I have a dozen maple doors with solid raised panels. Half are wider than 10" and will require two or more boards to get the necessary width. Half require 8" panels and I have several 9-10-inch-wide boards. They are kiln dried to 8-9%, flat-sawn, and are moderately cupped but I can get a full 3/4" thickness from them.
Is there any reason not to use the boards as they are? Or should I slice them in half to relieve any pressure and re-glue? Does that serve any purpose if I don't also flip one of the board faces? Lastly, is it generally better (in terms of minimizing cupping or twisting) to keep the panels as thick as possible, with a relief cut around the back edges, vs. making them 9/16" thick and no relief cut?
(Architectural Woodworking Forum)
From contributor L:
8-9% is a bit wet, at least for here. I don't think ripping and re-gluing without turning the alternating sticks is going to help. Wood only warps when it changes moisture content. Fix that, and on panels that narrow I don't think it will much matter. Also, I don't think it matters a whole lot whether you make 3/4 or 9/16 panels, either works fine. Keep the panel floating and pin only at the center, top/bottom.
It was a mixed bag of opinions about alternating grain and so forth. Bottom line is, if this is an exterior door, I personally would rip 10" boards in half and flip them. They are cupped now and will move in a cupped motion again, not simply in width as many say. A fielded panel, 3/4" or 9/16" thick, flat sawn, trapped in a groove where it can't cup, will crack. Yeah, they look better as a single board. It might look better if they weren't split down the center next winter though.
However I've also seen 15" wide single piece cherry raised panels that were flat as the day made. In your case maple is a very strong wood and I would err on the side of caution and rip and re-glue.
I start by rough milling my stock for the panels, sticker, set weights on top, and allow them to sit for as long as I can. If I am in a hurry that may be a few days, if I can I like to allow a couple of weeks. I then build my frames, and when they are ready I start working on the panels. I plane the faces and joint fresh edges then glue up. As soon as they come out of the clamps I like to cut to size, raise, sand, and pre-finish immediately.
The panels get dry fit/stored in the frames which really helps at preventing unwanted cupping or twisting. If this isn't an option I sticker them on a flat surface, and set weights on top. I work with allot of wide boards 13"-15" but I only have an 8" jointer. I prefer not to rip/glue unless I have to. Just make sure to allow for plenty of movement. Do the math or use one of the movement calculators. Rule of thumb is not to be trusted.
It is key to remember that one will not change its size or shape unless the moisture content changes. So, get the wood at the same MC that it will have in use, and you will be safe indeed. As mentioned, 8% MC might be high for an interior door in much of the USA. This MC level is more important and more effective than relief cuts (which do work). The fact that you already have some cup indicates that you are dealing with a cup-prone piece of wood and so extra care must be taken (extra care like correct MC and maybe even rip and flip).