Wood Movement Worries with Large Wainscot Panels
Oversized floating panels are likely to grow and shrink too much to be practical. Here are some explanations, and advice on substitute materials. August 12, 2014
Question
I have to make some full height raised panel wainscoting and some of the raised panels are 48" wide by 84" high. What is the best way for gluing this up? I'm worried about expansion and cracking of the panels.
Forum Responses
(Architectural Woodworking Forum)
From contributor L:
There are calculators for estimating how much movement a solid wood part will have with changes in environment. At 48" you are way beyond the width that I would do. That said, if this is a designers spec, get it down in writing that this is not recommended and not covered by any sort of warranty. Half that wide is pushing it. If you still do this you will need to make extra deep grooves for the panel to float in, use only quartered lumber checked multiple times for moisture content and finished front and back the same.
From Contributor G:
Make the panels out of MDF or particle board and wrap the edges with the same species a bit bigger than the bevel itself. Then you have the best of both worlds, looks like wood and is stable like MDF/PB.
From Contributor O:
Contributor G is right, although he left out the obvious - veneer the panels in the same species as the rest of the work. However, I have had this request for large panels several times and each time it was because someone in the mix thought it would be less expensive than having a bunch of smaller panels made. Once they were educated a bit, then they could lose the odd design parameter and get into something that was nicer and would be more appropriate.
From contributor H:
I'm about to make a door with 18" wide solid wood panels. There will be a 1" hollow space inside the door, between the layers of panels.
From Carl Hagstrom, Systems Administrator at WOODWEB
There is a wood shrinkage calculator at WOODWEB's calculators area that provides definitive values for panel movement (link below). You'll need to enter the species the type of lumber (flat sawn or radially sawn), and the moisture content swing.
As a point of departure, I plugged in cherry as the species (a "middle ground" movement species), and a MC swing of 6 to 11 percent (appropriate for a heated structure in a northern climate with no humidity control). When flatsawn lumber is used, the movement between the MC swing is nearly 5/8". Using radially sawn (or vertical grain) lumber reduces the movement to 5/16". To illustrate how much difference the species can make, substituting flat sawn sugar maple results in nearly 7/8" movement. As mentioned by others, using veneered panelized material would be a sensible way to go.
Hope this is of some help - misconceptions about wood movement abound. I've been fortunate to have learned from the best - Gene Wengert (AKA The Wood Doctor). There are dozens of articles in our Knowledge Base by Gene detailing wood movement, an event that can be accurately predicted.
Wood Shrinkage Calculator
From the original questioner
Thanks for the help. I think I will do the MDF with the solid wood banding and veneer the top.
From contributor E:
Glad you are going this route. It's better all around. It's less milling, you just cut your panels and some solids to wrap it for the bevel profile and cut some good miters. Set up a nice miter jig on the chop saw or table saw and dial it in perfect. It takes a bit of practice rim mitering large panels like that but after a while you just fly with it. After they are veneered and raised you will have perfectly stable and flat raised panels to work with. If you have a press, always veneer it instead of going with veneered MDF and just trying to rim miter them like that. It's really a nightmare to say the least and I wouldn't want to do it like that again. It's so easy to burn through the panel sanding it around.
From the original questioner
I do have a press and an Omga miter saw and I kind of thought I would have to do it this way, but I wanted to get some feedback. The only thing I'm not crazy about is if the top and bottom raises the grain, then it will be going the opposite direction, but that is the poison I’ll pick.
From contributor L:
You probably already know this, but be sure to balance the panel and veneer the back too. The method given: wrapping MDF with solids in the profile and veneering the faces will pass AWI premium grade. Make sure your moisture content is correct or the line between the MDF and solid may show through.
From contributor X:
Have you thought about gluing up a strip of short pieces of hardwood and then running them through the panel raiser to create the endgrains? That would look a lot more realistic than running the grain long ways on the ends.
From the original questioner
I would worry about the movement of that with it being locked up by the MDF core if it shrinks it will crack.
