Woodworking Talk banner
1 - 13 of 13 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter · #1 ·
I'm preparing to work on a china cabinet that is 18" deep and 72" wide. I'll be building this out of mahogany. Now, I know generally a lot of cabinet like work is done with plywood, however I'm having difficulty getting this near me. I do have access to 4/4 mahogany though. So I'm thinking to build this out of 4/4. Since it will be solid wood I know I will need to potentially deal with expansion and contraction. I might not have to do much since it's not that large, however I want to see what others think? Most boards are about 6-10" depending on when I go... average of 8" though. so at least 3-4 boards most likely for the top/bottom jointed together, most likely with a biscuit since I have that tool, or I might do something else. As I build the cabinet, though I want to make sure I take into account expansion. I just have never done something this large or had to think about this. So asking the group at large...

The base cabinet will be solid, with the top section being mostly framing with glass panels in the side front and a mirrored back.

How much expansion do I really need to plan for and with the size is it possible I won't need to deal with it really all that much?
 

·
Registered
Joined
·
447 Posts
I can't be very specific without knowing how you plan to construct the cabinet. However, in general, you must avoid gluing anything together with the grain on one piece 90 degrees to the other (called cross grain). Expansion and contraction generally occurs perpendicular to the grain. Hardly at all parallel to it. Draw up some plans showing how the joinery needs to be to put together for what you want. If you end up with a cross grain situation in your plans, post it here and we'll try to address it. While you are developing your plan, look up "frame and panel" and "solid panel" furniture construction.

When you are doing edge to edge glue ups to make a large panel like a top or shelf, you can use biscuits for alignment purposes but they will add very little to the strength of the panel. Also, be very careful where you put them. Usually, such panels are made a bit long and trimmed to length later. Don't put your biscuits where you will need to cut the panel later.

There are on line calculators that will help you to determine the amount of expansion/contraction based on wood species, and temperature/humidity changes. Just look up "wood movement calculator". Woodbin.com has a good one called "Shrinkulator".
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #3 ·
I can't be very specific without knowing how you plan to construct the cabinet. However, in general, you must avoid gluing anything together with the grain on one piece 90 degrees to the other (called cross grain). Expansion and contraction generally occurs perpendicular to the grain. Hardly at all parallel to it. Draw up some plans showing how the joinery needs to be to put together for what you want. If you end up with a cross grain situation in your plans, post it here and we'll try to address it. While you are developing your plan, look up "frame and panel" and "solid panel" furniture construction.

When you are doing edge to edge glue ups to make a large panel like a top or shelf, you can use biscuits for alignment purposes but they will add very little to the strength of the panel. Also, be very careful where you put them. Usually, such panels are made a bit long and trimmed to length later. Don't put your biscuits where you will need to cut the panel later.

There are on line calculators that will help you to determine the amount of expansion/contraction based on wood species, and temperature/humidity changes. Just look up "wood movement calculator". Woodbin.com has a good one called "Shrinkulator".
Thanks for the info. I do plan to keep the orientation all the same way. so if you were to look it might look like the wood wraps around in a circle. That way at least the expansion if any would all be in the same direction. Since the case is 18" deep, so figure a side panel being roughly 30" x 18" x 3/4". It's a fairly "Straight" cabinet I'm building so there isn't a lot of "Frame" to use a frame and panel setup. So was thinking to do a dovetail like slide in connection between the top/sides/inside walls and the bottom. Not sure just yet... still trying to figure things out. Since I'm trying to recreate a design based on some pictures, I'm just guessing, although I know the commercial version does use veneers, so probably plywood based or hardboard of some kind.
 

·
Registered
Joined
·
447 Posts
Sounds like you are heading in the right direction. A sliding dovetail is one method of dealing with a cross-grain situation. Plywood is sometimes useful also. Just keep in mind that plywood is stable in both directions whereas your glue-up panel is not. Also, if your grain is running horizontally all around, your wood movement is going to be up and down and there should be no conflict with tops, bottoms, and shelves. When you have the grain of all sides running vertically, there is where you start having issues.
 

·
Registered
Joined
·
27,647 Posts
You have to be very careful with any solid wood panels that are more than a foot wide. If you don't make the width of the panel where it can shrink then it's likely to split.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #6 ·
So based on the calculator that was posted, if I entered my information correctly, assuming width is the expansion direction, I'm only looking at 1/16" of an inch of expansion/contraction. With this little bit do the joints need to be free floating or could I actually glue them?
 

·
Premium Member
Joined
·
5,285 Posts
The 18" deep is not excessive. Typical of most small desk tops and furniture cabinetry. Normally an overall average of shrinking/expanding through the seasons is 1/8" / foot. I have read this over and over again so I will assume it is true but I have never experienced that much seasonal movement. Your design (the waterfall) is typical of most furniture. Your top bottom and sides will all move together, more or less, The front will be face-frame so I assume so there wont be much movement there. The rear could be plywood. It would be in the orientation of the least wood movement. This is all just for the bottom unit. I assume the upper part will be a separate unit.
If properly constructed, (waterfall), everything should move at the same rate. I would just glue it all up. There is nothing new or profound about this.
 

·
Registered
Joined
·
264 Posts
First, is the wood you are using acclimated to your location before you start? This usually means kiln dried lumber that has sat a while, say a month or so, in your workshop to complete the initial shrinkage. This is especially important if the wood came from a forest far away with a different climate.
Second, what is your local climate? With more seasonal variation the yearly expansion and contraction is greater. I'm in the upper Midwest with long, cold winters when the central heat relentlessly dries everything followed by damp springs that swell wood rapidly; so I see more wood movement than someone in a milder, more uniform climate.
 

·
Premium Member
Joined
·
2,021 Posts
On a solid panel carcase there is no issue since all the grain is running the same way. Same thing with fixed shelves and tops. Frame and panel sides with leg posts get around this issue.

The back can be made from plywood, frame and panel, or ship lapped boards (leave gaps).

The main issues in a solid wood carcase are any boards that go across the grain, such as drawer runners/dividers. They are fixed in place at the front and left to move rearward. I always leave them 1/4" shy of the back for insurance.

If you're making solid wood drawers, the time of year & anticipated expansion/contraction has to be considered. Build it tight in the summer, a little loose in the winter.

All that said, you're not going to get much change in 18" if the wood is dried to 6-8%, but you should still build it by furniture making principles.

How are you planning to build the carcase? This is a traditional way to attach the bottom & top to the sides. If there is a moulding around the bottom, you could do a rabbet with glue and screws (moulding to cover screws).


Wood Tool Flooring Composite material Hardwood
 

·
Registered
Joined
·
447 Posts
All good advice above. However, when using the "Shrinkulator" or something similar, I always like to assume worse case conditions, not just what I might have where I live. Assume what conditions might be like if, for what ever reason, the piece someday has to be put into a non-climate controlled storage. Under those conditions, is there enough allowance for things to expand and contract without splitting? There was a person that posted on one of the woodworking forums a short time ago that had that very thing happen. After retrieving his table from storage, that he had worked hard to build, he found that the table top had split probably because it was not free to move. Take the time to do it right and it can last several lifetimes. Don't you wish you could be there when someone says "my great great grandfather built that".
 

·
where's my table saw?
Joined
·
29,625 Posts
To simply, a cabinet has 6 parts, 4 of which form a perimeter "box/rectangle", the front and back are the remaining 2.
The rectangle is typically "wrapped" with the grain all going around lengthwise.
The back can be a glue up or plywood set in a rabbet.
The front typically has a 2" or so "border/face frame" with mitered corners, on half lapped joints. This is the part that may have grain meeting at 90 degrees of different direction, but because the dimensions are so small about 2", it won't matter.

The back is a different story.
If the back is a solid wood glue up (walnut), not plywood, it will matter if you glue it to the top and bottom of the rectangle structure because those grains run at 90 degrees. Most cabinet makers just nail the back in the rabbet, leaving about 1/8" for expansion. I use 1/4" plywood because it's easier and is not affected by expansion. If the back is glued up from 3/4" stock (walnut) it will be thicker and heavier than is required for strength or structure. The back is a critical structural member which prevents the cabinet from "racking" under a lateral load as when it might be pushed on the sides to move it about.

Typically, a center shelf is set into a dado to increase the structure. This dado may be located 30" or more from the end of the sides, so difficult to make on the table saw using the miter gauge. If this is the case, it can be done with a router and a guide or a router hand plane, not a common woodworking tool. Care must be taken to make the dado at the same location on each of the side panels so the shelf will sit perfectly horizontal/level.

After allowing the wood to acclimate, assemble it and apply a finish to both the interior and exterior to help prevent the absorption of moisture from the environment, a step often omitted. If the wood must be planed to thickness, flip the boards after each run through the planer to relieve any stresses. This procedure is often omitted also.

That's kinda "cabinet making 101 if that helps?

This cabinet is 10 feet long and 4 ft high, made of solid red oak and a 1/2" plywood back, glued in. The doors have mitered frames with cross splines. It does not have a face frame, only 4 vertical supports from which the doors are hung. The doors are set in flush with those. All the 6 primary shelves are set in dados. The others in the center section are resting on oak spacers that form "faux dados"
Brown Cabinetry Shelving Wood Shelf


Cabinetry Wood Drawer Hardwood Wood stain


Brown Cabinetry Building Furniture Shelf


Your cabinet is 6 ft wide and will have a mirrored back. The mirror will require a plywood back since it will not add any structure. I would not use a solid glue up on this size cabinet, but others may have a different opinion.
 

·
Registered
Joined
·
3,413 Posts
my "lesson learned" from years ago...

I glued up a 25" wide panel on a Friday (winter), came in on Monday am and it was 1/4" narrower. never forgot it!

a big factor is moisture content of the wood, and that you need to be aware of it. i wasn't back then...
 

·
Premium Member
Joined
·
5,285 Posts
Kiln dried means absolutely nothing. It must be quantified to give it some relevance. Normally furniture grade lumber is kiln dried to 6-8% moisture content (MC). Construction grade lumber is dried usually 12-18% M.C. Sawmill dried hardwood lumber? I learned not to believe them. Anyway, all can be legitimately called kiln dried if it was put in a kiln. Bring your own M.C. meter.
I have had bad luck with several sawmills. Everything from warping to wildlife living inside the lumber. Now I only buy from legitimate hardwood suppliers.
Woodturning is different, I will turn logs found along the roads. If they have guests living aboard it will be obvious.
Kind of comical when you turn the lathe off and all these little heads start popping out. Then the whole load will hit the dumpster immediately.
Experiences may vary.
 
1 - 13 of 13 Posts
Top