4 ms·

The figures I gave are annual movement. Initial shrinkage is larger when drying from green wood. The numbers (from the calculator) match my empirical observatio

by exDM69 1y ago

The figures I gave are annual movement. Initial shrinkage is larger when drying from green wood. The numbers (from the calculator) match my empirical observations very closely. By the way your relative humidity figures assume constant temperature. Wood cares about absolute humidity (mass of vapor per volume of air), and temperature is the dominant factor in absolute humidity. Rainy day at +1C (100% RH) is less absolute humidity than a sunny day at +30C. This matters to me a lot because half of my woodworking projects are outdoors or not temperature controlled indoors.

DannyBee 1y ago
"Initial shrinkage is larger when drying from green wood" ? It's not - it's exactly the same as anything else. The wood doesn't know it's green. The calculator you gave is shortcutting it, and has an entire article in how they shortcut it the same way as anyone else, based on the swelling coefficients/etc, but assuming thickness is small enough to not matter. If your projects are outdoors, you will be affected by more than just humidity - UV will also have a significant effect on the properties of your projects :) The moisture transport is also not as simple as you are making it out to be, and has a not insignificant effect. See: https://gupea.ub.gu.se/handle/2077/54179 https://gupea.ub.gu.se/handle/2077/54179 https://www.mdpi.com/2076-3263/8/10/378 https://www.mdpi.com/2076-3263/8/10/378 https://www.sciencedirect.com/science/article/abs/pii/S1296207416304496 https://www.sciencedirect.com/science/article/abs/pii/S12962...
- exDM69 1y ago
  Yeah, the coefficients are the same but the initial moisture content in green wood is much higher than the wood will ever get to after seasoning, it won't suck that much moisture from the air (unless you're in a swamp or something). So the annual absolute change in millimeters is lower than from green to seasoned. I have my woodworking projects in temperatures ranging from -25C to +100C (sauna) and extreme humidity changes from near zero to 100% RH. It is a form of art to make wooden things survive that, and I don't always succeed.
- kurthr 1y ago
  Ummm, most wood starts at a much higher moisture content (50%-200% noting that this is as a percentage of fully dried so it can easily be over 1) than it will ever have after drying (typically 5-15%). Frankly, the idea that a piece of wood after initial drying was moving even an in/ft (eg "only" 8%) would be pretty shocking. Even good joinery won't deal with much more than a quarter of that ~2%.
  - DannyBee 1y ago
    You missed my point, which is that initial drying is absolutely 100% not different than any other time. Wood, especially outdoor projects like the person is making, will definitely see states where the moisture content is as high, if not higher, than when the wood was originally dried. Also, most green hardwood starts at about 30%. No reputable lumber supplier is kiln drying hardwood that is 200% moisture content. That's crazy town. Even if they dried it super slowly, it would end up as mostly checked/warped garbage that they couldn't sell. Beyond that, wood is moving a lot, sorry you don't believe it, but its still gonna do it. Rather than say it's "pretty shocking", and dismiss it, care to present any studies that back up your assertion? I sent plenty, both in here and other comments. I'm not aware of any sourced, actual scientific research that says anything other than what i did, since I was careful to use cited figures from actual research studies, and not random pages on the internet about "wood movement" I think you are also assuming a lot about how it moves and what 8% radial swelling/shrinkage really means that isn't necessarily true. Also your point about joinery doesn't seem to make a lot of sense. While it's true that most joinery can't handle lots of flex, if everything expanded or contracted uniformly, it wouldn't be a problem. You seem to be assuming the opening will not expand the same as the thing going into the opening. It will. That is why you try not to mix conflicting grain directions in joints, and why you see so many joints that go out of their way to do that (IE 90 degree mated dovetail boards are not made by two conflicting grain directions, the pins and tails are made of the same grain direction that happens to mate at an angle) https://cad.onshape.com/documents/3e489410fcf65e1f0f82663d/w/eaa50df21f3410fa4bb63f91/e/2e8916bf9ccc18556d0dda51 https://cad.onshape.com/documents/3e489410fcf65e1f0f82663d/w... I made two tabs for you, one with a 25% transform and one without. Notice the opening gets larger when scaled. So would the mate. They would still fit fine. The same is true if you made a dovetailed box. It would just become a bigger/smaller box. I didn't bother to scale it differently for tangential vs radial but it wouldn't matter as long as the same scaling factors apply equally to the mate, and the mate is made the same way. As is true of most woodworking joints, on purpose. So the only issue is if (assuming 2% was the limit) the non-uniformness lead to >2% difference somewhere that mattered. All of this is also why wood glue has such expansion/contraction characteristics. if wood was only changing 0.1%, it wouldn't matter. So far i've seen a lot of doubt but nobody else actually seems to be bringing any real scientific rigor to that doubt, or saying some silly things. Please feel more than free, i'd love to see papers with real measurements that suggest something else.
ComputerGuru 1y ago
Yeah, the Midwest is cursed for this reason. Humid summers with incredibly high RH for being inland while temperatures push 100° F followed by bone-chillingly dry winters with temperatures falling to -20° F (and relatively little relative/absolute moisture). But all our homes are built of wood and the consequences are pretty drastic.

by exDM69 1y ago

DannyBee 1y ago

"Initial shrinkage is larger when drying from green wood" ? It's not - it's exactly the same as anything else. The wood doesn't know it's green. The calculator you gave is shortcutting it, and has an entire article in how they shortcut it the same way as anyone else, based on the swelling coefficients/etc, but assuming thickness is small enough to not matter. If your projects are outdoors, you will be affected by more than just humidity - UV will also have a significant effect on the properties of your projects :) The moisture transport is also not as simple as you are making it out to be, and has a not insignificant effect. See: https://gupea.ub.gu.se/handle/2077/54179 https://gupea.ub.gu.se/handle/2077/54179 https://www.mdpi.com/2076-3263/8/10/378 https://www.mdpi.com/2076-3263/8/10/378 https://www.sciencedirect.com/science/article/abs/pii/S1296207416304496 https://www.sciencedirect.com/science/article/abs/pii/S12962...

exDM69 1y ago
Yeah, the coefficients are the same but the initial moisture content in green wood is much higher than the wood will ever get to after seasoning, it won't suck that much moisture from the air (unless you're in a swamp or something). So the annual absolute change in millimeters is lower than from green to seasoned. I have my woodworking projects in temperatures ranging from -25C to +100C (sauna) and extreme humidity changes from near zero to 100% RH. It is a form of art to make wooden things survive that, and I don't always succeed.
kurthr 1y ago
Ummm, most wood starts at a much higher moisture content (50%-200% noting that this is as a percentage of fully dried so it can easily be over 1) than it will ever have after drying (typically 5-15%). Frankly, the idea that a piece of wood after initial drying was moving even an in/ft (eg "only" 8%) would be pretty shocking. Even good joinery won't deal with much more than a quarter of that ~2%.
- DannyBee 1y ago
  You missed my point, which is that initial drying is absolutely 100% not different than any other time. Wood, especially outdoor projects like the person is making, will definitely see states where the moisture content is as high, if not higher, than when the wood was originally dried. Also, most green hardwood starts at about 30%. No reputable lumber supplier is kiln drying hardwood that is 200% moisture content. That's crazy town. Even if they dried it super slowly, it would end up as mostly checked/warped garbage that they couldn't sell. Beyond that, wood is moving a lot, sorry you don't believe it, but its still gonna do it. Rather than say it's "pretty shocking", and dismiss it, care to present any studies that back up your assertion? I sent plenty, both in here and other comments. I'm not aware of any sourced, actual scientific research that says anything other than what i did, since I was careful to use cited figures from actual research studies, and not random pages on the internet about "wood movement" I think you are also assuming a lot about how it moves and what 8% radial swelling/shrinkage really means that isn't necessarily true. Also your point about joinery doesn't seem to make a lot of sense. While it's true that most joinery can't handle lots of flex, if everything expanded or contracted uniformly, it wouldn't be a problem. You seem to be assuming the opening will not expand the same as the thing going into the opening. It will. That is why you try not to mix conflicting grain directions in joints, and why you see so many joints that go out of their way to do that (IE 90 degree mated dovetail boards are not made by two conflicting grain directions, the pins and tails are made of the same grain direction that happens to mate at an angle) https://cad.onshape.com/documents/3e489410fcf65e1f0f82663d/w/eaa50df21f3410fa4bb63f91/e/2e8916bf9ccc18556d0dda51 https://cad.onshape.com/documents/3e489410fcf65e1f0f82663d/w... I made two tabs for you, one with a 25% transform and one without. Notice the opening gets larger when scaled. So would the mate. They would still fit fine. The same is true if you made a dovetailed box. It would just become a bigger/smaller box. I didn't bother to scale it differently for tangential vs radial but it wouldn't matter as long as the same scaling factors apply equally to the mate, and the mate is made the same way. As is true of most woodworking joints, on purpose. So the only issue is if (assuming 2% was the limit) the non-uniformness lead to >2% difference somewhere that mattered. All of this is also why wood glue has such expansion/contraction characteristics. if wood was only changing 0.1%, it wouldn't matter. So far i've seen a lot of doubt but nobody else actually seems to be bringing any real scientific rigor to that doubt, or saying some silly things. Please feel more than free, i'd love to see papers with real measurements that suggest something else.

ComputerGuru 1y ago

Yeah, the Midwest is cursed for this reason. Humid summers with incredibly high RH for being inland while temperatures push 100° F followed by bone-chillingly dry winters with temperatures falling to -20° F (and relatively little relative/absolute moisture). But all our homes are built of wood and the consequences are pretty drastic.