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PostPosted: Sun Apr 04, 2010 5:22 pm 
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... and push a dowel into it to be a tight fit. Now place the two in a warm dry place for a few days to reduce the moisture content.

With me so far? ...Good :D

Now the question is; after a few days will:

A) the dowel become loose?
B) the dowel become jammed tight?
C) nothing change?

Please explain your answer...

Ralph :wink:

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PostPosted: Sun Apr 04, 2010 6:23 pm 
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The dowel will become loose.
Loosing moisture will actulally increase the diameter of the hole drilled and the dowel will shrink in diameter.
Further: As the piece with the hole dries and the wood shrinks the hole diameter will enlarge same as if a piece of steel was cooled the hole will increase in dia. As to the dowel the wood shrinks and as a result the diameter of the dowel will decrease.

I know I am right but can't explaine it better.

Duan

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Last edited by Clipper on Sun Apr 04, 2010 6:29 pm, edited 1 time in total.

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PostPosted: Sun Apr 04, 2010 6:29 pm 
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I think Duan got this one...

Unless the piece is mesquite in which case the wood will laugh in the face of the idea of a "warm dry environment"

Lawrence


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PostPosted: Sun Apr 04, 2010 6:52 pm 
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I agree with Duan! :-D The dowel would get looser.
So, that means that idealy if you get both the wood and dowel as dry as possable, drill the hole and insert the dowel under those conditions and then put it into a more humid area the dowel should be immovable in the hole. BUT!!!! Would the humidity be enough for the dowel to split the board as it expanded??? :confused:

Rog

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PostPosted: Mon Apr 05, 2010 11:32 am 
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It’s been over 30 years since I took metallurgy (yeah I know we’re talking wood, but I think the principle is the same), if I recall that if you heat up a piece of steel with a small hole, the hole will get smaller. But, if it was a larger hole it would get bigger. I seem to remember a homework problem to calculate what size hole would not change in size.

So, if wood moves the same way it would depend on the size of the hole?

I’m sure Winston could confirm this to be true or false.

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PostPosted: Mon Apr 05, 2010 1:50 pm 
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Jeff,
I think I understand what you are trying to say but, it is the size of the hole in relation to the size of the plate that makes the difference. In a 12 x 12 steel plate with a 1/4" hole would react different than a 12 x12 plate with a 9" hole. It's the material between the edge of the hole to the edge of the plate that will expand more or less that makes the difference.
With wood it is more from mosture than heat that causes wood to expand or contract.

Rog

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PostPosted: Mon Apr 05, 2010 5:14 pm 
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Daun was the first one to get it so the point is his...

However, under normal conditions, the dowel will actually become tighter. Dowels are compressed and dried to a very low moisture content. The application of an aqueous glue, such as PVA, will cause the dowel to swell and make a firm fixing. When using dowels with other glues like Polyurethane (PU) it is a good idea to wet the dowels immediately before inserting them.

Ralph :wink:

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PostPosted: Mon Apr 05, 2010 5:24 pm 
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Hey Ralph,

I would say that it depends on how the grain in the dowel is oriented relative to the piece with the hole. Since the shrinkage is greatest radially and to a lesser extent axially, you can use this to you advantage to create a tight joint in green wood joinery. This is the concept outlined in "Make a Chair from a Tree" by John Alexander.

Tom

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PostPosted: Mon Apr 05, 2010 5:30 pm 
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Absolutely Tom, that is the wonderful thing about wood. My reference was to the normal workshop conditions of using seasoned boards and dry, commercially available dowel pins.

Ralph :wink:

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PostPosted: Mon Apr 05, 2010 7:08 pm 
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Yahoo my first point.
May it grow.

Duan

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