<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Hammer Shank Ratio</title></head><body> <div>Phil, Richard and all,</div> <div><br></div> <div>A couple of good posts from you today Phil.</div> <div><br></div> <blockquote type="cite" cite>Ron Overs replied:<br> </blockquote> <blockquote type="cite" cite>When our piano was exhibited at Reno, David</blockquote> <blockquote type="cite" cite>Stanwood made a calculation of the leverage ratio of the action using his weighing method. He got a figure of 5.5:1. Now I designed the action for</blockquote> <blockquote type="cite" cite>this piano on CAD to have a ratio of 5.8 (at the strike point).</blockquote> <div><br></div> <div>At 6:21 PM -0800 13/2/03, Phillip Ford wrote:</div> <blockquote type="cite" cite><br> What do you mean by a ratio of 5.8?  Hammer strike point moving 5.8mm for 1mm movement of the key?</blockquote> <div><br></div> <div>Precisely, as calculated on the CAD drawing with the key at half dip (in the case of our action with the jack/roller contact on the line of centers). As I have mentioned on previous occasions, the real ratio will deviate somewhat throughout the key stroke. However, as you said in your post of today, if we work with the same set of parameters when measuring different actions, it is certainly possible to work out appropriate settings for various different installations.</div> <div><br></div> <blockquote type="cite" cite><br> >  If you take the 5.8 ratio and multiply it by 130/138, you get 5.46. I<br> > believe this may explain the different figures arrived at via the two<br> > different measurement systems.<br> </blockquote> <blockquote type="cite" cite>Where do the 130 and 138 figures come from?  Are these actual numbers from your action?  On your attached sketch you showed 136 for hammer location.</blockquote> <div><br></div> <div>Yes they are the numbers from our action installation into our 225 piano, 130 mm is the distance from the hammer center to the center of the hammer moulding, while 138 mm is the distance from the hammer center to the strike point of the treble section hammers. The bass section strike points will obviously have a higher ratio than the treble since the distance to the strike tip is greater. Furthermore, the bass section hammers will be slightly heavier at the cross since the hammer tail is longer. This is a believe a causal factor of a tone break at the crossover, although the relative sound board activity with respect to the two bridge ends is the more influential factor. Nevertheless, in order to minimise the effect of the differing hammer weights between the bass and treble hammer across the break, we leave the treble hammer tails with more wood thickness that the bass tails to minimise any hammer weight transition across the break<font color="#0000FF"> (I've digressed again!)</font>.</div> <div><br></div> <blockquote type="cite" cite>On your attached sketch you showed 136 for hammer location.</blockquote> <div><br></div> <div>The sketch was copied straight from one of my CAD drawings so it is not scaled to reflect the numbers shown, which were taken straight from Richard's example.</div> <div><br></div> <div>Richard's posts have been interesting, his posts of a few weeks ago got me thinking about this again (although I am currently very busy on other aspects of piano making at present, so I'll need to do some more work later on to test a few things). The understanding of actions will always be a work in progress.</div> <div><br></div> <blockquote type="cite" cite>Another problem is that ratios derived from travel measurements that I have seen are based on traveled lengths.  Neither the hammer nor the key are traveling in a straight line so using lengths (such as 45mm of upward hammer movement happens in 8mm of downward key movement and therefore the ratio is 5.6) seems erroneous to me.  It make more sense to me to talk about traveled angles or arcs (such as 3 degrees of key movement results in 16.5 degrees of hammer and shank movement and therefore the ratio is<br> 5.5).  Perhaps measuring in this way would give better correspondence between travel and weight.<br> </blockquote> <blockquote type="cite" cite>Phil F</blockquote> <div><br></div> <div>I agree entirely with you Phil. The arc of rotation of the hammer tip relative to the arc of rotation of the key front is perhaps the significant factor. Of course it gets messy when we consider that there are so many different key stick lengths in use. So in practice, it is generally easier to measure the linear distance of travel of the arcs we are investigating. If you work out the error between the circumference of an and the linear distance it insignificant. We are more likely to make larger errors in the translation of the CAD data to the working action. I practice, I try to maintain dimensional accuracy to 0.5 mm or less.</div> <div><br></div> <div>Best,</div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div>_______________________<br> <br> OVERS PIANOS - SYDNEY<br> Grand Piano Manufacturers<br> <br> Web: http://overspianos.com.au<br> mailto:info@overspianos.com.au<br> _______________________</div> </body> </html>