Posted on August 1, 2022March 5, 2024 by Dale Phillips Guitar Outline Formula Guitar Outline Formula by Leo Bidne Originally published in Guild of American Luthiers Data Sheet #79, 1978 From taking several measurements of various guitars, I’ve discovered only slight differences from one to the next. These differences seem to contribute very little to the finished sound. The question is, what is the reason for making a guitar the shape that it is? What are the determining factors, besides the obvious ones? Can there be a “formula” that produces an “ideal” outline? This is what I set out to find. What I came up with, rather independently, so closely resembles, at least in dimension, the existing standard outline of the classic guitar as introduced by Torres, that I wonder if a similar technique may have been in use in the past, in some modified form. This formula, based on the string length, may be of no use to acoustical science, but it’s as fun as a math game, and twice as surprising. Although the information below describes how to derive an outline for a classic guitar with a string length of 65CM, joining the body at the 12th fret, it can also be used, with slight modifications, for other instruments, such as the flattop, the acoustic bass, the electric guitar, etc. Once the outline is established, the depth of the sound cavity can be adjusted with the sides, helping to establish the instruments sonority, as well as adjusting the soundboard bracing. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on August 1, 2022March 5, 2024 by Dale Phillips The Design Diamond The Design Diamond by Dan Neil McCrimmon Originally published as Guild of American Luthiers Data Sheet #100, 1978 The basic idea behind this geometry jazz is to have the elements of design organized in such a way to give a sense of cohesion to the total design. The drawing is of a classic guitar, other guitars will be different but should have simple relationships. I have not tried this with the violin but suspect it should fit in there somehow. The whole design is broken into simple subdivisions of the total length of the sides (i.e. 1/2, 1/3, 1/4). Line XY is half the length of AB. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on August 1, 2022March 5, 2024 by Dale Phillips Epoxy Epoxy by Paul Jacobson Originally published in Guild of American Luthiers Data Sheet #90, 1978 and Big Red Book of American Lutherie Volume One, 2000 For the contemporary luthier, epoxy opens up an entire realm of innovative techniques never before possible. It can be more than a mere substitute for earlier, less satisfactory materials; it can make way for totally new design concepts in the luthier’s art. Epoxy is so different from any material used in the past by luthiers that it requires a whole new set of assumptions about application possibilities and handling techniques. Many luthiers who have had any experience at all with epoxy think of it as merely a kind of glue and may substitute it on occasion for Elmer’s. To be sure, epoxy is an excellent adhesive, but to think of it as just glue is to have a limited concept of its basic properties and its vast potential in lutherie. Epoxy, the Material. Epoxy is one of a group of chemicals known as thermoset plastics in which change from liquid to solid occurs by endothermic chemical reaction rather than ectothermic hardening or volatilization of a solvent. The reaction is nonreversible; epoxy, once hardened, cannot be melted with heat or dissolved in any solvent. Heat of 150°F or higher will soften it slightly, but as the heat increases the epoxy undergoes molecular deterioration rather than melting and tends to turn crumbly. Become A Member to Continue Reading This Article This article is part of our premium web content offered to Guild members. To view this and other web articles, join the Guild of American Luthiers. Members also receive 4 annual issues of American Lutherie and get discounts on products. For details, visit the membership page. If you are already a member, login for access or contact us to setup your account.
Posted on August 1, 2022March 5, 2024 by Dale Phillips Questions: Tru-Oil Finishes Questions: Tru-Oil Finishes by Jeff Jewitt Originally published in American Lutherie #90, 2007 ■ Eric Nicholson of Northern Ireland asks: Woodworker magazine published an article on Stewart Adamson’s work regarding Tru-Oil finishes. His method involved a considerable amount of work with Micro-mesh during the process. I tried his method on my own guitars, both classical and steel string, with very satisfying results. Tru-Oil gives an attractive semigloss finish on all woods, but Adamson also goes on to say that for those that like a gloss finish, a gloss tung oil is now available only in the USA. Does anyone know of this gloss tung oil and where it is available in the States, or if it is now available in the UK? Jeff Jewett of Homestead Finishing in Cleveland Ohio responds: Tru-Oil is not pure tung oil. It’s a mixture of linseed oil, mineral spirits, and, according to the manufacturer, “modified oil.” It’s arguable that no tung oil is even used in this stuff. When finish chemists talk about “modified oil” as an ingredient they typically mean either chemical modification or heat modification. Chemically modifying a drying oil involves reacting it with chemicals and heat to form what are known as alkyds, which are used in varnish manufacture. Heat-treated oils basically jump start the drying/curing process. Pure heat-treated oils are used all the time in making finishes, but they rarely show up as “finishes.” The only pure heat-treated linseed oil I know of is Tried and True “Varnish Oil.” Pure heat-treated tung oil is sold in this country under the Sutherland Welles brand (www.sutherlandwelles.com). So I would be tempted to say that Tru-Oil is a mix of linseed oil and some sort of modified linseed or tung oil. Because it has a high oil content, it is not possible to produce a very glossy finish. High oil (also known as long oil) products tend to form microscopic wrinkles at the surface as they cure. There is one way to heat-modify pure tung oil so that it will form a glossy film. This involves careful and controlled heating of the oil to about 450°F. Very few people can cook tung oil properly nowadays, but you can buy it under the Sutherland Welles brand “Original Formula High Lustre.” I don’t know if they will ship overseas. It’s not an easy finish to do, and I’m not sure that it will match the gloss of a French polish, but at least you know it is real tung oil, along with solvent and some driers.
Posted on August 1, 2022March 5, 2024 by Dale Phillips Bridge Positioning Bridge Positioning by Eric Henderson Originally published in Guild of American Luthiers Data Sheet #7, 1975 One procedure I use which your readers may find useful is that on my guitar top all the cross bracing and fan bracing is made up from the cuttings from the top blanks. For the cross bracing, I have to laminate two pieces together with the joint at right angles to the top. This procedure, I feel, guarantees that the woods are compatible. Another thing I do is when gluing the bridge I drill two small holes approximately 1/16" diam. in the slot for the ivory saddle, and when the bridge is precisely positioned, I drill through the top. The bridge can then be glued without being concerned about it moving because I temporarily inset two finishing nails in the two holes. The finishing nails are removed before the glue has completely set. The holes remaining are covered up by the ivory saddle. These are just two small items, but I would like to see the members who want to share small items like this write them up. ◆
