Replies

1. 
   secondfret | Feb 16, 2008 10:27am | #1

   AL:

   I'll try to offer some ideas on mandolin sides. Your 7/64" (0.109") is a little on the thick side for mandolins. Typically they range from the low of about 0.65" to 0.80" and are bent with dry heat. If you make the sides too thick, you'll end up with compression bends on the inside of the curve. The max I've ever bent well is about 3/16" ( .187"), and that was a softwood like spruce. When you need something thicker, like for the linings, I'll usually laminate it after bending. 

   Traditionally you would lightly moisten the sides with water and  bend them by hand over a hot pipe clamped in a vise with a torch or other heating device in one end and an aluminum baffle on the other end to keep the heat from escaping too fast. The temperature works well around 275 degrees F- roughly hot enough to sizzle the water off the surface of the wood, but not so hot that contact will burn it. Too much moistire can cause the grain to splinter apart if it is highly figured wood like curly maple. When the temperature is just right, you will see the damp sides steam off the water in a very slow and controlled way. The basic process is similar to traditional steam bending; the wood and water get hot to the point where the water offgases as steam and the wood bonds give slightly and take the bent shape. Once you feel like the wood has taken the shape you are after, I like to clamp it to a mold of the final pattern to dry overnight. This helps to prevent springback.  Violin folks tend to prefer inside molds; steel string guitar builders, outside molds.

   This is one of the places where the only real way to get it down well is just time in the saddle and practice a lot on scrap materials of the same wood. Using a backing strip of thin .020" sheet metal to support the backside of the wood during the bend will help with the splintering out issue. You can also repeatedly dampen and reheat the wood to get a tighter radius bend. If I'm working with a new piece of wood, I usually make a few test pieces. I'll bend, scorch, and generally wreck them to learn the working limits of that particular piece of wood, as they all have different working and heat ranges. With a bit of practice, you should be able to bend that walnut into a pretzle knot.

   You mentioned using an inside and outside caul. This is a geat way to get very consistant resluts for your sides. With a specific shaped set of cauls, I'll use a flexible silicone heating blanket, available form Watlow supply company. It is basically a very thin flexible ruber sheet with internal electric heating elements that work on regular household voltage. In about two minutes time, it will heat up to close to 400 degrees F. I run a reheostat, such as a household light dimmer, in between the blanket and the electrical outlet. I'll also wire in a timer circut- an old darkroom timer or a wall mounted type sauna timer work great. The idea with those is that if the phone rings and you forget about the heat blanket, it will shut off automatically before the house burns down. I lightly wet the wood, sandwich it in between two thin sheet metal support strips along with the heat blanket, and very slowly clamp the entire assembly shut.  Depending upon the shapes desired, I regularly use push pull stlye cam clamps on a rigid fixture to bring everything together. I may also wrap the wet wood in brown paper to keep the oils or resins from getting all over my heat blanket and metal slats.

   I'm not sure where you are in the mandolin building process. Roger Siminoff's The Ultimate Bluegrass Mandolin Construction Manual (available at http://www.siminoff.net) is a great reference for building a nice mandolin. I would bet that the majority of the folks who are at the top of this field got started by using one of Roger's books. The Mandolin Cafe (http://www.mandolincafe.com) has a very good mandolin builder specific forum that can offer a world of great advice on all aspects of your building from some of the best folks around. When you get to the point of putting a finish on you new mandolin, make sure you get a look at the video here in the skills and techniques section for creating a sunburst finish!

   Good Luck.

   james condino

   http://www.condino.com