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| Veeery strange measurements for density on Spruce http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=29571 |
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| Author: | Corky Long [ Wed Oct 20, 2010 8:58 pm ] |
| Post subject: | Veeery strange measurements for density on Spruce |
I've been tracking density, measured in grams per cubic inch, on my tops for some time...and I've got some data for the tops I've bought and used, trying to get a feel for correlation between density of tops and sonic properties. Most of the spruce that I've got (regardless of species) is between 6.4 grams per cubic inch, and 6.9..... I just measured a top that I recently bought - really nice old Sitka, with silking, some bearclae, reaaaally tight growth rings. 7.7 grams per cubic inch. I don't have anything close to this (by comparison, I have some Koa that I measured at about 7.5..... Has anyone seen Sitka this dense? Thanks. |
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| Author: | Jeff Highland [ Wed Oct 20, 2010 9:46 pm ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
Grams per cubic inch?.....yah gotta be joking. |
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| Author: | Ti-Roux [ Wed Oct 20, 2010 10:23 pm ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
I'm not familiar with grams on cubic inch, cause I use Kg/m³, but I have seen very stiff sitka some time... |
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| Author: | Jim Watts [ Wed Oct 20, 2010 11:34 pm ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
Yeah, I've had some stuff that dense before, it was extremely stiff also. I decided not to use it. |
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| Author: | meddlingfool [ Thu Oct 21, 2010 12:03 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
The dread I'm working on now measured out to 8.4 g per cubic inch. Tons of bearclaw. I'm pretty stoked on how the box knocks. More bing than boomp, to get scientific. |
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| Author: | bill stewart [ Thu Oct 21, 2010 3:26 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
Yes we're getting British imperial and metric measurements mixed up. We don 't mix them it's either grams per cubic centimeter, (kilograms per cubic meter), or pounds per cubic inch (or foot). Didn't one of them space probe thingys shoot away off course some time back because somebody got their kilometers mixed up with their miles?.....  Bill S. 
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| Author: | Alexandru Marian [ Thu Oct 21, 2010 4:08 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
Making the conversion takes 3 seconds: type 77 and divide by 254 trice, you get 4.6988.... which means 468 Kg/m3. It is really not that scary. I measured Euro spruce at 480Kg+ Dunno what is the best density range for Sitka, but all the unusually heavy Euro I measured has poor stiffness/weight. I am sure these tops can sound great but you might need to beef the bracing after getting the plate light enough. |
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| Author: | Dave Stewart [ Thu Oct 21, 2010 7:27 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
The sitka I've used has been in the .425 to .450g/cc range so .468 is in the high range as Todd says, but should be ok. |
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| Author: | Corky Long [ Thu Oct 21, 2010 7:55 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
Thanks all for the feedback. Sounds like the measurements are on one end of the spectrum but not unprecedented. As for the mixing of imperial v. metric, I hear you. Happy to stick with one or another for purposes of ease of communication on the forum. Regards, |
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| Author: | Corky Long [ Thu Oct 21, 2010 8:13 am ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
meddlingfool wrote: The dread I'm working on now measured out to 8.4 g per cubic inch. Tons of bearclaw. I'm pretty stoked on how the box knocks. More bing than boomp, to get scientific. whoa.... That's off the charts. And that's Sitka? Interesting. As I ask more questions on this topic I come to learn that you can have many different densities of tops from the same tree. Makes it tricky when harvesting tops - can't count on one tree to produce tops within the same parameters. Interesting. I guess I've got to get serious about deflection testing...to know how much to thin these ones that are on one end of the spectrum.. |
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| Author: | Alan Carruth [ Thu Oct 21, 2010 3:20 pm ] |
| Post subject: | Re: Veeery strange measurements for density on Spruce |
That's pretty high, alright, but not off the charts. It should have proportionally higher stiffness along the grain, so you should be able to leave it thinner, but it will still end up being a somewhat heavier top than one in a more normal range of density. That's good for 'headroom', I think, but maybe not for power. A friend of mine isa long-distance racewalker. One time the editor of the local newsletter listed all of the race times in 'furlongs per fortnight'. Standard units are so nice... |
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