Stay in Tune vol #70
By Luthier Patrick Podpadec
I was reading some old articles the other day and realized that this Voice article marks # 70. I started my first article on repairing instruments on April 16th 2009. I've tried to cover a large list of repairs from building bone nuts to refretting guitars. I never seem to know the subject of my articles until I'm into about a paragraph or two.
Well this week it seem to be that I will be talking about jigs and fixtures. A couple of weeks ago I performed a workshop at a music festival “How to Bend Guitar Sides”. This involved a “machine “That I built about ten years ago from some plans that I saw offered in a Luthier Merchantile Catalog . It is not actually a “machine”, but it looks more like one than a “jig” or a “fixture”. This “jig” was designed and built from a luthier named Charles Fox. He has been very innovative in the luthier community for some time ( over 20 yrs for sure). His original design included high wattage light bulbs to create enough heat inside the chamber to bend the sides. It actually works quite well. Before this design , luthiers used various method of boiling wood in a trough or hand bending it over a hot pipe. The cool thing about the Bender is that it has a removable form that can be changed to accommodate any shape that you are building. The idea was to slip your thin wood in between a two layers of spring metal ( thin sheets of tempered stainless steel) and the heat from the 150 -200 watt light bulbs would create enough heat (about 275 degrees for most woods) to uniformly bend the sides. After the wood was warming up ( about 150 degrees or so) you would crank down on the center veneer screw to create the “waist bend”. You would then slowly pull down the “cauls that are attached to large springs to wrap around the form to hold the sandwiched wood and metal sheets onto the form. This required you to turn the bender on first and “preheat” the chamber for about a ½ hour to get the metal sheets warm enough to bend the wood. This method , although a bit time consuming worked very well and was very consistent in bending sides without cracking or any other unwanted hazards.
Now with the onset of every luthier trying to build a better “mouse trap” this design has developed into a very sophisticated machine. Instead of high wattage light bulbs for the heat source there is a new silicone heat blanket that was developed by a company called Watlow. These thin blankets (about a 1/16th) are made from a synthetic rubber that allows them to bend into almost any shape. They can produce up to 400 degrees and more in matter of minutes and can be sandwiched in between layers of metal sheets. The metal sheets are used so that the wood has a stable reinforcement on both sides of the wood while bending it . This helps it from cracking or twisting in directions that you don't want it to go. The heating blankets can also be set on a thermo controlled timer so that you don't accidentally scorch the wood and burn your house or shop down. The cauls that where attached to the jigs with springs have now been replaced with a new design too. They are fully adjustable cam clamps that slide on plastic rollers. (very cool!) This new method has produced a jig that looks more like a Ferrari than the original . It has dramatically improved the safety, time and effort that it used to take. Although I still use the older style bender, (which works fine) I hope to graduate to the newer one in the future You can visit Luthier Merchantile's website to watch a very cool video of this new bender in action ( http://www.lmii.com/CartTwo/Video.asp). This website is also packed with many more helpful and informative videos on many luthier related subjects.
Bending the sides is one aspect of the building process. To be able to maintain the shape of the sides it is important that you have a form to put the sides into so that when your attaching the neck and end blocks and the kerfing to the sides it will keep the shape of your intended design. The sides must have a neck block where the neck can be attached either by a traditional dovetail joint or a bolt on style . It also must have an end block so that there is some substantial wood to mount a end strap button to, It also helps with some weight to balance the guitar after attaching the neck. The kerfing is a small strip of wood that is glued to the edges of the side so that there is more material for the top and back to be glued onto . It also helps when there is binding or purfling cut around the edges for aesthetics Often when you look inside the guitar you can see this strip of wood and it has many cuts in the strip. This makes it much easier to bend around the shape of the guitar. It is possible to bend a solid thickness of wood but it is labor intensive and most luthiers agree that it does not improve the tonal quality of the guitar so that it is not usually done that way.
Getting back to the form, many luthiers build guitars without the use of a form, especially when building a “one time” design. I feel that when producing a design that is going to be produced more than once it is crucial that a good form is made for that shape. Remember that, “The better the form the better the guitar”. You can visit http://www.wood-n-strings.net/repairs/my-shop.html to view more interesting tools and fixtures that I have built to accommodate my building process. So until then, Please Stay in Tune!
Thanks Again !
Patrick From Wood-n-Strings/ Liam Guitars