Preventing Cupping/Warping - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 34 Old 08-02-2012, 09:54 PM
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I work in a non-climate-controlled shop. I have a hygrometer, but more valuable to me is the gauge I made out of a red-oak off-cut 23" wide and 2" long (short-the-long-way). I arranged a pointer assembly which exaggerates the movement of the oak, which is an astounding 5/16" per year. I build according to what this gauge tells me.
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post #22 of 34 Old 08-03-2012, 10:18 AM
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I work in a non-climate-controlled shop. I have a hygrometer, but more valuable to me is the gauge I made out of a red-oak off-cut 23" wide and 2" long (short-the-long-way). I arranged a pointer assembly which exaggerates the movement of the oak, which is an astounding 5/16" per year. I build according to what this gauge tells me.
That sound very interesting... could you provide a photo for us?
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post #23 of 34 Old 08-03-2012, 02:30 PM
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That sound very interesting... could you provide a photo for us?
I'll work on it, though I was able to copy/paste photos to these threads a while back, I have been unable-to lately, and I don't understand the tutorial on how to post photos.
If anyone can set down a simple set of steps, which does not involve URLs, whatever they are (do pictures in MY PICTURES have URLs?) it would help.
I'll attempt it.

I was able to put it in MY PHOTOS (see at left) so there it is.
The pointer is loosely-screwed to bot the wall-stud and the oak, the oak on the right and the wall about an inch to the left (neither of which you can see) and this allows the pointer to proportionally exaggerate the movement.

Last edited by JBSmall; 08-03-2012 at 03:19 PM.
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post #24 of 34 Old 08-04-2012, 08:38 PM
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never mind
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post #25 of 34 Old 08-05-2012, 10:26 PM
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never mind
...?
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post #26 of 34 Old 08-05-2012, 11:35 PM
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How to post pictures at WWT

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I'll work on it, though I was able to copy/paste photos to these threads a while back, I have been unable-to lately, and I don't understand the tutorial on how to post photos.
If anyone can set down a simple set of steps, which does not involve URLs, whatever they are (do pictures in MY PICTURES have URLs?) it would help.
I'll attempt it.

I was able to put it in MY PHOTOS (see at left) so there it is.
The pointer is loosely-screwed to bot the wall-stud and the oak, the oak on the right and the wall about an inch to the left (neither of which you can see) and this allows the pointer to proportionally exaggerate the movement.

Maybe this will help:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #27 of 34 Old 08-06-2012, 12:42 AM
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"wood cups towards the sapwood"
Better to think that drying wood moves to flatten the growth rings or if you like to cup towards the sapwood.
Wood keeps moving with humidity changes mostly related to the seasons. Therefore wood that was dry when you build in the late winter will take on moisture and warp or "cup" away from the sapwood the following summer.
No finish will stop the movement of wood. Different finishes slow the movement down a bit. The more like plastic film the more the movement is slowed.
Building has to be done to allow for the almost inevitable movement.
Woods vary in their change in movement and the orientation to the growth ring to which the board was cut dramatically affects the amount of change in dimension which I'd the cause of warping twisting and bowing etc.
The best book on wood technology including wood movement is almost certainly Bruce Hoadley's "understanding Wood". It is an interesting and almost must read f or any woodworker.
Breadboards, the dovetail cross piece mentioned or how it is attached to its neighbours if strong enough can restrain some of the movement.
Bob
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post #28 of 34 Old 08-08-2012, 06:43 AM
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The best book on wood technology including wood movement is almost certainly Bruce Hoadley's "understanding Wood". It is an interesting and almost must read for any woodworker.
Thanks for the tip! After reading Bob Flexner's book on wood finishing, I've realized the best place for information is from the experts. (Duh...) This book is in my local library, fortunately.

"Man's most valuable trait is a judicious sense of what not to believe." --attributed to Euripides
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post #29 of 34 Old 08-08-2012, 07:25 AM
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A lot of good ideas here but a couple of things haven't been said. Furniture makers for centuries have been attaching skirts to the underneath of a table top to help keep the top flat and stable. Also when it comes down to finishing be sure to seal the underneath side of the top to prevent it from soaking up moisture from the air. Normally when wood warps its because there is an imbalance in moisture content from one side to the other.
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post #30 of 34 Old 08-09-2012, 12:05 AM
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Flexner says that tables often cup b/c they are often wiped with damp cloths on the top but, of course, not underneath.

A poster here above said, "No finish will stop the movement of wood. Different finishes slow the movement down a bit. The more like plastic film the more the movement is slowed."

This is true, in part, but the finish is a stronger protection than implied. Again, Flexner: (p. 4) "...a finish in good shape stabilizes the moisture content of wood [...] Inhibiting moisture-vapor exchange effectively minimizes the stresses in wood that can be caused by wide swings in humidity."

Epoxy resin may be an exception to the rule that no finish provides an almost complete barrier against humidity. (p. 168) "...very thick layers can be applied (up to 1/16 inch each), achieving an exceptionally effective barrier against moisture-vapor exchange." (my emphasis)

I've also seen polyurethane applied in extremely thick coats, but it must be difficult to get it smooth b/c the job I saw was pretty messy.

In any event, it is important to maintain the finish after it's applied, in case it starts to thin or wear out.

"Man's most valuable trait is a judicious sense of what not to believe." --attributed to Euripides

Last edited by dglevy; 08-09-2012 at 11:44 PM.
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post #31 of 34 Old 08-09-2012, 07:03 PM
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At some point the site becomes Plasticworkingtalk.
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post #32 of 34 Old 08-09-2012, 11:40 PM
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http://www.finewoodworking.com/FWNPDF/011064059.pdf
-
I am unsure if this link will wok but nothing ventured.
If it does you can read an the article relating the research by the Forestry service. They did extensive research on moisture protection by an extensive list of finishes, this might put several false beliefs to rest and dispell some myths.
. They compared 1 2 and 3 layers of all the commonly used finishes.
Only a dip in paraffin wax gave 95 % protection to 3 weeks of humidity.
Epoxy was next best. None did more than slow down the taking on and movement with moisture.
It is important to coat all surfaces with the chosen finish to prevent fairly rapid taking on of moisture.
If the link won't work, I can summarise the rest of the results
Bob
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post #33 of 34 Old 08-10-2012, 01:38 PM
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How 'bout "Time is a flood"?

(The less you trust glue, fasteners, and finishes, the better your "woodworking" will be.)
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post #34 of 34 Old 08-11-2012, 09:37 AM
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Originally Posted by Midlandbob View Post
http://www.finewoodworking.com/FWNPDF/011064059.pdf
If the link won't work, I can summarise the rest of the results.
Very interesting! Thanks for posting. Unfortunately, though, the link won't work unless you sign up for a trial subscription and hand over your credit card #, etc.

You could summarize the results or, better yet, attach the pdf. (Or you can send it to me via private message and I'll convert it to plain text.)

"Man's most valuable trait is a judicious sense of what not to believe." --attributed to Euripides
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