Use an adjustable protractor to measure the actual angle of the inside corner. Divide this measurement in half to determine the number of degrees each cut will need to be set to.


Place the right side of the protractor against one wall forming the corning. Open up the left side of the protractor, extending it all the way open until it is perfectly flat against the wall on the other side of the corner.
Note that the protractor should be parallel to the ceiling and floor at this point.
Most corners will be roughly 90 degrees or only an angle or so off that mark, but for the sake of accuracy, it is important that you find out the precise measurement before proceeding.
Each piece of crown molding extending to that corner will need to be able to fit together. In order for this to happen, both pieces of crown molding need to match the measured angle of the corner, so both should be cut to an exact have of this measured angle.;
, Swing the blade of the saw to the left until the angle matches the halved measurement of your corner.
 Place the piece of crown molding in your jig and on the bed of your saw. Drop the saw and, while keeping your left hand on the molding, make the cut.


The bottom of the molding should be up when you place molding in the jig.
Keep the jig and everything else to the left side of the blade and safely out of the path of the blade. The jig must not be in the way of the jig.
Do not turn the saw as you drop the blade or make the cut.
 Swing the blade of the saw to the right until the angle matches the halved measurement of your corner.


Note that this measurement must be the exact same as the one made for the right inside corner. If not, the two pieces will not fit together correctly when the time comes to install them on the wall.
 Place the piece of crown molding in your jig and on the bed of your saw. Drop the saw and, while keeping your right hand on the molding, make the cut.


The bottom of the molding should be up when you place molding in the jig.
Keep the jig and everything else to the right side of the blade and safely out of the path of the blade. The jig must not be in the way of the jig.
Do not turn the saw as you drop the blade or make the cut.
 Hold one piece of molding up against the corner of the wall, bringing it to the corner. Slid the other piece into the corner, bringing the two pieces together.


You may need to make small adjustments to make them fit better. You should get a perfect fit with no gaps in it.
A nail gun works well for quickly nailing the pieces of molding into place.
Measure the angle of the corner.
Set a compound miter saw with the correct angles.
Cut the right inside corner.
Set the miter saw angle again.
Cut the left inside corner.
Fit the two pieces together before nailing them in place.
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