Murphy’s law, spring joints and skottbenks
Every once in a while, you have a project that “goes South” and then “goes South” over and over again. Ergo, the reference to Mr. Murphy and his law. The dining table I’m currently building is just such a project. The base is well on its way to being finished (another post on glazing is just around the corner). But when it came time to finish up to top, I was given quite a big surprise. The glued-up top had “cupped”, significantly, about 5/8″ in 36″, too much for the fasteners to “pull down”. Jointing and gluing up large panels is, at least in my experience, always a challenge.
Many “old hands” maintain that “springing” a joint is a good thing. And over the years I’ve found this to be a good practice, as much of the stock (air dried) I use has not, necessarily, achieved theoretical equilibrium. But it is one thing to spring a joint on 24″ door panel and quite another to spring a joint on a 7′ table top. It might seem that just a few thousandths of “spring” wouldn’t make much of a difference, geometrically. But the reality is sort of like saying that all triangles equal 180 degrees, until you lift one of the corners. Then, the universe begins to fold in on itself.
I began to consider my options. I certainly did not want to cut the thing apart and re-joint it. That would be a last choice. In the past I’ve had some success in straightening pieces by wetting and controlling the drying of two opposing surfaces, albeit smaller pieces. So, with the help of a friend, I toted the top out into the yard. I wet the grass, then positioned the top with the cupped side down. It wasn’t terribly hot but the sun was fairly intense. I went about my business, determined to check in on the process in several hours.
To my great surprise, within something short of an hour, the rough top appeared to have straightened. After laying a straight edge across the surface, I felt sure that I had been present as something of a miracle had taken place. It was dead flat. Upon raising the top, I realized that there was still a trace of moisture on the “grassy” side. I pulled some heavy cauls (3″x 4″x 48″) out of the shop and clamped the top to allow the remaining moisture to evaporate. After several days, I loosened the clamps and with each turn I watched the cup reappear. So much for that old trick!
As I said earlier, I’ve never had much luck at cutting and re-assembly. Time for a new top. (I’ll put the old plain sawn stock to some good purpose.) I made the decision to do the next top in quarter sawn oak. Stock movement should be very minimal. The only significant challenge will be jointing the long stock. Of course, there are numerous ways to joint long pieces of stock. You can joint them conventionally on a jointer (If you’re strong and steady or have the well coordinated assistance of an associate). You can hand plane them. If you have stock that is already “near straight”, you can “kerf-in” with a saw. You can use a track-saw on a straight edge. Or, you can use a skottbenk as Roald Renmaelmo would. The skottbenk is a jointing (or shooting) bench, unique to Scandinavia, that is mainly used for jointing and/or cutting tongue and groove joints in floor planking. It seems to me that it might be just “what the Doctor ordered” for anyone wanting to create long joints without the aid of electrically powered appliances.
Take a look at this video of Roald using a skottbenk. I think you’ll agree that it might have a place in world of table top construction. Hmm, now that I have some extra room in the shop, since the treadle lathe is gone…
Roald has just put another post on construction of a skottbenk on his blog, skottbenk.wordpress.com. He and his associates also do extensive research on traditional work benches and tools at hyvelbenk.wordpress.com. And be sure to check out all of the videos that Roald and the Norsk Folkmuseum have posted on Youtube. Grab yourself the refreshment of your choice, sit down and start watching. You’ll probably be surprised how long you can sit in one place. Just be careful that your legs don’t fall asleep and you collapse upon trying to stand. Remember the theory of “Unintended Consequence.”