Wood movement

[Lee Schierer]

Here is an example of what happens when you remove material from only one side of a piece of lumber. This is a piece of red oak has been in my shop for a couple of years and was flat. It is 30-1/2" long, 3 inches wide and 3/16" thick when I started work on it last night. Because the piece was too thin to run through my planer by itself, I attached it with double sided tape on a carrier board. I removed just under 1/16" of material from one side. When I finished up last night, I left the thin piece on the carrier board. This is what I found this morning when I went to the shop.
IMG_0746.jpg
The piece is bowed up 1/4" in the center of the 30 inch length. This won't present a problem as the piece is so thin and it will be glued in place when all is said and done.

[Ken Fitzgerald]

Thanks for posting this example Lee. I have experienced similar results but not to this extreme. It gives reason for rough sizing, planing and letting the wood rest overnight.

[John TenEyck]

I think it was more likely a lesson to not leave wood flat on your bench. By leaving it stuck to the carrier board you prevented that side from having the same moisture exchange as the top. Had the RH remained dead stable nothing would have happened, but that's rarely the case.

Take it off the carrier and lean it against a wall. Chances are it will flatten out again when the MC equilibrates.

John

[Bob Riefer]

I've heard that advice (about removing material equally from both sides) a bunch and have to ask...

With rough lumber, and especially rough lumber from certain sawmills, I find that I use the jointer to get a flat face on the "easy" side of the board... whichever is closest to flat already.

Then, I use the planer to copy that to the "difficult" side of the board. In order to get that surface down past any rough spots, while not making the board too thin, I necessarily take more off this side than the other.

My last and lightest pass is then the jointed side usually since I get a better cut on my planer.


So, to recap... one side of my typical board might get 2-3 passes on the jointer and 1 light pass on the planer, whereas the other side might get 6-10 passes on the planer.


Is this incorrect way to handle rough lumber? Or is the tip intended for board that come surfaced on both faces already?

[Brian Tymchak]

I've heard that advice (about removing material equally from both sides) a bunch and have to ask...
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Is this incorrect way to handle rough lumber? Or is the tip intended for board that come surfaced on both faces already?

Pretty much the way I do it, with just a small addition that once I get to smooth surface with the planer, I will flip sides each pass thru the planer to get down to my desired rough dimension. Then stack/sticker with weight on top for a couple days at least, making sure that pressure on the stack is more or less even along the stack. Then after a few days, plane to final dimension, again flipping sides with each pass. Edit: if I'm taking a bunch of thickness off in the rough milling, I will let the material set in stickers for a week or more.

I will follow the same process with rough and pre-planed lumber.

I've had good sucess with this process, although boards with twisty grain might warp anyway.

[Bob Riefer]

Pretty much the way I do it, with just a small addition that once I get to smooth surface with the planer, I will flip sides each pass thru the planer to get down to my desired rough dimension. Then stack/sticker with weight on top for a couple days at least, making sure that pressure on the stack is more or less even along the stack. Then after a few days, plane to final dimension, again flipping sides with each pass.

I will follow the same process with rough and pre-planed lumber.

I've had good sucess with this process, although boards with twisty grain might warp anyway.

Agreed - if I'm able to get smooth on both sides before I'm at final thickness, then I do flip back and forth as you mention.


In many/most instances, I get material into a sub assembly the same day. Is that risky? Hasn't hurt me yet, but that might just be luck?


If sub assembly is going to instead be the following day, I either sticker or lean against a wall with good air movement. This hasn't hurt me yet either.


And, if it's going to be longer wait period, I sticker and clamp it in position.

[Ken Fitzgerald]

Pretty much the way I do it, with just a small addition that once I get to smooth surface with the planer, I will flip sides each pass thru the planer to get down to my desired rough dimension. Then stack/sticker with weight on top for a couple days at least, making sure that pressure on the stack is more or less even along the stack. Then after a few days, plane to final dimension, again flipping sides with each pass. Edit: if I'm taking a bunch of thickness off in the rough milling, I will let the material set in stickers for a week or more.

I will follow the same process with rough and pre-planed lumber.

I've had good sucess with this process, although boards with twisty grain might warp anyway.

Brian,

your method is exactly what I do though I don't normally place weights on it while it's being stickered.

[Lee Schierer]

I think it was more likely a lesson to not leave wood flat on your bench. By leaving it stuck to the carrier board you prevented that side from having the same moisture exchange as the top. Had the RH remained dead stable nothing would have happened, but that's rarely the case.

Take it off the carrier and lean it against a wall. Chances are it will flatten out again when the MC equilibrates.

John

The piece was not attached to the carrier board over night. It has been laying concave side up all day on the carrier board and it is still bowed. The humidity in my shop at the moment is 30% and my shop is conditioned the same as the house year round. The piece of oak has been in my shop for several years since it was thinned down to the 3/16" dimension and measure 6% MC on both sides.

[John TenEyck]

The piece was not attached to the carrier board over night. It has been laying concave side up all day on the carrier board and it is still bowed. The humidity in my shop at the moment is 30% and my shop is conditioned the same as the house year round. The piece of oak has been in my shop for several years since it was thinned down to the 3/16" dimension and measure 6% MC on both sides.

If the moisture content was constant from surface to center to surface and your shop RH didn't change how do you explain that it cupped?

John

[Ken Fitzgerald]

If the moisture content was constant from surface to center to surface and your shop RH didn't change how do you explain that it cupped?

John

John, internal stress released by jointing and planing maybe?

What causes wood to trap on a table saw blade and cause kickback? The RH should be the same but internal stresses placed in the wood while it was growing?

[Curt Putnam]

Every time that I have left a board face down overnight, it has cupped or bowed.

[Ron Citerone]

Every time that I have left a board face down overnight, it has cupped or bowed.

I always put another piece on top so each face is equally "not exposed." or Stickered and equally exposed.

[Ron Citerone]

I've heard that advice (about removing material equally from both sides) a bunch and have to ask...

With rough lumber, and especially rough lumber from certain sawmills, I find that I use the jointer to get a flat face on the "easy" side of the board... whichever is closest to flat already.

Then, I use the planer to copy that to the "difficult" side of the board. In order to get that surface down past any rough spots, while not making the board too thin, I necessarily take more off this side than the other.

My last and lightest pass is then the jointed side usually since I get a better cut on my planer.


So, to recap... one side of my typical board might get 2-3 passes on the jointer and 1 light pass on the planer, whereas the other side might get 6-10 passes on the planer.


Is this incorrect way to handle rough lumber? Or is the tip intended for board that come surfaced on both faces already?

I wouldn't use the number of passes as a guide, it's more about equal thickness of material off of each side IMO.

I have learned not to joint the first face completely smooth, just until it lays flat on the jointer table. Then planer till it also lays flat. Now both sides are flat AND parallel with still some roughness. Then alternating light cuts on face to face. What you described in your post sounds problematic to me.

[johnny means]

I think it was more likely a lesson to not leave wood flat on your bench. By leaving it stuck to the carrier board you prevented that side from having the same moisture exchange as the top. Had the RH remained dead stable nothing would have happened, but that's rarely the case.

Take it off the carrier and lean it against a wall. Chances are it will flatten out again when the MC equilibrates.

John

Why would the "old" face lose or gain any more moisture? It's already reached equilibrium. More likely, the piece was under stress to start with. Removing one side allowed the other side to do what it wanted to all along.

[Ron Citerone]

Why would the "old" face lose or gain any more moisture? It's already reached equilibrium. More likely, the piece was under stress to start with. Removing one side allowed the other side to do what it wanted to all along.

I tend to agree, especially with oak...case hardening?