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 heightAnother say:
3/8" for width 1/4" for heightHow 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
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
Examples:
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?
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.
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?
Used 2 each side...
Chuck
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
Correct but also, if my panel is too thick and there is too much friction, 3 space balls will not prevent tilting.
Width and length of the panel are not too critical as long as you are close. The tightness I am talking about is the thickness of the panel going into the slot.
Also if the panel goes into the slot too far and the raised profile begins to go into the slot this can be a problem also. Basically you only want the "flat thin outer edge" of the panel to go into the slot. If the raised part of the panel profile is starting to go into the slot the panel is too wide or long.
I can draw a you a picture on a PDF file if you like.
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
I do the calculations referenced in another posting in this thread, but don't use spaceballs. I use brads and pin the panel with wire brads top and bottom in the center from behind. So far, so good.
For nails, use 1/8" for width. With space balls, use 1/2" for width (and height). Using nails would allow the panel to tuck in more.
Chuck
Oh, really? Suppose you have a panel of flatsawn white oak, 12" wide. An increase in moisture content from 8% to 12% (easily the result of the difference between winter and summer humidity) will cause that panel to expand in width by almost 3/16". If you allowed only 1/8" for expansion... you have a problem.
You can't use any arbitrary figure, without taking into account the width of the panel, the species of wood, and whether it's flat- or quarter-sawn.
-- 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?
The jury says I am guilty :) I did review a little on the link you provided. This is my last week of finals, so I am kinda rushing.
I really need to (and want to) study this part. Thanks for correction.
Chuck
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
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.
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
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
Mixed feelings that it would rattle. However, it would be nicer simple step than adding all those space balls.
Chuck
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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