I don't claim any originality for this but there might be the odd wrinkle that might help someone.
On my door project I needed to fit 3 hinges and the door jamb are made of softwood with a couple of mm of oak veneer so a bit ticklish to chisel even for those who prefer hand working.
So this jig is for use with a top bearing flush trim bit.
First job is to cut a template with a good fit to the hinges. Mine needed to fit 100 x 30mm hinges.
I ploughed mine out on the tablesaw.
The thickness of the template needs to match the router cutter so the bearing rides on the template.
In my case my cutter was 25mm plus the bearing so I chose 30mm.
Subsequently I did find a set of shorter bits here https://www.amazon.co.uk/YIXISI-Templat ... =1-14&th=1
I ordered those for future jobs. They might not turn out to be tip top quality but wont get heavy use but possibly good value overall.
Now we have the template we need a guide to position it on the edge of the door or jamb. This can be marked out from the template.
The dimensional accuracy of this is not critical and can be chewed out on the bandsaw
First cut
second cut
The final depth will get trimmed by the router on the first use.
To make the jig easier to clamp, mark off the corners on the template and remove on the bandsaw ot table saw if you prefer.
Screw the two parts together, I prefer not to glue just incase it needs to come apart for adjustment.
.
Now to give it a try.
Clamp to a test piece and sneak up on the correct depth.
Whilst the jig is still in place the two corners can be trimmed with a sharp glue scraper/paint tin opener or Chisel as some call them - yes I do use then but very sparingly
Then offer up the hinge and test the fit adjusting the jig or depth of cut to perfection.
The jobs a good'un.
Bob