Lumber prep question

[Bret Champoux]

I've got a question about lumber preparation. I just recently bought 2, 8ft pieces of 4/4 rough sawn red oak. I jointed one edge and one face, then planed them down to size. I then ripped the finished pieces into the size I needed on my table saw.

The pieces I ripped ended up bowed, almost as soon as I ripped them. What happened? Was it bad choice of rough lumber? Is there some way of avoiding this in the future? This has never happened to me before.

Thanks for any advice,
Bret Champoux

[Lars Thomas]

Tell us a little more about how you planed them. Specifically, did you flip for each pass through the planer (i.e.: taking the same amount of stock of both sides)?

It could be that cutting them relived some internal stress, in which case, there's not a whole lot you could have done. But it would be unusual for both pieces to bow - usually they would twist.

[Jim Becker]

It's not unusual for boards to do this when they are ripped. Almost every board has "some" internal stress, although hopefully minimal, and that shows in the manner you describe. This can be the result of the drying process or the growing process or both. Lars is correct that even planing is a good idea, but that will have less effects on rips as it will on bowing on the face. Usually, the board on the fence side of the blade will remain straight in the situation you describe, but even so, it's good to rip wide so you can return to the jointer if necessary to re-straighten. The board that pealed off on the outside of the blade will obviously need to be straightened.

In the latest issue of Woodwork magazine, there is an article on building a workbench. The author was quite clear that he mills his stock in more than one session; milling oversize first, stickering in his shop for a few days and then returning to the wood for final milling. In that manner, he reduces the characteristics of wood to move through the milling process to something that is more manageable. I use that method, too, especially since all my lumber is rough and most is dried locally, either by me or by the local purveyor of lumber I buy from.

[Steve Jenkins]

I always rough cut my stock prior to any machining. Normally about 1" long and anywhere from 1/4" or more wide depending on how the board looks. That way I am better able to deal with any warp or twist that shows up.Steve

[Chris Padilla]

Reading wood is an art unto itself. Look at the grain, see how it flows and do your best to go with the grain whenever you do something if at all possible.

For starters, it is always best to let the wood settle in your shop for a couple of days to a week--sticker it up and ignore it. You probably have no clue what its been through or where it came from so give it time to acclimate. Take a moisture reading if you can. Now observe it...has it changed at all? Any change should indicate how you handle the piece from there on. Twist/warp, crook/bent/dogleg, bow, cup/crown all need to be handled differently. See if the grain tells you why any of the above happend...it'll be a good clue how to mill the lumber.

Some folks also like to let lumber rest after milling steps--especially resawing. Were your two pieces bookmatched or recently resawn? I've seen slight bowing happen on freshly resawn wood...no big deal but it was there.

Was your lumber flat/rift/quarter sawn? You might see something in the grain at the point of highest bow or you may see nothing.

Sometimes bow can be take care of with proper jointery or you may have to cross cut the ripped pieces into shorter ones that have much less bow. Perhaps you could sticker it and add weight and let it sit for a little while...see if that helps.


Wood moves...sometimes very little and sometimes a lot. It may be obvious why at times while other times you've no clue. It is a fickle medium at times...we just need to roll with its changes. :)

Got any pictures? :D

[Kelly C. Hanna]

Chris is right on the mark about reading wood. I have begun to notice even in decking lumber there are clues to how the wood will behave when cut. Sometimes I even avoid those "sure to bind the blade" cuts by paying attention.

When I was building the Red Oak cabinets recently, I let the wood sit & rest after each step...sure made a difference.

[Tom Gattiker]

...can also cause this.

I let 4/4 stock sit in my shop (stickered) at least a week before using it. I think the general rule of thumb is 1 week of acclimation time per inch of thickness.

[Bob Hovde]

Bret,

When I built cabinets from red oak in Virginia (BTW, You need to update your information to let us know where you live.), I had the same problem. Some pieces of red oak just explode once you release them from their neighboring cells. The mill I used told me they made thinner pieces of red oak by using the jointer, rather than the table saw. It wasted more per piece, but saved overall.

Bob

[Jim Taylor]

:confused:

Can anyone describe the "why" of planing both sides of the board evenly. I have read this a number of times, but technically, don't understand concept.

How is the board effected, is it that you anticipate a difference in moisture content as you move through the board, and try to acheive a common depth on both face sides? Expecting to reach like moisture levels on both sides...

Otherwise, I can not understand how this general recommendation applies, as you can not generically determine wood cell structure in any board. Meaning, it seems impossible to generically predict stress in wood so that the "plan evenly" makes sence to me....

-Jim

[Jim Becker]

Can anyone describe the "why" of planing both sides of the board evenly. I have read this a number of times, but technically, don't understand concept.

How is the board effected, is it that you anticipate a difference in moisture content as you move through the board, and try to acheive a common depth on both face sides? Expecting to reach like moisture levels on both sides...Jim, you're on the right track. Moisture content can and will vary throughout the thickness of the lumber with less moisture near the surface. This is true even of supposedly "dry" wood. By planing a relatively equal amount of material off of both sides of the material, you'll reduce the amount of stress that can result from uneven moisture distribution if you only take off one side.

Sometimes, you "have" to thickness mostly on one face due to the features of the board, itself, such as sap or other undesirable figure on the "back" side. In this case, it's really important to sticker the material with weight after milling and let it re-aclimate to the MC of your shop before proceding with your project. Actually, you really should do that with all material after milling, leaving just a little extra to take off in final dimensioning once everything is ready to go.

[Jim Taylor]

Thanks Jim,

I have read quite a few WW books, but don't remember any of them saying.... do this because....

Moisture content makes sence.

[Larry Browning]

You guys have been talking about kiln dried lumber where the moisture content is higher inside the board. Is this also true for very old air dried boards. Most of the wood I am using now is 20+ years old air dired lumber. I would think that after so long it would be pretty uniform throughout the board. Is this correct?

[Chris Padilla]

Larry,

Only as uniform as the RH surrounding it assuming it all has adequate air flow.

[Jim Becker]

You guys have been talking about kiln dried lumber where the moisture content is higher inside the board. Is this also true for very old air dried boards. Most of the wood I am using now is 20+ years old air dired lumber. I would think that after so long it would be pretty uniform throughout the board. Is this correct?
It is likely that you will have a more uniform distribution of the moisture, but as Chris said, "it depends". Further, internal stress can still be in the wood; particularly that caused by growth/weather/etc., while the board was still "on the hoof".

[Keith Outten]

Bret,

Try another lumber supplier. My guess is that the lumber you are using was steam dried too quickly using an improper drying schedule. I have an Ebac dehumidification kiln that I have been using for 15 years and have never had any of the problems you are experiencing with the lumber I dry. Two of my friends also purchased Ebac kilns and we have all had nothing but success producing top quality lumber.

Dehumidification drying schedules are very slow and use very low temperatures. The gradual extraction of moisture from the air in the kiln allows the lumber to give up it's moisture slowly and reduces internal stress. I usually try to acquire lumber right from the sawmill and get it right into my kiln without any air drying. This way I can control the drying rate and the ends of the boards will not split or check at all. It adds two weeks to the drying time but the end result is worth the time invested. Lumber quality and color is pristine.

In my local area there is only one supplier that I purchase from that dries their lumber using an appropriate schedule. When I need to purchase lumber that is not a local species (Virginia hardwood) I have learned to stay away from all of our local yards except one.

Fortunately for me a neighbor and close friend has a Woodmizer Sawmill. He also has an Ebac kiln he purchased after seeing the quality of my lumber and he keeps a very large lumber inventory. Our problem is that we have too much lumber these days and I keep way to much inventory which means I have storage problems since I stopped selling lumber years ago.

[Gary Whitt]

"Our problem is that we have too much lumber these days and I keep way to much inventory which means I have storage problems since I stopped selling lumber years ago."

Most of us woodworkers would call that a blessing, not a problem! :rolleyes:


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[Donnie Raines]

Everything stated are viable issues to your situation. Sadly, the only one you can truely have some control over is the idea started by Chris P.(reading the wood). That is intrumental not only to the stabilty of the wood. But, often the visual the lumber portrays. Meaning this: take rails and stiles for example. The straighter the grain, the more uniorm the the rails and stiles will match up with each other. But, straighter grain(IE..qrt sawn or rift sawn for that matter) is normally more stable...simple because of the layout of the cell structure within the board. So, straight grain equals a more pleasing finished product,plus, the straighther the grain the more stable the lumber will be.

Keeping in mind(sorry for the spin here..but it is true) that if the board has built up internal tension, or has been dried incorrectly or has been stored poorly since being dried, you have little to know control over what happens when you start to rip that board down.

[Larry Browning]

Chris,
I have been trying to figure out what RH stands for. Round Hole? no, doesn't make since. Really Hot? Not technical enough. Red Hat? No, wait that's a computer thing.
Help me out man!
[edit]
Wait! I think I've got it! Relative Humidity. Well, considering I live in a rather high humidity part of the country, and this lumber was stored stickered without the ends painted in an abandoned turkey house for 20 years, what are my chances of having it dryed well?

[Chris Padilla]

Larry,

Take a few moments and read up here a bit:

http://sres.anu.edu.au/associated/fpt/drying/kiln.case.html

I think you'll get some ideas.