Wood Movement

[ztifpatrick]

Hello, I'm new to the forum. but thought this would be a good place to get some feedback on a project I'm about to start. I've attached a PDF from sketchup for a visual. I've offered to make a new podium for my sons school. I want to use solid mahogany with either walnut or ebony accents. My concern is the center coulumn which is 3 sided and has a few shelves of the open side. The grain on the sides, shelves, base and top are all running in the same direction. The face of the column would be 13" wide and would be mitered to the sides. The face is the only part where the grain will be running at 90 degrees to the other parts. I planned on attaching the sides to the base and top with dominos, but I was not going to attach the face to either because of movement. Now I wonder if 13" is wide enough to cause a problem with the mitres? I know I could use ply, but would rather not.

All thought welcomed.

Chris

Podium view 2.pdfPodium view 3.pdfPodium view 4.pdf

[Beechwood Chip]

You can use The Shrinkulator to check, but I think 13" is enough to worry.

I think the most obvious joints will be the two long joints where the front meets the sides, so I'd make those fixed and let everything else move.

I'd fix the front to the sides, so the sides move with the front. Then, you can either build the horizontal stuff (shelves, base, and top) with the grain going the same way as the front, so it all moves together.

Or, build the horizontal stuff with the grain going side to side, so the movement is front to back.

Either way, fasten the horizontal stuff to the sides to allow movement. There will be less movement because that is your smallest dimension.

I hope this makes sense.

[Bobby Slack]

how about http://woodshopwidget.com/

[ztifpatrick]

You can use The Shrinkulator to check, but I think 13" is enough to worry.

I think the most obvious joints will be the two long joints where the front meets the sides, so I'd make those fixed and let everything else move.

I'd fix the front to the sides, so the sides move with the front. Then, you can either build the horizontal stuff (shelves, base, and top) with the grain going the same way as the front, so it all moves together.

Or, build the horizontal stuff with the grain going side to side, so the movement is front to back.

Either way, fasten the horizontal stuff to the sides to allow movement. There will be less movement because that is your smallest dimension.

I hope this makes sense.

Thx, it's food for thought. No easy answer. I don't want the grain of the top, base and shelves running with the front for aesthetic reasons. It's a bit hard to get my head around because if I run most of the grain with the wide front piece, then if it expands I will be pulling the sides apart with even grater force? I could keep it the way it is, anchor the front face in the middle and allow it to expand/contract about 1/32 at the corners. If I really had a strong joint in that mitre with dominos etc, it may work?

[Beechwood Chip]

It's a bit hard to get my head around because if I run most of the grain with the wide front piece, then if it expands I will be pulling the sides apart with even grater force? I could keep it the way it is, anchor the front face in the middle and allow it to expand/contract about 1/32 at the corners. If I really had a strong joint in that mitre with dominos etc, it may work?

Here's the way I see it. The wood is going to move. If it was really thin (veneer, or a layer of plywood) you could lock it down to prevent it from moving, but other than that, the wood is going to move. If you try to prevent it from moving, then you'll get cracks, gaps, warping, and other problems over time.

The "force" comes from having things fighting the grain movement. Making things move together doesn't make the problem worse, it makes the problem go away. If everything between the sides is moving together, then there's no stress, everything moves in harmony. It's only if you prevent the movement that you get stress.

You just have to find all the places where two things are going to move differently, and use some sort of joint that allows the movement. Floating panels, figure-8 fasteners, screws, dowels, or tenons in oversize holes, or just having shelves sit in dados, on cleats, or on adjustable pegs: there are tons of ways to join things that will allow movement.

I think the best solution is to make the front a floating panel, sitting in grooves but not actually fixed to anything (except maybe in the center).

There's another solution I can think of, but it's a little involved...

You make the front and two sides the way you want, with reinforced miters. you also put a cross piece at the bottom across the opening.

The base has grain going from side to side, so the base and the sides will expand and contract in unison. You cut two grooves in the base for the front and the back cross-piece to sit in. They are secured in the center, and there are notches in the corners so that the back and front can expand and contract in the grooves. The sides sit on the base and are not secured, so they can move across the base as the front and back expand and contract.

The shelves are not fixed to anything. They rest on movable shelf pegs, or on cleats. The shelves are sized so that there's room for wood movement in all directions.

You could fasten the top the same as the bottom, or, you could fasten the top to the front with hinges, so that the top lifts up to give access to the top shelf. If you go with hinges, elongate the holes to allow for movement. The holes in the center should remain round.

It's after midnight and I've had too much caffeine, so take all of this with a grain of salt. Me, I'd probably make the front and sides floating panels to eliminate the wood movement problem and save on weight and material cost. It can still be "real wood" (not plywood), but it can be much thinner.

[ztifpatrick]

Here's the way I see it. The wood is going to move. If it was really thin (veneer, or a layer of plywood) you could lock it down to prevent it from moving, but other than that, the wood is going to move. If you try to prevent it from moving, then you'll get cracks, gaps, warping, and other problems over time.

The "force" comes from having things fighting the grain movement. Making things move together doesn't make the problem worse, it makes the problem go away. If everything between the sides is moving together, then there's no stress, everything moves in harmony. It's only if you prevent the movement that you get stress.

You just have to find all the places where two things are going to move differently, and use some sort of joint that allows the movement. Floating panels, figure-8 fasteners, screws, dowels, or tenons in oversize holes, or just having shelves sit in dados, on cleats, or on adjustable pegs: there are tons of ways to join things that will allow movement.

I think the best solution is to make the front a floating panel, sitting in grooves but not actually fixed to anything (except maybe in the center).

There's another solution I can think of, but it's a little involved...

You make the front and two sides the way you want, with reinforced miters. you also put a cross piece at the bottom across the opening.

The base has grain going from side to side, so the base and the sides will expand and contract in unison. You cut two grooves in the base for the front and the back cross-piece to sit in. They are secured in the center, and there are notches in the corners so that the back and front can expand and contract in the grooves. The sides sit on the base and are not secured, so they can move across the base as the front and back expand and contract.

The shelves are not fixed to anything. They rest on movable shelf pegs, or on cleats. The shelves are sized so that there's room for wood movement in all directions.

You could fasten the top the same as the bottom, or, you could fasten the top to the front with hinges, so that the top lifts up to give access to the top shelf. If you go with hinges, elongate the holes to allow for movement. The holes in the center should remain round.

It's after midnight and I've had too much caffeine, so take all of this with a grain of salt. Me, I'd probably make the front and sides floating panels to eliminate the wood movement problem and save on weight and material cost. It can still be "real wood" (not plywood), but it can be much thinner.

Thank you for taking the time to think about this. I'll go back to Sketchup and see if I can incorporate these ideas.

[Pete Bennett]

Hello, I'm new to the forum. but thought this would be a good place to get some feedback on a project I'm about to start. I've attached a PDF from sketchup for a visual. I've offered to make a new podium for my sons school. I want to use solid mahogany with either walnut or ebony accents. My concern is the center coulumn which is 3 sided and has a few shelves of the open side. The grain on the sides, shelves, base and top are all running in the same direction. The face of the column would be 13" wide and would be mitered to the sides. The face is the only part where the grain will be running at 90 degrees to the other parts. I planned on attaching the sides to the base and top with dominos, but I was not going to attach the face to either because of movement. Now I wonder if 13" is wide enough to cause a problem with the mitres? I know I could use ply, but would rather not.

All thought welcomed.

Chris

Podium view 2.pdfPodium view 3.pdfPodium view 4.pdf

If you make two matching frames for the ends and have floating panels within, either plain or fielded or whatever and mortice a top and bottom rail at front and back you can place the front panel in grooves also this makes your column completely safe regards movement of solid wood panels. Next run a groove round the inside top frames and fix the solid top with buttons, but for God's sake eliminate those cleated ends! You may know them as breadboard ends. They may help? to keep the top flat but I can guarantee you will either end up with the panel protruding beyond them or shrinking in from them either way it'll look a mess in a year's time.

The way to attach the bottom (if you are simply going to use a solid board with your bun feet attached, with one central screw only or they will cause problems also.) is to cut a slot across the grain about ten or fifteen mm. beneath each end frame about 25mm in from each end and screw up into the long sections of your frame, not into the end grain of the up rights. That takes care of any movement in the base. The easiest way to attach the shelves would be to joint cross members into the frame as you construct it. Making sure they are thin enough to go behind the end panels. First run a small groove in each and then place small buttons in and attach them to the shelves from underneath. Everything is attached,and if done well will look better than simply plain boards jointed flush. Also every piece that wants to move can. If you really wanted to you could eliminate the shelf bearer idea and by running the appropriate grooves in the end frames you could fit slotted brass shelf supports like the ones used in Libraries and have a fully adjustable shelf system that would not impede movement in the shelves. But the first idea helps to keep the shelves flat.

Hope this is of some help. If you're confused I could always do you a drawing.

Pete

[ztifpatrick]

If you make two matching frames for the ends and have floating panels within, either plain or fielded or whatever and mortice a top and bottom rail at front and back you can place the front panel in grooves also this makes your column completely safe regards movement of solid wood panels. Next run a groove round the inside top frames and fix the solid top with buttons, but for God's sake eliminate those cleated ends! You may know them as breadboard ends. They may help? to keep the top flat but I can guarantee you will either end up with the panel protruding beyond them or shrinking in from them either way it'll look a mess in a year's time.

The way to attach the bottom (if you are simply going to use a solid board with your bun feet attached, with one central screw only or they will cause problems also.) is to cut a slot across the grain about ten or fifteen mm. beneath each end frame about 25mm in from each end and screw up into the long sections of your frame, not into the end grain of the up rights. That takes care of any movement in the base. The easiest way to attach the shelves would be to joint cross members into the frame as you construct it. Making sure they are thin enough to go behind the end panels. First run a small groove in each and then place small buttons in and attach them to the shelves from underneath. Everything is attached,and if done well will look better than simply plain boards jointed flush. Also every piece that wants to move can. If you really wanted to you could eliminate the shelf bearer idea and by running the appropriate grooves in the end frames you could fit slotted brass shelf supports like the ones used in Libraries and have a fully adjustable shelf system that would not impede movement in the shelves. But the first idea helps to keep the shelves flat.

Hope this is of some help. If you're confused I could always do you a drawing.

Pete

Thank you Pete, I hate to take you up on your offer but a sketch would help. I understand about the frames and the floating panels, there would be three frames, 2 side and 1 front, correct? I understand about the buttons for the top, treating it like any table top, so to speak.Attaching the column to the base, your suggesting an elongated hole for the screw to move in? I could attach the front to the base in the same manner except the hole would not need to be elongated, that would force all the movement backwards? Sorry, the shelves i don't follow, though they could be fixed to the side as the grain would be going the same direction.As for the breadboard ends. THey are purely aesthetic (for me). I'm fond of Greene & Greene and would make them longer on purpose and rout in a decorative spline.

Thanks for taking the time to consider this!