By Hannah Beckett, RPT
Addressing key fit at the front rail mortise, balance rail mortise, and balance pin hole can transform the touch of a piano. Since the keys are the pianists’ primary interaction with the piano, proper key fit is critical for a well-regulated, responsive action. A compressed key bushing in either mortise makes key travel hard to control, and a tight balance pin hole causes sluggish response and sticky keys. Key care as part of your regulation process will enhance your work as a technician, eliminate callbacks, and satisfy your clients.
After you have prepped the keyframe, examine the bushings at the front and balance rails. Key bushings commonly become compressed over time. Depending on how extreme the side play is, a VS Profelt treatment or full key rebushing may be in order.
Front Rail Sideplay
Balance Rail Sideplay
VS Profelt does an excellent job of closing the gap on moderately loose bushings when the cloth is visibly compressed by the side of the pin. VS Profelt will not restore worn bushing cloth. Apply a drop or two (enough to wet the bushing without saturating the wood) with a hypo oiler on the bushings and insert the corresponding caul. Allow to dry overnight or for at least six hours. Check for proper fit when reinstalling on the keyframe. Profelt lubricates the bushing. Using the caul irons the cloth, restoring it to a uniform, smooth surface.
On bushings that have more extreme side-play, you should rebush the key. Read our key rebushing article here.
It will take time for you to recognize when to use Profelt and when to rebush, but as a general rule, if the key bounces back to position when you move it side-to-side, Profelt will likely do the job. If the key can be repositioned on either side and does not bounce back to the center, you should assume a rebushing job is necessary.
An oversized key bushing causes sticking keys. Simple compression with key easing pliers solves this problem. There are three options for these pliers on Schaff. You’ll want to get a pair that can easily service grands without having to remove the stack to access the front rail mortise. Pliers #3120 and #3121 do this well. Compress the bushings very gently as it is easy to over-compress and cause a wobbly key.
Key easing pliers: Schaff #3121
Key easing pliers: Schaff #3120
These can also be used with the stack on (great for field technicians!):
Be sure to engage the damper pedal when checking for sluggish front rail bushings. The weight of the damper returning to rest position can mask subtle sluggishness:
Once the bushings have been sized correctly, check the balance rail hole for excess friction:
Note: Before addressing balance holes you must have first cleaned and polished the pins. In many cases, balance hole issues go away after cleaning.
Balance pin hole friction is common in humid areas. The key balance hole easer (Schaff #43) makes quick work of resizing the hole. In rare cases, a balance hole reamer will be necessary to remove material from the opening, but you should first use the easer to avoid over-sizing the hole. Insert the easer into the balance hole from the top of the key and lightly rotate taking care not to force the tool through the bottom of the key. Less is more here as you can always compress the wood, but it is not as simple to undo an over-sized hole.
There are two types of reamers available. Schaff #3156 is a universal reamer. Be very careful with this tool so that you don’t remove excess material! Pianotek sells individually sized reamers that are much precise. If you are using the Pianotek reamers, select one that is .002” - .003” larger than the balance rail pin.
The goal is for the key to fall to rest position smoothly when lifted slightly from the front of the key:
While it is rare for a pianist to request that you address key fit, making this an assumed part of your regulation process gives your clients the gift of key control, which is one of the most critical requirements for any pianist of any level.