Bushings... That's where the action is at!
I was dealing with a Yamaha upright today that had some "sticking" keys. A "sticking" key could literally be almost anything. Through some detective work (which is a whole other article in and of itself) I narrowed it down to a tight whippen bushing.
If you don't have much experience working with action bushings let me say now that the title of this post is no joke. Without exaggeration, action bushings are the heart and soul of a piano action. The sizing, quality, and installation of the bushing felt can make the difference between a mediocre action and a great one.
While installing a new bushing is serious business, reaming a tight bushing is fairly easy. First, you need the right tools. Your list should include:
1. A good center pin removal tool (while there are a variety of center pin removal tools, the one pictured is solid and cheap)
2. A good micrometer (which will allow you to identify the size of pin needed)
3. Reamers (I prefer the Don Manino reamers which are graduated)
3. A selection of center pins (A note about center pins: make sure that any pin you use is clean, free of tarnish, and smooth)
4. Center pin cutters
5. Gram weights (Or a gram gauge)
Removing the pin and measuring it are self explanatory. What takes some experience is knowing how much to ream in order to get the right amount of friction but not go too far and end up with too little. This is where the Manino reamers really shine. They are graduated so you can match the reamer size to the pin size. And, they have a rough spot (circled) that gently reams the felt while the smooth area burnishes it. Burnishing the felt after you ream it helps to lay the felt fibers down so your center pin can rotate more smoothly in the bushing.
Using the Manino reamers is simple. You slide the flange onto the reamer, pass it a couple times across the rough area, move it around the smooth area to burnish, and then check the bushing by poking the center pin into each side and gauging the resistance by feel. You could assemble the part and use your gram weights but getting to know the feel of a properly reamed bushing will save you a lot of time.
Once you've got a flange that measures with the right weight, cut the excess pin and you done. The right weight for a whippen in this case is 2-3 grams (Just for comparison, hammer shanks are also 2-3 grams). If you happened to have reamed too much, you'll need to select a pin that's a size larger and start over. Also, if the original size pin is at all loose in the bird's eye, go a size larger from the beginning.
So, the next time you go to a piano factory, pay humble appreciation to the action bushing operators. They hold the piano action's life in their hands.
Is something about bushings reaming you? Leave it in the comments.