I built a 6' x 3' x 3' church alter. Basically a big plywood box with a 7/8" maple shell (skin). Not a solid shell on 4 sides, the back has 2 doors that open to reveal drawer banks. The maple is joined to create the shell but there are design ribs where some of the joinery occurs. The shell is 1/2" larger than the plywood box to allow for shrinkage and movement and culled in a few places to attach the two pieces. Thought I had everything covered!! 3 months later in an extremely dry church (pianos has been ruined in this location from dryness in the past) and the maple ripped apart from shrinkage. Outside corners pulled 3/8 - 1/2 apart, joints separated, what a mess.
Now to the rebuild. Eliminate the plywood interior and thicken up the shell to solid 1 1/2+- thick walls? Solid 1 1/2? Laminated, cross grain, 1 1/2+- Stick with maple (soft maple, it's a painted finish) or softwood like basswood or poplar. Don't want to make this a 3rd time.
I know RH is the big factor but I had no way to know how dry the church was going to be. Structural soundness is what I'm trying to figure out now. Thanks gang.
From contributor Da
Panel and frame?
From contributor Ne
Plywood generally will not shrink due to changes in RH. It can move a bit, but very little - thousandths of an inch in a 4' panel.
And if it did shrink, would more ply make it not shrink? I don't think I have the right picture.
From contributor vi
Thanks for responding, guys. It's a plywood interior cabinet with a maple exterior shell. The plywood remained stable. The maple shrunk like a bastard and split apart from the tension against the plywood.
Frame and panel? No. Smooth flat surface with 1/2 round vertical rib 12" apart and a horizontal 1/8" cerf cut the entire perimeter. I'll try loading a picture later.
From contributor Ch
Post a pic. I don't get it
From contributor Da
I sounds as if you created a classic situation where solid wood was fastened to plywood - irresistible force vs an immovable object - and you lost.
Frame and panel was developed in the 1300's as a way to minimize the effects of wood movement - a stable frame with a floating panel. It is not a decorative thing, it is a technical thing.
You cannot attach solid woods to the plywood and not have problems (unless it is small moldings, small cross sections, etc). Either all plywood, or all solid, but both can cause problems if you don't know how to handle it.
Go back to the design professional and explain to them that they will need to come up with a design that will work.
From contributor D
Without seeing the exact piece my thought is to use slotted type of holes where you fasten the solid to the plywood to allow movement without destruction .
Sounds like the design did not have wood movement in mind.
From contributor Ma
Im envisioning a 6' wide solid wood glue up (front face of "the box"). Sounds like you never had a chance.
From contributor vi
Thank you guys. Mark, you hit on the nose. Here are some pics. You can see the interior plywood carcass from the back. The exterior faces are jointed maple. I thought I left enough expansion room for the shell to shrink but I wasn't even close as you can see, and it just ripped apart when it reached the plywood interior. What you can't see are the individual joints that failed as well.
So now to the rebuild. One wooden box no plywood. I have a choice, I can use 8/4 stock, so milling the ribs won't compromise the joint integrity and give me a sturdy structure, or I can laminate 2 layers of 4/4, alternating grain and joints to get a solid structure. Unless there's some other way. Best case?
From contributor D
The picture helps , with a slight redesign you could be successful with frame and panel construction , even with the plywood interior box.
Also curious if the solid was painted on both sides ?
From contributor Ma
It looks like youve got some tooling and a shop, and without sounding mean, the first thought that comes to mind is "what were you thinking"? That front panel is 6' wide, solid. Its going to move a mile over the course of a year. I'd guess shrinkulator would call out close to 1/2" of movement and there is no allowance for it.
I dont understand the need for a box within a box though had you incorporated the partitions into the 6' wide panel it would likely have trapped the drawers.
From contributor vi
Hi Mark, it's hard to see in the pics but the maple was 4" stock. The 1/2 round ribbing created it's own challenge. The top cluster of 8 is attached to the solid bottom member. The flanking full vertical 1/2 rounds are cut into their respective flat panels then joined to the 8. Those connecting joints reduce the glue surface of those unions from 7/8" thickness of the panels to about 1/2"-7/16". Knowing the instability of those joints, the plywood interior was meant for strength.
From contributor Ma
Right, but if I am interpreting this correctly, that entire front panel (six feet wide) is one large edge glued panel. Regardless of what parts make up that panel, if it is a large edge glued panel, it acts as a single board expanding and contracting along its width (the six foot axis). If thats the case the panel could likely grow and or shrink over the seasons in excess of 1/2" or probably more.
You can google shrinkulator and input your dimensions to see an estimate of the calculated movement.
The sub structure could never resist this movement and thats what your seeing. The panel simply tore itself apart because the movement was not accommodated. It has nothing to do with the church's environment.
From contributor Ma
Why not just make the whole thing out of MDF? It looks like its painted. Scrap the wood all together.
From contributor vi
Thanks Mark,
I was actually thinking about MDF when planning this originally but I worried about longevity. The alter mimics the church's architectural detail of the pews and pulpits. Everything is wood and I was trying to keep with tradition. Also, the alter is on wheels and is moveable. It's already hard for some of the staff to move because of its weight. I was afraid the MDF would put so much more weight to it
To D. Brown, the back of the maple is sealed with a vinyl sealer but not painted.
From contributor Ma
If its paint, and changing the design to incorporate frame and panel is out, Id be building an internal frame/structure and using MDF. Your only talking about a couple sheets total, much of which will be milled away with the beads.
From contributor Ad
One must be careful in working in religous settings. Many people would consider the use of MDF in the construction of an edifice of God to be sacrilegious.
I do have to say that you've provided us with one of the most egregious violations of woodworking 101. You need to know your materials before constructing such a project.
From contributor Ga
Is there any way you can salvage what you've already made? For instance, if the maple's only split on the corners, could you add large corner caps fastened only into the plywood. It might not look too out of place considering all the beading . The corner caps could lap over the carcass panels without restraining them. Also pull out any screws connecting maple to plywood, and elongate the holes in the plywood. Just an idea, it seems like a lot of work down the drain. You could also do something similar by cutting down the panels in width and making some type of corner assembly which mates to the panel with a tongue and groove...
From contributor Ri
Maybe I missed it, but did anyone mention all those screws through the plywood into the hardwood? If you had clearance around that plywood box to start, it might have worked if you hadn't locked it all together with screws. Use elongated holes, and washers under the screw heads to allow the hardwood to move.
From contributor vi
Rich, I did have almost 3/8' clearance on all 4 sides to allow for some shrinkage but I missed elongating the holes. regardless, my guess is the front panel (72") shrunk almost 3/4" -1". I've never seen that much variation before. As I said in the original post, our Pastor told me that in the past they've had 2 different pianos shrink up to destruction from the dryness of this location. He tells me that after the fact of course.
Gavin, there's not much to salvage. Even some of the joints opened up where internal screws bound them up. I'm thinking now to rebuild it a solitary shell. 8/4 hardwood, alternating grain, with few culls to true it. I can still build the interior cabinets just not fasten them to the front wall.
This is for the Church and needs to have a long, durable, life so I can't in good conscious use MDF. This should be heirloom quality and last for many years. This one only made it 3 months.
From contributor Ma
There is no need for 8/4. Just a sound design.
From contributor Da
Vinnie - I applaud your view to the long term and the avoidance of MDF. The stuff is garbage for most of its uses, and has almost no durability. A waste of limited resources and one's limited time.
I also would think that salvaging the existing is out of the question since it has most likely been thoroughly defamed by barbaric language and generous usage of Anglo Saxon idioms, rendering it useless for the sanctified.
Proper frame and panel, all solid wood is fine, with perhaps going to 5/4 or 6/4 stock to avoid thin ares at the beads.
What I see in the photos is close, careful work, so you are to be commended for that. How you missed the wood movement, I don't know.
From contributor vi
Dave, thank you. I'm really embarrassed by the wood movement. I had no idea that it would be as extensive as it was. Understand that in measuring the gap at the corners coupled with the shrinkage of the inline boards, this baby shrunk 7/8" - 1". That is incredible to me! You would think I soaked the maple in water before assembly.
From contributor Ri
I agree with the others saying not to use 8/4. Thick hard maple can also have it's trouble if the kiln operator is off a little. Frame and panel doesn't have to mean looking like cabinet doors. You can make a straight cut around the panel, leaving the panel flush with the frame, and only have a shadow line around the panel. Of course sized to live in that church located in the Sahara.
From contributor La
RE: "with few culls to true it." Careful with those or you will be right back where you started from! This was designed to fail from the start! Skip the 8/4, it will have it's own problems. The only way I'd make such a thing is frame and panel. This was an expensive learning process but from your responses I'm not sure you've learned.
From contributor Je
I don't think he's learned either unfortunately:>( Simply remaking it with thicker stock is not going to solve the problem, it will just make it worse and more expensive. You have a solid wood panel on one side and not the other. Even without the inner plywood box and with just the shell it is going to start out as a rectangle, but one side is going to shrink and the other is not…..what happens to the rectangle??? FWIW that result would have happened in more locations than not, so it's not entirely on that particular church's environment.
You simply cannot build it the way your thinking. By refusing to see this simple fact your tying your own rope.
I would go with either mdf or ply with your design. You can either fit the materials to the design, or fit the design to the materials. Your doing neither but trying to force materials into a design everyone can see is doomed to fail. Not to get into the religious aspect but I'm not sure that any God would care what an alter is made out of??? Seems kinda silly and pointless to use that as an excuse to me….no? Rather build a product that will look beautiful and last. Different materials exist for us to use when and where needed. If you absolutely can't get your head around using a more appropriate material than you have to change the design. By refusing to do either your just going to repeat a mistake.
I wish you luck, I think your going too need it,
JeffD
From contributor Br
I don't understand why you would have used solid wood in the first place. It didn't make a better product.
From contributor Ge
As their is no source of moisture in a heated church in a cold climate (a home has showers, cooking, house plants), the interior can easily be under 25% RH or 5% EMC. What you need to do is take all the wood components and put them in a small room, or even a polyethylene plastic room, and put a dehumidifier in the room set for 25% RH. Dry everything out...MDF, lumber, trim, etc. Then, when building, put things in the room overnight. The finished item can be stored there too until ready to move. Or store the finished, low MC item in a large, sealed plastic bag. Unfortunately, the high RH in the summer can create some problems with swelling. But such changes are slow, compared to the rapid change from your shop (not using a DH) into the church, especially if you do not heat your shop 24/7.
From contributor Da
Dr Gene - Not to be argumentative, but definitely curious to a fault, if the OP had followed the 25% RH room suggestion, do you think his original build would have succeeded? That is, it would have been 'pre-shrunk' so as to not self-destruct?
And beyond that, are there shops that routinely keep things at a lower RH/MC due to the product going to churches or other non-residential places (almost any commercial space). Conversely, are there shops that intentionally have higher RH/MC for their products going into relatively high RH environments? Sauna doors come to mind.
From contributor Ge
Chance of success would be very high...95% plus.
There are many shops that adjust their humidity to be close to the customer's humidity indeed. Other shops adjust their humidity based on a wives' tale and still have problems. And there are a lot that have no humidity control. I can guarantee that those that adjust properly have minimal problems.
From contributor jo
Gene is right. This is how finish carpenters deal with solid wood in the field. If the interior is climate controlled then the wood can be acclimated before assembly to reduce(not eliminate) distortion. That being said I would have no problem redoing that with exterior grade mdf. Anyone who says otherwise is just being snobby
From contributor vi
Dr Gene, thank you for the insight. The RH in a church as oppose to a home makes perfect sense and answers a lot of ongoing issues with other furniture inside the church.
After all the comments I thank you all for your input. Pretty interesting discussion. It's obvious where I went wrong. I'm going to do some small test builds using differing techniques suggested here and see which one is the most successful. I'll keep you all posted.
Thank you all again. I've participated in these forums for years and I will say that they are a valuable resource for craftsmen of all ranges of experience.
Thank you
From contributor Fr
The concept of aclimating materials to site conditions can only supplement proper construction, that allows for any and all potential wood movement.
Furthermore. Very rarely do we see buildings that have perfectly controlled temperature, humidity which remain constant year round.
From experience in another line of work that involves building and installing and complex musical instruments in churches, I can tell you that Church buildings are notorious for having temperature, and humidity that vary significantly. Furthermore you run into even greater problems with heat being turned down significantly during the week, and then cranked up excessively on the weekend.
We are not talking about commercial buildings such as hospital's, nursing homes, or office buildings.
It is certainly important to consider site conditions and if possible acclimate your own shop so that it is simaler. Ultimately however the fact remains that wood moves, and we cannot stop, or prevent this. This is a proven fact. Not a wives tale as some may suggest.
This is why in any basic woodworking training programs the very first thing you are taught after learning how to mill a board four square, is that wood moves, and how we must deal with it.
Learn from this. Certain construction methods WILL not work with solid wood, and failure is certain. I have broken the rule in the past, and have certainly gotten away with things I would not due now, since they were located in a building with stable conditions. However I have also seen failures myself, from my own work, where I neglected to follow the basic rules of wood movement.
