I started doing it a bit differently a few years back. I created two wedges marked with incremental thickness indications (1mm, 2mm, 3mm etc) sort of like what Ron N uses to slide under the stretched string when you test crown (which I use these for as well). The two wedges (picture attached-sorry for the poor quality) I use are: the smaller one for the string rest area and the larger one for the bridge top. I do this procedure, btw, with the bridge decapped, the bridge screwed to the soundboard and the soundboard screwed to the rim with the plate height determined and set. I don't prestress the board. The smaller gauge is used for string rest area and the thickness point at which the string contacts this is calculated based on the anticipated deflection and the targeted residual bearing. So if I want to target say 3 degrees of predeflection bearing then I calculate the string contact point on the gauge (in millimeters) as .44 x number of degrees x backscale length (in inches) + the height of the string rest (or height above the plate of the vertical hitch if there is one). The number .44 mm comes from sin of 1 degree = .0175" converted to mm). Let's say that number is 5 mm. I do this, btw, with the bridge decapped and if it's a new board with the board screwed together and screwed down to the inner rim, the plate height located. I don't prestress the board. So then stretching the string from the agraffe or capo to the string rest point behind the bridge I rest the string on the small gauge at the 5 mm point with the gauge sitting where the string rest will be. The string is then stretched over the top of the uncapped bridge and there will be a gap of some distance, of course, over the bridge. I take the other gauge and slide it under the string on top of the uncapped bridge until it just touches the string. That gauge, btw, is made about the width of the bridge pin array-though it doesn't really matter, it should positioned ideally where the strings would be touching the bridge. Whatever the thickness of the gauge is at that point is the thickness of my bridge cap. I do this along the entire bridge every whatever marking on the bridge top the thickness of the to be made cap. Then I make the cap to the desired thickness usually with the front edge of the bridge about 1 mm higher than the back to insure positive front bearing-this may vary depending on the piano though. Typically I make the bridge about 1 mm higher than needed and then sand it back to the final desired height. If you are using laminated bridge caps this allows you to make the bridge cap the right height to begin with (important) and otherwise not have to deal with cutting those stupid little slots. Having a plate float system and/or vertical hitches gives you some wiggle room should you need to tweak the final settings later. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of William Truitt Sent: Monday, January 11, 2010 9:30 PM To: pianotech at ptg.org Subject: Re: [pianotech] Rebuilding tips Scoop out the bridge under the string line until the string just grazes the top of the bridge whilst held tight and down onto the particular shim. Done at 3 locations on the bass bridge and about 9 or 10 on the treble bridge. Then plane the bridge tops down to those markings. Will From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Monday, January 11, 2010 11:34 PM To: pianotech at ptg.org Subject: Re: [pianotech] Rebuilding tips What is your "as usual from there"? David Love www.davidlovepianos.com I just reach into the box and get the thickness I want, run the string through the agraffe and over the bridge, and lower it onto the top of the shim. Adjust bridge height as usual from there. Will Truitt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100112/0e353a0d/attachment-0001.htm> -------------- next part -------------- A non-text attachment was scrubbed... Name: P7230083.jpg Type: image/jpeg Size: 30177 bytes Desc: not available URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100112/0e353a0d/attachment-0001.jpg>
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