Phil, Ron N and all, > > . . . and how > >manufacturers decided on that spacing. > >. . . there's more aggravation to be had on this subject. The >farther apart the >row spacing, the less precision required in lateral pin placement to >achieve a target stagger angle. The closer the spacing, the greater the >required precision. Meanwhile, if I was designing the bridge, I'd want the >pins in far enough from the edges for good support, yet close enough to the >edges to minimize the amount of wood I'd have to remove to cut the notches. >No sense making life harder than it has to be. That means that as the >bridge angle relative to the strings narrows, I'd increase the row spacing. >It takes a little more time and thought in planning and layout, but >anything that cuts down (sorry) notching labor is definitely my friend. I >make nice clean notches, mind you, it's just that I don't much enjoy doing >it. Maintaining the row spacing through the whole piano works fine too, but >you spend more time hunkered over a chisel producing it. Someday, a power >notcher. Indeed and what a useful labor saving device it will be. A power notcher is at the CAD stage in our workshop as you speak. >Of course, if you are working with a re-capped bridge on a soundboard that >isn't being replaced, you can't mess around too much with row spacing >unless you want to rescale with the newly resulting speaking lengths. Not >that it's a problem, but it bears consideration. If by the happiest >circumstance, you're making your own bridges, you can correct the log >progression deviations across the treble breaks, smooth the transition >across the bass/tenor break, and generally build about anything the plate >will let you get in the piano. That's when it gets fun. > >Ron N Good post Ron. In the lower bass we might prefer to keep the front/rear spacing distance to a practical minimum for the bass singles, to gain the longest possible back scale in shorter to medium length scales. When using a spreadsheet to design the top elevation, it is worth making the front/rear spacing gradually increase in the tenor region as the bridge angle relative to the strings narrows, to satisfy the objectives Ron N writes about. Another area of bridge layout which some manufacturers occasionally ignore to their peril is the bridge pin spacing between adjacent unisons. This spacing should allow for the provision of sufficient bridge wood between pins to allow for adequate pin support. If the spacing is insufficient, there is a risk of the cumulative side bearing on each pin group causing cap failure. Some of the smaller Grotrian designs of the sixties and seventies were particularly prone to this 'disease'. Some years ago a client of mine purchased a replacement bridge cap from the factory, in which the pin spacing was so tight that there was just room for the wire between the pins - what a disaster in waiting (no surprise then that the original bridge of his 220 had failed). Surprisingly, the earlier Grotrians (1920s) were better designed in this respect. Why was the design expertise which clearly existed at the factory at an earlier time lost? Perhaps contemporary designers should start out by learning all the old tricks first. Ron O -- ______________________________ Website: http://www.overspianos.com.au Email: mailto:ron@overspianos.com.au ______________________________
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