Let's simplify a bit more. Take the scenario below and let's say there's a 15mm spread between the front and rear bridge pins. What would the reading need to be to indicate a total bearing (front plus rear) of 1 degree. I just need a baseline. I use this for checking bearing on a strung piano at tension. A couple mm difference in the bridge pin spacing isn't that critical for this operation. David Love davidlovepianos@comcast.net -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of David Love Sent: Tuesday, July 05, 2005 5:33 PM To: 'Pianotech' Subject: RE: Reading a dial gauge Let's simplify. I zero the three prongs on a level surface. I place the center plunger on top of the string in the center of the bridge. The two outer prongs are resting on either side of the bridge. The dial reads .018. Do I have 1 degree of overall bearing? And if it reads .036, I assume I have 2 degrees. Do I have that right? David Love davidlovepianos@comcast.net -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of Sarah Fox Sent: Tuesday, July 05, 2005 4:22 PM To: Pianotech Subject: Re: Reading a dial gauge Hi David, That's a great question for a math nerd. ;-) What angle are you trying to measure? Backscale segment to speaking segment? Backscale to bridge and speaking to bridge? I assume you're putting the plunger at the center of the bridge. Yes?? The sine of 1 deg is roughly .018. That reading would correspond to the angle from "horizontal." Then double the angle to go the other way. In other words, the total angle between speaking and backscale would be 2 deg. A 1 deg angle would give you a reading of .009. This of course assumes that your bridge has no width to it, like a violin's. That's a very bad assumption, of course. The distance between the front and read bridge pins is an important factor. If you measure across the bridge, with the plunger at the center of the bridge (which is how you do it??), then you would estimate the total downbearing angle (between speaking and backscale segments as... A=2 Arcsin(d/(1-b/2)), where A=downbearing angle d=deflection (gauge reading) b=bridge width from front pin to back pin Downbearing pressure would be estimated as... P=2Td/(1-b/2), where P=downbearing pressure T=string tension Of course these formulas assume an angle near zero and are only approximately correct, but they work very well for the first several degrees. They also assume a sharp angle in the wire, with no arching across the bridge. Peace, Sarah ----- Original Message ----- From: "David Love" <davidlovepianos@comcast.net> To: "'Pianotech'" <pianotech@ptg.org> Sent: Tuesday, July 05, 2005 6:03 PM Subject: Reading a dial gauge So I picked up this dial gauge from Schaff and I'm not really sure how it works. The center prong is the plunger and the two outer prongs are 1" from the center. The smallest increments that can be read are .001". So if I put the plunger on the center of the bridge with the two outer prongs resting on the front and back segments respectively, does a reading of .018" equal 1 degree? Or would that be 1/2 a degree since the total reading must be split between the two prongs at a total of 2" apart? Yeah, I shoulda paid more attention in trig class. David Love davidlovepianos@comcast.net ---------------------------------------------------------------------------- ---- > _______________________________________________ > pianotech list info: https://www.moypiano.com/resources/#archives > _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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