I had a few request for this so here we go. I used this jig for the Really Rustic Chair and several other similar type projects.
You want the hole to be a little bigger than the tenon size you want. You will need to make a template for each size. I had a couple more made but one got broke and the other lost in my shop move.
This is the adjustable stop. It determines the lenght of the tenon. I usually make the tenons long and cut them after.
I made the router base from aluminum because thats what I had. Any siutable base should work.
Add an 1 1/2” round nose bit.
clamp it tight.
I then slightly taper the log. Use a hacket, saw, jacknife, what ever you like. Its not reqiured but makes starting them easier.
Spin the log as you insert it. Starting it take a little practice. I don’t recommend getting the gingers to close unless you fell your fingers are to long.
It comes out a little rough, and should be a little larger than you want. Here you can use a rasp, plane ir power sander to get it down to size.
Off to the bandsaw to cut the slot for the wedge.
And I think you know what to do from here.
I wanted a bigger tenon, so I made a new template.
I shaped out the bit hole with the bandsaw.
I cut a 2” hole for a 2 ” tenon.
Then tapered the edges.
Hope it helps
-- Master hand plane hoarder. - http://timetestedtools.com