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Seeking advice on Floating Panel Box Tops ???

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Blog entry by Blake posted 10-21-2007 02:44 AM 2641 reads 1 time favorited 4 comments Add to Favorites Watch

I have never quite been sure what the rule of thumb is for floating panels in box tops.

I am relying on some of you seasoned folks on this one. I know there are a lot of different opinions on the application of floating panels. When is it necessary? When is it not? Are there certain sizes, widths, woods, or thicknesses that you can get away with without floating the panel?

I have not made enough boxes to know from experience. As you can tell from my projects, I pretty much try something totally different every time. I have made a few different types of floating panels. I have used those little rubber balls, or just wedged it in. I have read several different approaches to floating panels.

One problem I have had with large panel box tops is that the front of the frame (on the box top) is so long, skinny, and unsupported since it is not actually attached to the panel that it tends to twist or bow out. It sometimes doesn’t align with the box front even though it was cut from the same piece of wood… I have mostly used the method of building the box in one piece and then cutting the lid off (separating it) on the bandsaw.

I have seen fairly high-quality, commercially made “handmade” jewelry boxes in a local artisan’s gallery. They were probably 10”x12” but didn’t have floating panels in the tops. Doesn’t this defy the laws of the universe? Or did they use wood from Mars that doesn’t move?

Do you have any advice for me?

Thanks,
-Blake

”The advice we give will meet any two of the following criteria:

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Good, Fast advise will not be Cheep.
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-- Happy woodworking! http://www.openarmsphotography.com



4 comments so far

View Douglas Bordner's profile

Douglas Bordner

3971 posts in 2817 days


#1 posted 10-21-2007 03:16 AM

I would be nervous using a glued down panel that big. Something has to give over time. Granted, different species will vary in the amount of movement, and that variance will co-vary within species depending on whether the wood is rift or quartersawn.
Were those commercial boxes veneered over some sheet-good stock? Were they glued directly onto the box sides, or were they let into a rabbet with the box joined with miters? My experience with just sticking that wide of a panel down with glue has been abysmal. And like your dust collector, I suck at mitered box corners (or maybe it just my !@#%#* sawas if). I’ll be looking at this post to see what more seasoned folks have to say. Don, Thos., Lee, you guys out there?

-- "Bordnerizing" perfectly good lumber for over a decade.

View Dorje's profile

Dorje

1763 posts in 2750 days


#2 posted 10-21-2007 10:06 AM

If you’re doing a frame and panel top, I’d say the safest thing to do is to always float the panel…That is the whole idea behind the frame and panel to begin with. Float the panel to allow for the movement. If it’s a solid panel (w/o a frame) you have to allow for movement in your design of the top.

Douglas, in his comments above, is right on track. Here’s some more:

How to do it all depends on what type of wood, the width of the stock, the cut, what the moisture content is, and how the panel may change over the year…

If you have access to FWW articles, see this one:

http://www.taunton.com/finewoodworking/SkillsAndTechniques/SkillsAndTechniquesPDF.aspx?id=27129

Or…if you have access to the Nov/Dec 2006 issue of FWW…it’s in there. From the article:

“You can predict
pretty accurately how much
a board will move simply by
knowing: (1) the species, (2)
the grain orientation (flatsawn or
quartersawn), (3) the width, (4) the
current moisture content (MC), and (5)
the expected highest and lowest MC.”

And this chapter (referred to in the article) is a MUST have…especially Table 12-5 – to look up the coefficients for varying species, that you plug in to a basic formula: something like, width of the panel X the appropriate coefficient X the percentage of moisture content change expected for the particular piece.

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch12.pdf

So for example, take a 10” Alder panel, let’s say that’s it’s flatsawn, for which the coefficient is .0026. If we choose to be on the safe side, the most this piece can change is roughly by 10% – if we don’t know where it will really end up in the country and we’re assuming it’s inside! (In the article the author says that the range of interior moisture content changes is from ~4% to ~13%). So our calculation is 10 X .0026 X 10 = .26 or call it a quarter inch of potential overall movement. If the woods is at 8 or 9%, we can expect it to move up to an 1/8” in either direction over the course of the year as it becomes more or less humid. When you’re fitting your panel you have to consider all these factors in order to decide what the right thing to do will be. The coefficient for the same width in Alder that’s QS would be .0015. And if you put that in the equation you see that you’ll get about a 1/2 less movement than the flatsawn panel. Also, from what I’ve read, thickness of the wood isn’t a contributing factor.

-- Dorje (pronounced "door-jay"), Seattle, WA

View Dorje's profile

Dorje

1763 posts in 2750 days


#3 posted 10-21-2007 10:26 AM

Another thing: if you’re getting twisting and bowing of any of the pieces in your box, it sounds like the wood is still changing quite a bit (in it’s moisture content) and was not stable to begin with. Do you primarily see this with the wood you harvest from your property?

-- Dorje (pronounced "door-jay"), Seattle, WA

View gizmodyne's profile

gizmodyne

1765 posts in 2843 days


#4 posted 10-21-2007 04:31 PM

Is the top hinged? If so it should not matter since it is not attached at the ends unless it is inset. Frame and panel exists to solve wood movement problems. If the top sits on top lifts as on a toy box or piano lid it is fine without frame and panel.

What are you making?

-- -John "Do I have to keep typing a smiley? Just assume it's a joke." www.flickr.com/photos/gizmodyne

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