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David Marks And Loose Tenons - Revisited
George:
I never saw your reply below, to my comments until I did a google search on the thread. For some reason, my ISP dropped some of the posts from that thread - maybe from other threads for all I know. I've pasted in my last comments and your reply to them below and will insert my current comments within. George said... You are incorrect. The fibers will expand and contract when the moisture gets to them, and at the same rate, less compression set. You may slow the arrival with occlusive finishes, but wood loves water and will find a way .. This does not make sense George. It does to wood technologists. RH correlates directly to moisture content. Yes it does and that simple corelation makes sense to everyone, not just to wood technologists. The reason I say it makes not sense is that your statement above does not take into consideration the constraint placed on the tenon by the mortise. I completely ignores the mechanical principle at work in this joint. Wood fibers that are constrained can only absorb water to the point that they equal the force placed on them by the joint. At that point they effectively reach their saturation level. Wood does not continue to obsorb moisture until it reaches the point that its moisture content is equal to the surrounding air, it absorbs it to a maximum it can hold and that maximum is limited by the cell's ability to contain that moisture. Constrain those cells and they are capable of holding less moisture. Incorrect again. The fibers adsorb moisture at the molecular level, binding to the cellulose. There is a lot of air left inside any board, indeed, inside the cells themselves, which spaces are shrunken by the inexorable gathering of moisture, though they do compression set - they don't return to full expansion - which condition exacerbates the one caused by shrinkage of the fibers themselves once the wood begins to seek EMC with lower RH. No - very correct. Whether the fibers absorb moisture at the molecular level (not true), or at any other level, they can only absorb as much as they are allowed to hold by the mechanical constraintes placed on them. A tight joint will not absorb as much moisture as a plank laid out in the same high RH environment. What you say above about absorbing moisture and releasing it above is otherwise true, but it does not address the mechanical constraint. Nor does the article. Wonderful, well-documented stuff here http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm to read. Start with chapters 2 and 3. Yes - excellent documentation, and thanks for the link. But... it does not really point out anything that has not been already accepted and understood throughout this conversation, and it does not deal at all with the exception I am talking about which is a mechanically constrained joint. -- -Mike- |
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"Mike Marlow" wrote in message ... George: I never saw your reply below, to my comments until I did a google search on the thread. For some reason, my ISP dropped some of the posts from that thread - maybe from other threads for all I know. I've pasted in my last comments and your reply to them below and will insert my current comments within. No - very correct. Whether the fibers absorb moisture at the molecular level (not true), or at any other level, they can only absorb as much as they are allowed to hold by the mechanical constraintes placed on them. A tight joint will not absorb as much moisture as a plank laid out in the same high RH environment. What you say above about absorbing moisture and releasing it above is otherwise true, but it does not address the mechanical constraint. Nor does the article. Sorry, but until water is no longer influence-bonded to the cellulose (read FSP), and until you squeeze all the air out by collapsing the cells and tracheids completely, you are incorrect. Since both are not possible... draw your own conclusions. Wonderful, well-documented stuff here http://www.fpl.fs.fed.us/documnts/fp.../fplgtr113.htm to read. Start with chapters 2 and 3. Yes - excellent documentation, and thanks for the link. But... it does not really point out anything that has not been already accepted and understood throughout this conversation, and it does not deal at all with the exception I am talking about which is a mechanically constrained joint. |
#3
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"George" george@least wrote in message ... "Mike Marlow" wrote in message ... George: I never saw your reply below, to my comments until I did a google search on the thread. For some reason, my ISP dropped some of the posts from that thread - maybe from other threads for all I know. I've pasted in my last comments and your reply to them below and will insert my current comments within. No - very correct. Whether the fibers absorb moisture at the molecular level (not true), or at any other level, they can only absorb as much as they are allowed to hold by the mechanical constraintes placed on them. A tight joint will not absorb as much moisture as a plank laid out in the same high RH environment. What you say above about absorbing moisture and releasing it above is otherwise true, but it does not address the mechanical constraint. Nor does the article. Sorry, but until water is no longer influence-bonded to the cellulose (read FSP), and until you squeeze all the air out by collapsing the cells and tracheids completely, you are incorrect. Since both are not possible... draw your own conclusions. Sorry George, but again, your response does not speak to the point in question. Mechanical constraint poses different influences on a piece of wood than does the absence of it. -- -Mike- |
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"Mike Marlow" wrote in message ... "George" george@least wrote in message ... "Mike Marlow" wrote in message ... George: I never saw your reply below, to my comments until I did a google search on the thread. For some reason, my ISP dropped some of the posts from that thread - maybe from other threads for all I know. I've pasted in my last comments and your reply to them below and will insert my current comments within. No - very correct. Whether the fibers absorb moisture at the molecular level (not true), or at any other level, they can only absorb as much as they are allowed to hold by the mechanical constraintes placed on them. A tight joint will not absorb as much moisture as a plank laid out in the same high RH environment. What you say above about absorbing moisture and releasing it above is otherwise true, but it does not address the mechanical constraint. Nor does the article. Sorry, but until water is no longer influence-bonded to the cellulose (read FSP), and until you squeeze all the air out by collapsing the cells and tracheids completely, you are incorrect. Since both are not possible... draw your own conclusions. Sorry George, but again, your response does not speak to the point in question. Mechanical constraint poses different influences on a piece of wood than does the absence of it. Mike, you need to think. You cannot compress a tenon into a mortise so tight as to remove all the air from the tenon. Period, end of sentence. Since there is available air space, water, an incompressible, will expand the cellulose to compress the air spaces. This is so basic, I don't understand what you might be thinking. |
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"Mike Marlow" theorized incorrectly: Wood fibers that are constrained can only absorb water to the point that they equal the force placed on them by the joint. At that point they effectively reach their saturation level. Mike- think about it like this- wood compresses. if it is compressed very much, it crushes. once crushed, it will not return to it's original size. water causes wood to expand. the force exerted by the water is very high (remember hydraulics?). given enough water and a tight enough joint, the expansion force of the water exceeds the crush limit of the wood. remove the water and you have a loose joint. items that will have to endure repeated wet/dry cycles need to be held together without relying on constrained jointery. |
#6
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"bridger" wrote in message ... "Mike Marlow" theorized incorrectly: Wood fibers that are constrained can only absorb water to the point that they equal the force placed on them by the joint. At that point they effectively reach their saturation level. Mike- think about it like this- wood compresses. if it is compressed very much, it crushes. once crushed, it will not return to it's original size. water causes wood to expand. the force exerted by the water is very high (remember hydraulics?). given enough water and a tight enough joint, the expansion force of the water exceeds the crush limit of the wood. remove the water and you have a loose joint. items that will have to endure repeated wet/dry cycles need to be held together without relying on constrained jointery. You are assuming that expansion of the wood in the mortice will crush the tenon locally..It would seem to me it might deform a little but basically this would be within the "elastic limit" of the wood. Bare in mind wood is a very complex material regarding it's engineering properties and has a different moduli depending which grain direction you are considering .. Getting back to the crushing situation again from my standpoint and even considering the preceeding and even realizing that wood is not a homogenious material iof it cannot move in one axis I would at least some movement in another unconstrained axis.resulting in a reduction of pressure [stress]. Again considering the "hydraulic" aspects the pressure in the joint is pretty much the same as atmospheric and always will be regardless of how well the finishes seal the wood . mjh |
#7
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"George" george@least wrote in message ... "Mike Marlow" wrote in message ... "George" george@least wrote in message ... "Mike Marlow" wrote in message ... George: I never saw your reply below, to my comments until I did a google search on the thread. For some reason, my ISP dropped some of the posts from that thread - maybe from other threads for all I know. I've pasted in my last comments and your reply to them below and will insert my current comments within. No - very correct. Whether the fibers absorb moisture at the molecular level (not true), or at any other level, they can only absorb as much as they are allowed to hold by the mechanical constraintes placed on them. A tight joint will not absorb as much moisture as a plank laid out in the same high RH environment. What you say above about absorbing moisture and releasing it above is otherwise true, but it does not address the mechanical constraint. Nor does the article. Sorry, but until water is no longer influence-bonded to the cellulose (read FSP), and until you squeeze all the air out by collapsing the cells and tracheids completely, you are incorrect. Since both are not possible... draw your own conclusions. Sorry George, but again, your response does not speak to the point in question. Mechanical constraint poses different influences on a piece of wood than does the absence of it. Mike, you need to think. You cannot compress a tenon into a mortise so tight as to remove all the air from the tenon. Period, end of sentence. Since there is available air space, water, an incompressible, will expand the cellulose to compress the air spaces. This is so basic, I don't understand what you might be thinking. Going back to my original point - I stated that while yes, the tenon will swell some with higher humidity, so will the mortise, and the mechanical constriction placed on this joint will serve to limit the expansion from changes in humidity. This is not to say that the joint members will not take on the moisture, but that they will not take it on in the same manner as a plank laying unencumbered in the same environment. My point was in response to the number of posts which proclaim "explosions" of MT joints. This simply does not happen on a regular basis and there is more to wood and its reaction to its environment than simple moisture levels. -- -Mike- |
#8
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"bridger" wrote in message ... "Mike Marlow" theorized incorrectly: Wood fibers that are constrained can only absorb water to the point that they equal the force placed on them by the joint. At that point they effectively reach their saturation level. Mike- think about it like this- wood compresses. if it is compressed very much, it crushes. once crushed, it will not return to it's original size. water causes wood to expand. the force exerted by the water is very high (remember hydraulics?). given enough water and a tight enough joint, the expansion force of the water exceeds the crush limit of the wood. remove the water and you have a loose joint. items that will have to endure repeated wet/dry cycles need to be held together without relying on constrained jointery. I realize I'm speaking a bit of heracy here, but think about the large number of MT joints we are surrounded by on a daily basis. How many of those do we find loosened by humidity? By racking, as in a chair that gets rocked in, sure, but by simple humidity? We just don't find that to be a huge problem. While I agree that wood compresses and crushes, it takes significant pressure to do this. My point is that the mechanical constraints caused by the joint itself make normal humidity cycles unable to consistently cause this type of pressure. We're not talking about putting the joint under water here, we're talking about what furniture is exposed to every day. I have personally brought furniture home from the Orient where humidity levels are monsterous, and some of that came back to the States, to Utah where humidity is near zero. No problems. That same stuff then made it across the country to NY where humidity does vary considerably throughout the year. Still tight as the day I bought it. Don't misunderstand what I'm trying to say here - I'm not arguing that tight jointery alone is suffiecient for long term survival of the joint, such that glue would not be necessary. I started this thought in response to the posts about humidity causing MT joints to explode. -- -Mike- |
#9
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"George" george@least wrote in message ... Mike, you need to think. You cannot compress a tenon into a mortise so tight as to remove all the air from the tenon. Period, end of sentence. That's correct. I never implied it could be done. Since there is available air space, water, an incompressible, will expand the cellulose to compress the air spaces. To some point, but we're talking about humidity here George, not water under pressure. -- -Mike- |
#10
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"Mike Marlow" wrote in message ... "George" george@least wrote in message ... Mike, you need to think. You cannot compress a tenon into a mortise so tight as to remove all the air from the tenon. Period, end of sentence. That's correct. I never implied it could be done. Since there is available air space, water, an incompressible, will expand the cellulose to compress the air spaces. To some point, but we're talking about humidity here George, not water under pressure. Mike, you're starting to change your tune now, so I assume you've finally caught on to the fact that moisture changes within a M/T joint, and can cause compression sets to the fiber which will become gaps later as the joint dries. The joy of the joint, as mentioned way back, is that it holds mechanically even when loose in the load direction, when pinned to keep the shoulders registered against the face of the mortised piece, it even survives the other five load directions when glueless. As to your latest - once again your knowledge base is too narrow. Man has been pouring water onto wooden wedges to break blocks from quarry walls for thousands of years. |
#11
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In article , "George" george@least wrote:
As to your latest - once again your knowledge base is too narrow. Man has been pouring water onto wooden wedges to break blocks from quarry walls for thousands of years. Pouring water directly onto a piece of wood is a bit different from exposing it to atmospheric humidity, don't you suppose? -- Regards, Doug Miller (alphageek at milmac dot com) Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time? |
#12
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"Doug Miller" wrote in message . .. In article , "George" george@least wrote: As to your latest - once again your knowledge base is too narrow. Man has been pouring water onto wooden wedges to break blocks from quarry walls for thousands of years. Pouring water directly onto a piece of wood is a bit different from exposing it to atmospheric humidity, don't you suppose? Only if I didn't understand wood. I heartily recommend the study of the material whose name is in the title of this group to you. The incompressible fluid replaces the air, then the adsorption at the molecular level produces the rest of the hydraulic force to split. This is what happens to wood with humidity cycling. It adsorbs moisture, bonding at the molecular level. Whether or not there was expansion of the fibers themselves was the original bone of contention. If you're in the temperate zone you can get some extra oomph by waiting for nighttime and the freeze.... |
#13
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In article , "George" george@least wrote:
"Doug Miller" wrote in message ... In article , "George" george@least wrote: As to your latest - once again your knowledge base is too narrow. Man has been pouring water onto wooden wedges to break blocks from quarry walls for thousands of years. Pouring water directly onto a piece of wood is a bit different from exposing it to atmospheric humidity, don't you suppose? Only if I didn't understand wood. I heartily recommend the study of the material whose name is in the title of this group to you. The incompressible fluid replaces the air, then the adsorption at the molecular level produces the rest of the hydraulic force to split. This is what happens to wood with humidity cycling. It adsorbs moisture, bonding at the molecular level. Whether or not there was expansion of the fibers themselves was the original bone of contention. By making no distinction between the two cases, you appear to be suggesting that the magnitude of the force exerted is the same when a small amount of moisture is absorbed from the atmosphere, as when a large amount of moisture is absorbed from immersion in liquid. If this is the case, I heartily recommend to you the study of logic; if this is not the case, I heartily recommend to you the study of the English language, in particular William Zinsser's book "On Writing Well" in which he makes the point that the purpose of writing is not to be understood, but to make it impossible to be misunderstood. -- Regards, Doug Miller (alphageek at milmac dot com) Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time? |
#14
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"Doug Miller" wrote in message . com... By making no distinction between the two cases, you appear to be suggesting that the magnitude of the force exerted is the same when a small amount of moisture is absorbed from the atmosphere, as when a large amount of moisture is absorbed from immersion in liquid. That was your idea. Mine was that the principle of wood adsorbing moiture and exerting force was well-known Sorry that your were ignorant of it. If this is the case, I heartily recommend to you the study of logic; if this is not the case, I heartily recommend to you the study of the English language, in particular William Zinsser's book "On Writing Well" in which he makes the point that the purpose of writing is not to be understood, but to make it impossible to be misunderstood. Nah, after grade three, the reader is supposed to know what's on the page and what's in their imagination. |
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In article , "George" george@least wrote:
Nah, after grade three, the reader is supposed to know what's on the page and what's in their imagination. That explains why so much of what you say makes so little sense. -- Regards, Doug Miller (alphageek at milmac dot com) Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time? |
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