As both a functional and structural component of a piano, a pinblock (wrestplank) is a major contributor to a piano’s structural integrity, adding in tuning ability and stability. Primarily, the pinblock is responsible for securing the tuning pins in a manner that holds them tight enough to support over 300 pounds of torsional pull, with a collective tension of over 38,000 pounds, while at the same time keeping them loose enough to be turned for the purpose of tuning. This is achieved by maintaining a given tolerance between the diameter of the tuning pin and the insertion whole within the pinblock.
As pianos age this tolerance increase rendering the tuning pins loose and unable to support the necessary tension of the strings. In addition, the tuning pin whole elongates under pressure allowing the tuning pin to pull forward. This effect renders the strings unstable. At this point, pinblock replacement is required.
Following are the steps in the process of duplicating and installing a replacement pinblock:
- Removal of Old Pinblock
- Making Copy of Pinblock
- Fitting a Pinblock to a Plate
- Installation of New Pinblock
Note: The pinblock being replaced shown in theses pictures is not the original factory pinblock.
Removal of pinblock – anchors such as screws, wood dowels, and glue joints need to be removed .Various methods are utilized depending on the specific style of installation.
The pinbock is cut on one end providing relief so the block can move and absorb the force of pounding and wedging without causing damage to the piano rim or stretcher.
Once the ends are free, the pinblock is wedged away from the stretcher to loosen the dowels and/or glue joint. Great care must be taken so no damage to the stretcher occurs.
Pinblock Copying – The old pinblock is used for tracing a rough copy onto new stock material. This provides a rough pattern for cutting of new pinblock blank.
Cutting the new Pinblock Blank – the new blank is cut using a 1″ band blade. Set-up of the machine is critical for a precision cut. The more precise the cut is the less work there will be in fitting the block to the plate, assuring an exacting fit.
Fitting the pinblock – involves grinding the blank to fit presicely along the plate flange. This is most critical since the pinblock supports more than 38,000 pounds of collective string tension. A liquid transfer chalk is used to mark the flange/block relationship. If the block is not fit correctly it will move, allowing the string tension to change causing tuning instability. I have had to replace blocks in very young pianos for this reason alone.
Matching of new pinblock plank to old pinblock before grinding.
Transfer chalk leaves indications of high contact points and non-contact points of new block after being test fitted against plate.
Meticulously, the new block is fitted by grinding high spots indicated by transfer chalk. There is no short cut to doing this. Some have used filler between the block and plate flange. To me this is an unacceptable practice. However, I have seen where once the block is fitted correctly a bonding substance is applied to make the contact absolute. This is acceptable, although I have never done it.
After tedious effort measured in hours, the new block has complete contact across the entire surface of the plate flange. Once the piano is strung, this block will have no ability to shift under tension.
The new block is dry-fitted to the rim and stretcher before being cleaned and installed.
Many instruments are designed with the pinblock as an integral component of the rim. Meaning, the pinblock is adhered to the stretcher. When rebuilding, this must be duplicated when part of the piano design. Here you can see my method of dowelling the block to the stretcher. First image is a scribe used to mark hole location in the block, second is the bore, and third is inserted dowel.
After all fitting is complete pinblock is molded into the rim.
New Pin Block being drilled