My interior doors are typical “builder grade” six-panel, hollow core doors. When you cut into them you will find they are exactly what they say they are…hollow.
I cut out the top four “raised panels” on the door. This cut doesn’t have to be “exact” but try to keep it fairly “square.” I used my skill saw to cut the straight runs and then a jig saw to cut out the corners.
After I cut the hole in the door, I added bracing between the “skins.”MOST hollow core doors will measure 1 1/8” between the skins, but measure the INSIDE between the skins…that will give you the width of your bracing.