with the sanding pad. Remember, that any flat surface will sand a flat spot. The rubber will bend and allow you to form a nice smooth ark.
I go from 120 to 220 to 320 and finish with 400 on plastic and delrin, then buff a bit.
Then I use the scroll saw with a fine blade to cut a small slot for the reed to be inserted.
I do the same thing.
First issue: Even though I am using a press, drilling through the center of a 5/8" piece of delrin is a challenge.
Don't force it. Drill in 1/4 inch, back out clean the bit, go in 1/2 inch, back out and clean the bit. Back out and clean the bit twice as much as you think you should. Also, drill as slow as you can. Keeping a clean hole and drilling slow are the keys to a straight hole.
A router will work, and I use one for some of my boards, but you need a jig of some sort and you really have to be careful or you're going to hurt.
Again, forget about opening up the exhaust. It doesn't matter.
Second trouble: Getting the reed cut evenly and then fitting well and snugly
Cutting reeds is an art form. I refuse to do it anymore and generally use the reeds for deer grunt calls. They are about the right width, and all you have to do is cut the end.
As for holding the reed on, you do not want to have it so tight it bends the material. Castration bands work well of 5/8 inch boards. So do O rings. You can use two of them to hold the reed in place.
The real trick in making open reed tone boards is the reed itself.
PAY ATTENTION - This tip is going to save you YEARS of trouble tuning open reed calls. It aint mine, but it is my modification.
Years ago, I spent an evening on the phone with an old coyote calling god from South Dakota. He knew his stuff. He gave me a tip, that over time, I modified, and I am going to pass it on to you.
First, it is a rare thing to get a piece of plastic, acrylic, or even delrin to form a perfect ark. And having a perfect ark is the key to no pitch breaks, and a good sounding call. The way most guys make tone boards, causes mylar and duralar reeds to try and conform to the tone board. If it isn't a perfect ark, it will break and sound bad. The tip I got that night was to "lift" the reed off the tone board just a bit, by placing a small piece of mylar under the reed at the point where they castration band holds it on so that the reed can bend naturally. Both Mylar and Duralar have a "memory" and want to ark smoothly. By lifting them off the tone board a bit, you allow them to do just that. They are not forced to follow the tone board, and therefore, the reed plays a nice even pitch unless you have some really really bad flat spots in your board.
This works well, but keeping that piece of mylar in there was a problem.
My modification was to cut the reed about 3/4 inch longer than you need, and then you take the very end of the reed, and bend about 1/2 inch under itself. Like this
Then insert it in your tone board, so that the bent under part lifts the reed just slightly off the board. If it is too tight a fit, tap the bend with a small hammer and it will flatten it out.
Trust me, this is the tip of a lifetime when it comes to open reed calls.
Always trim your reed to where it sits RIGHT at the VERY END of the tone channel. The closer you get, the better the call will sound.
Dog earing the reed at the end will vary the sound. The more the angle, the higher pitch you will get.
Round over one side of the tone channel by just passing a piece of sand paper on your rubber sanding block over it. Just a bit. This will increase rasp. Doing both sides will give more rasp, but you can over do it too.
Some guys will have you believe that making tone boards is a science, or alchemy, or magic. or some other weird stuff. Bull. Every tone board that I sell in my shop is made from a flat blank, and I NEVER use a jig. I just file the ark in, then I sand it and eyeball it, and put a reed in just like I showed you above. I then blow it and see how it sounds. Every now and then, I will make an adjustment, but 99% of the time, the tone board is ready to hunt.
By the way, bending your reed like this helps prevent spit lock up as well.
Now, finally, I want to stress that this is for Open Reed DISTRESS tone boards. Howler boards, are a different ball game completely. While you can use an open reed distress board for a howler, the boards are really different. Longer, not as arched, and the reed is thicker. Usually a .014 reed as opposed to a .010 for a distress.
Hope that helps some...
Al @ THO Game Calls