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2nd July 2008, 01:43 PM #226
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2nd July 2008 01:43 PM # ADSGoogle Adsense Advertisement
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2nd July 2008, 01:45 PM #227
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2nd July 2008, 01:47 PM #228.
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2nd July 2008, 01:47 PM #229
You don't see the humor in someone supporting the Domino and castigating dowels because of their shrinking availability in hardware stores, when the tool he is supporting is completely unavailable in such stores?
I apologize if my sense of humor is too subtle for the hoi polloi here.
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2nd July 2008, 01:48 PM #230.
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2nd July 2008, 01:49 PM #231
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2nd July 2008, 01:52 PM #232Cro-Magnon
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Lignum, this is a geniune question, not an attempt at point scoring. Sorry I have to add that.
Why don't you get shrinkage in a traditional M&T?
I'm thinking of a tenon on, say, a quarter-sawn rail, where the lines of the grain are in the "short" or "cross" dimension. Won't the maximum shrinkage then occur across the tenon? And if so, what stops this shrinkage from causing joint failure ... just the increased surface area?
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2nd July 2008, 01:54 PM #233.
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2nd July 2008, 01:56 PM #234
Sigh....
A dowel mortice, because of it's shape, consists almost entirely of end grain. Surely you must comprehend that. So what you have is a mostly end-grain to long-grain gluing surface. This results in a weak glue bond. I hope you accept that because it is an established fact.
On the other hand, the mortice for a rectangular tenon oriented so that the long face is with the grain, as they nearly always are, presents mostly long grain. This yields a long-grain to long-grain gluing surface which results in a strong glue bond. I hope you accept that because it is, likewise, a well established fact.
So I conclude that a dowel presents an inferior gluing surface when compared to a rectangular tenon, all other things being equal.
This Dowelmax joint appears to base its strength on the tightness of fit of the tenon in the mortice, rather than providing a better glue bond. It relies upon using these 'high quality compressed dowels' to achieve this tight fit. If the tight it is ever diminished by shrinkage, which I also hope you accept occurs in ALL wooden objects, you are relying on an inferior glue bond to hold it together.
I resent having my contributions to this discussion dismissed as trolling. Try to keep your comments to the topic and above the belt if you can. I know it's hard."I don't practice what I preach because I'm not the kind of person I'm preaching to."
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2nd July 2008, 01:58 PM #235
Ron, I know the question was not directed at me, but someone else said in this respect that "I believe that historically M&T joints were subject to the same types of failure you have seen with dowels. That is why you see many old M&T joints made with pins. That way if the glue failed there would still be a mechanical connection."
I think the M&T joint will shrink and fail as well, but after a longer time due to there being no loose tenon, and then it is easily repairable with pinning etc.
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2nd July 2008, 02:04 PM #236.
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A qtr sawn rail will expand top to bottom, A leg has 2 mortices both moving in different orentations. Some get to caried away and align the longest rail where the leg mortice runs the direction as that rail, thats the minimun movement on both. But its not an issue as the surface area of tenons is masive to that of a dowel so the percentages are on the side of the tenon to hold up a lot longer
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2nd July 2008, 02:04 PM #237
The bond is actually created by the glue's adhesion to the surfaces, not by the mating of grains. With a modern glue the wood around the joint will fail before the join fails. With a multi-dowel joint the total amount of glue adhesion and holding strength of a joint is far in excess of the Domino tenons, as the tests show.
I hope you can accept that.
So I conclude that a dowel presents an inferior gluing surface when compared to a rectangular tenon, all other things being equal.
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2nd July 2008, 02:07 PM #238.
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2nd July 2008, 02:08 PM #239The bond is actually created by the glue's adhesion to the surfaces, not by the mating of grains.
I'm comparing any number of dowels to a flat tenon. They ALL have the same poor glue surface. Mostly end grain to long grain."I don't practice what I preach because I'm not the kind of person I'm preaching to."
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2nd July 2008, 02:13 PM #240
Hmmm, you don't understand modern polyurethane glues
http://www.vise.com.au/super_strong.shtml
eg:
# It is especially strong when applied to timbers being joined end-grain to end-grain
# Imagine the cores of the timber to be like drinking straws. Polyurethane glue will be drawn into these cores as it cures, expanding into them and creating an incredibly strong bond"
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