This is a process that Joshua Hendy used to hold his Stamp Mill Feeder frames together. The assembled feeder below shows the mortis & tenon feeder joints (*) on completed feeders. The joints look better than running a piece of all-thread through the entire cross member.
We will go through the fabrication of the mortis joints first using Figure A. You should use a drill press to make the holes straight as possible and a 1 ½” drill auger to make the 3 holes the proper depth of 2”.
Once the 3 holes have been drilled you need to use the sinking tool or a conventional wood chisel to remove the excess wood. I like the speed and accuracy of the sinking tool. The picture below shows the results of the cuts:
The next step is to cut the tenon with a Sawsall or a band saw. Figure C below shows the dimensions of the tenon cuts. It is pretty self explanatory.
Now that both the mortis and tenons are fabricated, we need to join them with all-thread. Figure D below shows the all-thread installed in the timber. This is done by placing the mortis on the tenon and drilling a ½” hole 2 ¾” from the top of the interface with the tenon to a depth of 7 ½”. Next you have to drill a 1” hole approximately 2” deep, as noted. You should then use your sinking tool or the chisel to make room for the ½” washer. Slide the all-thread into the tenon and place the washer and the nut on the all-thread, install the mortis on the tenon/all-thread and bolt it together. This completes your joint attachment.