All,
I’m making a chess board that was featured in the Dec. issue of Popular Woodworking. The plans call for using a spline to connect the chessboard to the sides of the box…in other words the chessboard is splined (1/4×1/2″) into 3/4″ walnut that has mitered coners. I don’t see where any provision has been made for expansion? The chessboard measures about 16×16″ with alternating squares of maple and walnut, 1/2″ thick. I’m a bit worried about the strength of the top…there is no substrate…and it is connected to the sides with a rather thin spline. Should I be concerned? any suggestions?
Replies
BG,
Never having seen an issue of popular woodworking, I'll take a stab at answering your reply.
Typically, here, timber is sold 'kiln dried' but still slightly green - our equilibrium moisture content is 12.7%, timber typically sold about 15% moisture content, I'm led to believe, so the timber will shrink slightly before settling down. I assume (a dangerous word here) that this is what's expected in this project.
Bear in mind also that you have two different species of timber that expand and contract at different rates - there may be a 1% difference in tangential expansion and up to a 3% difference in radial expansion/contraction. Typically, these numbers run at about 4% tangential and 9% radial (green to dry). So ensure that the blocks are glued with the radial direction aligned, or else you may end up with splitting if you have a radial cut face glued to a tangential one (difference in size will be about 0.25mm/10 thou due to expansion difference.)
For the same reason, I'd suggest a satin/matt finish to partially hide any cracks that may occur.
When we were trained, chessboards were a standard veneering exercise - avoided the expansion issue and allowed for the use of fancy wood, eg: wenge/silver ash.
Cheers,
eddie
eddie,
This project will probably end up being a diaster. The magazine always has some interesting projects..but its always a bit shy on the details.
I had some scrap black walnut and thought it would be a good project for improving some skills...its actually a box with coved sides and a chessboard top that you can lift up and store the chess pieces. The first challange was making sure the chessboard looks perfect...its not like it won't be noticed....lol. When it starts to expand I'm sure no one will notice the mound...lol
If you alternate the direction of the grain of the squares, the board area will probably move around a quarter of an inch in both directions. If the grain all runs the same way, the cross grain dimension will move almost a half inch between winter and summer while the parallel to the grain dimension won't move at all.
In either case, if the board is tightly fitted into the mitered frame, with no room for expansion, there will be a lot of stress on the corner joints.
John W.
Edited 3/21/2004 11:40 am ET by JohnW
JohnW,
The plans called for two glue-ups. First the alternating strips of 1/2x2" light and dark wood were glued ...then cross cut and laid out in the alternating square pattern. It actually has all the grain running the same way. The stock I used is quarter sawn...pretty much.
I've been wondering how thin does stock have to be so that one can ignore expansion issues...such as with veneers. In other words, is a quater inch veneer so thin that expansion issues don't really need to be addressed?...or does it need to be thinner? I'm asking because I'm wondering if I were to take some kerf cuts, say 8-1/4" deep, on the underside of the chessboard would that allow for expansion....or course I'd need to attach the board to a substrate for strength if I did the kerf idea. What do yo all think?
The only way you can get away with ignoring the expansion problems with wood is to get down to veneer thicknesses, around a sixteenth or less, and then gluing the veneer to a stable base material like a plywood. Even at an eighth of an inch thick the face of the pieces glued to a rigid backing might show small cracks instead of just stretching like a thinner veneer.
Starting from scratch, I would take one of two approaches with making a chess board. One way would be to use veneer thin squares glued to a good backing. This way would create a stable panel that could be framed without having to worry about movement of the panel.
The second way would be to make the panel a half or three quarters of an inch thick out of solid wood squares and then treat it like an ordinary wood panel and float it in a frame so it could move with moisture shifts. You could sandwich the chess board panel in the frame with a plywood backing, that wasn't glued to the chess board, to make the board stronger if something pressed hard against it.
John W.
JohnW,
Okay, I think you may have given me a solution. The chessboard is 1/2" thick and the plans call for a 1/4"x1/2" spline between the chessboard and the box sides(3/4" thick). What if I attached (float)a 1/2" ply panel to the sides(typical panel connection) and attached the chessboard on top of that with a touch of glue in the middle only..and let the splines between the chessboard and box sides float(eg.cut grove for splines 1/4x3/4). That would give me a solid base and let the chessboard top float, but becaused it was glued in the middle, not slide back and forth with seasonal swings.
Edited 3/21/2004 4:52 pm ET by BG
Your method should work. However, you can glue the splines into the frame surrounding the chessboard, leaving the splines as a loose fit in the grooves around the edge of the chessboard. This time of the year, in most places, the wood will probably have shrunk to its smallest dimension, be sure to leave room in the bottom of the grooves for the chessboard to expand.
John W.
JohnW,
Thanks for your help, I think I'm good to go now.
I'm going to use 1/4" ply for the spline material and set the chess board with a 1/4" gap between it and the box sides. The splines will be 1/4x3/4 and the groves will be 1/4" on the box sides and 1/2" in the chess board edge.... I will use a plywood backer with a touch of glue in the center to keep the chess board from sliding...and provide support for all those end joint glue ups.
I built just such a framed chess board about 25 years ago. It was made in Kansas in dry weather, and then moved to St. Louis. The first wet spring that board swelled up enough to buckle in the frame, push the mitered sides apart, shear dowel pins that were holding it in the frame, and generally ruin the whole piece. There had easily been 1/2" of expansion across the board.
So your intuition is right. And I have yet to discover a sleek way of framing such a glued-up chess board to allow for the expansion. The nicest solid chess board any student of mine ever made had the squares sliding on french dovetails atop the framed drawer that held all the pieces. The top was pinned to the center of the dovetails, so it would expand/contract equally left and right.
4DThinker
4DThinker,
French Dovetail?? I'm sitting here with Joyce's book and can't see any reference to such a style.
a French dovetail?
Thats a dovetail with a tounge !!
Do a google search for "french dovetail" including the quotes. You'll find plenty of references there. It is simply a long single dovetail cut (groove) with a mating long single dovetail shaped tongue. Essentially a locking tongue and groove joint. I've heard "sliding dovetail", "long dovetail", and a few versions with swear words mixed in.
I'm guessing you need another book beside's Joyce's.
4DThinker ;-)
4DThinker,
You're right, I should have googled before I asked, tons of references out there on "french dovetails".
I don't have enough books on or about woodworking. My wife is the book buyer, I prefer to hit the library first to see if the book has real utility to me....or if its just another pretty face that'll quickly end up on the book shelf.
To you other point about shrinkage, I made up the chessboard last weekend and have it sitting on a flat surface with stickers and a bit of weight on top. I took final measurements last night of the chessboard before mitering the coved box sides....it shrunk 3/16" on one dimension. It has stayed flat....but it appears to be a bit less dry than it should be for this application. Oh well, live and learn...
The board will be gaining and losing moisture, and shifting in size, forever. At this point, having probably reached equilibrium with the moisture levels in your shop's air, it can't be too dry or too moist. Six months from now it might very well have regained that 3/16".
The whole point to floating the panel is to allow the panel to move as it expands and contracts. You need to take an educated guess, based on the humidity in your shop, about which way the panel will be going in the future and make sure you leave room for it to move.
John W.
Edited 3/25/2004 11:01 am ET by JohnW
JohnW,
I'm leaving about 3/4" for expansion on the 8 squares of alternating walnut/maple ...measuring about 14.5 inches across....hopfully that'll be enough. thanks
Live and learn I have, BG. My failure to consider shrinkage cost me one job in the past. Failure of at least one manufacturer to consider shrinkage in their chair design cost them several law suits and 100's of thousands in settlements when that chair self-destructed. I was an expert witness for one of those cases.
4DThinker
Ouch!
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