I made a big rectangular template for the tenon and mounted that on the template holder.
I used a pattern cutting bit with the router. This bit is a bit longer than a regular 1/2" router bit because it also has a bearing attached. The bit extends 4 cm beyond the collet, so that's how long my tenon ended up.
Chip removal is a bit of a challenge, especially as the router gets nearer to the workpiece and obstructs the opening. I had to back the router away a few times to clear the chips. Also, I made sure I didn't have too many chips in the cavity when routing near the edges. Extra chips getting in between could affect the quality of the cut.
My other pantorouter doesn't have the flat area around the router, so it would have been better at letting the chips out.
I anticipated needing to make minor adjustments, and I made the mortise template slightly tapered so I could slightly increase the size of the mortise. But I already cut the mortise at the smallest end of the template's taper.
I'm guessing that my 1/2" router bit cut slightly larger than 1/2".
I get a lot of suggestions about adding dust collection to the pantorouter, but I don't know a good approach, nor have I seen one that is very good. There are dovetail machines with dust collection, and the Leigh FMT jig (which does mortises and tenons) has dust collection capability. But for a machine as flexible as the pantorouter, it's much more difficult. It would be possible to design dust collection shrouds for very specific operations, and if I had to cut 1000 tenons, I'd probably design one for that. But I cut so many different types of joints, and I want to be able to see and film the operation, so dust collection is just not practical.
Update: Kuldeep has designed a pantorouter dust collection hood that actually works, though that one doesn't fit on the pantorouter XL.
The gap all around the mortise was very even, so I was confident that the pantorouter was not introducing any distortions (like it did before I tweaked it)
Looking at what I made, I figured, this might make a neat little box if I cut the tenon much shorter. But then I had the idea of hollowing out the tenon. So I made a really big follower to go with the tenon template. That way, I can cut a smaller mortise with the same template in the end of the tenon.
I have never built a "bandsaw box" (too many videos on that topic already). I guess I should call this my "pantorouter box".
Placing the top on the box, it takes about two seconds for it to drop all the way down because the air can only escape through a very narrow gap.
The box also makes a very satisfying "plop" when pulled apart rapidly. But I really need to grip the two pieces firmly while doing that - because there is considerable air resistance to pulling the pieces apart rapidly.