I am building a fairly large table and asked about dealing with the wood
movement a few days ago.
After much thought I have decided to securely fasten down the middle of the
aprons perpendicular to the grain and fasten the ends of those aprons down
with clips.
The aprons parallel the grain have to be able to move .8". I will glue
fiberglass dowels into them, and have the dowels ride in blocks attached to
the table. Does this seem reasonable?
Questions:
1) As the wood expands, will the holes in the blocks get smaller or bigger?
I am guessing the hole will get larger, but I am not certain about that.
2) What woods have minimal movement. Would nice oily teak be good? I have
some scraps of that laying around. (I have some lignum vitae also, but that
seems like overkill.)
"alexy" <[email protected]> wrote in message
news:[email protected]...
>
> Or, think about it for two minutes and come to the opposite, correct
> conclusion!
>
Classic!
Sun, Sep 24, 2006, 7:01pm (EDT+4) [email protected] (Toller) doth
puzzedly queryeth:
<snip> Questions:
1) As the wood expands, will the holes in the blocks get smaller or
bigger? I am guessing the hole will get larger, but I am not certain
about that.
2) What woods have minimal movement. <snip>
1. Think about it for a minute. Before you ask next time. Wood
expands - smaller holes. Wood shrinks - larger holes. Pretty basic if
you think about it. Or aren't trolling. This post is reminiscent of
one of those troll dopplegangers.
2. Petrified wood.
Try google, or the archives.
JOAT
You'll never get anywhere if you believe what you "hear". What do you
"know"?.
- Granny Weatherwax
> Sun, Sep 24, 2006, 7:01pm (EDT+4) [email protected] (Toller) doth
> puzzedly queryeth:
> <snip> Questions:
> 1) As the wood expands, will the holes in the blocks get smaller or
> bigger? I am guessing the hole will get larger, but I am not certain
> about that.
> 2) What woods have minimal movement. <snip>
>
> 1. Think about it for a minute. Before you ask next time. Wood
> expands - smaller holes. Wood shrinks - larger holes. Pretty basic if
> you think about it. Or aren't trolling. This post is reminiscent of
> one of those troll dopplegangers.
I'm sitting here thinking about it and what you are saying doesn't make any
sense to me.
Here's my reasoning:
Suppose you have a square piece of wood that's a thousand layers across, in
both transverse and longitudinal directions. Suppose further that there's a
central hole that's five hundred layers across. Square hole or circular, I
don't think it matters.
If each layer starts out at t units in thickness, then the total span s of
the hole is 500t. Now let the wood shrink by delta (d) in each layer. The
new layer thickness is t' = t - d. What's the span of the hole now? s' =
500( t - d ). Therefore the hole is SMALLER by 500d, not larger.
To take care of different shrinkage rates depending on orientation with the
grain, just use a different value for d. Use sines and cosines to your
heart's delight for orientations on an angle. You're still going to get a
different result from what you just said.
We heat bearings to make them larger for long enough to slip them over an
axle. They cool and shrink onto a tight fit around the axle. Same
mechanical principle, just a different mechanism.
As wood shrinks the hole will expand if you constrain the edges of the wood
containing the hole. But then you're facing a split, and that's a different
situation altogether.
- Owen -
"Toller" <[email protected]> wrote in message
news:[email protected]...
>I am building a fairly large table and asked about dealing with the wood
>movement a few days ago.
>
> After much thought I have decided to securely fasten down the middle of
> the aprons perpendicular to the grain and fasten the ends of those aprons
> down with clips.
>
> The aprons parallel the grain have to be able to move .8". I will glue
> fiberglass dowels into them, and have the dowels ride in blocks attached
> to the table. Does this seem reasonable?
>
> Questions:
> 1) As the wood expands, will the holes in the blocks get smaller or
> bigger? I am guessing the hole will get larger, but I am not certain about
> that.
> 2) What woods have minimal movement. Would nice oily teak be good? I
> have some scraps of that laying around. (I have some lignum vitae also,
> but that seems like overkill.)
One wood with very little movement is mesquite.
todd
> Wood expands -- hole becomes elongated across the grain. Wood shrinks --
> hole
> contracts across the grain. Diameter of hole along the grain does not
> change.
>
So I can't maintain a good fit. If I use a fiberglass dowel, the hole will
expand and contract on the dowel, in one dimension.
If I use a wood dowel, the hole and dowel will expand and contract evenly in
one direction, but unevenly in the other.
Maybe a fiberglass dowel running through a plywood hole...
Yeah, I know I am making this more complicated than it has to be.
In article <[email protected]>, [email protected] (J T) wrote:
>Sun, Sep 24, 2006, 7:01pm (EDT+4) [email protected] (Toller) doth
>puzzedly queryeth:
><snip> Questions:
>1) As the wood expands, will the holes in the blocks get smaller or
>bigger? I am guessing the hole will get larger, but I am not certain
>about that.
>2) What woods have minimal movement. <snip>
>
> 1. Think about it for a minute. Before you ask next time. Wood
>expands - smaller holes. Wood shrinks - larger holes. Pretty basic if
>you think about it.
It *is* pretty basic. The trouble is... you're mistaken. Perhaps you need to
spend more than a minute thinking about it. <g>
Wood expands -- hole becomes elongated across the grain. Wood shrinks -- hole
contracts across the grain. Diameter of hole along the grain does not change.
--
Regards,
Doug Miller (alphageek at milmac dot com)
It's time to throw all their damned tea in the harbor again.
[email protected] (J T) wrote:
>Sun, Sep 24, 2006, 7:01pm (EDT+4) [email protected] (Toller) doth
>puzzedly queryeth:
><snip> Questions:
>1) As the wood expands, will the holes in the blocks get smaller or
>bigger? I am guessing the hole will get larger, but I am not certain
>about that.
>2) What woods have minimal movement. <snip>
>
> 1. Think about it for a minute. Before you ask next time. Wood
>expands - smaller holes. Wood shrinks - larger holes. Pretty basic if
>you think about it.
Or, think about it for two minutes and come to the opposite, correct
conclusion!
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.
"Toller" <[email protected]> wrote:
>I am building a fairly large table and asked about dealing with the wood
>movement a few days ago.
>
>After much thought I have decided to securely fasten down the middle of the
>aprons perpendicular to the grain and fasten the ends of those aprons down
>with clips.
>
>The aprons parallel the grain have to be able to move .8". I will glue
>fiberglass dowels into them, and have the dowels ride in blocks attached to
>the table. Does this seem reasonable?
Yes. Make sure to attach those blocks to the table with screws not
glue, though. Otherwise it might be a little hard to get the dowels
into the holes, or remove the top if you want to at a future date.
>
>Questions:
>1) As the wood expands, will the holes in the blocks get smaller or bigger?
>I am guessing the hole will get larger, but I am not certain about that.
Pretty sure you are right.
>2) What woods have minimal movement. Would nice oily teak be good? I have
>some scraps of that laying around. (I have some lignum vitae also, but that
>seems like overkill.)
Are you talking about for the block? Why do you want minimal movement?
I think you should use the same wood as in the apron, so that as the
apron moves (and with it, so does the dowel), the hole will move along
with it.
>
--
Alex -- Replace "nospam" with "mail" to reply by email. Checked infrequently.