Question: Can you have too many clamps?
Sunday, October 9, 2011
Question: Can you have too many clamps?
I think you know the answer...
A lot of woodworkers like to read books, magazines and posts about their craft. There are literally hundreds of authors who discuss dovetail drawers, finishing methods, the best tools, etc. I am no different. I have bought books that I was sure would be poorly written and contain misleading information just so I could read them and be proven right. I have many old and out of print books which also were essential for my career. I not only have all the magazines, but I have the promo leaflet for FineWoodworking which was sent out before the first issue.
In all this material, there is one aspect of furniture which is difficult to address: proper clamping methods. Sure, there are stories on vacuum bags, some on veneer presses, a few on specific clamping issues, and so on, but so far I have not seen an article which clearly addresses what I call "vector clamping."
I am sure that my mathematics, geometry and "proper" education in those fields lets me think differently about clamping, but at the same time it is said: "If you scratch the surface of a woodworker, you will find an engineer." This statement was proven at the first SAPFM dinner so many years ago. I found myself sitting at one of the tables in the front with Underhill, Breed, and a dozen other veterans, in a room with about 200 members. The speaker asked the group, "How many of you are making a living at traditional woodworking?" Most of those sitting at my table raised their hands, in total about 10% of the group. Then the speaker asked, "How many of you are engineers?" It was a clear majority.
So I assume that, when I use the term "vector," many woodworkers will know what I mean. A vector is a little arrow which shows the direction of the force under consideration. So a clamp applies pressure in a direction perpendicular to the face of the clamp. Of course, this pressure is not constrained in a single linear vector, but forms a cone of force as it leaves the surface of the clamp. As an example, my veneer press screws exert pressure over 81 square inches, or a 9x9" area, and I placed them on the press 9" apart to form a grid.
The primary purpose of discussing vector clamping is to illustrate how I restore antiques, which very often have curved surfaces. Tripod tables, cabriole legs, bent wood windsors, and many, many traditional forms of furniture rely on curved elements, which often break. These breaks can occur at a joint, like the leg on a tripod table, or in the grain of the wood, like the foot breaking off of a cabriole leg.
In many cases these breaks are treated in a way which makes my life miserable. The repairman will take some synthetic glue, epoxy or "the strongest glue on planet earth" and paint it on the break, then frantically search for a way to clamp it before the glue sets. The result is a mess, and I am constantly trying to undo the damage, scraping off the glue and starting over.
I usually will tell the client: "If you had not had it repaired before, I could do it for half the cost."
Assuming you have a fresh break with good wood surfaces, the first thing you need to do is determine the center of the break or joint, and imagine a vector line perpendicular to that point in space. (Editor's note: see comments below) If you are able to put pressure with a single clamp on that vector line, it will clamp the repair properly. That is all there is to it.
Now, it is often the case that the vector line which pushes directly perpendicular to the center of the break goes off into air, away from the wood surface. Like the curved leg on a pedestal table, the line goes off the curved top edge of the leg, and a clamp will not gain a purchase there. That is why you need to create a proper place for the clamp to press.
Select a softer wood than the object, like pine, poplar or other wood. Shape the wood to exactly fit the surface of the curve, and leave a length of wood for another clamp to hold it in place. Clamp this new piece in position and locate the vector line on it. Draw a perpendicular line on the new piece which crosses the vector line at 90 degrees and cut to this line with a saw or chisel. This will be the place to put your clamp for the repair.
In every place where you need it to press directly on the vector line for the repair, you will need to cut a softer piece of wood and clamp it in place. Do this before you reach for the glue. Now your repair has little pieces of soft wood clamped all over it in places where you need to make the repairs. Grab your glue and put it on the repair, place the pieces in position and use a single clamp to press the vector line together.
It is rewarding to see a single clamp pull a complicated joint together, without slipping to one side or another. When done, all the soft wood pieces can be kept in a box for reuse in similar jobs which will certainly happen.
I do not need to stress that you use animal protein glues...