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| What part of back is radiused? http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=7725 |
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| Author: | John Elshaw [ Thu Jul 27, 2006 1:52 pm ] |
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When bracing a back for a classical guitar, do you radius all the braces so the entire back is radiused, or do you only radius the braces in the lower bout similar to the front so mostly the lower bout is what's radiused? The Spanish foot is approx. 90 mm tall, so I'm finding if I radius that entire part, it's going to really cut down on the side height there. I guess I should have left the foot a little taller, but now I'm thinking I just might need to reduce the radius instead of sanding the sides down so much. So far, fitting the back has consistantly given me the most trouble in all my builds. John |
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| Author: | Dickey [ Thu Jul 27, 2006 2:35 pm ] |
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Hi John, Gee, never built a classical, but on the steel strings the whole back is domed, edge to edge, and end to end. All the same on mine 15 Foot Radius. Think of a beach ball with a slice off the outside, it's kind of like that. Can you glue a mahogany slice onto your foot and then radius it? A Laminated foot would be stronger wouldn't it? Just an idea.... |
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| Author: | MSpencer [ Thu Jul 27, 2006 3:28 pm ] |
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John, great question, I am working on my first every Classical myself or maybe it's a modified Classical, who knows. This guitar is for my own playing enjoyment so not tied to traditional approaches, just like to play classical music and currently don't have a gut string unit in the house. I have looked at this myself and I am planning on doing a 15' radius on the lower bout using my ladder braces. I was going to a 20' at the waist then to a 25' on my next above the waist then to flat on my last brace and to the neck block. I don't have a clue if this is right or wrong or how it will look and work. I am having fun and it might look cool at least to me. I'm also tapering my body width slightly from the tail block height down to the neck block height and not going as flat in this direction either. My Engleman Spruce top is already Fan braced and done on a 25' radius sitting in the dish and GoBar deck as we speak. I pulled the wrong template and mis-cut a B&S set of high figure Beeswing Bubinga, so I cut it down further to my Classical mold and shape. Going with a Spanish Cedar neck, got a really nice rossette in place that has some red in it as well. I am thinking of binding this with curly maple with a BWB side purfling and putting a Herringbone purfling on the top. The set which was originally going to be a Dread already has a Herringbone backstrip. At any rate, hope some of the classical guys answer the question so I can know what the right thing to do is on my next, I am proceeding as planned on this one. "Onward through the Fog" Good Luck Mike White Oak, Texas |
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| Author: | Alan Carruth [ Sat Jul 29, 2006 10:16 am ] |
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As far as I know, most people just dome the back the same all over. There is not as much reason to use different radii in different places on the back as there is on the top, and it's a whole lot easier to fit, and therefore looks better, if you make it uniform. |
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| Author: | Michael McBroom [ Sat Jul 29, 2006 11:49 am ] |
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John, This is a really great question. I'd like to know what others do, as well. I used to radius all my back braces the same, but with the last couple of builds I've stopped doing it that way. The reason is, as you mention, the foot. I don't contour my sides in a sanding dish the way many folks do. Instead, I follow a more traditional approach, and plane down the sides from a high point more or less even with the bridge, to the heel/foot area, and also plane down the sides a bit toward the tail block. Once I've done this and installed the linings and side braces, I use a sanding board (mine happens to be 18" x 27") to level the sides with each other AND with the foot. I check the evenness across the upper bout with a straight edge, making sure that the foot is the same height as the sides. Now at this point, I attach the back. Problem with the old way I did it was that the brace closest to the foot -- maybe an inch away from it -- had an arch, while the foot didn't. The result was, I would get dimples in my back around the foot, and sometimes I'd have a slight gap between the base of the foot and the back. I really didn't like the looks of this. So, a couple of builds ago, I started installing the first brace without any radius, but I still radiused the other two. This worked. No more dimples in the back. The back itself is flexible enough to handle the slight change in radius over a distance of 5" or so between the first and second braces, so I think I'll just keep doing it this way until I find a better way to do it. I'll admit, the ideal way to do it, I'm thinking, would be to use a sanding dish that is the same radius as the back braces. Maybe one of these days I'll give that a try and see if it works as well as my current method. I don't see why it shouldn't. Best, Michael |
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| Author: | John Elshaw [ Sat Jul 29, 2006 2:28 pm ] |
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Michael, That's the exact situation I am running into. I think I will try your method for these next guitars. I have three identical Hauser models ready to close up, but I still need to brace the backs. I think I will follow your lead and leave the top brace flat. For my next build I think I should leave the foot a little higher, but for this time, it's too late to put the toothpaste back in the tube. Thanks for the info. I'll let you know how it all turns out. Cheers! John |
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| Author: | Robbie O'Brien [ Sat Jul 29, 2006 2:54 pm ] |
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John, There are two approaches. One is the traditional method where the braces are installed into the kerfing, radiused and then the back attached. The other approach, I believe influenced from the steel string builders and modern radius dishes is to radius the rims and then the braces to the same radius. Then attach the braces to the back and then attach the back to the rims. The first method leaves the end of your back braces about 6mm tall and they fit inside the sides below the binding line . The second method leaves your braces only around 2.5mm tall and they go all the way through the kerfing and side and are covered by the binding. I remember you asked recently about my DVD and how I show to cut the side radius before bending them. Remember the sides are tapered from about the waist to the heel block by about 7mm. From the waist to the end block they are the same height. If you try and radius the sides like a dome in a radius dish you will remove too much of your heelblock at this point. If you "inlay" your braces into the kerfing and lay a straightedge from heel block to end block you will see there is a "radius". Now use a plane to radius the braces across the back. Use your straightedge like I show on the DVD on the braces to check the radius. Once the braces are radiused across the back then you need to remove material from the braces so that there is no gap under the straightedge when it is laying across them from heel block to end block. Then adjust the heelblock slightly to accompany the radius of the braces from end block to heel block. Basically the lower bout is radiused across the width of the guitar. The sides are flat. The upper bout is radiused across the back and the sides are tapered from the waist forward. Then the enitre back is radiused along the length from the heel block to the end block but only in the braces. In the classical guitar DVD I show how to do the traditional method using a handplane and straightedge and a radius dish as well because the traditonal method with a hand plane can take some practice to get right sometimes. I thought some might find it easier to use a radius dish. When using a dish you will remove sid ematerial so plan on that when installing your kering and cutting your heel block height. This sounds about as clear as mud! I hope you understand this. If not, let me know. |
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| Author: | John Elshaw [ Sun Jul 30, 2006 3:02 pm ] |
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Hi Robbie, Actually, your explanation makes perfect sense, and your description on the dvd is also very easy to follow. I cut the radius in the sides like you mention (from the e-mails), and it came out great. With the sides on, there is a very nice radius from pre-cutting those sides. The problem I am having stems from the fact that I didn't leave my heelblock tall enough. If I place the plane on the last brace and heelblock, it is too steep of an angle, and the plane blade will only take off material from the heelcap (does that make sense?). John |
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| Author: | Robbie O'Brien [ Mon Jul 31, 2006 2:22 am ] |
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John, I am glad to hear that the side radius came out good. Now, if you place the straightedge from the heel block to the end block you should have gaps under the straightedge and some of the braces or heel block. Plane the first brace down maintaining the radius across it until it removes the gap under the straightedge and the heel block. It sounds as though the first brace is too tall if your plane will only remove material from the heel cap. Remember that if you remove material from the first brace you will also have to adjust the other braces until there are no gaps under the straightedge and the braces. It is trial and error. Just a couple of passes is enough to remove a lot of the gap. It becomes easier the more you do it. Good luck. |
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