# Panel Expansion Allowance

What is the length and width for Panel Expansion Allowance? I like to use space balls.
One say: 1/8" for width 1/16" for height
Another say: 3/8" for width 1/4" for height
How to figure the allowance if it's preferences? When I did samples (with space balls), I mark the panels with pencil, then take it apart and see it's tilted.
Chuck
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Change in length is so close to zero that you don't need to make any allowance for it whatsoever.
Change in width depends on the type of wood, the width of the panel, and the amount of change in moisture content.
It can be estimated using this formula: D = W * k * (M2 - M1) where - D is the change in dimension - W is the width of the panel - k is the dimensional change coefficient, which is different for each species and different for radial and tangential expansion - M1 is the original moisture content in percent - M2 is the new moisture content in percent
Sample values of k: Cherry: 0.00126 radial, 0.00248 tangential Sugar maple: 0.00165, 0.00353 White oak: 0.00180, 0.00365 Walnut: 0.00190, 0.00308
Formula and coefficients taken from "Wood Handbook: Wood as an Engineering Material", chapter 12, available online at http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch12.pdf
For flatsawn lumber, use the tangential coefficient to figure the change in width; for quartersawn lumber, use the radial coefficient.
Examples:
1. A panel made of flatsawn cherry, 12" wide, increasing in moisture content from 8% to 12%: D = 12" * 0.00248 * (12 - 8) = 0.12" In other words, this panel will increase in width by nearly 1/8".
2. A panel made of quartersawn white oak, 18" wide, decreasing in moisture content from 13% to 7%: D = 18" * 0.00180 * (7 - 13) = -0.194" (note the negative sign) In other words, this panel will *decrease* in width by about 3/16".
Hope this helps.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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I am see the differences in between the depths of 3/8" and 7/16" router bits. Using (1/4") space balls, the 3/8" depth will only leave ~1/8" left for the panels to tuck in, while 7/16" will leave ~3/16" left.
I have yet to study the following. I am wondering if the following affects (still talking about raised panels projects):
1) If the project was to be build in south (FL, TX, AZ, etc) and to stay there, would this (shrinkage) still matter?
2) If I was to build something in the summer (north, WI, IL, MN, OR, etc), I should expect the wood is in it's full stretched position?
3) As to #2, if I was building the project in the summer, but a cool basement (most would have dehumidifier running), what would the "barometer" be?
4) If I was building a project in the winter (north), the wood would be in it's most shrunken? The house (indoors) humidity doesn't count as the outside?
Forgive me if this is none sense or too techincal. But, gotta ask away!
Chuck

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Yep. Air conditioning can dry things pretty well.

Building in the basement, perhaps. Upstairs, no

Now there's a question with no answer.

Warmer air is capable of holding more water - absolute humidity - than cold. The cold outside air, warmed, lowers the realtive humidity in the heated area.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/fplgtr113.htm
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Do you mostly dry fit the rail and stiles first (using clamps and the likes) and then measure the panel (from in-groove to in-groove then subtract the allowance)? Or you do the calculations and trust on that (get all the numbers from whatever math used and cut the work without second thought or measuring twice?)?
I am asking because all the samples I did was for one-panel assembly and the Excel worksheet worked "perfectly" but when I tried the two-panel assembly, something went off (could be me or the arithmetic).
Chuck
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Why not forget the space balls and use Dugs figures for panel expansion with a brad at the center of the panel both top and bottom

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Mixed feelings that it would rattle. However, it would be nicer simple step than adding all those space balls.
Chuck

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Correct me... warm air (summer), the wood EXPANDS cold air (winter), the wood SHRINKS
Also, I am still trying to understand this... in a summer time, I am building something in the cool basement with the dehumidifier running, should I still consider the wood is already in it's full expansion?
(still in summer in cool basement) if the wood is in full expansion, I should then make the raised panel tight, since it will only shrink when the winter comes. Correct?
Chuck

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CNT wrote:

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CNT wrote:

Wood expands when it absorbs moisture. Wood shrinks when it dries. Humidity causes the change. Temperature has little to do with the change other than cold air usually contains less moisture.

No. It could expand further if the final place for the piece has a higher humidity than your dehumidified basement.

See above.
--
Jack Novak
Buffalo, NY - USA
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OK... so, when I am plan doing the work that day, I just turn off the dehumidifier, open two little windows the day before and during the work day. That should give enough time for the wood to drink?
I am finally finish with school and have summer off! Time to study this topic. David, I will read that link you gave me SOON.
Chuck

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You might consider staining door panels BEFORE assembling the door so that future shrinkage, if it occurs, will not result in a light band of unfinished wood, spoiling the appearance.
Dave
CNT wrote:

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NO. The last thing you want is for the wood to be absorbing and releasing humidity - thus changing size and shape - while you're still working on it.
Keep the dehumidifier running all the time. Or none of the time. Ideally, you want to work the work under approximately the same humidity conditions as it will be exposed to as a finished piece. In a centrally heated and air conditioned house, with a basement workshop, this means running the dehumidifier.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Incorrect. *Humid* air, the wood expands; *dry* air, the wood shrinks. If your house has central heat and central A/C, and in the spring and fall you run *neither* but leave your windows open, the greatest expansion will occur during the spring, not the summer.

I shouldn't think so, not with a dehumidifier.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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The slots that my panels fit into are about 1/2" deep. The space balls are just over 1/4" in diameter. I make the panels to be 1/2" total longer and 1/2" total wider than the inside of dry fit rails and stiles. The space balls compress slightly and hold the panel evenly suspended. Basically 1/16" to 1/8" larger than the available space between the balls.
If your panels are mounting "tilted" your panels may be fitting too tightly in the slots and not floating properly.
The trouble with many raised panel cutters with back cutters is that the back cutter may not cut enough or cut too little for the panel to float properly with in the door frame.

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Or he may be using only one SpaceBall per side - should be two.
-- Regards, Doug Miller (alphageek at milmac dot com)
Nobody ever left footprints in the sands of time by sitting on his butt. And who wants to leave buttprints in the sands of time?
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Used 2 each side...
Chuck

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wrote:

Correct but also, if my panel is too thick and there is too much friction, 3 space balls will not prevent tilting.
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I thought I submit a reply and it didn't show up (yet)?
Anyway, I did another sample (doing samples with pine makes it "more comfortable/familiar"). After figuring out the measurements (with the Excel I got from a nice guy from here :), looks like I finally got it all together. With the space balls, pencil mark it, I got 1/8" (each side) tucked in on the stiles and 3/16" (each) in the rails.
Now, I think I should be ready for a real project... but first I like to make a sitting chest for the bedroom, then the main project I have been planning on for a long while.
Chuck
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So, lets say you have 7/16" bits (which is almost 1/2"), you cut another 1/4" alone off in D ( D from my picture in previous post)?
Or you just adjust the panel size in that only ~1/4" tucks in each sides (with space balls inserted)?
I think you're right, I may have attempt to assemble things too tight.
Chuck

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