Here is a question for you concerning table tops. I am making a rustic dining table with legs and stretchers of birch in the round, and a top of Burr Oak planks — set closely, but not edge glued or joined. The widest is about 8″, the narrowest is about 5.” Have been debating in my mind how to fasten them down. Was thinking about pegs, for the rustic look.
The question is, will planks of that width go wrong if pegged, mortised, or firmly screwed in place?
Joe
Replies
Not if each of them is fastened in the middle of the plank with a space between planks.
Frosty
Yes, I thought about that, but wondered if there were any other ramifications to a single point of hold like that .
Joe
Single point attachment without something to keep the adjoining edges of the planks in line with each other will lead to problems of misalignment when the planks move. The classic solution is to use tongue and groove edges with the attachment close to one edge.
John White, Shop Manager, Fine Woodworking Magazine
John:
Misalignment in which way? As a rustic plank top, the original concept is for them not to touch at all, or only barely. Maybe I should reconsider?
Joe
Joe,
The wide boards will cup with changes in humidity, some boards will cup upwards and some down, depending on their grain orientation. The edge of one board could end up quite a bit higher than the next, a 1/4" or 3/8" difference is quite possible and the rounded surfaces of the boards will make everything on the table a bit tippy. All of this depends on whether or not the wood will be exposed to large swings in humidity.
John W.
That cupping is exactly what I was afraid of. Is there no alternative to tongue and groove? I can do that, but had not planned to joint the boards, hoping instead for a more rustic look. The table is for my cabin so I'll have to live with it for a long time and I;ll do what I must -- am just having to re-conceptualize quite a bit is tonguing and grooving is necessary.
The space in which the table will be is not air conditioned or centrally heated. It only gets heat from a fireplace and a space heater for a few weeks a year. It is a generally humid area, at the side of a large lake in northern Minnesota, so most humidity swings will just be due to weather and season. Probably a similar climate to the one you are used to.
J
Edited 4/26/2007 7:35 pm ET by Joe Sullivan
A board will cup so that the interior of the board bows out. If you attach your boards to the skirt so that the growth rings all "cup up" (heart to the sky, bark to the ground) and fasten the center of the board to the skirt using a screw, then the natural tendency of the board to cup will force the free ends tighter into the skirt (and thus essentially staying flat).
You can put two screws within 2" of each other; board movement will not be so great that such a short distance will move much.
Good luck. Northern Minnesota? So it won't be frozen for two weeks of the year, during which time the mosquitos will carry off the table and small babies.Recommending the use of "Hide Signatures" option under "My Preferences" since 2005
Joe
What is the support system for this table top. If you have an apron, you could easily use figure 8's from the underside to keep the boards firmly in place while still allowing for seasonal movement. They are my fastener of choice for all my table's, and I've never once had a problem arise.
Jeff
Jeff:
There is a leg structure at each end, with a stretcher between, refectory-table style (except made out of birch logs in the bark). At the top of each leg structure is a cross member a little less than the width of the table. Two half-logs a little less than the length of the table are joined to the ends of the cross members (but these are not yet made and I could add more).
I envision the top to be a nearly free unit with three or four cross members to which the planks will be pinned; indeed, the planks could be just laid over the supporting framework, but I prefer more stability.
Joe
Pinning of the boards to the tables structure does not allow for wood movement, and is thus bound to fail. Either the boards will split, or the joinery will be pushed apart. Using the figure 8's (or another table top fastener allowing for movement) will allow for the necessary movement without looking like the top is attached, as it is done from the bottom. Do as you like, but if you always need to account for wood movement when attaching any tabletop made from solid wood.
Jeff
Jeff:
I take you at your word on the pinning. Had assumed that would be the case, which is why I posted this. WHat are the figure-eights? Can they be used on the individual planks to help resolve the differential cupping problem that JophnWhite has mentioned?
Joe
Joe
Here's a link. http://www.rockler.com/product.cfm?page=786
Good luck, and yes, they will hold the top tight to the apron.
Jeff
Thanks, Jeff. Embarassed to admit it, but I don't quite get how they work. I gather that a screw through one whole holds the top and one through the other fastens to the supporting member? If the wood expands, wouldn't the figue 8 shape tend to have a camming effectt that would push boards out of alignment?
Ignorantly yours.
Joe
One screw goes "down" into the table apron, right at the edge. The other goes "up", into the table top. When the top moves, it is only slightly, and the fastener is allowed to move side to side enough to not break anything.
Jeff
Here's a picture to show them in application.
IMHO, you can fasten each plank at the end center, and loose spline the length of the others in between. That would allow for movement and support. Use ply for the spline. Breadboard the ends to conceal the splines.
Here is kind of an off-the wall concept. See what you think. This table top is made of burr oak planks that do not quite touch on the edges. I hate to visualize it like this, but think "picnic table." I really don't have a convenient way to edge join them even if I change the design, as none of the tools to do the job are up there -- 1,300 miles from my primary workshop.SO, how about this --suppose I run a rows of pegs about an inch from each edge of each plank -- say , 2 feet apart. However, instead of pegging the plank firmly to anything, I run them through slotted oak boards that will support the planks (the slotted boards would run from side to side of the table). The pegs would protrude below the boards and have squares of oak wedged to the ends. The result would be a sliding joint wherein each peg would be free to move with seasonal humidity changes, yet the boards would be held down firmly and less likely to cup.Maybe it would have something of the effect of a sliding dovetail.Do you think this would work? How about you, John White? Any serious reservations? Anyone else?Joe
Edited 4/29/2007 2:06 pm ET by Joe Sullivan
Hey Joe,
What you doing with that gun in your hand?Did I write that out loud?
Instead of a peg that's really a through-tenon in an oversized mortise, times twenty, why not consider dovetailing battens across the underside of the top, or screws in oversized holes, with endgrain plugs that look like pegs?
Ray
Had thought about using screws that way. Not sure which would be better. Screws do tend to work loose over time. As to dovetailing -- VERY limited tools up there, and my main workshop is half a continent away.
Joe
That would do it. As long as they are free to move laterally.
They'd have complete lateral freedom. I would hope that the pegs/through tennons would resist cupping, too. Would think that the two-point hold with freedom to move would remove that problem.
Any thoughts?
J
Well, each board or panel unit can be glued and screwed/fixed at its center, which would help with cupping. Then your great idea of the sliding dowel holds will accomodate the issues at the edges. I think you're onto something now.
Thanks. I sure hope so.
I plan to use the finished table for the rest of my natural life -- with luck that will be another 30 to 35 years, possibly more, given our family history. It will go into a log cabin built by Fins for my great uncle back in 1931. If possible, I hope to keep it in the family after I pass on. I don't want succeeding generations to be cursing my table or cutting it up for firewood.
Joe
Edited 4/30/2007 11:20 am ET by Joe Sullivan
Edited 4/30/2007 11:20 am ET by Joe Sullivan
Put the arc of the boards up, so they want to cup up in the middle, if they do.
Drill 3/8 or 1/2-inch holes on the support the boards will rest on, and attach them at the center with a lag screw coming up from the bottom with 2 washers, and 2 lock washers, (washer, lock washer, washer, lock washer), and tighten just until the spring in the lock washers is starting to be taken up. If the boards cup, the lock washers will act as springs. Choose the boards for the outside edges based on which 2 are least likey to cup, use 5/16 holes for them, and just one washer/lock washer pair.
Things are free to move, but held securely.
Not fine furniture, but, I picutre something similar to a Forest Service picnic table.
Good advice.
Don't know what a FS picnic table looks like -- but the table is certainly rustic. The finished piece will be in the style found in the old Adirondack "camps." it will be rustic and naturalistic without being rough. That is of a piece with the older furniture already in the house.
Joe
The Forest Service picnic table is made from 4X10 or 4X12 boards. Big heavy things. Little finesse but extremely practical and durable.
Joe,
You got a lot of good info on "normal" ways to handle wood movement on table tops. There is a lot written about how to join table tops to the base. I would guess that any library would have a book which covers lots of options. Many were listed in messages to you.Then the topic of "off the wall" concepts came up. That is MY specialty. I deal in off the wall concepts. They are fun because, they make you think, and then you can go back and do it one of the normal ways.But you could reduce the need of the wood to expand and contract with changes in humidity by preventing air from contacting the wood. This is possible by making a tray that is a half inch longer on each side than the table. Then pour in about a half inch of liquid fiberglass with the hardener added. Let it dry. Then lay the boards in on top of the bottom layer of fiberglass. Now make up another batch of fiberglass and pour it over the boards and the bottom layer. Do this a few more times and you will have a nice fiberglass table top which encases your boards. This will be heavy enough that you don't have to attach it to the bottom table structure, or you could screw or bolt it if you want to.I have seen this done with ship hatches. They are encased in fiberglass and used as table tops, mostly coffee table size. What I am recommending is DEFINITELY NOT in the tradition of FWW. But it is "off the wall" and "out of the bun". It would be a "one of a kind", and a conversation piece. If the idea catches on, you could be the next Krenov. Everybody might start copying your style. You will be a woodworking God. Or maybe you should just make a normal table top.
Have fun.
MelMeasure your output in smiles per board foot.
Hmmm. Interestng concept. Maybe another project...
J
Joe
There are many different ways to allow for wood movement for a table top. I suggest picking any one of the many suggested here that you are most comfortable with, as well as one that you will enjoy doing, and go for it. None are better than the previous, or the latter, as long as they allow for proper wood movement, which can't be avoided. When you understand wood movement and allow for it in your joinery, 2/3's of the battle is officially over. After that, it's time to get creative!!
Oh, and by the way, get yourself a hand plane or two to solve the remoteness of your location. No need for a jointer when you have one of these.
Jeff
Good points, Jeff.
Actually, I do have several hand planes and know how to use them-- although not as many as you, and doubtless not as well as you. And I am reasonably comfortable with wood movement. The real challenge here is that this cabin is 1300 miles from my main residence , AND at this stage of life I am only there about three weeks a year, four at the most -- usually wih guests(the real uses of the cabin are hunting, fishing, canoing, and family stuff -- not woodworking). It is a whole lot of trouble to haul tools back and forth by air or to ship them back and forth to myself. On the other hand, there is a limit to the number of tools -- especially expensive, limited use ones like planes, that I want to pay for and leave there to be used a few days a year at best. So, I have to be resourceful in this project. You know, that is kind of fun in itself.
Now, I do haunt estate and garage sales up there, and if I find planes that duplicate ones at home, I'll leave keep them at the cabin.
I do appreciate everyone's help and advise, as always. You are all very generous with your time.
Joe
Joe
Your place sounds like a little piece of heaven, if there is such a thing. Enjoy it to the fullest while you can. BTW, I never intended to infer that you didn't know what to do with a plane. I have to be careful what I write, as my dry wit is frequently mistaken as just being a jagoff, which may be true, but completely unintentional.
A rustic table sounds like just the thing for your "up yonder" cabin. Don't forget to take some photo's and post them here. Good luck, and please spend more time fishing and hunting than messin' around with this table. I would!
Jeff
Oh, I wasn't put off at all, Jeff; just 'splanen. I am happy and grateful that everyone was so helpful, and I look forweard to getting up there in a month and making a little more progress.
Joe
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