---------------------- multipart/mixed attachment --=====================_58842090==.REL >I need a crash course on bridge building (long bridges, bent laminated >type). Could use some suggestions on how I might go about getting >information, how to make a template, what tools I might need, materials, >etc.. Whatever can be offered would be appreciated. > >David Love Hi David, It's coming up on pumpkin time, and I'm about to collapse for the night, but I'll try to do a quick outline for you. I use a rubbing (paper template) from the original configuration (before I take the strings off) as a point of departure. After re-scaling, I use that template to establish the new speaking lengths, which I use to lay out the new bridge. Once you have the template for the new bridge, you need to decide how you are going to build the bridge. You can cut it out from solid stock, joined at the scale breaks to keep the grain running roughly parallel to the bridge, or you can laminate it. You can laminate it horizontally, putting the joints in each lamination in random places so the strength of the assembly won't be compromised, which works fine. Or you can laminate vertically, which means building a jig of some sort for clamping the laminations to the required curve. I've done bridges with continuous vertical laminations, but it's a lot more work than should be necessary for a one-off bridge. You need laminations at 2mm or under to make the dogleg bends at the struts to maintain a semi-log speaking length progression, and a tremendous amount of clamp pressure. An easier way to do a vertically laminated bridge root is to use the lamination thicknesses to supply the dogleg offset and not have all the laminations continuous for the length of the bridge. Terry Ferrell asked about this a while back, and it looked like a good idea to me, so I tried it. It works very well. Thanks Terry. You just have to build half a jig to accommodate it, clamping the lamination stack against it without needing a caul on the far side. Actually, I used backing strips to spread out clamp pressure, but still didn't have to cut out a full caul. Since the core laminations don't have to be forced into an extreme bend, it's considerably easier to manage and takes much less clamp pressure. It just takes a little more pondering and planning before the fact. Cutting out a solid root and putting a cap on top is still easiest, but I like laminations. Just not all that bright, I suspect. That short stack of maple just above the bridge in the photo is the laminated cap (1.5mm laminations), waiting to be cut and fitted to the root. The bridge root is still rough cut here (hacked, actually), and will be smoothed and contoured before the cap is installed. bridge laminations.jpg The laminations in this bridge vary from 2mm to maybe 5 or 6mm. I used what I had lying around from previous projects that added up to the offsets I needed for the doglegs. It's a tad over 30mm wide overall. To do this, you need a way to produce the required laminations - be it a table saw or band saw, and (ideally) thickness planer. You need lots of clamps (naturally), and scrap(able) lumber for building the jig. You also need a glue that is reasonably hard and creep resistant. I use Titebond. Realistically the glue used for laminating doesn't need to be able to hold continents together without shifting under billions of PSI. Gluing the cap on top, and the panel on the bottom of the root laminates will effectively insure that nothing is going to slide apart with a reasonably decent glue. The rest is just the usual bridge work - or you can send me the original rubbing and the offset revisions (or?) and we can work something out. Did I miss anything? --=====================_58842090==.REL A non-text attachment was scrubbed... Name: bridge laminations.jpg Type: image/jpeg Size: 47257 bytes Desc: not available Url : https://www.moypiano.com/ptg/pianotech.php/attachments/cb/38/14/88/bridgelaminations.jpg --=====================_58842090==.REL-- ---------------------- multipart/mixed attachment Ron N ---------------------- multipart/mixed attachment--
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