I am working on the design for a coffee table out of b. walnut approx 4′ square. My original design has been scratched after reading and studying “Understanding Wood” by Hoadley. Even the slightest movement would have destroyed it. Hence, I have tried to redesign w/ movement in mind.
I have attached a picture to help explain. I would like to design the table w/ 4 distinct triangles. The grain direction is indicated on the picture. In order to accomodate different levels of movement, I am considering using sliding dovetails between the 4 tri-joints and then with a “key/wedge” in the center to lock everything together. I realize this will prove interesting to accomplish. One of my concerns is whether this will still inevitably fail due to the diff. levels of expansion/contraction between the end-grain miter joints? Secondly, would their be any way to have an inlay as indicated that did NOT fail?
I do not feel “right” using a stable substrate, such as plywood, covered in veneer as I feel as though I am cheating the system. WW has been around long before these stable materials and truly fine pieces have been designed out of solid wood. I guess you could say I am a (stubborn) purist. Please understand this is my own personal opinion and preference.
Any thoughts/advice/suggestions would be Greatly appreciated!
Z
Edited 8/4/2005 5:36 pm ET by Zombeerose
Replies
Have you considered doing this with veneer? A stable substrate would still be a good thing.
Pete
Veneer is the way to go. I don't think it's possible in solid wood if you will be gluing the four pieces to each other. You might consider a subbase to which the four pieces will be attached with a small gap between the four triangles. The subbase can accommodate the wood movement for each triangle separately. The gaps between the triangles would be a "design feature".
What you show will not work. Long miter joints actually change angles as the wood expands/contracts across its width.
Given that the wood will not change in length, when the section gets thinner, the angle will change and no longer be 45 degrees.
What you want to do is normally done with veneers.
BTW, veneered substrates have been around since the time of the Egyptians. Veneer items have been found in their burial sites. Plywood and veneers are not new. Most of the highest quality 17th and 18th century furniture was made with veneers.
Z
Let's first understand what motivates you. I think there's a little bit of, "If it can't be done I'll show em", in you. You've got some illustrious company. There were people who couldn't accept the fact that the earth was flat, so they set out to prove otherwise. They may have risked a lot more than a few pieces of wood. Plenty of earlier woodworkers didn't understand wood movement as evidenced by the many pieces of furniture (some of which are worth lots of money) that have big splits where they are coming apart. Perhaps you can work around it.
My first thought was what has already been suggested - veneer. But that's too obvious, and besides, you had already discounted that idea. So what you need is a margin between each piece which could be an actual void or you could fill it with something having a bit of elasticity. Something that wouldn't be too brittle and prone to shattering,
Now it's time for the chemists to come aboard. Something that would set to the point of not being sticky, yet stay in place. Would a resin or epoxy work? We have people of varied backgrounds in this forum - if we can get them to do a little brainstorming.
I'm for you, and I'll bet you succeed.
Roy
You would be correct in your assumption that I basically don't like to take no for an answer. In a global sense, I see things that people said yesterday couldn't be done and then tomorrow they can. I'm therefore prompted to wonder "why can't I reach an agreement with the wood (movement)?" Thanks for the suggestions - I'll have to ponder the elastic gap-filler concept. :)Z
I did a very small three section table top out of solid material some years ago. It is still together, but like I said, it's small. I also live in a somewhat stable climate, so that helps. I would not attempt to do what you want to undertake in solid lumber. The expansion/contraction from seasonal changes in humidity will simply be too great. You can design in some reveals to hide the gaps, but it doesn't sound to me like that's a design element that you want. Actually from the sound of your post, you are bound and determined to "buck the system." Well, more power to you. But, you really ought to do a lot more research (this means doing some actual woodworking), and be prepared for some disappointment.
Jeff
Life is short- Go for it- Just do it- If you don't, you'll always wish you had-
That'll work, cause all the pieces will expand/contract at the same rate. If you use a spline, just have the grain running across the joint. Seal it on the bottom and on the top to minimize absorption of moisture. Don't glue the top to the legs, but let it float with slotted connections.
One thing that might look nice would be to route a groove about 3/4" wide and 1/16" deep centered on each joint. Then glue in strips with the grain oriented perpendicular to the direction of the joints. That will also hide slight bobbles in the joints.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)
PlaneWood
I think the other posts are closer to correct. If the pieces expanded equally in length as they do across the grain, the outer points of the miters would remain closed .... but that's not the case. I've seen the wreckage of a card-table top .... approx 36 " square .... made this way and it's a sad sight. The outside points lack 3/8" coming together. I'll try to rescue this top this Fall and post a picture.
John in Texas
Yeah, your right. Gee's, did I have a brain fart!!!!!!!
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Thx John,
I would certainly appreciate a picture of such a "disaster" if you can find it. :)Z
It's refreshing to see someone actually learn about wood movement before they start building ambitious projects.
As someone already explained, the joints will be stressed because the expansion and contraction of the wood will cause the angles to change in addition to the linear changes in the size of the four elements. I think this is explained in Hoadley's book with an illustration of movement in a mitered frame.
To build this piece out of solid wood the four triangles will have to float, either in some kind of a frame or they will need to be supported on a stable sub top that allows the triangles to shift as they move.
In either case there are going to be visible gaps between the elements that get wider and narrower with seasonal changes and the gaps can create esthetic and practical problems with dirt and spilled drinks getting down into the openings, but the table can be built. You can build the table with oversized gaps between the elements for a dramatic effect, that is also easier to keep clean, but large gaps can create problems with drink glasses or coffee cups tipping if they are placed directly on a gap.
To be honest, while the four piece top will look nice, it isn't that strong a design element that it would be worth going to extraordinary efforts to make it out of solid wood.
John W.
Thanks for the feedback John. I wish I could claim that I had learned about w. movement prior to any projects but that is not the case. I have suffered the repercusions first hand and wanted to "fix" my design problems before working on more substantial projects.Indeed the miter issue is explained in Hoadley's book. I guess I was hoping that my interpretation of the material was wrong. I hoped wrong...Thanks for the suggestions. Back to the drawing board - again. :OZ
Zom,
If you join the triangles together using loose tongues, and the table has a supporting frame under the top,attached in one of the usual movement accommodating ways, it will not fall apartor otherwise fail- BUT- there is no way you can avoid gaps along the edges due to seasonal changes (other than veneer)
So with the above in mind I suggest you build into the design something that lessens the visual impact of those gaps. For example, you could use a small roundover on the meeting edges.
Have you considered how you are going to deal with the centre of the table where the four points meet? There will be short grain here-very delicate when you are doing the inevitable "adjusting" to fit----if I were you I would avoid that one by inlaying a suitable design to hide this intersection. Even if you did get it perfect, it still probably will not look right.
I attach a pic of a table top I did-it is veneer,using contact glue so not great, but you can see what I mean at the centre.BTW- that glue has lasted 32 years and looks good for a lot more....
If you ran the grain in your triangles in the same direction, it could work, but there's not a lot of point in doing that unless you use contrasting species (of matching expansion).
The traditional way would be to use a frame and panel construction, so that each triangular panel can move within its frame, and the exposed wood looks good because of the design of the join.
Another possibility would be a glass top over floating triangles with the small gap filled with something like black velvet that will simply darken the gap, whatever its size.
Built by your original plan, it might survive if you totally encapsulated it in several coats of epoxy to seal out water. But that would be less like solid wood than a veneered substrate.
Edited 8/9/2005 11:50 am ET by AlanS
Something that is not a conventional approach would be to make the top out of many layers of shop sawn veneer--a lamination. What I mean by this it to resaw wood to about 1/10" "veneer" and cut the triangles for the top-most pieces--the triangle design. Then cut more triangles the same size, but w/ the grain oriented so that it would run at 90 degrees to the previous layer.
Think of the way that plywood is made. The only drawback to this method is that the edges would show the layers of the wood; however, this may be avoided by glueing an edge piece to correct for the grain descrepencies. If you attempt this, make sure that you use strong glue--I would recommend urea resin, or an epoxy of some sort.
All this being said--If I were doing a project like this, I would definately use veneer, as I have learned my lessons the hard way over the years.
Good luck to you.
Peter
jpswoodworking.com
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