Thanks. That's helpful. So while 55% represents the maximum, what is your typical target? Additionally, is there a standard ratio that you target between the inner and outer wrap on a double wrapped string. David Love davidlovepianos at comcast.net www.davidlovepianos.com -----Original Message----- From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of John Delacour Sent: Saturday, May 26, 2007 3:22 AM To: Pianotech List Subject: Re: Bass string scaling question At 12:13 am -0700 26/5/07, David Love wrote: >What is the maximum differential between the core wire diameter and the >outer wrap diameter before you need to go to double wraps? There are two questions here : first, what harmonic distribution are you aiming for in the string, and second, what is actually possible from the string-maker's point of view. I'll answer the second: Too thick a single cover on a thin core wire will at best cause the flattening to twist and at worst cause the wire to break on the machine. To give a real example off the top of my head (with 20 years of commercial string-making experience as a guide), if you take a No. 20 (1.125 mm.) core for the top single -- anything thinner being rather unusual -- then you could continue with single covers on this core, if you so chose, up to 1.75 mm. in diameter. At that point the string-maker (at least this one) would begin to hold up his hands. The minimum core required for a 2.00 mm. cover (the thickest in common use) would be a No. 22 (1.225 mm) and that would be risky. You will rarely find a 2.00 cover on a core wire less than No. 24. The reason is that a certain tension is required to achieve a good tight cover and that tension cannot be applied unless the core wire will survive it without twisting so much as to turn the flattening into a spiral and/or snap. From this you will see that one has a fair degree of latitude, since the thinnest core you are likely to specify is capable of taking a fairly thick cover. To give a simple answer to your question, I quickly typed into Excel a column of core diameters followed by a column of the diameter of copper I would normally regard as a maximum for the given cores in practice, and the results were rather neat, showing that a cover 55% thicker than the core is the thickest I would normally be appy to use, and I think other string-makers would give you a similar answer. JD
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