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Forum topic by vonfalken posted 02-29-2016 11:17 PM 341 views 0 times favorited 4 replies Add to Favorites Watch
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vonfalken

59 posts in 283 days


02-29-2016 11:17 PM

I recently made a box outta 50 year old maple from a church pew, 6×7x3 the wood was in my carport in damp weather for 3 weeks, the carcass of my box is fine, no problems..the lid however cupped abot 1/16 of an inch. it is 1/2 inch thick with 1 inch of the inside dado cut a 1/4 inch thick, was it the weather causing this? or am I doing it wrong? any input would be greatly appreciated thanks

-- vonfalken


4 replies so far

View TheWoodenOyster's profile

TheWoodenOyster

1275 posts in 1401 days


#1 posted 02-29-2016 11:43 PM

Probably the weather. I’d bring it into the house and see if it flattens back out.

-- The Wood Is Your Oyster

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WDHLT15

1572 posts in 1942 days


#2 posted 03-01-2016 01:43 AM

Yes, moisture change from the environment. If you lay it flat, and the wood is not in equilibrium in that environment, then the top will dry or gain moisture, whatever the case may be, more than the bottom that is not exposed to the air, so cupping can occur. Make sure it can get equal air on all sides.

-- Danny Located in Perry, GA. Forester. Wood-Mizer LT40HD35 Sawmill. Nyle L53 Dehumidification Kiln. hamsleyhardwood.com

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JBrow

819 posts in 386 days


#3 posted 03-01-2016 01:46 AM

vonfalken,

Moisture is the likely culprit, assuming the panel was dead flat 3 weeks ago and no finish has been applied. I suspect there is a little more moisture on one face than on the other – the crown side of the panel having more moisture. This can result when one face was fully or partially protected while the other face was fully exposed to the air. It seems more moisture can enter and a leave lumber that has been freshly milled by sanding or planning for example. But even if a finish was applied, moisture will continue to enter and leave the panel, juts at a reduced rate.

Lumber and panels should be stored by Stickering. Stickering affords all six sides of the lumber roughly equal access to the air, allowing moisture to enter and leave the lumber evenly.

I have had success returning a cupped glued-up panel to flat. In my case, the cup resulted when freshly sanded glued-up panels were simply stacked one atop the other on the workbench. Air could only interact with the exposed face of the top panel. Overnight the top panel developed a crown that when one edge was clamped to the workbench with crown side down, the opposite edge rose ¾” off the workbench. The cupped panel may have returned to flat on its own with air being able to get to all side. However, I did not want to wait.

To return the panel to flat, I placed it on the workbench (a flat surface) crown side down. I carefully and slowly clamped cauls (one at each end) across the width of the panel until the panel was flat on the workbench. Then I moistened the entire face of the panel and laid the damp cloth over the panel, to keep it from drying out. The damp cloth remained on the panel until it flattened out. Every hour, I unclamped the cauls and measured the raise of one edge off the workbench. I kept a close eye on the progress because I did not want to add too much moisture and introduce a crown in the opposite direction. After about 3 hours, the moisture in the panel equalized and returned to flat. I then Stickered the panels, including the formerly cupped panel. All remained flat.

If your panel has a finish applied, I am not sure how well the method I described would work. I suppose it would depend on the type of finish.

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vonfalken

59 posts in 283 days


#4 posted 03-01-2016 01:53 AM

thanks guys,,,what I did was seal and shellac the top of the lid and not the bottom and put the lid on the carcass and it sat on a shelf a few days so the moisture probably got in the unsealed side more than the sealed side. and I suspect the dadoed edge might have contributed to the cupping by giving it more surface area,,,,, your answers are more than helpful

-- vonfalken

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