Today I returned to "Pinetop" Perkin's former piano, which you may recall from this post. The mission - to solve an pervasive issue of double-striking/bobbling hammers. This condition often occurs when an upright piano's overall key height has decreased with time due to compression and settling of the balance rail. With the key height lowered, the front of the key doesn't have enough travel distance (key dip) and therefore cannot move the mechanical components of the piano action through a complete cycle of motion. This results in the top of the jack not rotating fully out from under the hammer butt - the hammer rebounds from the string then bounces off the top of the jack back to hit the strong once or twice more than the single blow desired.
image courtesy of http://www.balaams-ass.com/piano/dblblow.htm
If all the keys have inadequate dip, a powerful fix is shimming up the balance rail with card stock - this raises the fulcrum point of the keys while the termination point of the key fronts travel on the front key rail stays the same, resulting in increased key dip. Pianos with inadequate key dip will feel shallow and weak to the pianist (insufficient leverage) and will likely have other problems such as the double-striking hammers on this piano which made it incredibly frustrating to play.
Below you'll see that I had to remove keys to find the screws in the balance rail, which I loosened before slipping card stock (with a v-shaped cutout for the screw) under the balance rail to set a proper height.
After some slight bit of trial and error to dial in the various sections of the keyboard (which had settled unevenly due to different levels of playing - obviously the middle gets the most use!) to a proper dip, I checked across the keyboard with a 3/8" key dip block and was happy with the results.
While adjusting backchecks, capstans, and let-off buttons to ensure that all hammers behaved correctly, I noticed some especially prominent clicks that stood out above the general clickiness of this ancient action. Here's a photo of a misaligned backcheck that wasn't capturing the hammer on rebound, allowing it to bounce back towards the string.
Smiling pliers placed around the bridle wire (the wire connected to the red bridle strap above - more on that later..) to grab the backcheck wire facilitated the proper re-alignment via bending without the torque one would apply with regular pliers, which is not as specific an application of force and damages other components.
Now enjoy this picture of the unusual stickers found on a player piano...
At the bottom we have the capstans, which in a tall piano do not directly contact the wippens (a complicated piece that transfers the basic upward motion of the back end of the key to various other essential components) but transfer motion through the vertical wooden stickers seen here. Normally the stickers are just a simple vertical stick of wood, but here they have extra buttons which the player piano mechanism would have contacted to play the notes - it would've had fingers which lifted directly up on each sticker (taking the place of human fingers lifting up on the sticker via downward pressure on the front end of the key).
This is all well and good, but the cushions on the bottom of some of the stickers were so worn out and hard that they produced a prominent click against the capstan when they fell back down after a key stroke. Therefore I made replacement cushions out of some spare buckskin and thin felt balance rail punchings I had - after I glued these bad boys to the bottom of the stickers, the clicks magically disappeared.
The last major clicks I noticed came from another common culprit - bridle wires clicking on backcheck wires - you can see the contact below.
A simple bend to the left solved the problem - I double checked everything and was quite happy with the results. My mentor described balance rail lifts on verticals as "magical" and I'm inclined to agree - it's amazing how much improvement in feel, power and functioning results from restoring the keys' fulcrum point to it's proper height. The next step of noise reduction on this old piano is some fresh felt on the hammer rest rail and the back rail which supports the back ends of the keys - but we'll take that as it comes. Another balance rail lift - another satisfying experience in piano improvement.