Small Detail Work - Technique Question

Quoted text begins.My question is: I need to cut some deep inside right angle corners in
tight areas.
End of quote.

A easy way to cut deep accurate corners is to drill a small hole to the
depth you need, right in the corner to start with. This dovetails nicly with
the question about drilling in stone. Drill the hole and use it as a guide
as you cut out the corner with your chisel.
George Graham