You are making this way more complicated than it needs to be. This is such
basic carpentry that I was probably 10 years old when I did it the first
time with no power tools and only very basic hand tools. You take a piece of
wood, any wood but pine without knots is easier to work, sand or plane one
side and one edge, flat and smooth. You saw or plane it to slightly wider
than the mortise, saw off about a quarter inch thickness and saw to length,
glue into the mortise and when set, plane to flush with the door edge and
side. If needed touch up with wood filler. Done.
Durham's Rock Hard Water Putty. Easy to use. Works great. Available at
Ace Hardware and probably Lowes, Home Depot, etc. Comes in a round can.
Here's what it looks like:
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.