Del wrote: > ....Compression-set in wood is not a uniform thing. It > occurs first and most in the late-wood portion of the annual ring. So there > will be more compression set in an individual board having a higher > percentage of late-wood. Why would late wood be more subject to compression set that early? Late wood is more dense, hence stronger. I would think the early, less dense wood would compress more. Is it that the late wood, being more dense, does not "bounce back" (bad phrase, but I mean that late wood is not as resilient) as well as the early wood? Terry Farrell ----- Original Message ----- From: "Delwin D Fandrich" <pianobuilders@olynet.com> To: <pianotech@ptg.org> Sent: Sunday, June 10, 2001 11:44 AM Subject: Re: Soundboard Compression & Cracks > > ----- Original Message ----- > From: "Farrell" <mfarrel2@tampabay.rr.com> > To: <pianotech@ptg.org> > Sent: June 10, 2001 6:31 AM > Subject: Soundboard Compression & Cracks > > > > Take a compression-crowned soundboard that is not collapsed (still has > some > > crown) that also has a few cracks through which you can see daylight. How > > can this be? The only thing that gives the board crown is the lateral > > compression across the grain as the wood gained moisture after its initial > > drying during construction. Now if you have daylight cracks in the board, > > does this not mean the board is not under compressional forces? Or is it > > that the inter-crack areas are still under compression from being glued to > > the non-dimensionally changing ribs (relatively speaking)? But then > why/how > > is it that one area of the board can be under compression and an inch or > two > > away, the board is under tension???????? > > You pretty much have it. Compression-set in wood is not a uniform thing. It > occurs first and most in the late-wood portion of the annual ring. So there > will be more compression set in an individual board having a higher > percentage of late-wood. Note that this does not necessarily relate to the > overall width of the rings but to the proportion of a single ring that is > late-wood vs early-wood. > > Unless some kind of distortion has set in, such as that typically found > around the low tenor bridge or around a cantilevered bridge base, crown > tends to average out due to the longitudinal stiffness of the ribs. It would > be pretty hard to isolate individual spots of soundboard panel compression > vs individual spots of tension. > > -- ddf >
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