Repinning Action Centers

By Hannah Beckett

The piano action is made up of parts that are both moving and stationary; while they are all essential, their point of connection -- also known as the "action center" -- might be the most important part.

The "action center" is the hinge between the action's moving and non-moving parts. If the action center is not working properly, the entire action system is compromised. That's why every piano technician should be able to size, replace, and repair these action centers correctly. There are many action centers on a piano, but thankfully, the sizing process is the same.

Basically, action centers = part + flange. There are many types of flanges on an action, but they are generally screwed into the action as an anchor to then allow its action part to move freely.

Similar to a door hinge, the action part and the flange are connected by a pin. It is important to remember that the pin is fitted tightly through a hole in the part called a "bird's-eye" while the flange is fitted so that it can swing freely around the pin. The pin should never rotate in the bird's-eye.

The fitting of the pin will determine how easily the action center can move as a whole. Pinnings with too much friction may cause the part to freeze. Pinnings with too little friction will make the part difficult to control.

Flanges can be found on nearly every part that makes up the piano action:

There are also parts that have built-in flanges that do not move freely (the repetition lever and jack). Different flange connections require different ranges of friction. Flange friction can be measured with a gram gauge. Here are some examples of common friction measurements:

Visit Handy Dandy Little Help for a printable chart of friction measurements to keep in your tool kit.

To repin the action center so that it has the right amount of friction, here are the tools you will need:

Pin punch (Pianotek #CPT-1)

End cutting nippers

Center pins (Pianotek #CP-X)

Flange bushing broach set (Schaff #220)

Small metal file

Micrometer

Gram gauge

Remove the old center pin using the pin punch.

There are two methods you can use to select a new pin:

Using a micrometer, measure the old center pin.

Use this chart to find the corresponding pin:

Now, pay close attention: Regardless of whether you need to increase or decrease friction, select a pin that is one size larger than the original pin. Remember, an action center must stay firm in the bird’s-eye so the flange can rotate around the pin. There is never a time when you will replace a pin with a smaller pin. Always move up a pin size to ensure a stable connection between the bird’s-eye and the flange. Then you can size the flange to rotate around the new pin.

Select a small pin size, such as 19 or 20. Test the fit in the bird's-eye. If the pin slips through the bird's-eye, move up a few pin sizes until you find one that grips the bird's-eye with the tip of the pin, and can support the weight of the part when lifted.

Reaming is a sizing process that involves both removing material from the bushing cloth, and compressing the cloth for a smooth fit around the pin. The broach set removes and compresses simultaneously.

Once you have selected a new center pin, find a broach from the flange bushing broach set that is one size smaller than the new center pin. Being careful to only ream one side of the flange at a time, move the flange over the rough surface of the broach (reaming one side at a time allows for equal sizing in each hole). Check the feel of each flange bushing by manually pushing the new center pin in and out of the flange. Developing a sense for the proper feel of the pin in the flange bushing takes some practice. Essentially, the pin should move freely in and out of the flange bushing while still having a bit of resistance, or “bite,” before it starts to move smoothly. When the pin moves through each side of the flange with equal resistance, re-pin using the pin punch.

Note: When using a broach set, be very careful not to let the sharp edge of the tool puncture the flange bushing cloth. I recommend slowly twisting the broach while letting the tool work its way through both holes without forcing it to move quickly.

Now, measure the friction of the flange with a gram gauge to determine if you have sized the flange correctly.

To use a gram gauge, hold the gauge firmly on a flat surface. Slowly push the flange against the feeler tab, noting the number at which the flange begins to move. If the flange begins to move within the range of friction specified on the chart, then you’ve done an excellent job and can re-install the part in the action!

If you are re-pinning a hammer flange, you can also measure the fit by counting the number of swings before the hammer stops moving. Use one hand to firmly hold the flange upright , and hold the hammer head at a 90-degree angle with the other. Release the hammer and count the number of swings until the hammer stops. A good repinning job will generally result in somewhere between 3-7 swings.

Pro Tip: Hammer flange pinning friction should be graded from bass to treble. Bass hammers should swing closer to 3 swings with gradually decreasing friction as you move up the scale into the treble section.

When you are happy with your new center pin, cut off the end of the pin with flush-cut nippers. It is important that the pin is smooth and flush to the surface of the wood. A small metal file can help you clean up any roughness that may be leftover from the cut. Your newly-pinned part is now ready to re-install in the action.