David Stanwood: >Yes! And the degree of fineness is very important to know. In my >experience, especially >with hammers, finer fiber means a finer quality of felt and tone. >I'm interested to know if >Wurzen felt uses finer (smaller diameter) fiber than everyone else. >There is always >something to learn by looking more closely at things... especially >with a scanning electron >microscope. I don't agree. Diameter (fineness) is but one of many fibre parameters that affect the compressional behaviour of felt. Others include fibre length, Young's modulus, torsion modulus, fibre material density, crimp (curliness), and surface texture (especially important for friction). All of these may vary independently of fibre fineness, so knowledge of the latter is not necessarily of much use in predicting the compressional properties of a piece of felt. An electron microscope will not reveal very much about many of these important fibre properties. The properties of the fibre assembly as a whole (i.e. the structure of the felt) are influenced by the feltmaker's skill. Depending on the application, a given fineness of fibre can be made into felt of vastly different properties, e.g. soft fluffy loose material vs rock hard ultra dense polishing felts. The feltmaker varies the structure by the processes applied, pressure, heat, duration, and so on, using possibly the same wool for each one. Our felt research has been active now for a couple of years. The most recent grad student (Wolfgang Stamm) finished a thesis last year called "Compressional Behaviour of Felt". This involved quite a bit of experimentation with felt - it's very strange stuff - to support the development of a model for use between components in the action model. So we're well along in characterizing felt, at least limited to uniform non-stressed sheets. However, even under this limited scope, the behaviour is very complex and no simple model is available yet. [By the way, Wolfgang's work on felt will be published soon if anyone is interested to read about this]. Now limit the size of a felt "sheet" in relation to the impacting object, which may also take on some geometric surface shape that affects the pressure distribution on the felt (e.g. the top of a jack). Then allow the impactor to be resiliant (a nonlinear spring, e.g. like a piano string). Then take the piece of felt and wrap it around the hammer core using one of a variety of possible pressing and stressing techniques and subsequent processing operations. Last manipulate the felt further directly on the manufactured hammer by applying voicing techniques. Now how much do you really think that fibre diameter is going to tell you about the tonal response of that hammer?? >Richard... There is ample grounding for the correctness of using >cloth for front rail >punchings. Its use has evolved through the total experience of the >whole piano industry >over all of time and we all use it because the test of time shows >that it is the best construction >of felt for that application in the piano. So I would think twice >if you're going to throw out all >that history, experience, and collective knowledge. Just because we've "always done it" doesn't necessarily make it "correct" (which cannot even be defined - better would be "does it do the job in the manner we desire better than something else can?"), nor does it preclude that Wurzen felt punchings might be preferable to traditional woven felt. New innovations in piano design can be valid alternatives to traditional methods and materials. By the way, what kind of felting is your wife involved with David? Stephen -- Dr Stephen Birkett, Associate Professor Department of Systems Design Engineering University of Waterloo, Waterloo ON Canada N2L 3G1 Director, Waterloo Piano Systems Group Associate Member, Piano Technician's Guild E3 Room 3158 tel: 519-888-4567 Ext. 3792 fax: 519-746-4791 PianoTech Lab Room E3-3160 Ext. 7115 mailto: sbirkett[at]real.uwaterloo.ca http://real.uwaterloo.ca/~sbirkett
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