The Angled Slots

This photo shows several angled keys installed onto their rear key pins. Test each key to make sure they move up and down freely. If a key gets stuck and doesn't move freely, either the balance rail mortise is too tight or the back slot is too tight. If you lift the front of the key 1/4" [6.35mm] and it doesn't drop back down, the balance rail mortise is too tight. If the key does drop back down, the rear slot is too tight or bent. Repair as needed.