How does one decide when a set of keypins need replacing as opposed to a simple polishing?

The deciding factor is if the surface of the keypins has succumbed to corrosion or not. If the pins are simply tarnished, a gentle polishing may be all that’s necessary to restore things to good order. If the surface of the pins has become pitted, however, replacement is necessary. Corrosion becoming noticeable on a set of keypins is similar to rust bubbles appearing on the surface of a car’s fender. It’s almost certain that the damage is more than what meets the eye. In the case of keypins, even if a piano technician were to grind off the corrosion, the slippery nickel plating would be gone, and the dimensions of the keypins would be changed.

In the above photo, the front 3/4″ of a set of three keys has been cut away to reveal the keypin / bushing system that stabilizes the keys and allow for nearly frictionless up and down movement of the keys. Smooth, polished keypins and good quality bushing felt (the red felts on the insides of the mortises) are essential for this system to work efficiently. The bushing are sized so that the felts make gentle, but positive contact with the keypins. Ideally, there is a nearly imperceptible resistance on the keys but an absolutely smooth movement up and down with no play (wiggle) perceived to the right or left.

The only solution in a case such as this is to carefully remove the old pins and replace them with a new set of highquality keypins.

How is the removal of the old pins accomplished?

The keys need to be removed from the piano to access the keypins. Additionally, the keyframe itself is typically removed so that the repair work may be done on a workbench. In the case of a grand piano, the action is removed, then the upper stack is taken off of the action to access the keys.

Front rail pins are here being carefully removed from the keyframe with a pair of visegrips. By gently turning the pins back and forth as the pins are being pulled out, the holes that the pins are driven into are not put out of round. Careless removal by an untrained technician can result in loose fitting replacement pins, making a bad situation worse.

In the photo to the left, balance rail pins are shown being tapped out from the underside of the balance rail. Again, care is taken not to damage the original hole. The old pins will be measured with a micrometer to determine their exact size. The new pins, when they are driven in, will be tight as long as care has been taken in removing the old pins.

What are the basic procedures for installing a replacement set of keypins?

Front rail pins being pushed into place using the “press” feature of a drill press. Careful measurements are taken to ensure that correctly sized keypins are installed into the keyframe.
To avoid marring the surface of the new pins (typically nickelplated), a press is often used to push the new pins into place to the correct depth. With the piano disassembled to this point, it is an opportune time to complete any work related to the keyframe which might be needed. In the case of the key frame shown in these photos, mice had done considerable damage to the portions of the framework made of basswood (the fronttoback supporting members).

The balance rail and front rail, being made of hard rock maple, were untouched by the mice. New basswood parts were cut to match the old, the rails were sanitized with baking soda, and the resulting framework was as good as new once the work was finished.

Is there other repair work which would complement this job?

New front and balance rail keypins, ready for the installation of a rebushed set of keys.