The right way and the wrong way
Take a descent key to start with (one that has not very low cuts) and get you a 1cm square file. NOW file down each grove to it's lowest cut WHILE leaving as much meat on the peaks as possible (you will inevitebly take quite a bit off of the peaks). Your key should look like this VVVVV .....NO GAPS BETWEEN CUTS. That is the "key" here. The theory here is with NO gaps (and you have made the key correctly) when you pull back one click the pins will resting right at the bottom of the valleys. This allows the pins to "ride" up the peaks and open the lock with the "slightest" of taps. It took me a few tries to key a good key made, but when made correctly you will tell a very big difference in the performance of your bump key. Just be very careful with that file and your strokes. Take your time. I'm new here, so I wanted to contribute. SO, if I have posted any info that I shouldnt have please take the post down. I hope this helps someone. Try it and let me know. Oh and to get your spaceing right, this is what I did, I went on ebay and bought a set of "depth" keys, a set of all the most popular keys. They're all cut down to the lowest setting (with huge gaps between cuts), but I took them and put them against my key I was gonna cut on and drew some marks on it (from the middle of the cuts) to make sure when I was cutting it down that I was still in the right place. Riff