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View Full Version : Keeping boards flat. Can this work??



Jason White
12-24-2009, 6:09 PM
I'm making a dry sink out of eastern white pine with rough stock obtained at a local sawmill. I only have a 6" jointer, so lots of glued-up panels with biscuits!

Due to daily temperature and humidity changes in my shop (freezing cold at night and running the heater during the day), and the pine still being a bit wet despite acclimating in the shop for 2 weeks, the panels are twisting very soon after final milling and assembly (we're talking hours here, not days).

To try and keep the panels flat until I can finish cutting and assembling them, I came up with this idea. 40-pound bags of stove pellets on top of the panels to push them down flat against the workbench, with some clamps on the ends for good measure.

Any problems with this approach?

Jason

Chip Lindley
12-24-2009, 6:36 PM
You may need those stove pellets this winter BEFORE that wood is dry enough to use for panels. Until your sawmill pine has reached equilibrium moisture content (over months of air-drying, NOT weeks or days) you will find that the green wood is very uncontrollable. Even *construction* pine from a lumber yard which has undergone (sort of) kiln-drying, suffers movement of all sorts, when used for *woodworking* rather than building.

Would be much better to let the rough lumber air-dry to a usable moisture content, THEN mill it and make something with it. Many a *green* log cabin builder, using lumber straight from the sawmill, has been very disappointed to see their best efforts disintegrate into bowed walls, warped ceilings or uneven floors. Speaking of floors, the tangental shinkage of green wood causes tight flooring joints become *cracks* sooner than later.

Frank Drew
12-24-2009, 6:40 PM
Jason,

You want the panels to stay flat, but you also want them to lose moisture, and that arrangement won't allow them to, with the board flat on the bench and stacked on top of each other. Better to sticker them with some weight on top.

Are these recently sawn boards, or have they been kiln- or air-dried? Personally, I wouldn't work them up into furniture until they've reached an equilibrium with an indoor environment.

[In other words, what Chip said. :D]

glenn bradley
12-24-2009, 6:41 PM
I did very much the same thing with some construction grade fir. I clamped it, stickered, for two months so that it couldn't move while it acclimated to my shop. When I removed the clamps they twisted like pretzels. I had so much waste I could've bought good material and saved money.

keith ouellette
12-24-2009, 6:49 PM
I tried something similar once and it didn't work for me either. as stated above the wood moves after the clamps are off. Think of the wood a compressed spring. When the thing that is holding the spring in its compressed state is removed the forces in the spring make it move.

The wood will do exactly the same thing and from what i have read what you are doing could make matters worse.

Michael Schwartz
12-24-2009, 7:08 PM
rough mill your parts oversize and sticker them to allow uniform air flow. Then put a little bit of weight on top and just let them do there thing and freak out while they acclimate.

After a few weeks, mill them again but take them to final dimension.

A few extra tips are to remove material equally from each face when milling, otherwise the board will want to cup on the exposed face. Keep this in mind too when re-sawing since the wood in the center of the board is going to be moister than the wood on the outside

When finishing do the same, equal coats on both faces as well.

The bottom line is that wood can and will move and often the best thing is just to let it do what it wants to do and then deal with it later.

Jason White
12-24-2009, 7:52 PM
I was told by the sawyer that the timber he slabbed these boards from had been sitting in his lot for at least a year, maybe two. I figured they would've been "dry enough."

Perhaps not...




You may need those stove pellets this winter BEFORE that wood is dry enough to use for panels. Until your sawmill pine has reached equilibrium moisture content (over months of air-drying, NOT weeks or days) you will find that the green wood is very uncontrollable. Even *construction* pine from a lumber yard which has undergone (sort of) kiln-drying, suffers movement of all sorts, when used for *woodworking* rather than building.

Would be much better to let the rough lumber air-dry to a usable moisture content, THEN mill it and make something with it. Many a *green* log cabin builder, using lumber straight from the sawmill, has been very disappointed to see their best efforts disintegrate into bowed walls, warped ceilings or uneven floors. Speaking of floors, the tangental shinkage of green wood causes tight flooring joints become *cracks* sooner than later.

Jason White
12-24-2009, 8:01 PM
I had rough milled the boards and stickered them inside my shop when I got them home, then milled to final dimensions a couple of weeks later. This isn't my first experience with rough-sawn lumber, but it is my first time dealing with lumber directly from a sawmill.

I guess I'd better get a moisture meter and take it with me next time! :o

Well, the panels are already milled and glued up. I guess there's no turning back now.

A lesson learned. Can't beat the price, but this is probably the last time I'll get my wood directly from a sawmill, since I usually need to use it soon after I buy it.

Jason


rough mill your parts oversize and sticker them to allow uniform air flow. Then put a little bit of weight on top and just let them do there thing and freak out while they acclimate.

After a few weeks, mill them again but take them to final dimension.

A few extra tips are to remove material equally from each face when milling, otherwise the board will want to cup on the exposed face. Keep this in mind too when re-sawing since the wood in the center of the board is going to be moister than the wood on the outside

When finishing do the same, equal coats on both faces as well.

The bottom line is that wood can and will move and often the best thing is just to let it do what it wants to do and then deal with it later.

Scott T Smith
12-24-2009, 10:19 PM
I was told by the sawyer that the timber he slabbed these boards from had been sitting in his lot for at least a year, maybe two. I figured they would've been "dry enough."

Perhaps not...


Wood does not dry in the log, and what minimal drying it does do is usually affected by some type of degrade.

I've milled oak logs that had been down for 3 years and it was still 45% MC in the bulk of the log.

Faust M. Ruggiero
12-24-2009, 10:47 PM
Jason,

Even the old adage about green wood drying at a rate of 1" of thickness per year isn't really that simple. Depending on the wood's location and the relative humidity of the area in which it is stored, wood can only dry to a certain level. If the relative humidity is 30%, the wood can never get below that. the wood will only dry when the air around it contains less moisture than the wood.
Do yourself a favor. Buy professionally kiln dried wood for your projects. If you want to buy a batch of green lumber and sticker it in a dry breezy spot on your property, that's fun. Just don't expect it to be as stable as properly kiln dried wood.
Acclimating it to your shop is the last step prior to dimensioning kiln dried wood. The wood already should be free of sap moisture, the moisture trapped in the cells of green wood. It's really the free water moisture the wood is acclimating to. Your shop air will contain an amount of moisture relative to the outside air and the temperature in your shop. Warm air holds more moisture than cold air. When your shop goes from freezing nights to warm days, the even kiln dried woods cannot get acclimated.
Bruce Hoadley wrote a wonderful book called "Understanding Wood". Buy it and read it. Read it often. It will save you a lot of disappointment and help you build with allowances for the live nature of wood.
Sorry about rambling but I know that building furniture without knowing how the wood will act afterward can be frustrating.
butch ruggiero

Rich Aldrich
12-25-2009, 10:09 AM
One thing about pine compared to hardwoods is that you have to set the pitch so the pitch doesn't bleed. There is a point in the kiln drying process where the kiln is heated up to a temperature above the temperature the wood will ever get so the pitch doesnt bleed. Construction grade lumber that can be used in an attic can be exposed to quite high temperatures in the summer. The kiln operator at our local sawmill said they normally set the pitch at 125 degrees for this area.

This is why I would not air dry pine for any project unless it is a structural project where pitch bleed doesnt matter.

Jason White
12-25-2009, 12:06 PM
I'll try to find that book. Thanks for the suggestions.

The boards don't seem to have much sap in them, if any. Seems to just be water moisture.

Jason


Jason,

Even the old adage about green wood drying at a rate of 1" of thickness per year isn't really that simple. Depending on the wood's location and the relative humidity of the area in which it is stored, wood can only dry to a certain level. If the relative humidity is 30%, the wood can never get below that. the wood will only dry when the air around it contains less moisture than the wood.
Do yourself a favor. Buy professionally kiln dried wood for your projects. If you want to buy a batch of green lumber and sticker it in a dry breezy spot on your property, that's fun. Just don't expect it to be as stable as properly kiln dried wood.
Acclimating it to your shop is the last step prior to dimensioning kiln dried wood. The wood already should be free of sap moisture, the moisture trapped in the cells of green wood. It's really the free water moisture the wood is acclimating to. Your shop air will contain an amount of moisture relative to the outside air and the temperature in your shop. Warm air holds more moisture than cold air. When your shop goes from freezing nights to warm days, the even kiln dried woods cannot get acclimated.
Bruce Hoadley wrote a wonderful book called "Understanding Wood". Buy it and read it. Read it often. It will save you a lot of disappointment and help you build with allowances for the live nature of wood.
Sorry about rambling but I know that building furniture without knowing how the wood will act afterward can be frustrating.
butch ruggiero