If I understand Phil's explanation (and my small experiment), the KR is a function of the combination of the contact point with the key and contact point of the top of the capstan with the wippen heal. On a straight up capstan there is not difference. If the capstan is angled back at a 45o angle, the KR as measured from the very top of the capstan will not be equal to the KR as measured from a point on the key directly below the point of contact with the wippen heal. It will be something between the contact point with the key and the point directly below the contact point with the wippen heal. Therefore, angling the capstan does lower the ratio (assuming the the same contact point on the wippen), you just don't get the full benefit of the new position vis a vis the contact point with the key. But maybe someone can provide the math. David Love davidlovepianos@comcast.net -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of V T Sent: Monday, April 18, 2005 6:08 PM To: pianotech@ptg.org Subject: Capstan angle Hi David, ========================================== David Love wrote: I'm not sure why that wouldn't improve the key ratio. You have a straight up capstan with a key ratio of, say .52 (using the Stanwood method). You relocate the capstan keeping the contact point with the wippen heel the same but moving the capstan key contact point closer to the balance rail by angling the capstan. The measured key ratio will now be less than .52 and the overall SWR will have decreased as will. ========================================== I would like to backtrack to see how you measure the key ratio. Using Stanwood's method, you would wrap a piece of lead wire weighing 10g around the capstan. You may be tempted to wrap the wire around the capstan so that it rests on the key stick. Now, if you have angled the capstan, this method will imply that you have changed the key ratio, but actually you haven't. The 10g mass should be placed right on top of the capstan exactly where it contacts the heel. Only with a 90 degree capstan angle will you get the same result regardless of where you place the wire. Does this explain the contradiction? ===================================== David Love wrote: I'm not sure I even understand what is meant by "What they have accomplished is to move the contact point between the top of the capstan and the wippen heel a little closer to the balance point, so that the key ratio has changed." Do you mean by virtue of the capstan leaning it now contacts the wippen heal on the front edge of the top of the capstan? I would say that is probably insignificant. Much less, anyway, than the repositioning of the capstan/key contact point. David Love ====================================== Take a heel with a 16mm felt length. Assume a capstan with an 8mm diameter. If the factory did a nice job and the capstan was centered on the felt, there is now 4mm of free space between the edge of the capstan and each end of the felt. If you keep a 90 degree capstan angle, you will run into trouble once you move the capstan 4mm or more. If you tilt the capstan so that you are making contact with the edge of the capstan, you can change that 4mm to almost 8mm. Assuming a 7mm move, an average key will change its ratio approximately 6%. The next thing that happens has to do with the wippen ratio. As you move the contact point on the heel, you are reducing the ratio of the wippen as well. Let's assume a factory installed wippen ratio of 95mm/65mm=1.46. Now, let's change the 65mm number to 65+7=72mm. This gives a wippen ratio of 1.32 ... a 10% change. The combined effect is a 15% strike ratio reduction, if I haven't made a math mistake (I am prone to that). As you see from the example, the change of ratio comes from two places; the change of the capstan contact point with the heel has a bigger effect on the wippen ratio than the key ratio, but both contribute significantly. So, my opinion is that the entry point of the capstan is not a factor, but the contact point with the heel is. Vladan __________________________________ Do you Yahoo!? Plan great trips with Yahoo! Travel: Now over 17,000 guides! http://travel.yahoo.com/p-travelguide _______________________________________________ pianotech list info: https://www.moypiano.com/resources/#archives
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