How to figure panel size

[gsmittle]

As most of you know, I'm no math whiz. I'm building frame and panels for the first time, and I'm wondering if there's an easy way to figure the size of the panel. I'm making them just large enough to fill completely the frame, with no room for wood movement.

How do I figure this out?

g.

[chopnhack]

I will assume that the panel is plywood.
Length + dado depth x 2 by width + dado depth x 2. I would still leave yourself a 1/16" in each dimension so that the panel doesn't bind when you go to assemble in case something is not perfectly square.

[cabinetman]

Take your overall dimensions, and reduce the size by the width of the R&S up to the depth of the groove for the panel. IOW, lets say you have a panel/door for a 16" width, and the stiles are 2", and the groove depth is ¼". Subtract 4", and add ½" (for the two grooves), or just subtract 3½". Your panel will be 12½" wide.

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[jussi]

If you decide to use spacer balls, make sure to take that into account.

[LCHIEN]

sure you want to leave absolutely no space? If you are off a little in the wrong direction then the frame will never close up. If it fits perfectly but then some wood parts shrink or grow it could bust open the frame. I'd consider leaving at least a 1/32" extra room, maybe more if its a big panel.

[leehljp]

For me, I did not know how either, so I built the frame - rail & stiles and assembled with a band snugly - but not glued. Then I measured the dimensions inside the slot from side to side with kind of a story stick. I had a stick that would fit inside, made it too long and then kept cutting off about 1/32" until it fit. I did this for lenght and width. I cut the panels to this size minus 1/16" and then routed the panels on a router table.

The way that I did the panels was like this: I set the panel bit and fence to where I wanted it and locked the fence down. Then I placed about three 1/4" layers of ply and one 1/8" ply on the front side of the fence. The 1/8" was next to the fence.

I made a pass, on all panels, removed a 1/4 ply layer, made another pass, and so on until all were done. It worked for me but there are other ways to do it just as well and maybe even better - as mentioned above.

I agree with Loring on sizing. Wood shrinks and expands over the years and can tear a joints apart.

[cabinetman]

Wood shrinks and expands over the years and can tear a joints apart.

Generally speaking that is true. For the dimensions of R&S, I've experienced no joint separation that I've noticed. The stock is narrow enough and has the ability to move outward, or, IOW away from the panel. I've glued in plywood panels to a R&S type frame and a direct glue in to a rabbet without incident. It makes for a very rigid door.

To "float" a solid wood panel in a R&S panel or door is more for the benefit of the panel, not the frame. If the stock for the frame has been questionably acclimated, there stands more of a chance for warping than the joints separating.

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[woodturner]

If it fits perfectly but then some wood parts shrink or grow it could bust open the frame. I'd consider leaving at least a 1/32" extra room, maybe more if its a big panel.

+1 - can't tell you how many panels I have had to repair because the original maker did not allow room for the panel to expand. When the panel did expand, it forced the joints apart in some cases, split the rails in others (if the joints were pinned or otherwise mechanically secured).

I'd look at the expansion rate for the wood used for the panel, then size the gap accordingly.

If plywood panels are used, it might work to have a small to zero gap, since plywood is more dimensionally stable than wood.

[gsmittle]

Some details I left out: the frames & panels are hard maple, solid panels, no plywood. All pieces are 3/4" thick, the dadoin the styles and rails is 3/8".

Let me see if I have the basic procedure: measure the width of the styles and rails, subtract that number from the panel, then add back in a hair less than 1/2".

Now all I gotta do is do all the adding & subtracting correctly.

Thanks for the help!

g.

[conwaygolfer]

Leave a small amount of wiggle room for an easier assembly. After you apply the finish coat, the door panel will be sealed in and tight without any "noise".

Conwaygolfer

[cabinetman]

I'm making them just large enough to fill completely the frame, with no room for wood movement.

How do I figure this out?

g.

Since you stated that the panel isn't plywood, you're finding out that a solid wood panel needs some gap.

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[woodturner]

Some details I left out: the frames & panels are hard maple, solid panels, no plywood.

Here is a calculator for wood movement

Using this calculator, seasonal movement for a typical 15" maple panel should be in the range of 1/4" - so make the panel maybe 1/8" smaller than the slot to slot distance if it is the "wet" season when you make it, and 1/4" smaller if it is the "dry" season.

[mpc]

Another type of story stick that works almost foolproof for R&S doors, drawer bottoms, etc:
Just cut two square skinny sticks from scrap. Mill one end of each stick small enough to fit in the slot. With the R&S dry fit (or drawer sides dry fit, etc) and clamped, put the milled end of each stick in opposing slots and hold the sticks together. Draw a line across the two sticks to mark their relative positions to each other and you now have an "inside the slots" measurement. This measurement is the absolute maximum the panel can ever expand to so actually make the panel a bit smaller than the stick measurements to account for wood movement. It's basically the same story-stick idea some folks use to measure diagonals in a drawer or cabinet body.

When I do this 2-stick measurement trick, I start with the sticks at one end of the opening - e.g. at the top of the panel. Once the distance is set & marked, I slide them down the R&S pieces to the bottom of the panel. This lets me double-check that the R&S is a square/rectangle rather than a trapezoid and it verifies the grooves are a consistent depth.

To help keep the panel from rattling, various ideas I've seen/read about over the years:
1: special-purpose space balls
2: plain old foam or soft rubber tube-style weatherstripping material slipped into the slots
3: gluing just the center half-inch or so of the panel in the slots on the edges that won't experience wood movement (i.e. if the panel will mostly change in width apply glue to the centers of the top & bottom edges). This keeps the panel centered as the wood moves. Similar to the idea of fastening one specific point in a tabletop or counter top and allowing the rest to be free to move back and forth.

Also, because the panel may shrink in the future... apply the finish to the panel, or at least the portions that fit into the slots, before assembly. Otherwise, when the panel shrinks you'll have thin sections of unfinished panel wood visible.

mpc

[cabinetman]

Most door and panel manufacturers (and there are a lot of them) don't use any calculators to determine E&C. There are too many variables involved with getting specific data. What does happen is a selection, handling, and storage routine that sets a schedule for the frames and panels.

For the hobbyist, If too much gap is left when the MC is high, an edge of the panel could get exposed when it dries out. Determining the MC could vary quite a bit on the method used (meter and places checked). In some areas where the humidity swings are spontaneous and wide in range, the stock could read one percentage in the morning, and late afternoon read another.

It's not really a hit or miss. For those that have experience making doors there are basic guidelines for how the parts should be to get positive results. I'm not an advocate of using calculators to get specific results. The input data could be slightly different than it actually is, and the resulting information would be worthless, IMO. The amount of expansion and contraction will vary from one panel to another, as the stock is different on their own.

The "floating" panel, needs to float, for the benefit of the panel. For the frames themselves, the joint damage is very rare, unless the panel size has been misjudged, or poor acclimation, or shoddy fabrication. For the joints themselves, the C&S is a cross grain to a long grain. If damage to the joint is of question, it would happen most likely if the rail(s) moved, and being glued would be affected by the stile. With the thousands of doors that are made (probably daily) that method is still used.

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[leehljp]

Generally speaking that is true. For the dimensions of R&S, I've experienced no joint separation that I've noticed. The stock is narrow enough and has the ability to move outward, or, IOW away from the panel. I've glued in plywood panels to a R&S type frame and a direct glue in to a rabbet without incident. It makes for a very rigid door.

To "float" a solid wood panel in a R&S panel or door is more for the benefit of the panel, not the frame. If the stock for the frame has been questionably acclimated, there stands more of a chance for warping than the joints separating.

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You are right. I spoke on the wrong problem. I had a rail and stile come loose on one end, but it wasn't because of the panels. In looking back, I had to stretch my memory as to why mine came apart. And I had to go look at it. Finally I remembered: to prevent the gluing in of the panel I evidently used too little glue or made a poor glue joint. It came apart during its trip from Japan back to the US, but I reglued it. The outer edge joint did break some wood off from the opposing mated side. Can't see it from the outside thankfully, but the same joint closer to panel (inside) came apart at the glue joint. Meaning - I aparently didn't add enough glue so as to prevent gluing the floating panel.

Gluing rail and stiles takes a balance of enough. Starve the joint and it will come apart, but two or three drops too much might glue the panel. Not a problem for those with experience but something to watch for on the first time around.