When I was a lad working as an apprentice, many woodworkers didn’t have hand routers and machine router salesmen were often laughed out of the shop because a skilled craftsman could set hinges much faster than a router back then. We made any router we needed from a scrap of pine like this one here in a matter of two minutes and we were on the job.
Bore a hole at an angle as shown. Any angle 40-55-degrees will work. The hole diameter should be about 1/16” smaller than the width of the chisel you want to use so, as in this case where I amusing a 3/8” chisel, my hole size is 5/16”.
Set the required depth by trying it against the depth gauge line. This is simply a question of forcing the chisel into the block or easing it backwards for a shallower setting. Because of the leverage against the chisel as the cutter, the depth remains accurately set and does not generally withdraw or deepen as you might expect.
You can also refine the shape for greater comfort by chiselling the shape and creating thumb scallops either side of the cutter.
Make sure the chisel sides bit into the wall of the hole to create a good friction fit.
The router is now ready to use.