At 23:52 -0600 7/1/09, Michael Magness wrote: > ...manufacturing margin of error as well. If a hammer flange is 2gr >or 4gr I can adjust so it works, but if it is designed to be 1 gram, >it had better be one gram not .6 less or it fails. > > So I am curious, and open minded about it. Why lower friction in >flanges by design? I get your drift and probably tend to agree, but every time I read about centre pin friction being so many grams or so many swings I flinch. Grams where and swings of which hammer? I ask myself. Grams as a unit of torque is quite meaningless. Torque must be measured in one of a dozen more units, the most convenient in this case being 'grams force per millimetre'. With the flange horizontal, the intrinsic torque will be directly above the centre of gravity of the flange, which will vary in distance from the centre according to the design of the flange, a Schwander flange having its centre of gravity further from the centre than a Steinway flange. The amount of intrinsic torque will vary slightly also according to the wood used, whether maple, hornbeam or service-wood. The total torque is the intrinsic torque added to the force applied at the centre of gravity required to overcome the friction at the centre and begin to move the flange, this divided by the number of millimetres from the centre to the centre of gravity of the flange. Whatever intuitive methods we use to approximate to this measurement, the indisputable fact remains that friction is measure in units of force PER unit of length and cannot be measure in units of mass, such as 'grams'. As to "swings", hammer number 1 will swing more than hammer No. 50 for a given friction, and so on. The most reckless of backstreet motor mechanics is not shy of speaking of 'foot pounds' as he screws down a cylinder head, so why should we be so shy to use proper units instead of quite meaningless units. >Now for another matter of opinion............ >How large a required pin in a flange is too large for a new piano? >22.5 in a 6 month old piano should have a new part? 22, 21.5??? >How enlarged is too enlarged a birds eye are deserves a new part while >under warranty. I know this is subjective, and I will make my own >determination in the end, but others opinions will weigh in. For high quality work I don't like to use a pin any fatter than two or three half sizes fatter than the original pin, so if the original pin was an American 20 (1.27mm) I would hope to use a 20-1/2 and feel unhappy using a 21-1/2. As to finding out what the original size was, if someone has previouly recentred the parts, it is not difficult for an experienced workman to know this. I very rarely use new parts. For example, in the case of the rebushing described in my recent article, I had hornbeam shanks or service-wood (sorbus) flanges and they had been previously recentred with a 21-1/2 pin (1.35mm). I was pretty sure the original pin would have been a 19 or 19-1/2 (1.25 mm) both from knowing common practice at the time and from familiarity with the action maker in question, and this was confirmed when I had swelled out the flange drillings and discovered that using the centre cutters I could push in a 1.25 pin using just the right amount of pressure, good and tight but not creaking, if you like. I have described before how to reduce the diameter of the drilling in parts that have been re-centred with fatter pins, and this method has never failed. Not only is it very quick but it saves the cost of getting new parts which are very rarely exact and almost always of inferior quality, Renner not excepted. I can use bushing cloth of the best quality and pins to match rather than risk trying out the latest fad from Japan or Germany. In the case of standard modern pianos such as Steinway I will simply weigh up the costs when deciding whether to use new standard parts, but with the pound at its present level against the euro it is nearly always going to be better to restore the original parts. JD
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