I am building some sapele book-cases.
The interior has been pre-finished before glue-up ( 4 coats shellac, 4 coats AquaCoat grain filler, 4 coats GF High Performance, with Fuji HVLP).

I have now reached the point of finishing the exterior. General Finishes says "wipe off alcohol from High Performance in a timely manner", so I figure the interior poly will be reasonably safe from the shellac I put on the front. My concern is applying the poly to the front face junction with interior.

If I spray the front with the rest of the exterior, I am worried that I will get a certain amount of dry spray on the interior surface.

I could mask the interior, but have concern of leaving a line. However, there is a small chamfer on much of the edge that may help to hide the transition.

Or, I could apply the poly with a brush to the front face. It might not look as good as a sprayed finish, but when spraying the rest of the exterior, I could go over most of the front face at an angle that does not put poly towards the interior.

Any suggestions on the best way to tackle this ?

HI,

Masking is probably your best bet. However, the paint brush could work also. It comes down to whatever you feel will work best for you.

Sorry we have no other options to offer.

So I just finished spraying the boxes (6). Came out pretty good.

What I did was first mask off a couple of inches of the interior. Then fitted a cardboard plug to the front.

I first gave the front face three coats of poly with a brush, figuring I would stay just off the tape, and then just give it a coat or two of spray to give it a smooth surface. But that was not the best idea because I couldn't stay off the tape and properly finish the edge, so I might as well have just sprayed the front from the start. That endeavor only increased the time the painter's tape was on the box, by a day.
The next day, I sprayed four coats of High Performance on the exterior of each box. It went on really nice with my Fuji MiniMite 5. But by the time I finished, I was getting real nervous about how long the tape had been on there, and that I might lift the poly when pulling off the tape. So as soon as the last coat was dry to the touch, I pulled off the tape (successfully).
Only a very small line that is not really noticeable because it is on the edge. I will wait a couple of weeks for a more complete cure and then see if I can buff it out.