My bindings are always 2mm or more, the sides never over 2mm.
When I work I alternate the scoring of the side with cutting from the face down, in other words I treat the binding same as the purfling. I switch from side to face cutting and eventually the two scored lines will meet. I always find myself dreaming for a second gramil and I never have the $ for it. Readjusting it every few minutes is a bit annoying.
Normally I start by doing a solid scored line around the sides. I don't need it full depth, just big enough to be easily seen. The I start chiseling the rosewood away. A sharp chisel, often re-honed, is really important. I stop when i see the lining. Often larger sections of rosewood can be popped-forced off the lining but for this you need nice grain and a good score-cut. Once most of the rosewood is off I score again, this time it is little left and easy to reach the lining. Now i can readjust the gramil to round and 2mm or whatever depth and cut from the face down. Either clean the rosewood and glue residue from the lining, or eventually go a bit deeper in. At this point you don't really need the chisel as the gramil cuts easily down through the soft lining. Eventually you can readjust and score the side again etc. The very last op is to chisel the edge of the side square, as it is often a bit over 90 thanks to the top or back doming. If you don't refine this part you might end up with gaps. Alternatively you can sand a a bevel in the binding or side purfling but I prefer to chisel the side.
Do more guitars like this and it gets easy
