This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Re: Making bridges ----- Original Message -----=20 From: Ron Overs=20 To: davidlovepianos@earthlink.net ; Pianotech=20 Sent: May 08, 2003 7:40 AM Subject: Re: Making bridges What's a scarf joint? David Love davidlovepianos@earthlink.net A scarf joint is a variation on a butt joint, which instead of being = vertical, is leaned over at an angle to present a longer and stronger = gluing surface between the pieces being glued. A good scarf joint can be = approximately 90% of the strength of the wood. We use Titebond Extend = for all scarfs since it has a tensile strength of around 3,600 psi. However, a standard scarf joint will result in the two pieces being in = a line, which is not satisfactory for the manufacture of a bridge. The = joint required for bridge manufacture is the compound scarf joint, which = has the standard angled scarf joint (typically angled at a slope of 1 in = 5) with an added angle to cause the two pieces to be joined at an angle. = This is necessary to allow all of the bridge stock to follow the outline = of the bridge. Once all scarfs are joined (usually there are two per = long bridge), the bridge outer profiles are then cut out with the band = saw. Ah, Ron, we can tell you're not a wooden boat builder! A good scarf = joint will equal the strength of a solid wood beam. And it will have a = slope of 1:8 (non-structural use) or 1:12 (structural use). The amount = of slope also varies with the glueability of the wood being joined. = Spruce bonds very easily, maple somewhat less so. Finger-joints, by the = way, are simply a form of scarf-joint. In this case the scarfs are made = short and are stacked for less wood waste. We can compromise on the slope of the scarf in the construction of piano = bridges because it is a "non-structural" application. The absolute beam = strength is not critical.=20 Del ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/69/7e/12/dd/attachment.htm ---------------------- multipart/alternative attachment--
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