Suggestion by hapagirl
your miter saw should cut it you just might need a bigger blade.i used my miter to cut 41/2 base board
Suggestion by ugly joe
I would use my 12 inch craftsman sliding miter box. The blade is mounted on a slide much like a radial arm saw.
Suggestion by Just Me
Most 12″ miter saws have a 6-5/8″ vertical crown molding capacity. Dewalt is a good brand.
Suggestion by James M
Lowes sells for $ 15 a tool to measure and cut crown molding by laying it flat. One measures the exact angle of the corner with this tool. then set the saw for both angles and cut right thru the molding laying it flat.
You can also use this tool with a tablesaw and your angles will come out perfectly for any heigth of molding, including your 6 1/2 inch crown molding. .
It is not recommended to cut inside corners by miter cutting them. The shrinkage over time will cause those corners to open up. You need to “cope” those in with a coping saw.