THE FLIPOT

I like this word - it's pronounced fleepo -it translates as "shim".

Have a cool tool for this work - it's a brass shoe with a v-shaped blade protruding from the base. You insert the blade into the offending crack & hammer the shoe gently to the end of the crack.

Then you cut the flipot/shim from the appropriate wood (in this case spruce) rub wood glue into the slot & bang in the shim, wait a while for the glue to take & cut it flush & this is where we've got to in the picture.

Much more to be done!