Efficiency, Resonance, Bending, 5 Guys
The month of November isn't really a month in the shop. It's more like three weeks in the shop and one week of eating... hopefully with family. December is very much the same way. So, expectations regarding shop production need to be curbed. I'm just being realistic.
October ended without completing the shaping of braces on all five guitar projects. Much was learned regarding production efficiency. Building a single guitar requires the shaping, joining and carving of 18 braces on the top and back. That's 90 braces for 5 guitars.
When only one guitar is being made, there's no need to worry about efficiency. There won't be any. One must accept that and just maintain quality. Building several guitars at once, however, introduces the challenge of doing things efficiently in order to maintain quality.
Long story short: Quality tapers off as fatigue increases. Efficient methods, therefore, go hand in hand with quality control.
In regard to bracing the guitar top and back efficiently, rough-carve the braces (preferably on a machine) before they are glued down. Final carving and tuning of braces is still done after the glue on the braces has fully cured.
Resonance tuning of the top is an interesting subject that we can't explore very well here. Carving of the X-braces, however, has a direct affect on the top's resonance frequency. There is no single recipe. The style of play and the target tonal qualities will determine the target resonance of the top. Here we enter the land of subjective judgement and preference. (It's like religion and politics... except worse.) For the record, all five of these tops have resonance frequencies between Bb3 and C4.
On we go. Woody is trying to complete 5 guitars by Easter. We are probably 1/3 of the way.
Notice that the guitar in the middle is smaller. This will be a 3/4 guitar for a small person, a child or just a convenient instrument to carry or have in your lap as you watch TV with the sound off.
The tops in the photo are lined up under their respective backs. From left to right, the backs are mahogany, rosewood, cherry, mahogany and padauk. All of the tops are sitka spruce.
There was some time in November to bend a set of sides for a mahogany guitar. To bend sides I use an LMI side bending jig. The machine has heating blankets with thermocouples to monitor the temperature of the wood as pressure is applied for bending. The machine works quite well but that does not mean it is automatic. Vigilance is required because one cannot see the wood as it is being heated. There is a lot of feel involved which means that experience in bending wood by hand, on a heated pipe is very useful.
It's a good idea to turn off shop music and cell phones when learning to bend with a machine. If one proceeds as demonstrated in the LMI video, it will only take 10 minutes to bend a side.
For mahogany, I set the target temperature for 280F. After only a couple of minutes one can hear as the wetted wood reaching the boiling point of water (212F). That's a signal to tighten up your focus! The temperature of the wood will soon rise to the bending point depending on the thickness (and species) of the wood. The machine control will not allow the temperature to rise beyond the set point. Harder woods are more dense and generally less flexible. These woods (Rosewood, Padauk, etc.) will require a higher set point.
Once the target temperature is reached, the wood needs to be bent very slowly as you monitor its resistance. Once you can feel the wood stretching, proceed slowly but deliberately. When the side is completely bent to the shape of the mold, reduce the heat and allow the wood to cool down while still clamped in with the heat blankets. Ideally, the wood should cool to room temperature before it leaves the bending machine. Then it should go directly into your mold.
As with all manufactured tools and equipment, practice and experience are the only way to understand the machine's quirks and limitations. Just be aware... there will be quirks and limitations. For example: The temperature of the wood will not be uniform under the heated blanket. When learning this machine, make sure that the thermocouples are placed between the wood and the heating blanket near the point where the bending is most severe_ i.e. at the waist and upper bout. It's not a bad idea to have four thermocouples instead of two.
The Gibson got some attention this month too. I had to make a harness to wire up all the pickup hardware that will have to go into the guitar (through the hole routed for the neck pickup). Then, with the help of Lindy Fralin, who also has a shop here in Richmond, all of the wires were soldered in place on the harness. I can't wait to hear how these Fralin pickups will sound in that old box.
See you next month.