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This is a general overview of the process of setting proper down bearing, and is not an exhaustive set of instructions.. This is only for example purposes, and should not be followed as directions, without proper guidance by someone familiar with the process. |
Setting up bearing specs for a rebuild… 1- First , Measurements must be taken to document speaking lengths etc. 2- Bridge patterns need to be made of the pin locations. 3- Then with the strings removed, you will need to measure the amount of crown existing in the piano at different stations on the soundboard… This is done by creating a straight line from each end of the underside of the board next to the specified ribs on the chart… The mid point of that line is then measured up to the crowned point on the board at the rib center and then documented. 4- The new bridge or cap is then set at a higher plane than the original height, so as to leave material to remove for setting the proper bridge height. 5- Using the crown measurements, a new set of down bearing specs are created, using the Bearing spec chart. |
Setting down bearing on a new bridge… 1- With Bearing String secured to the Tuning area or Agraff, of each specified note on the chart. The bridge is then cut using a Wide kerf saw , to the specified heights at different points along the bridge. For example…. If you measured .100 crown on the middle or longest rib, you would set the bearing above on the bridge with the .080 gage, and by the chart, note 88 would be set to 2/3 rds of that figure, which would be approximately the .060 gage……. And so on….. Gages are placed on top of the aliquot for each note corresponding with the chart, for the correct down bearing. The depth of each cut is finished, when the tightened bearing string just makes contact with the gage top, as it runs thru the new channel in the bridge. Back bearing, is measured to about half of that of the front specs… 2- More cuts are then made every 6" or so between the original cuts, interpolating as you go. 3- The cap is then planed to meet all of the cuts, blending them together, creating a smooth tapered bridge cap, that can then be marked and drilled for new pins, and restringing. 4- The cap is then Marked with punches and drilled at the proper angles for the bridge pins. 5- The top of the bridge is then coated with black graphite paint, Sawn , Cut and Notched. 6- Pins are then Inserted to the proper height. 7- The pins are now Filed flat and even. |