re-pinning a piano mechanism (insight only)
All piano mechanisms (hammers, levers & dampers) work by a series of very small parts that pivot backwards and forwards inside, to allow the parts to move freely. Each upright piano note has on average four pivot points that work like a hinge. so a complete piano mechanism has over 600 pivot parts. On average, a 88-note piano has 176 hammer pivots, 130 damper pivots and 352 undercarriage & jack pivots. A grand piano mechanism has about double this quantity for the dampers and levers. Each pivot hinge is held in place by a CENTRE PIN ---- if they need replacing, this is REPINNING.
Before we explain in some detail about re-pinning, note that "tuning pins" have nothing to do with centre pins. See image >>
Before we explain in some detail about re-pinning, note that "tuning pins" have nothing to do with centre pins. See image >>
<< Tuning pins are large steel pins (c. 6-7mm diameter/ 50-60mm length) that are driven into the wrest plank, each pin has piano wire wrapped around it forming coils - these pins are turned during a piano tuning to put the piano back in tune. Can be easily viewed at the top of your piano.
Tuning pins are correctly named "wrest pins" as they are driven into the wrest plank.
PIVOT (HINGE) PARTS - centre pins
Deep inside the mechanism are the pivots. Each pivot consists of two parts to make a hinge; 1. Wooden flange 2. Centre pin
UPRIGHT PIANO MECHANISM
Deep inside the mechanism are the pivots. Each pivot consists of two parts to make a hinge; 1. Wooden flange 2. Centre pin
UPRIGHT PIANO MECHANISM
Each pivot (hinge) moves at a different time for optimum performance of the mechanism, to allow perfect synchronisation of the parts.
Apart from some end section notes, the centre pins cannot be seen unless the individual part is removed from the mechanism.
WOODEN / PLASTIC FLANGE + CENTRE PIN (Pivot parts)
Apart from some end section notes, the centre pins cannot be seen unless the individual part is removed from the mechanism.
WOODEN / PLASTIC FLANGE + CENTRE PIN (Pivot parts)
(Example showing a hammer flange)
A wooden or plastic block, cut out into a [ shape is called a flange. This part is attached to the hammer butt (lower region) by a centre pin. Each flange has a felt - bushed hole at both ends to allow the pin to pass through smoothly, and the cut-out area is where the pin is push-fitted into the hammer boss - this prevents the pin from moving and is locked into position.
The large hole (with washer) allows the whole pivot to be secured to the action frame.
When a hammer pivots, the butt, shank and head only move (not the flange or pin) - so all the main hammer parts move around the centre pin, which is in a locked position by friction.
The bushed holes at each end of the flange must only allow a small amount of friction for the pin to circulate around it - if too tight, the part will not move freely, and if too slack, this may cause damage to the flange and hammer butt.
Re-pinning occurs when the flange bushings become swollen, and/or if the centre pin has become bent or corroded. Any additional friction to these parts are very sensitive to the movement, and will cause the mechanism to either slow down or stop working.
REAMING THE FLANGE BUSHINGS
Before a new centre pin can be fitted, each left and right bushing (per flange) must be reamed out to accept a new over-sized pin. By selecting the right reaming tool (similar to a needle file), the bushing cloth is very gradually skimmed in a circular motion, only removing about 0.001mm of felt at a time, then tested each time with a new centre pin. Only an experienced piano technician will know the right friction point and tolerances allowed.
CENTRE PINS
CENTRE PINS
A "centre pin" is a small chrome steel pin which is used for all pivots - this part secures the flange to the main component such as the hammer, damper or lever. Centre pins vary in diameter from 1.2mm up to 1.5mm (with 0.5mm gauges between), and each have a sharp point, manufactured to a length of 16mm - 20mm; this allows extra width according to the flange size, and then the excess is cut off with steel cutters. Centre pins can only be used once, and carefully guided through each bushing + boss hole by the sharp point. When the pin is fitted, the part is tested for its "swing" ( pin uncut) - at this stage the pin can be removed and used again if uncut for more reaming, however once the excess has been cut off, the new pin cannot be used again.
SLOW OR SEIZED PARTS
SLOW OR SEIZED PARTS
SLOW RETURNING OR SEIZED HAMMERS
As can be seen by this Steinway mechanism, four of the hammers have not returned to their rest position, but instead are resting against the strings. It may transpire that these hammers could return at different intervals, possibly assisted by the bridle tape or hammer butt spring.... however, if the note is needed again for repetition or quick scale passages, this can be annoying to wait!
In most circumstances, any part that has seized in its "on" position or returns in slow motion will need to be re-pinned. The most common cause of this occurs at the top end of the treble hammers, that are seldom played, and/or the mechanism may have experienced some damp such as a cold room. The odd re-pin is quick and easy that may require a replacement bridle tape aswell, however, if MOST or ALL of the hammers, jacks, undercarriages and dampers are seized / return slowly / combination of both, then the whole mechanism will need to be re-pinned..... a long job that can take around two days to complete alone. On average it takes about 10 - 15 minutes to re-pin one part (including removal/ reaming/ new pin/ assembly).... you can do the maths? .... multiply that by 300?
OLD PIANO MECHANISMS
Flanges come in various different sizes and shapes for pianos - damper flanges also house a large spring. Depending on the age and condition of the piano mechanism, when using centre pin extractors, this involves using force to remove and insert centre pins. If a flange becomes dry and brittle, if it has not broken in half during a simple removal procedure from the action rail, then it is more at risk from breaking when pin punching tools are used to extract the old centre pins. In some cases the flange can be glued & clamped back together with PVA, however in some cases a new flange has to be hand-made from scratch.
NOTES NOT WORKING / INTERMITTENTLY WORKING ?
If a note works first attempt, then doesn't work immediately after playing the note, or if a note does not work, then there may be a problem with the undercarriage PIVOT sections. Sometimes the hammer may "wink" forward towards the string, but may not reach the string, or the note may play "weak" - requiring extra force to play the note.... in all these cases, any intermittent fault will usually lie with the undercarriage lever and jack, and will require re-pinning. If the note works well without the sustain pedal, but then when the sustain pedal is pressed, if the note works intermittently or stops working, this is usually a problem with the undercarriage lever pivot itself - not the jack. In most cases like this, if the action springs are working and in tact, then the most common cause of these problems lies with the flange pivots and centre pins - re-pinning usually is the answer.
As can be seen by this Steinway mechanism, four of the hammers have not returned to their rest position, but instead are resting against the strings. It may transpire that these hammers could return at different intervals, possibly assisted by the bridle tape or hammer butt spring.... however, if the note is needed again for repetition or quick scale passages, this can be annoying to wait!
In most circumstances, any part that has seized in its "on" position or returns in slow motion will need to be re-pinned. The most common cause of this occurs at the top end of the treble hammers, that are seldom played, and/or the mechanism may have experienced some damp such as a cold room. The odd re-pin is quick and easy that may require a replacement bridle tape aswell, however, if MOST or ALL of the hammers, jacks, undercarriages and dampers are seized / return slowly / combination of both, then the whole mechanism will need to be re-pinned..... a long job that can take around two days to complete alone. On average it takes about 10 - 15 minutes to re-pin one part (including removal/ reaming/ new pin/ assembly).... you can do the maths? .... multiply that by 300?
OLD PIANO MECHANISMS
Flanges come in various different sizes and shapes for pianos - damper flanges also house a large spring. Depending on the age and condition of the piano mechanism, when using centre pin extractors, this involves using force to remove and insert centre pins. If a flange becomes dry and brittle, if it has not broken in half during a simple removal procedure from the action rail, then it is more at risk from breaking when pin punching tools are used to extract the old centre pins. In some cases the flange can be glued & clamped back together with PVA, however in some cases a new flange has to be hand-made from scratch.
NOTES NOT WORKING / INTERMITTENTLY WORKING ?
If a note works first attempt, then doesn't work immediately after playing the note, or if a note does not work, then there may be a problem with the undercarriage PIVOT sections. Sometimes the hammer may "wink" forward towards the string, but may not reach the string, or the note may play "weak" - requiring extra force to play the note.... in all these cases, any intermittent fault will usually lie with the undercarriage lever and jack, and will require re-pinning. If the note works well without the sustain pedal, but then when the sustain pedal is pressed, if the note works intermittently or stops working, this is usually a problem with the undercarriage lever pivot itself - not the jack. In most cases like this, if the action springs are working and in tact, then the most common cause of these problems lies with the flange pivots and centre pins - re-pinning usually is the answer.
