If you use the Paul Sellers method with a guide block, you will notice that Paul is paring the mortise after chopping it. This will make the mortise a little wider than the chisel (even if he is removing only a fraction of a millimeter).
So make your tenon and mortise marking a little bit wider than your chisel. How much? In function of your chopping and paring skill 😉
By the way, one doesn’t always have the desired chisel width.
see this blog which shows how to make a wide mortise: https://hyvelbenk.wordpress.com/2014/03/16/hovelbenken-i-mariestad-er-pa-fotene/
It is in a Nordic language but the pictures are self explanatory.
- This reply was modified 3 years, 7 months ago by Benoît Van Noten.