Crown in lumber

[Redoverfarm]

Just curious as to what contributes to the crown in lumber? Is it the manner in which it is milled and when it dries it is drawn to one side or the other?  Almost every stick of lumber has a crown. Some are more prominent than others. Peg I am sure you will have the answer as well as other. For me I do not.

[FrankInWI]

this won't be as much fun as PEG's response, but bood version of the response could be this one from Southern Pin: 


Warp can be traced to two causes...
Warp in lumber is any deviation of the face or edge of a board from flatness or any edge that is not at right angles to the adjacent face or edge. Warp can be traced to two causes: (a) differences between radial, tangential, and longitudinal shrinkage in the piece as it dries or (b) growth stresses. Warp is aggravated by irregular or distorted grain and the presence of abnormal types of wood, such as juvenile wood or reaction wood. The six major types of warp are bow, crook, twist, oval, diamond and cup. Splitting and cracking result from the lumber's reaction to wet and dry moisture cycles. Exposed surface areas expand when wetted by rainfall and contract when dried by the sun. This continual process sets up stresses that can cause cracks and grain separation (checking). Protecting lumber from the elements with proper covers during storage and at the building site can help minimize warp and crack. 

              http://www.southernpine.com/expert/faq.pl?leafcode=33

[Redoverfarm]

Yeah and no.  I am just wondering if that warp they are referring to is the same as the crown in lumber. When building especially with rafters or floor joist I had been tought to turn the crown up.  Almost every piece of lumber that is used has this. Like I said before some may be slight while others are huge.
Thanks again Frank.

[glenn kangiser]

Wood is pretty much an inexact science - heart wood- sap wood - sawyers or maybe computers cut choices can all effect it.

[PEG688]

  My Oh My I have to be witty and informative , BOTH   I'll do my best, 

  Crown is different than twist , bow or warp.

Yes most dimensional lumber has crown it cause to differential radial shrinking.  So it's caused by how the piece is cut, in relation to grain direction.

Twist and warp sort of are the same thing , they go both ways on the board across the grain and lengthways .

Bow  / cup is across grain.

So crown is common on joist, purlins , rafter things that bear weight and are generally run  not up perfectly  right  the crown goes up .

On wall when  frame the walls laying down I put the crowns up or what will be outside on exterior walls , crown on studs has to be less extreme or the walls will look bad , you'll see the bow in the wall. Of course even on joist and rafters extreme crown can be a issue.


Not very fun , did I tell you the one about.............

On stud wall badly crowned stock is cut up for blocking backing etc , things other than studs.   

[glenn kangiser]

Boy, am I glad you arrived, PEG.  I was trying to humor them until you got here, but they were having none of it.

It seems they didn't think I was witty, informative or as pretty as you.