How to size a floating, raised panel

[Spokaneman]

On both ends of a large, built-in bookcase I'm adding a raised panel assembly. The case will be painted, not stained, and the raised panel assembly will be made of poplar. I am trying to determine how to size the floating panel.

All that I read indicates that the panel should not be glued and should be allowed to be somewhat loose within its frame. And this is what troubles me. If the panel is loose and the entire case is painted, I worry that dried paint will crack around the edges of the panel and detract from the appearance of the structure. On the other hand, if I make the panel an exact fit, I worry that expansion of the panel may harm the assembly.

Would the use of "space balls" in the groove of the frame solve my problem? But still wouldn't the dried paint tend to crack?

[ed kerns]

First off, I think your concerns are well founded. A large raised panel made of Poplar will expand and contract. Gluing them in to the frame is not a good idea. Space Balls only allow them to expand and contract without rattling in the frame, so the paint lines will certainly show. A couple of options; my first choice since its a painted cabinet would be to make the panel out of MDF. Nasty (dusty) stuff to rout, but it takes a finish well, stays flat and stable and can be glued into the frame. Alternatively, if you decide to use a Poplar panel, paint the panel before it is installed in the frame. That way there are no 'tell tale' lines when the panel moves. Because these are the end panels of your case and not a door subject to constant opening/closing, I doubt rattling of the panel would be a problem. Good luck with the project!

[mbholden]

as Ed points out, the key to frame and panel construction is to finish the panel BEFORE putting the frame around it. This can be awkward to keep the panel pristine while completing the work and putting a finish on the frame, but that is the way to do it.

[Scoony]

It has been my experience that panels will shrink, but not expand all the way back to original milled size. If time allowed, I would bring the panel pieces into the house for a few weeks prior to final milling.

I will usually bring chest lids into the house for several weeks before inseting lock pieces, otherwise the locks never line up correctly.

[WoodTinker]

Paint the panels before assembly and do not glue the panel in place.

[barnowl]

WoodTinker said:

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Paint the panels before assembly and do not glue the panel in place.

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THIS, and assemble with space balls.

Often, I cut them in half with a utility knife.

[mbw]

If I was doing this as you described, I would make the panels from good quality mdf, and not worry to much about them expanding or shrinking.

My 2 cents

[YSU65]

I finish the panel before installing. I also add a few drops of a silicone into the midpoint of the rails. Silicone is compliant, not a hard adhesive. This allows the panel to expand in either direction but is held from rattling around in the frame.. Works for me

[jteneyck]

If you want to use solid wood you really should get Bruce Hoadley's book "Understanding Wood" and read the section about seasonal expansion/contraction. Actually, read most of it. He explains how you calculate how much a panel will move based on which species it is, its moisture content, and the expected seasonal swing in RH. Guessing leads to grief. Build tight in the Summer, loose in the Winter is all well and good, but how tight or how loose? The answers are in Hoadley's book. If you get FWW, Christian Becksvoort had an article in it a couple of years ago that covered the same issue.

John

[jppierson]

How about building the floating panel so that it fits proud of the rails and stiles? Basically groove the panel along all four edges, and groove the rails and stiles. The panel then fits proud. It would be easier to maintain the paint later since you could tape off the panel edges and paint the rails/stiles. Also any cracking of paint would potentially be easier to disguise in the shadow line of the joint.