Step 3: Cut the top
To hold the key securely, I measured the stem and drilled a matching hole in a wood block which I could fit in the vise of the drill press. Here I made the mistake the first time I cut the top off. I held the drill press down till the outer ring popped off. Several times the whole key started spinning. I did not pay attention to this first but plastic is quite soft and got slightly twisted and marred in the hole of the wood block. When I put the keys back in the keyboard, many steps later, I noticed that these keys stuck. Bummer! Nothing helped and I had no choice but to buy a new keyboard. So you better be careful here!
On my second attempt I made a cut from the edge towards the stem as kind of stress relief and used several light pushes downward to cut the outer ring off. If you want to stay completely on the save side, cut the outside of the keys with heavy scissors.
Anyway, repeat this about 100 times. Scrape off any plastic from the top and sand it lightly. Make sure you keep these keys as well as all the screws and all the parts you take off save in boxes or jars. I like to use e.g. old pill bottles, empty margarine/soft cheese cups or a glass jar.