<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Bridge Pin Offset</title></head><body> <div>Terry,</div> <div><br></div> <blockquote type="cite" cite>Hello Ron Overs - or anyone else that cares to chime in - in your.....not-so-recent post below, you indicate that you use 10 degrees of string offset (between front and back rows of bridge pins), and a 20 degree pin inclination.<br> </blockquote> <blockquote type="cite" cite>I was laying in bed this morning trying to work through the process of punching some holes in a bridge top (well, actually, the process of locating the holes).</blockquote> <div><br></div> <div>Yes, its amazing how much design occasionally goes on when one is in the horizontal position.</div> <div><br></div> <blockquote type="cite" cite>Now I can do a pretty good job of copying a pattern off an old bridge and transferring it to a new one - I can even straighten things out a little bit. But one should be able to start from scratch and get a straight line from the tuning pin, under the capo, down the speaking length, get the targeted offset angles across the bridge and come out with a wire oriented parrallel to the speaking length on its way to the hitch pin.</blockquote> <blockquote type="cite" cite><br></blockquote> <blockquote type="cite" cite>It sounds simple enough, but when you actually get down to it, it appears difficult to do with precision. Many take the course of marking the bridge top with two dots along a straight line from the capo/agraffe to the hitch pin. While that may be "good enough" in many cases, I would feel more comfortable having complete control over this process.</blockquote> <div><br></div> <div>Yes I agree with you. Some designers deliberately angle the speaking lengths towards the plate struts as they get closer to them<font color="#0000FF"> (ie. at the bridge)</font>. This allows for the dog-leg under the strut to be reduced without compromising the speaking lengths. Therefore, in these cases it is not advisable to make the speaking lengths nominally aligned with the hitch pins. Furthermore, as Ron N also mentioned in his post, the hitches are rarely placed accurately. Nevertheless, it is amazing how good you can make it all look with a bit of care.</div> <div><br></div> <blockquote type="cite" cite>There are several factors that will conspire to make this process a less-than-straightforward one: varying string diameter, bridge pin angle (and resultant string position away from bridge pin hole in bridge top), distance between forward and aft bridge pins, hitch pin position, and softness of bridge cap (I suppose we are using maple/boxwood/whatever hard enough to not worry about this?).<br> <br> Do you have a methodical approach for locating new bridge pin holes that result in the desired 10 degrees of string offset? Thanks.<br> </blockquote> <blockquote type="cite" cite>Terry Farrell</blockquote> <div><br></div> <div>Yes we do. The problem of establishing the correct bridge pin position to produce the desired string offset angle is one which has plagued most of us who do bridge work. As you mentioned, pin diameter and inclination, wire diameter and front to back pin group distance all influence the resultant string offset angle.</div> <div><br></div> <div>For some years now we have been using a formula<font color="#0000FF"> (which I wrote)</font> to calculate the required rear bridge-pin-hole offset from the straight-through point. This formula is also incorporated into our piano design spreadsheets to take the guess work out of calculating string offsets<font color="#0000FF"> (this is an area of advice in Wolfenden's wonderful<i> Treatise on Pianoforte Construction</i> which I found to be wanting)</font>. When designing a new piano on a spreadsheet, the desired string lines and termination points are calculated first, then the bridge-pin-hole positions are calculated from the theoretical location of the string 'kink'<font color="#0000FF"> (in terms of its X and Y values)</font>. The smaller spreadsheets which we use for small workshop repairs give us information expressed as millimeters of offset required from the straight-through position<font color="#0000FF"> (ie. offset of the rear pin relative the front pin)</font>. These are wonderfully handy sheets, since they help to limit errors to the hand skills department.</div> <div><br></div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div><font color="#000000"><br></font></div> <div><font color="#000000">       OVERS PIANOS</font></div> <div><font color="#000000">Grand piano manufacturers</font></div> <div><font color="#000000">________________________</font><br> </div> <div><font color="#000000">Web:   http://www.overspianos.com.au</font></div> <div><font color="#000000">Email: mailto:ron@overspianos.com.au<br> ________________________</font></div> </body> </html>