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jshelton5040 -> RE: Runout on guitar Tops (Feb. 25 2010 8:22:55)
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quote:
ORIGINAL: malakka
I've read about "runout" on spruce guitar tops and how it results in an inferior guitar top. I was wondering if someone could explain that- for example, how it looks or what to look for, how it effects the strength of the top and the resulting sound.
Unfortunately trees tend not to grow absolutely straight. Some have bends, some grow with a twist. Resaws cut in straight lines so when you saw tops out of billets from trees that are not perfectly straight you cut through the bends or twists. The resulting tops have grain that reverses usually diagonally from corner to corner.
When you book match the two panels of the guitar top the grain will be running the exact opposite on each side of the center line. It makes planing, scraping, etc. very difficult. Tops with lots of runout tend to be less stable and are weaker structurally than straight tops. One learns to deal with moderate amounts of runout by altering the top thickness, taper and bracing but building a good guitar with a top that has substantial runout is pretty much impossible.
If you look at a finished guitar that has runout in the top it will reflect light differently on each side of the center line. The amount of variation in reflectivity from side to side is an indicator of the amount of runout.
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