I put this together a while back but never published it as their are a couple tutorials on this already. Not sure if I can add anything to these but I am going to give it a shot.
I have been building these for quite some time and have a lot of luck with them. About 4 times a year, we do a couple events that are loosely based strictly for squirrel hunting and are teamed up with some pretty good people in a couple of the right places. This usually makes a couple weeks work for me just building a ton of these once a year.
Here is how I go about the process of mass producing them in the hundreds.
First, I order in a lot of wood blanks, (doesnt really matter the type) 1.5" square by 12". Each blank is then cut into 3" blocks and the ends are marked for center. Then I put them in my drill press vise and a 1/2" hole is drilled through.
Next, I chuck up the trusty ol' pin 1/2" pin chuck and turn to the basic shape. These are much like my duck calls in shape and size so it becomes pretty easy for me to clone them and be pretty repetitive.
Once I am satified with the overall shape, I hollow out the end of the call using a fabricated one of a kind, High Speed Steel cutting device ( my sharpened screw diver from harbor freight)
Then, I turn the call around on the mandrel. I am not so picky as to line them up perfectly, those that use a pin chuck will know that it tends to off center the turning by a hair. It really doesn't show on these if you are off by a little as bad as if you were trying to band a call per say. As I said it doesn't have to be perfect, it just has to work. I start the tenon by measuring the bellow's outside dimensions where it slips onto the call with my calipers and turn this to shape. I also made a couple of marks on a wooden dowel of where the little lip is on the inside of the bellow as well as the basic length the tenon needs to be.
Once I have all the dimensions roughed in I finish off by turning to size and length as well as putting the grove in the tenon for the lip in the bellow. The reason for measuring the outside diameter of the bellow comes into play here. I will slightly dovetail the tenon so that the end is the OD that I measured while next to the call it is roughly the inside diameter of the bellow's mouth. This gives the bellow something to hold on to, limits slippage and keeps everything good and tight.
Finish sand by going from 100 to 320, both against the grain and with it, (this one burned) and then a quick couple of CA coats. Again, while on some I might be after that "oh my god" finish, for the most part I am just trying to protect the call. 10 coats of CA ins't necessarily needed but 4 or 5 work well. I will polish this up quick with some wet sanding and mother mag wheel polish to bring them to a shine.
If I am not using CA, I will oil these with Velvet, Danish or Teak depending on the wood and what I have around the shop, this varies so you just have to find what works for you. I then line dry them, re applying the oil over the course of a couple days and let them dry before buffing them with Tripoli.
I blade the reed heavily (basically bending the metal reed upward till I get the raspiness I am looking for) and insert it into the call with the reed facing into the bellow. Some face the reed into the call. I find that they sound better with the reed pointed into the bellow, lots more rasp and much more responsive. Once I am okay with the sound I attach the bellow and run a little 3n1 oil onto the call with a toothbrush being sure to get every crack and crevasse and call it done.
Hope this helps! Have fun! They are easy to make, work well and make great gifts.