I posted a few days ago regarding bandsaw mills. I have decided to hire a portable mill and operator to cut up the logs i have this year. i have a few questions though.
the logs i want to saw are maple, walnut and poplar. they have been laying on the ground for some time now (not sure exactly how long but i can find that out if need be) and i’m worried they will start to decompose, or if they have already started. how long does it take for degeneration to begin? i wont be able to get them sawed up for a few weeks yet so i would like to know what to expect.
My next question refers to drying the lumber.
The gentleman i spoke to who will be cutting up the lumber told me i have to kiln dry the lumber. i had planned on simply storing it properly in my shop to let it air dry on its own. i know this will take a while but i dont mind. i am going to be using this wood for furniture. is this feasable? i would otherwise kiln dry it but it becomes costly for me to ship it out to the kiln for drying and the kiln charges $.70 per foot. if i do air dry it should it be done indoors or outdoors?
Thanks for the feedback!
Replies
To make it fit for use as furniture in a modern, centrally heated house wood needs to be properly dried and unless you can wait several years, then you need to get your wood kiln dried.
The essential point about kiln drying is this, to give up its moisture wood needs to be held at an elevated temperature while the water vapour released is extracted from its surroundings. Pay the extra and get it kilned, it's worth it
john
Can't imagine there's any reason you have to kiln dry that lumber. It can be air-dried either inside or out. You have plenty of time to do the research on various ways to accomplish that. Here's a Google link to start with, and various ag extensions have printed info:
http://www.google.com/search?sourceid=navclient&q=lumber+air%2Ddrying
As to decomposition, it's started already to different degrees for the different woods, but whether it's significant is another story. Can you get a chainsaw and cut a couple rounds to see what's going on inside? Would be interested to know from the experts here at Knots what they think the possibilities would be of you getting some nice spalted maple out of what you have.
I have some Alder that's been down for about a year. The outside layers are a little soft, but the inside is nice and dry and no signs of decay. Alder pretty fast to decompose.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
I believe outdoors would be better. It's liable to dry too quickly indoors in the winter, leading to surface checking. Outdoors, covered, with some air circulation, it will dry more slowly. Even with the wood starting out green it won't get decay in the winter because of the cold.
You'll lose a lot of wood by end checking if you don't seal the ends.
I'd recommend reading up on the details (stacking, stickering, temperature, humidity, etc.) in a good reference. Hoadley's Understanding Wood is one good source. There may be good ones on the web, now, too.
Well, in view of what the others have said I guess it all comes down to how long you can wait for the wood to dry. Air drying outside is ok if the humidity outside where you live is approx the same as the humidity where the furniture is going to be used.
John
The air drying can be followed by stacking the lumber inside in a drier environment to further bring down the moisture content (MC). The advantage to air drying is that you can avoid the nasty kiln drying problems such as case-hardening.
See this quote from Woodweb's knowledge base:
It would seem that wood put up now could be pretty close to 25% by next summer. At that point, a solar aspect could be added to the drying arrangement (outside) and probably bring the lumber down to where it's desired for building furniture.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
All the wood I use is kiln dried and I have not had any problems with it. What is this 'case hardening' you refer to?
25% MC is a long, long way from what is required for indoor furniture. Unless the temperature of the wood is raised significantly (kilning) then the rest of the drying process is going to take many months even in a drier than usual indoor atmosphere.
John
Casehardening is the state all wood is at after drying no matter which way you dry it. The confusion is two fold: 1) most people don't know how to properly take prong tests which is the method to determine the degree of casehardening and 2) is the degree sever enough for the project you are working on for it to show up.
What actually happens is that a the start of drying the outside dries first and the center does not allow the ouside to shrink, which stretches the outside. As the inside dries, the stretched outside does not allow the inside to shrink and you end up with mechanical stresses in the wood. When this wood is sawn down the middle it cups. To eliminate casehardening you inject steam into the kiln after the lumber is dried properly.
Many people think that air-drying and solar drying avoids these stresses because of the slow nature of air-drying and the cyclic nature of solar drying. However, air-dried material experiences sever conditions which does produce high stresses but then there are times the conditions are mild to wet so the total drying takes a long. With solar drying, the cyclic behavior is no different than in a commercial kiln just over long times. You see, in a commercial kiln the fan is reversed every six hours. To understand how this reversing is the same as solar drying realize that the side which the air exits the stack is more humid than the entering side. When the fan reverses the entering side which is dry now becomes the exit side which is more humid. It is humid enough so that the wood absorbs water and actually swells. temporarily releiving stresses - not different than solar drying. It does not take much loss od water to develop high stresses resulting in csehardening. The final % loss is enough to create casehardening.
Well said jim.
There are very few people that frequent this forum with extensive knowledge about drying lumber. Stanley Neimiec, Jon Arno and some loose cannon by the name of Jim Fuller.
If this Jim is Jim Fuller he knows his stuff.
For a method of air drying lumber I wrote an article that appeared in Fine Woodworking #151, October, 2001. Back issues are available through the links at the top of the page.
Lee
Lee Grindinger
Furniture Carver
Lee,
Am I that unpredictable? Thanks for the compliment.
Jim
Jim,
I am approaching the end of drying 500 bd feet of 8/4 walnut in my "homemade" DH kiln.
All is going well; i was careful with the rate at which i extracted water and did not exceed the SDR of 3.3% per day. After 44 days i was at 16% MC.
I stopped at that point to let things settle down; now i'm running it again to get to 10%.
BUT... i pulled a piece to see how things were going and it all looks beautiful. However, i cut several wafers and checked for "case-hardening"; and it is already pretty sever. the prongs have crossed each other.
I realize this is not the case-hardening that Hoadley describes.
I'm assuming the cause is 8% MC at the surface and 16% MC at the center; thus setting up stress.
When i get the center to 10% or so.... will i be able to heat the kiln to 180 degrees and pump it with water vapor to relieve the stress in the wood... or will i just have to live with the results?
Thanks,
David Wheeler
[email protected]
You addressed your question to Jim but perhaps I can help.
For a DH kiln you want to get your MC down to about 6% and hold it there for a period of time for equalization. At lower temps, around 120, I'd give 8/4 a week and a half or more. If you're running up around 180 give it 3 or 4 days. The longer the better here, up to a point. Equalize with the EMC at 4% or slightly higher. Check your MCs throughout the load, not just in one spot.
After equalization check for case hardening with the fork test.
If the lumber needs conditioning raise the EMC to 11%. The duration for this process depends on temperature and the degree to which the lumber is case hardened. Conditioning could be done in as little as 12 hours, or it could take several days depending on the Temperatures. Do fork tests on samples throughout the load to determine when the conditioning is done.
You could probably use "Dry Kiln Operator's Manual" It's the bible for kiln operation. It's available through...
The Hardwoods Research Council.
P.O. Box 34515
Memphis, TN 38184-0518
901-377-1824
Call the number to order one, last I heard they ran $30 plus $7 shipping.
Lee Lee Grindinger
Furniture Carver
3.3%/day is a safe rate for 8/4 walnut.
It is casehardening as Hoadley describes but is not the time to evaluate it now.
If it was because the shell was 8% and the core was 16% only, the prongs would be bowed outward not inward. Since they bowed inward, this indicates casehardening.
Follow Lee's advice and equalize to an average MC of 6% at an EMC of 4%. 180F is fine if you can acheive it. Then as Lee says condition with an EMC of 11%. If you do not have a steam source and the floor of the kiln is hot pouring buckets of water on the floor will raise the EMC some - maybe 11%. 12 hours is plenty for walnut; any longer, the stressses are not being relieved, only moisture is being gained. If the lumber has been conditioned excessively let the cross scetions used for the prong tests sit over night on your workbench so that the moisture gradient is flattened before evaluating them.
Use the 2-sample prong test I mentioned above. The "Dry Kiln Operators Manual" does not mention how to cut them nor how to evaluate them. The book I suggest to get is "Wood Drying Essentials" a new publication written by some loose cannon who is looking for a printer.
Jim, I have the 1991 revised edition of "Dry Kiln Operators Manual" and it gives a quite thorough description of the prong test...how to cut them and evaluate them (pages 126 and 127) as well as waiting periods for casehardening evaluation (page 215).
I think it would be great if your book addressed DH dryers and schedules as well as alternative dryers such as solar and vacuum which "Dry Kiln Operator's Manual" treat as a sidebar. I believe that there is a lot to be added to the wonderful content in "Dry Kiln Operator's Manual" but it's still a great resource.
Good luck finding a publisher. John Kelsey (Cambium Books) might be interested and I know Ellis Walentine still dabbles in publishing special interest books. You might run your idea past them.
Lee Lee Grindinger
Furniture Carver
Prospero has so screwed my account that the e-mail at the top will not work. If you need to e-mail me go through my website.
Lee,
After being at the FPL for about a year, I had this same discussion with a person that had been in the Forest Sevice for more than 20 years and we afterwards agreed upon the following.
While the figure looks like the prongs are cut such that they are 1/3 of the board thickness it does not state so. I have seen people cut them all sorts of thicknesses and lengths. It can be shown that prongs react quite a bit differently when cut either 1/4 of the board thickness or 1/3 of the board thickness.
Also, the "DKOM" does not state how long the prongs are. Since the prongs do not bend but bow, the prongs don't move twice as much when the prongs are twice as long but 4 times as much. When they are 3 times as long, they respond 9 times as much. The length of the prongs is critical. A prong test that is 3 inches long will seem not to move much while a prong test with the same stress level that is 9 inches long will cross and seem to indicate much higher stresses. The prongs of both tests will curve the same and trace out curves matching the same size circle.
While page 215 in"DKOM" mentions waiting 24 hrs it still does not mention prong thickness and length nor how the prong response is affected by them.
I get into this in detail including comparision of air-drying, DH, solar and conventional kiln drying. In fact, a discussion here on Knots a few years ago on the comparision of air-drying vs kiln-drying is what got me into writing the book. The book goes into how water is lost, drying stresses and more including a special chapter on odd ball drying situations. Things loose cannons enjoy.
Jim and Lee,
Thanks for the quick responses.
For clarification... my DH kiln runs about 115F to 120F degrees while drying... any higher and my DH ceases to function.
However, I'm assuming i can raise the temp to 180F or so for conditioning... the DH will no longer be a factor. I haven't conditioned any wood yet. I figure i can induce moisture via a wallpaper steamer.
My primary source of info has been "Drying Hardwood Lumber" by Denig/Wengert/Simpson.
In no way am i a pro at this; i'm just a ww that has access to green lumber whenever i want it; but need to find a way to get it workable w/o ruining it... like i did with my white oak. I was very careful with my first load of 8/4 walnut... i made sure to stay at least 25% below the maximum SDR. After the first week or so my DH wouldn't be able to exceed the SDR anyway.
Okay... i will get the book suggested by Lee and be patient. To go from 16% to 6% in my kiln will take a while. But since i already have CH, it will probably only get more sever.
Thanks
Here is a picture of to accompany Jim's explanation (note the prong-test piece on the right, of which Jim spoke):
View Image
Pic is from Hoadley's "Understanding Wood", page 149.
This is a condition that must be prevented in air-drying, as there's no option to condition it out at the end of the process. This means not drying it too fast early in the process, hence the advisability of stacking outdoors.
I have not been so lucky as to avoid case-hardening in kiln-dried lumber, and it's very frustrating to have a piece of stock leave the table saw during a ripping operation showing that fatal curve that means it'll be worthless for my purposes. Doesn't happen often, now that I've changed where I buy lumber, but still.... We've had a couple of posts here at Knots from people who've sent their self-milled lumber off to a poorly-operated kiln and it's come back with problems. At least with air-drying in your backyard (followed by inside) it's under your control.
As to bringing the outdoor-dried lumber down to the final low MC for building, that can be done indoors. If I ever have access to trees that I'd like to mill, I envision a large outdoor drying stack, from which I would select portions every few months to bring inside and stack for final drying. Of course, it'll take a bigger shop than the one out there now! Adding a solar option here in the Northwest isn't likely to work, and I don't fancy myself building a drying shed with the mechanical stuff required to dry and vent.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 9/17/2003 12:58:16 PM ET by forestgirl
So, to sum up, air drying does NOT prevent case hardening. It would seem from what is being said that the best way to avoid it is to have the wood kiln dried by a competent operator who will inject steam when the drying is complete
It would also seem that to avoid bad cupping on resawn board one should buy one's wood in the thicknesses required if possible so as to avoid having to resaw. I would expect a 2" board to cup if resawn to 1" no matter how carefully it had been dried. The only variable would be the degree of cupping
Although I am in the UK I normally only use kiln dried American hardwoods, mostly white ash, and have found it to be easy to work and very stable
John
John, air drying properly does prevent case-hardening, as by definition, if the wood becomes case-hardened during the air drying process, it will stay that way and show up when milled. ["This is a condition that must be prevented in air-drying, as there's no option to condition it out at the end of the process." -- from my last post]
There's is plenty of documentation available on how to air dry properly, and no doubt millions of BF of lumber have been cured this way over the centuries, up to and including today. If I recall correctly, the originator of this thread was asking about a statement made by the portable mill owner that the lumber must be kiln-dried. The answer is, "No, it does not."
Kiln drying does, by the nature of the process, induce case-hardening, which is then "adjusted out" by another process. Nothing wrong with this. As I'm sure you know, kiln-drying is a complicated process that involves continuous monitoring and adjustments of temperature and humidity throughout the drying process. It's a fine line between allowing some case-hardening but not enough to create severe problems such as honeycombing and checking. There are plenty of good kiln operators around, and also a number of smaller operators who aren't so skilled and careful.
As to the comments about resawing and proper selection of lumber, I was not referring to resawn stock, I was referring to ripped stock (e.g., ripping a 2-inch width of board off of a 6-inch wide piece of stock).forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Actually, all air-drying produces casehardening, just to what degree. It is impossible to dry any material without a moisture gradient at ambient air pressure.
You mention ripping 2" off 6" wide board and casehardening in the same sentence. Casehardening is not related to bow in the longitudinal direction. While a small amount of drying stresses do develop in the longitudinal direction it is insignificant. The problem of longitudinal bowing is related to abnormal longitudinal shrinkage caused by reaction wood and is unavoidable with wood containing reaction wood. It can be reduced by injecting steam at a higher temperature than the wood was dried at.
The proper way to perform the prong test is to cut two cross-section from each board you want to test. Each of the prongs of one test should be 1/4 of the board thickness. The other one should have prongs 1/3 of the board thickness. Both sets of prongs should stay straight. using only one prong test does not give the needed information. I have done a lot of work on prong tests. There are about a dozen books and manuals that tell how to perform the prong test. They all disagree on at east one aspect or another. Some don't tell how to cut it. Some don't tell what results you want.
Edited 9/17/2003 4:04:10 PM ET by jim
Perhaps related, perhaps not... I have a large, hanging cabinet, that takes at least two normal-size people to handle, but better with four. Years ago my father attempted to remove it from a wall by himself. Whack. Anyway, it sat around for years (50 or so) badly warped. Given it was built by my grandfather (AKA Poppie) I really wanted to make use of it, but I couldn't, for the life of me, short of disassembling it, figure out what to do. Finally I checked with an individual who restores furniture. Mark thought about it for a while, then suggested a linseed oil soak. It worked.
View Image
My limited experience in drying wood (large timbers) suggests that, besides painting the ends, slopping the piece (with some frequency) with a hot linseed oil/turp mix seems to help the tendency of the pieces to warp and check.
Jim, point taken about incorrectly using "case-hardened" in reference to a logitudinal defect. I'll have to think through that one better.
With reference to the definition of the term "case-hardened" -- I'm using Hoadley's book as a reference, and he specifically defines case-hadening as the state of wood that is in Stage III of drying, wherein the core is below fiber saturation point, tries to shrink, and is in tension (being "held outward by the shell"), which then pulls the shell into compression.
This is well past the state of basic moisture gradient that takes place during the earlier stages of drying. I think it's important not to confuse the state of being case-hardened with simple moisture differences within the wood that occur during the drying process.
The point being, with regard to air-drying, that if done properly the wood would never reach Stage III (core in tension, shell in compression) and therefore would never be case-hardened and present the accompanying defects, such as honeycomb checks (internal).
According to his section on kiln drying, the lumber is allowed to develop "some case-hardening" but "not severe enough to develop honeycombing." forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Any wood drying questions I have I direct to http://www.woodweb.com cutting and drying forum. There are years of experience there and they can help find sawyers and kilns reasonably since most of them run one or the other. Dr. Gene Wengert is an expert on the subject and moniters the forum.
Tony
Thanks for the link. Some place else that I won't mind getting lost.
Who ever invented work didn't know how to fish....
While casehardening does not become evident until the last stage of drying, casehardening is initiated in air-drying in the "first stage " of drying by the very fact that the shell is restrained by the nonshrinking core and is stretched. It does not take high temperatures to create casehardening nor EMC's down around 4%. A clear spring day with a mild breeze is sever enough to cause high drying stresses and setup casehardening. The most critical stage of drying is the first. It is when all the damage is started and casehardening initiated.
I agree you do not have to kiln dry wood to have no problems with it - depending on how the wood will be machined and where it will be used.
As a cabinetmaker, carver and research scientist in wood drying I have air-dried and kiln-dried and have taken measurement on lumber pertaining to drying stresses and related topics, I am intimately related to this subject.
Edited 9/18/2003 8:28:36 AM ET by jim
Jim, I think we'll have to agree to disagree on the definition of case-hardening. As I only have one research source at this point, I'm going with Bruce Hoadley's definition of it as being present only in Stage III of the drying process. His technical definition, which presents measurable parameters for the condition, makes sense to me, and I assume it's universally accepted as he is a professor of Wood Science and Technology with a doctorate from Yale, and a well-known author.
Case-hardening, by this definition, is a specific state of stress in the wood, wherein the core is in tension, pulling the shell into compression. This is a reversal of the stresses present in Stage II. My scientifically-inclined mind does not deal well (in this situation) with terms such as "initiated" and "evident." Case-hardening either "is" or "is not" as verified by the physical state of the wood. Obviously, it has to go through Stages I and II to get to Stage III, but it still isn't case-hardened until it gets to that specific state of reversed stresses, a state that will not be reached in proper (albeit, slow) air-drying.
BTW: During Stage I, there are no stresses in the wood. Stage I is the state of the wood when the moisture is above the fiber saturation point throughout, and free water only is being lost from the surface. The stage you describe above is Stage II where the core is in compression (above FSP) and the shell in tension (below FSP)
I have no doubt that you are exceptionally skilled in the process of drying wood and know infinitely more than I do about it. I am simply trying to understand and get specific about the actual definition of this "state" that lumber achieves in certain environments. Confusing the actual state of case-hardening with the beginning of Stage II drying is like confusing rapidly dividing cancerous cells in a tumor with a normal cell division. Obviously one cannot exist without the other, but they are not the same things.
forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Edited 9/18/2003 12:34:54 PM ET by forestgirl
gecko
You may be in luck. If these logs have been down between 6mo. and 2yr you may have some nicely spalted maple. This should also have helped you on the walnut as letting it lay a little while evens the color out making the sapwood look more like the heartwood. Same as steaming before kiln drying but without imparting the bluish tint. I don't know what the time may have done to the poplar, if anything, but I doubt it has hurt it any. Wood dries very very slowly in log form. I would not trim the ends of the logs before sawing even though they may be checked in a ways. Leave it there and the lumber is not apt to check any further in. Trim it off after it's dry as you need it. You may want to dry the lumber outside untill it's down to 20%-25% then move it indoors and when it's down to about 15% put it up in the rafters of the garage or in an attic untill it's down to 8%-10%. This whole process may take three or four years (maybe more) depending on your location.
Hope you have some good usable stuff.
Rich
The Professional Termite
Hi Gecko,
I had some red oak logs sawn with a bandsaw mill a couple of years ago. I was extremely pleased with the results. The logs had been sitting under a tarp for between 3 and 5 years, and some areas had minor rot, which i suspect started while the trees were still standing. I beleive maple and walnut weather fairly well, but I don't know about the poplar, it's definitely not an outdoor wood.
I air dried the wood outdoors under a heavy tarp to keep them dry and weighted down to keep them flat. Make sure the base is level and flat. I ended up with about 25% checked beyond use or with dry rot or some other problem that created firewood. I inquired with the guy who planed the wood for me about kiln drying and he said to let it dry for about a year and it would be fine. (Note this was in Northern Wisconsin so your results may vary.) I bought a wagner moisture meter and tested the wood before having it milled, and it was about 10% MC, so i was happy. If you want the wood faster than one year you might want to look into kiln drying.
I suspect your sawyer was trying to push some work his friends way to keep his costs down!!
Matt
FG, you may want to go here: http://www.fpl.fs.fed.us/documnts/FPLGTR/fplgtr117.pdf
It is a Forest Service publication on Wood Drying and is a primary source for Hoadley's book.
I describes two types of casehardening. One is "transverse" (across the board) and the second is "longitudinal" (length of the board).
QUOTE
Occasionally, the transverse casehardening test shows no
stress, but the lumber bows immediately when resawn or
ripped. Bowing or curving is caused by longitudinal stress
resulting from either longitudinal tension set in the surface
zones (similar to transverse casehardening) or longitudinal
shrinkage differentials caused by tension wood.
END QUOTE
Edited 9/19/2003 6:33:47 PM ET by Howie
Thanks for the link, Howie, but it's coming back "Page Not Found." Maybe a server glitch, I'll try later.
So does that mean that I may have been correct in referring to my ugly ripped board as being case-hardened? Ooooo, cool. LOL.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
FG, try it now. The period I put at the end of the sentence caused the problem. Sorry.
Oooops, I usually notice those things! Sorry. I'll give it a try now. Cheers.forestgirl -- you can take the girl out of the forest, but you can't take the forest out of the girl ;-)
Answer me this -
I live near Houston and the humidity here tends to never go below 90%. Today it is 100%.
I keep my kiln and air dried lumber (Cherry, Walnut, Oak) out in a closed shed with no AC. Some of it has been out there for over 10 years. It's layed flat and stickered in the shed.
Yet, the lumber works fine and hardly ever warps or bows (I hand pick all my stuff to get as close to quarter sawn as possible). I never let the lumber 'condition' after bringing it in to my shop. I do however plan for expansion and contraction when building larger pieces. I only run the AC here in my shop on the very hottest days.
So, my question is this - Why am I not having trouble with the lumber? For instance, a couple weeks ago I ripped and cross cut a 2x6x6' air dried walnut board into 2x2x2' pieces. After jointing with one pass on each side I stored them here in the shop. After 2 weeks the pieces are still straight. The lumber sands well and take a finish well.
ps - i keep the exotic stuff (cocobolo, rosewood, etc) here in the shop. Never had any problems with it but I only make smaller stuff with it.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Planewood,
You say you take only one pass on each side, how heavy? If it is not much that is part of the answer. Remember I mentioned the thickness of the prong test is critical for the results. You're not changing the stresses much by taking a light pass and you are taking the same off each side, keeping it all balanced.
Second, you are letting it sit in your shop for a few weeks letting it equilibrate a little.
Third, You are ripping, not resurfacing heavily or resawing. As mentioned earlier, bowing after ripping involves longitudinal stresses usually caused by reaction wood which has high longitudinal shrinkage. Not drying stresses.
From your wording, I assume you do not heat or air condition your house which I also assume is the primary destination for your work. This more or less keeps the MC constant which restricts any movement. With little change in the MC most of the change is just on the outter surface. So the bulk of the wood has no moisture change. You also mention you use almost exclusively quarter sawn material which cups even less than flat sawn material. Not everyone wants to only use quarter sawn material nor does the primary destination remain at a constant EMC as in your situation. Things would be easier if so. Enjoy your ideal setup.
Edited 9/21/2003 7:05:32 PM ET by jim
Jim -
Yes, my house has AC and heat as do all my kids houses. My house is full and I'm now working on filling up my kids houses with my creations. My gosh, one would die down here without AC!!!
And, that was just one example. The point is, I have never experienced ill results with lumber having a high MC. Like I said, down here one MUST plan for expansion and contraction due to constant humidity changes.
I think that once it has cured, that later fluctuations in MC has little effect on workability or appearence.
I generally reject boards where the grain does not run the full length. I don't buy quarter sawn lumber, but what I select is about as close as u can get.
One would think given the discussions here that if your lumber was not at 8% MC, that you were doomed to failure. I don't find that to be the case.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Some people like flatsawn grain which does cup and is more pronounced in wide boards. You mention ripping to very narrow strips. You also must do a good job of designing for movement. Not all projects can accomodate such designing. Count yourself lucky with having no problems.
Edited 9/22/2003 9:50:48 AM ET by jim
Jim,
I'm struggling to get my mind around this. In my case my 8/4 walnut is dried to 16% MC internal; the "outer shell" is around 7%. Obviously this load is not "done". But when i take a prong test... 1/4 and 1/3 wafers and 8" long.... they crossover after 24 hours.
I thought they would do this because the outer shell is restricted from compressing due to the inner core which has yet to shrink completely. So, as i was thinking, when the restrictive inner core is removed via the prong test the outer core would react "violently" and close up.
Am i thinking correctly? and is this process "case-hardening"?
So then, when the load is "done" and at 6% MC at the inner core... as the outer core takes on moisture to equalize with the environment, it will be unable to expand because the inner core will be restricting it from doing so. In this event, adding moisture (conditioning) will not relieve the inner stress... but make it worse. Whereas conditioning in my first case WOULD relieve the stress, wouldn't it?
Am i all screwed up in my thinking?
You're on the right track. You do have casehardening and when you add moisture during conditioning, the shell will try to expand and can't. Now, just like when the shell was drying and trying to shrink but could not, it stretched because of something we call mechano-sorptive strain which occurs during MC change during the presence of high stresses. Now you have a change of MC and the presence of high stresses again and mechano-sorptive strain occurs in the opposite direction so the shell compresses. This is what stress relief is.
The only thing you missed was the second occurence of mechano-sorptive strain.
Edited 9/22/2003 9:55:20 AM ET by jim
You mentioned a book you researched. Is it available?
-David
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