Is thick wood more stable than thin?
Jamie_Buxton
| Posted in General Discussion on
Is thick lumber more stable with humidity changes than thin lumber, or is it less stable? For extra credit, explain why.
This isn’t just an academic question. I’m building a piece with frame & panel doors. The panels are veneered MDF, so the doors’ flatness is set by the lumber frame. The doors are inset, so I can make the door frame lumber any thickness I want. I want the doors to stay unwarped, so the stability of the frame lumber is the issue. Should I make the lumber thicker or thinner?
Making the lumber thick will make it stiff, which seems good. On the other hand, with thicker lumber, differences in expansion on the two faces have more leverage to make the lumber move.
Anybody got an answer?
Replies
I'm not sure I have an answer, but I have some opinions. I hope others with more experience/information will correct me if I go astray.
I believe the primary factor in determining whether or not your frames will remain unwarped is the type grain in the frame members. Straight grained wood is less likely to warp with age and/or environmental changes.
That being said, I am also pretty sure that I have read that when reducing a board's thickness it is better to remove material from both sides to give a better chance of keeping the internal stresses in balance. However, there is no guarantee that the internal stresses are evenly distributed and that removing equal amounts from each face will leave the material unwarped. This leads me to believe that if you have material that is already flat and straight at a given thickness, you are better off to leave the thickness alone rather than to risk unbalanced stress by removing material.
These are just my opinions, and I would welcome additional information to educate me...
Dick Baker
Sunnyvale, CA
A thin piece of wood has fewer internal stresses than a thick piece and reacts to its environment more quickley due to lesser mass. So, yes, a thin piece of wood is less stable than a thick piece. That being said, if you don't choose your wood carefully and build accordingly, thick or thin, the most prominent door in the cabinet will probably warp.
How about a more difficult question. Are thick sandwitches more stable than thin ones?
Glendo. ;~)
OK what's the maximum thickness that law applies to? My timberframe timbers were pretty stable as long as they were as thick as they were wide (ie 12"x12") however the 6"x9" timbers would weave around a hootchie cootchie dancer.
If only it were that simple. Stephen Hawking could probably give you a series of calculations that would answer your question, however, it would serve no practical purpose. Your 6" by 9" beams are now stable in their current state,though not in the configuration you were hoping for. Bummer.
I'm still thinking about those hootchie cootchie dancers.
Glendo.
the only reason the dang things are stable is I've nailed, screwed lag bolted and moticed and tenioned 'em to death.. I swear they were wigglin as they died, made me miss the nail head too often to be anything else!
Normally, the word "stable" or "unstable" is applied to how much a species of wood will expand and contract given a change in its moisture content. If that is the context of your question, it makes no difference what the thickness of the lumber is, it will expand and contract the same percentage.
You can go to http://www.woodbin.com and click on the "Shrinkulator". Plug in the species, width, and range of either moisture content or relative humidity and it will calculate the expansion/contraction.
Stable and unstable is sometimes used in referring to the propensity of a board to warp as it expands and contracts. This is an incorrect use of the word(s) but there are certain woods that are more prone to erratic movement than others and, wood that may have been incorrectly dried may exhibit erratic movement (warping) as it expands and contracts.
Straight grain
Stable species have lower tangental to radial shrinkage ratios. Perfect would 1:1
Quarter sawn wood helps alot.
Thickness has more to do with the abilty of the piece to withstand it's intended use in service and the type of joints you want to use.
Your mdf panels panels flatness are not set by the frames. The mdf is flat and stable and will stay that way as long as the veneering is balanced. In fact your panels can be a structural part of the doors which will then be even stronger than if the panels float.
John O'Connell - JKO Handcrafted Woodworking
Life is tough. It's tougher if you're stupid - John Wayne
Edited 1/9/2003 4:05:11 PM ET by ELCOHOLIC
Jamie, in making the stiles and rails for your doors what is the range of tolerance for thickness of the stock realistically? Maybe a quarter to half an inch? Say 3/4" stock vs. 1" stock? Or maybe 7/8" stock? See where I'm going with this?
Over the relevant range, whilst still considering aesthetics, I'd say you don't have a problem; let the design dictate the thickness.
Edited 1/10/2003 4:24:51 PM ET by BossCrunk
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