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My end table cupped.... Possible culprit?

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Forum topic by BLarge posted 12-08-2011 03:31 AM 838 views 0 times favorited 11 replies Add to Favorites Watch
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BLarge

159 posts in 1210 days


12-08-2011 03:31 AM

I brought up a side table for a spare bedroom, my wife wanted to see how it was going to look int the space…. It was not finished. She put a laptop on the top, and before I noticed two days later there was a slight cup upward, and I planed that thing flat as the flat….

Could there have been enough heat from the the heat sink to cup that top? Also, it would cup in the direction of the heat source, I am guessing the heat dried one side more that the bottom side?

The only other culprit could be a 5-10 degree basement to main floor temp difference…. But I have not issue with a slight temp difference before, although in the winter the heat is going…

This lumber had been in my shop for months, and I flipped th grain during glue up….

Thoughts?


11 replies so far

View Moron's profile

Moron

4724 posts in 2641 days


#1 posted 12-08-2011 03:41 AM

newtons 3rd law

for every action there is an equal and opposite reaction

either the wood wasn’t dry or you applied more finish to the exposed wood, then that which you don’t see

or lastly, ………….wood sometimes twists in unimaginable directions, no matter what you do

-- "Good artists borrow, great artists steal”…..Picasso

View Bill729's profile

Bill729

240 posts in 1829 days


#2 posted 12-08-2011 03:52 AM

Could there have been enough heat from the the heat sink to cup that top? Also, it would cup in the direction of the heat source, I am guessing the heat dried one side more that the bottom side?

—I think the answers are basically “yes”. If you just stack a bunch of cut boards, the one on top may cup because it’s top is more exposed to the air (i.e. differing humidity, see below). Of course, the direction of the cup would be to “straighten” the rings in the wood, I believe—at least if the wood was drying, and not sucking up water.

The only other culprit could be a 5-10 degree basement to main floor temp difference…. But I have not issue with a slight temp difference before, although in the winter the heat is going…

—I wager that it was really the change in humidity which caused the cupping. Of course, a temperature change may produce a humidity change.

As Roy Underhill explains it, there an inseparable relationship between wood and water. Basically, you can’t have wood without having water.

I hope that helps. There are surely those who know a great deal more than I do about this.

Bill

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BLarge

159 posts in 1210 days


#3 posted 12-08-2011 04:00 AM

Thank you, guys…. It is a pretty small top, 17 by 15, and I have never had such a small glue up cup on me like that… It ha d to be the laptop, it was pretty warm… But I figured I might put it out there….

View Bill729's profile

Bill729

240 posts in 1829 days


#4 posted 12-08-2011 04:31 AM

Thank you, guys…. It is a pretty small top, 17 by 15, and I have never had such a small glue up cup on me like that… It ha d to be the laptop, it was pretty warm… But I figured I might put it out there….

—I think it was the “move from the basement” (and not the laptop). Maybe move it back and see if it returns to its earlier condition! Curious minds wand to know! : )

Bill

View HerbC's profile

HerbC

1213 posts in 1607 days


#5 posted 12-08-2011 04:42 AM

Moron,

He has not applied finish to the table top yet according to the post…

BLarge,

I feel pretty sure the heat from the computer caused the top to dry more than the bottom and that caused the cupping. I’d take it back to the shop, lay a damp cloth on the top overnight and then let things settle out before finishing the table. Obviously both sides of the table top will need to be finished.

Good Luck!

Be Careful!

Herb

-- Herb, Florida - Here's why I close most messages with "Be Careful!" http://lumberjocks.com/HerbC/blog/17090

View Sawkerf's profile

Sawkerf

1730 posts in 1816 days


#6 posted 12-08-2011 04:54 AM

How is the top attached to the leg assembly? You need to make the attachment so the top has a little “wiggle room” to handle expansion and contraction – whether it’s due to heat, humidity, or both. I use figure eights and have never had a problem.

-- Adversity doesn't build character...................it reveals it.

View William's profile

William

9270 posts in 1590 days


#7 posted 12-08-2011 02:18 PM

Wood is a funny thing. I have worked on projects that required multiple panels similar in size that you’re working with. I remember one time, for example, I clamped up eight panels (I think I remember them being about 14×24) and then had to leave them for four days before I could get back to the project. They were all clamped up identically using the same type wood, same thickness, everything was the same. However, when I came back to the shop four days later, six of them were just as I’d left them. One of them was well on its way to looking like a half circle across the grain and another was very similar along the grain. The point is that while six done just what I expected, there were two that did whatever they wanted to do.
Since all of them were dried the same, assembled the same, clamped the same, everything the same, then your guess on why that happened is as good as mine. It could have been a number of factors. I seem to think it had something to do with the cell configuration in those two panels. This goes back to my original statement about wood at the beginning of my response. Wood just does some crazy stuff sometimes without any clear cut explanation. We know wood always moves regardless of what you do or do not do to it. What really keeps it interesting though is that we never know HOW it is going to move until we see it.

-- http://wddsrfinewoodworks.blogspot.com/

View CharlieM1958's profile

CharlieM1958

15795 posts in 2966 days


#8 posted 12-08-2011 03:40 PM

Just turn it upside down and put the laptop on the other side for a few days. :-)

-- Charlie M. "Woodworking - patience = firewood"

View miles125's profile

miles125

2179 posts in 2753 days


#9 posted 12-08-2011 03:49 PM

I don’t know why they call em laptops. You ever set one in your lap for an extended period?

-- "The way to make a small fortune in woodworking- start with a large one"

View ScottN's profile

ScottN

261 posts in 1427 days


#10 posted 12-08-2011 04:25 PM

I’m guessing the heat from the laptop had a lot to do with it. A pic would help determine the cause, but I suspect with the heat, humidity change and the board grain selection used, all played a part in it. Maybe this pic will help.

-- New Auburn,WI

View DS's profile

DS

2132 posts in 1168 days


#11 posted 12-08-2011 06:10 PM

My wife fell alseep once with a laptop running on her lap and woke up with 2nd degrees burns.
They put out a lot of heat.

EDIT: FWIW, my first thought was the same as Charlies… put the laptop on the other side for a while.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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