Beautiful butterfly keys that work.

When it goes to plan, this can be the most rewarding task in woodworking... Way better than trying to use an inlay kit (which dont get as good a re

I used a bench plane to cut off the excess prior to sanding.  Can you see my first 2 attempts... The top Key was even made with the grain going the wrong way so it has absolutely no structural support what so ever. Always cut your key with the grain following the length of the key... Thankfully this was just a practice piece so I didn't have to worry about that... :-)

Clean up the glue with a damp cloth

Gentle persuasion needed to install the glued up key.

Only glue up to about half way and have a damp rag ready to wipe up ALL of the glue that seeps out.

If you don't know at this point which side goes up... You could need to start over... Always mark the top side and I also recommend a small mark to define the top right corned just to add certainty and piece of mind.

Ok so it takes a few steps to get to this stage, here we go:

Sand the wood to 400 grit
Make your butterfly key however you prefer but make absolutely certain that the angle between the bottom face and the sides all round are PERFECTLY 90º.
Make sure the key is slightly thicker than the hole it's going into.
place a piece of double sided tape on the bottom of the key and write "TOP" on the top face so you know which is which... Don't be tempted to ignore this advice, that's how you'll make your first mistake if you do I promise...

position the key where you want it to go and press down onto the tape.
with a marking knife (or at a push a utility knife could do), VERY CAREFULLY mark the wood around the key. If you slip and overshoot, you can sand it later but you'd rather not have to so take your time here.
Having marked perfectly around the key, lift it off gently (remove the tape) and put it to one side.
Using a router with a small straight cutting bit, carefully cut down into the wood removing material to a depth slightly shallower than the key thickness and DONT CUT ALL THE WAY TO THE LINE YOU SCORED IN THE WOOD. Leave about 1/16th from the cut line.
Using very very sharp chisels, par away the material right up to the line and clean up all the corners. cut either perfectly straight down or a tiny back angle to allow for glue. One way or another you need to make it so the key goes into the hole with a bit of persuasion but without ANY gaps around it once it is in place. Lots of practice needed.