George Tokarev
11-18-2004, 9:48 AM
So how does wood dry, anyway? The folks at Forest Products Lab have done a lot of research on the subject, and made their results available on the web. For purposes of my experiment last evening, all references will be to http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr117.pdf Page references will be as printed on the document followed by the pdf page.
Subject : Acer rubrum, a soft maple
Form: Small 5.375 " diameter bowl 3.25" high, 0.5625" basic thickness.
Cut Date : 11/04/04
Evaluation date : 11/17/04
Initial Evalualuation: Weight at time removed from the lathe unknown, though an evaluation of any soaking method would certainly require it to determine solution strength. Condition was flinging wet, so as a minimum, assume at the FSP of ~30% moisture content by weight. (P14/18) Weight at time evaluated was 231grams after storage for 13 days. Relative humidity at time of evaluation was 70%, though RH was not recorded through the process. Probably was a bit drier earlier, as the last two days have been foggy. "Storage" as pictured, on a table waiting for a trip to the shelves in the back room. Second photo shows circularity, as compared to a bowl cut yesterday. 5.375" at max, 5.1875 thin side at minimum.
Question: Without interference in drying, can a piece this thin already be at EMC with the environment after 13 days? 1" lumber could be at 20%, according to FPL within 30 -120 days (P24/28), and a bowl like this is almost entirely endgrain, which dries at a more rapid rate.
EMC for 70% RH equates to 13% MC by weight.
Method: Drying to bone dry by microwave excitation, determining if total loss is equal to 30 grams, which equates to 13% MC or 70% RH.
Cyle 1 in a 1 KW microwave, 50% on, 2 minutes duration, on a motor-driven plate. Remove for 30 minutes.
Initial 231 g 5.375 x 5.1875 (thin) End 220 g 5.375 x 5.125 (fat) No evolved liquid, merely steam.
Cycle 2, as before.
Initial 220 g 5.375 x 5.125 (fat) End 208 g 5.375 x 5.125 No liquid, steam earlier in cycle.
Cycle 3, as before.
Initial 208 g 5.375 x 5.125 End 204 g 5.375 x 5.125 Surface does not feel damp.
Cycle 4, as before.
Initial 204 g 5.375 x 5.125 End 204 g 5.372 x 5.125 Smoldering snuffed after removal.
Evaluation:
Total weight loss was 27 grams rather than the theoretical 30, which may have to do with drier weather up until two days ago. The bowl may be in process of adsorbing moisture from the more humid air
Distortion of 0.25 Tangential/Radial is within the predicted 4%-6% (0.21-0.3) for this radial to intermediate-grained piece where grain is at 60 degrees to vertical. (P19/23)
Conclusion: The work of FPL appears to be verified, as does the concept that wood dries rapidly without interference under proper conditions. The 11.7% MC arrived at by the experimental method is 10% less than the theoretical 13, and may be attributed to a rising RH or the reluctance of the experimenter to further aggravate a spouse who had patiently endured this abuse of her microwave by trying to force an additional three grams from it. A 1/4" thick control piece cut over a month ago gave a 12.2% MC.
Note: After ten hours at 72% relative humidity, the bowl weighed a thin 208 grams. I have every confidence that, given an additional 48 hours it would again be at EMC with its environment. It will, however, be a finished bowl or firewood (again) by that time.
Subject : Acer rubrum, a soft maple
Form: Small 5.375 " diameter bowl 3.25" high, 0.5625" basic thickness.
Cut Date : 11/04/04
Evaluation date : 11/17/04
Initial Evalualuation: Weight at time removed from the lathe unknown, though an evaluation of any soaking method would certainly require it to determine solution strength. Condition was flinging wet, so as a minimum, assume at the FSP of ~30% moisture content by weight. (P14/18) Weight at time evaluated was 231grams after storage for 13 days. Relative humidity at time of evaluation was 70%, though RH was not recorded through the process. Probably was a bit drier earlier, as the last two days have been foggy. "Storage" as pictured, on a table waiting for a trip to the shelves in the back room. Second photo shows circularity, as compared to a bowl cut yesterday. 5.375" at max, 5.1875 thin side at minimum.
Question: Without interference in drying, can a piece this thin already be at EMC with the environment after 13 days? 1" lumber could be at 20%, according to FPL within 30 -120 days (P24/28), and a bowl like this is almost entirely endgrain, which dries at a more rapid rate.
EMC for 70% RH equates to 13% MC by weight.
Method: Drying to bone dry by microwave excitation, determining if total loss is equal to 30 grams, which equates to 13% MC or 70% RH.
Cyle 1 in a 1 KW microwave, 50% on, 2 minutes duration, on a motor-driven plate. Remove for 30 minutes.
Initial 231 g 5.375 x 5.1875 (thin) End 220 g 5.375 x 5.125 (fat) No evolved liquid, merely steam.
Cycle 2, as before.
Initial 220 g 5.375 x 5.125 (fat) End 208 g 5.375 x 5.125 No liquid, steam earlier in cycle.
Cycle 3, as before.
Initial 208 g 5.375 x 5.125 End 204 g 5.375 x 5.125 Surface does not feel damp.
Cycle 4, as before.
Initial 204 g 5.375 x 5.125 End 204 g 5.372 x 5.125 Smoldering snuffed after removal.
Evaluation:
Total weight loss was 27 grams rather than the theoretical 30, which may have to do with drier weather up until two days ago. The bowl may be in process of adsorbing moisture from the more humid air
Distortion of 0.25 Tangential/Radial is within the predicted 4%-6% (0.21-0.3) for this radial to intermediate-grained piece where grain is at 60 degrees to vertical. (P19/23)
Conclusion: The work of FPL appears to be verified, as does the concept that wood dries rapidly without interference under proper conditions. The 11.7% MC arrived at by the experimental method is 10% less than the theoretical 13, and may be attributed to a rising RH or the reluctance of the experimenter to further aggravate a spouse who had patiently endured this abuse of her microwave by trying to force an additional three grams from it. A 1/4" thick control piece cut over a month ago gave a 12.2% MC.
Note: After ten hours at 72% relative humidity, the bowl weighed a thin 208 grams. I have every confidence that, given an additional 48 hours it would again be at EMC with its environment. It will, however, be a finished bowl or firewood (again) by that time.