I'm considering making a well insulated interior door and need to understand the door thickness implications for the getting a door knob. The door could be upto 3" thick – less if getting a door knob becomes a problem. I'd like to use a cheap off the shelf knob – possibly adding extensions.
Doors – door knob for thick interiour door
doorknobdoors
Related Solutions
This style lockset is known as a mortise lockset.
Dis-assembly and cleaning won't hurt.
While you've got it apart, print the Baldwin diagram below, and note your dimensional differences. Some will be critical (holes for knob and deadbolt), others may be compensated for by strike plate adjustment or wooden block supports (under a shorter mortise body).
Backset (the distance from the door edge to the center of the knob) is a critical dimension that will determine what replacements are available. Modern backsets are usually 2 3/8", many older mortises are 2 1/8 and 2 (the new one below is 2.5)
This page lists some Baldwin mortises, they cover a range of backsets and door thicknesses. Googling "mortise locksets" will net you many choices.
Personally, I'd get the table saw a portable folding stand, you can do basically everything you need with the tablesaw and can build any of the jigs you need.
You could also do most of the work with your circ saw and router but getting the wood to the correct dimensions is going to be easier with a table saw since you don't have a planer or jointer.
Instead of mortise and tenon, look at doing half laps for the corner joints and for a support brace or two across the middle. You can probably get some nice looking metal braces to strengthen up the corners as well. You should be able to do half laps using your circ saw or router. You can also profile all the edges with the router to making look nice.
Best Answer
A standard lockset could be inset into the face of the door, so that 95% has full insulation. You will also need to consider hinge screw locations in the edge of the door.