A mystery solved ...

I just finished doing the initial sanding of the keytops for the sharps and now they are ready to be glued to their keys.

As I mentioned before, the spacing for the sharps is quite tight in a few places and the C# above middle C has been giving me some cause for concern. There is (just) enough clearance for the key, and I know that with a little careful filing of it and the adjacent keys it can be made to work, but I have been puzzled about why the problem exists in the first place and wondering whether it is because of some mistake that I have made. In particular, I don't want to start filing things to make them fit until I am sure that is the correct way to make the adjustment.

As far as I can see, everything else looks OK - the balance pins are all perfectly straight and vertical, and the keys are all lined up nicely and evenly spaced. I was beginning to suspect that there might have been some small inaccuracy in the way that the keys were cut, but I wasn't sure and then, a few hours ago, I finally saw something that had been staring me in the face since I started working on the keyboard.

Here is a closeup of the problem area of the keyboard:


The problem is that the space between keys 25 and 27 into which the C# keytop has to fit is just slightly narrower than it should be and, now that I have seen it, the reason is obvious.

If you look closely at key 25, just to the right of where the number "25" is written on the key you will see a pencil line running along the right hand edge of the key and disappearing under the keycover at the front of the key. You don't see that line on any of the other keys, and you shouldn't see it because that is one of the marking out lines that indicates where that key should have been cut.

So, the answer is simple - space is a little tight because the right hand edge of key 25 (middle C) is about 1.5mm further over than it should be.

... and, oddly enough, knowing that makes me happy because now that I know what the problem is I am much more confident about being able to fix it correctly. I don't have to win back all of that space - just enough to ensure adequate clearance - taking about 0.25 mm off each side of the C# keytop and the adjacent keys should be more than enough, and I will try to get away with less than that if I can.