# Preventing Cupping/Warping



## eldaneo (Jul 4, 2012)

I am wanting to build a dining table out of 8/4 white oak, and I am concerned about it cupping after it is glued up and planed. 

It will be roughly 8' long and 3' wide. What is the best way to glue it and ultimately design it to prevent it from warping with the change in temps?


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## sawdustfactory (Jan 30, 2011)

First make sure your wood is well acclimated to your shop. Cut/plane to close to your final sizes and let sit overnight and then finish to final dimension. Alternate growth ring direction every board. Use clamping cauls when clamping. Finish all sides equally.


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## firemedic (Dec 26, 2010)

sawdustfactory said:


> First make sure your wood is well acclimated to your shop. Cut/plane to close to your final sizes and let sit overnight and then finish to final dimension. Alternate growth ring direction every board. Use clamping cauls when clamping. Finish all sides equally.


He said it... I'll just add that it's also very important to have a floating top.


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## eldaneo (Jul 4, 2012)

Thanks for the help! Will doing this prevent future issues. Is the use of a breadboard necessary?


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## firemedic (Dec 26, 2010)

eldaneo said:


> Thanks for the help! Will doing this prevent future issues. Is the use of a breadboard necessary?


Absolutely not. Unless executed properly a breadboard can be the death knoll for a table. If you WANT to do it that's fine... It can be done and done well. However it's in no way necessary for a stable table top.

ps
I missed the "future issues" part somehow.
Yes, all of the advise you've gotten thus far will minimize future issues if not prevent them all together.

Do you understand the concept of a "floating top?"


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## woodnthings (Jan 24, 2009)

*what they said...*

And look for the straightest grain wood you can find. Avoid figured wood that looks like stacked or staggered "c's.on the wide face. Quater sawn wood will cup the least. The end grain should be vertical or perpendicular to the wide face. Arcing curves will cup or warp more.

Do not reduce the thickness of wood drastically, remove only 1/16" from each face ..... alterately. :yes: bill


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## GeorgeC (Jul 30, 2008)

sawdustfactory said:


> First make sure your wood is well acclimated to your shop. Cut/plane to close to your final sizes and let sit overnight and then finish to final dimension. Alternate growth ring direction every board. Use clamping cauls when clamping. Finish all sides equally.


I assume that this table will be used in your house. If your house is air conditioned I would prefer to acclimate the wood to that environment.

I would give it a couple of weeks.

George


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## Midlandbob (Sep 5, 2011)

It's not the temp change but the change in moisture content due to humidity changes that causes the warping.
The use of quarter cut wood almost eliminate warping but not change in width.
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3 feet of red oak will change in dimension from summer to winter in central heated northern home by 4 mm or a 1/4 inch (give or take a 1/4) so the "floating or attachment that allows movement is vital.
Breadboards do protect the end grain and can be more visually attractive. It will help hold a table flat and is valuable but it may not have the power for 8/4 oak so it would be more for visual reasons. if someone had problems with them it is due to not designing and attaching them properly. (only the middle can be fixed).
Good luck; it will be a solid heavy table.
Bob


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## panofish (Sep 24, 2009)

It if very important when planing to final thickness after the boards have climatized to your shop.... when you plane one side of a board to also plane an equal thickness from the opposite side of the board. The grain structure of a board can impose a constant internal stress which can be released when you remove opposing stresses and the board will want to cup or curve.


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## dglevy (Feb 3, 2012)

In addition to all the comments here above, I'd recommend you go to the public library and take a look at Bob Flexner's book, "Understanding Wood Finishing". He has several pages on wood movement that explain it in more detail than I have seen anywhere else. Additionally, I think sealing the wood properly might be important -- and maintaining the finish thereafter. His book will really help with that.


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## Rick C. (Dec 17, 2008)

dglevy said:


> In addition to all the comments here above, I'd recommend you go to the public library and take a look at Bob Flexner's book, "Understanding Wood Finishing". He has several pages on wood movement that explain it in more detail than I have seen anywhere else. Additionally, I think sealing the wood properly might be important -- and maintaining the finish thereafter. His book will really help with that.



+1 on Bob Flexner's book, But I bought it and use it for reference often.
1/4 sawn oak is definitely more stable. Check to see if there is a cabinet shop near by. After the glue up it's nice to be able to run the whole top through a sander, and much faster.


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## woodbutcher360 (Jul 1, 2012)

Flat sawn boards always warp towards the sapwood. As said b4 in the above responses, moisture will determine when warp occurs, so it is a must that the wood be acclimated to your shop befor milling.


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## Dominick (May 2, 2011)

+1 on bob flexner understanding wood finishing.


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## smokey1945 (Feb 20, 2009)

firemedic said:


> Absolutely not. Unless executed properly a breadboard can be the death knoll for a table.
> 
> My dumb question for the day (learning question?). What is a "breadboard" as referenced to a table? Thank you:blink:


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## cabinetman (Jul 5, 2007)

smokey1945 said:


> My dumb question for the day (learning question?). What is a "breadboard" as referenced to a table? Thank you:blink:


A "breadboard end" is basically a board that is installed across the ends of a planked table. Methodology is that the ends of the planked boards are grooved, and the breadboard end has a tongue. The tongue and groove isn't glued, but allows the planks to move side to side. The groove can be done to both the planks and the breadboard, and a spline can be used. The groove on both the planks and the end board don't run out the ends, but rather are stopped (so called "blind").

The breadboard can be mounted with a fixed screw to the middle board of the table, and through other boards with a slotted hole to allow those to move without being restrained by the end board. The breadboard is both a decorative addition, and somewhat structural in keeping the planks flat to eachother.










 







.


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## GeorgeC (Jul 30, 2008)

woodbutcher360 said:


> Flat sawn boards always warp towards the sapwood. As said b4 in the above responses, moisture will determine when warp occurs, so it is a must that the wood be acclimated to your shop befor milling.


\]

Why would you acclimate to the shop environment if that environment is different then where the table will reside the rest of it's life?

If the shop and dinning room will always have the same environment (which I would think would be unlikely) then there is no problem. Most people's shops have an evnironment similar to the outdoors. Most dinning rooms are in a heated/cooled house. Remember, an airconditioned house has less humidity then the outdoors.

George


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## JBSmall (Jul 6, 2012)

An excellent option for keeping a tabletop flat is the use of sliding-dovetailed battens. Properly done, these will eliminate a lot of movement out-of-plane, while allowing the top to shrink and expand across its width, which oak does in excelsius.


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## GeorgeC (Jul 30, 2008)

JBSmall said:


> An excellent option for keeping a tabletop flat is the use of sliding-dovetailed battens. Properly done, these will eliminate a lot of movement out-of-plane, while allowing the top to shrink and expand across its width, which oak does in excelsius.


An excellent suggestion.

George


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## woodbutcher360 (Jul 1, 2012)

GeorgeC said:


> \]
> 
> Why would you acclimate to the shop environment if that environment is different then where the table will reside the rest of it's life?
> 
> ...


Hmm, we're in the middle of summer. Would you suggest moving the shop into the dinning room? Some of you are pros, so you get a commission to make a piece of furniture and go from start to finish in a workmen like manner. Most of us don't work that way at a hobby. I'd like to hear from the pros. Do you acclimate the materials at your customer's houses or you shop? Is your shop heated/AC ?
Just wondering.


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## firemedic (Dec 26, 2010)

woodbutcher360 said:


> Hmm, we're in the middle of summer. Would you suggest moving the shop into the dinning room? Some of you are pros, so you get a commission to make a piece of furniture and go from start to finish in a workmen like manner. Most of us don't work that way at a hobby. I'd like to hear from the pros. Do you acclimate the materials at your customer's houses or you shop? Is your shop heated/AC ?
> Just wondering.


My shop is not climate controlled... I've never had a customer experience any wood movement problems... The wood moves but as intended and designed to.

EDIT:
I also do not use KD lumber... All air dried.


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## JBSmall (Jul 6, 2012)

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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## panofish (Sep 24, 2009)

JBSmall said:


> 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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## JBSmall (Jul 6, 2012)

panofish said:


> 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.


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## woodbutcher360 (Jul 1, 2012)

never mind


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## firemedic (Dec 26, 2010)

woodbutcher360 said:


> never mind


...?


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## woodnthings (Jan 24, 2009)

*How to post pictures at WWT*



JBSmall said:


> 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.
> 
> ...



Maybe this will help:


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## Midlandbob (Sep 5, 2011)

"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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## dglevy (Feb 3, 2012)

Midlandbob said:


> 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.


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## Steve Neul (Sep 2, 2011)

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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## dglevy (Feb 3, 2012)

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.


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## JBSmall (Jul 6, 2012)

At some point the site becomes Plasticworkingtalk.


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## Midlandbob (Sep 5, 2011)

http://www.finewoodworking.com/FWNPDF/011064059.pdf
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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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## JBSmall (Jul 6, 2012)

How 'bout "Time is a flood"?

(The less you trust glue, fasteners, and finishes, the better your "woodworking" will be.)


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## dglevy (Feb 3, 2012)

Midlandbob said:


> 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.)


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