MARKING AND MEASURING: TRADITIONS, CONVENTIONS AND COMMON SENSE
Until a few years ago, I had a collection of old textbooks, some from as far back as before 1940, when I was still a boy. Those books complemented what was taught in trade schools. The books as well as the trade schools have long since disappeared, along with the elementary knowledge that every woodworker ought to have, such as:
The reliability of your measuring tools and related tools
Ideally, you should use the same ruler all the time, and a good-quality folding wooden ruler should be your first choice. Unfortunately, this is only good – at best – if everything you do is smaller than two metres or six feet in size. Sooner or later, you need a measuring tape. When you do, you know (or should know) that the measurement you take with the tape hooked over the end of something (hook extended) is not the same as the measurement with the hook pushed up against something (hook retracted). The manufacturer of the tape has allowed for this discrepancy, but it is never perfect. The only dependable and correct measurements are those you transfer directly from one piece to another, or from a drawing (on wood) to a piece of wood. When a high degree of accuracy is called for, make your marks with a knife or with a hard pencil with a fine point – 3H, for instance. Hold your wooden ruler on edge, i.e., make the markings on your ruler run straight down to your work. If you use a tape measure, allow a little extra for a more precise trimming later.
There are two methods of making a square. (fig.1) Two separate pieces are joined and held together by brass pins. A good example is the beautiful antique square made of rosewood, blued steel and lots of brass. The other method is to make the whole thing out of one piece of metal, like a carpenter’s square, for instance. Don’t be in a hurry when you buy a square. You need time to make sure that the square you are taking home is square. If you are looking at a one-piece square, it is especially important that you buy one that is perfect, as it is much work to correct one that is not. A two-piece square, depending on its construction and quality, may become out of square. Falling on a hard floor may do it. It is easy to put it right; a few taps with a wooden mallet may be all you need. Check your squares often.
Trivia: Experienced woodworkers do not need a square to make a square cut. They look at the reflection of the board on the blade of their saw. If the edge of the board they are cutting continues in a straight line with the reflection of that edge, the cut will be square.
Just like a square can become no longer true, so can a level. For this reason, it is good practice to always use the longest level you have and to use it twice. By this I mean that after you have checked something once, you turn the level end for end and check the same thing again. Identical readings mean that your level is in perfect condition. Fixing a level can be difficult. With some levels, it is impossible. It involves breaking the plaster of Paris, or similar material, that holds the vial in place, cleaning it, and returning it to its place. You must do this work in a location that is perfectly level and not subject to inadvertent bumps or shocks. Use plaster of Paris, epoxy or whatever else you think may do the job.
If you can afford it, because this is wasteful, the ideal grain direction for legs (table, desk, chairs) is as shown (fig.2).
Doing it this way produces legs that have all four sides the same and all legs are alike.
The grain pattern, or figure, in a vertical piece should be as shown (fig.3).
If it is like fig.4, it is wrong because, as one of my school books put it, “it is upside down; trees grow only one way, and that way is up.”
If drawer sides have a tendency to bow, they should do so towards the inside of the drawer. Doing it that way guarantees that the drawer will not bind. Secondly, if the grain of a drawer side runs from front to back, it will be easy to plane the side in case adjustments need to be made.
Doesn’t everybody do it that way?
Then it must be right! Right? Think of a bridle joint, for instance: two pieces of equal thickness joined to form a 90° corner. Invariably, you will see the thickness of both pieces neatly divided in three and all surfaces nice and even, as in fig.5.
This is a poor joint to begin with. It has no mechanical strength, meaning that without glue, the pieces will not stay together. To make it worse, the amount of wood taken from one piece (to create a mortise) equals one third of the thickness of that piece. In contrast, the piece with the tenon lost two thirds of its thickness, which is too much. Whatever joint we make, no piece should ever lose more than half its thickness, lest the piece – and therefore the joint – becomes too weak. Instead of dividing the thickness in three, it should be divided in four (fig.6). This will result in equal amounts of wood being removed from both pieces. What makes this joint a poor joint is that none of the pieces are captured; they are free to move as the seasons change, and eventually nature wins. The joint will slowly begin to open up around the outside edges. It may take a long time for the pieces to separate, but in the meantime, the joint is uneven and looks bad. A proper mortise and tenon is much better.
Here is another thing that we sometimes see (fig.7).
The principle makes sense. A shelf, or a rail, is used to keep the sides of a bookcase, a cabinet or a chest of drawers from bowing out. Only one of the three examples shown should be used. The first one to be rejected is the double one. To make this one is much more work than it is to make a single dovetail, and it is not any better. Also, if you have to make corrections or adjustments to get a perfect fit, you may end up with a rail or shelf that is just a little too low or too high. This becomes important if you are making a drawer opening. The second reject is the dovetail at the bottom of the shelf. Any cut across the bottom of a shelf reduces the load-bearing capacity of the shelf. This is important in a bookcase. But even if it is not important, this joint should be rejected because it does not look right.
This leaves the joint with the dovetail at the top. This one provides all the required strength, and it does not affect the load-bearing capacity of the shelf.
Having said all this about dovetailed shelves or rails, it puzzles me why we see this joint. I do not mean that this joint should not be used. On the contrary, it is good practice. I just wonder why some people want the public to see what they did. Doesn’t a blind dovetail joint look much better? And I am sure that a blind dovetail joint takes less time than a joint that invites the public to closely inspect and to touch. I am also sure that there is no difference in performance between a concealed joint and an exposed joint.
Being right 50% of the time.
If you are not certain which way to go, you risk being wrong, and here is an example. A plank door (or barn door) is easy to make and suitable for garden sheds, barns, log cabins and other rustic buildings. Such a door consists of a number of vertical boards held together by crosspieces at right angles to the vertical boards, and kept from sagging by a diagonal brace. The most important part in such a door is the diagonal brace; it determines whether the door will keep its shape and will not sag (fig.8) shows a door inside a door opening. The diagonal brace runs from the top at the hinge side to the opposite corner, the bottom of the lock side. This brace does little or nothing to prevent the lock side from sagging. The next door (fig.9) is properly made. This brace is effective in keeping the door square. Also shown (fig.10) is the proper way to join the diagonal brace and the horizontal cross braces; this construction distributes the pressure of the compression joint equally across all members.
Adrian C. van Draanen
Marking and Measuring Traditions
Lee Valley Wooden Folding Rule
Auto-Lock Write-On Measuring Tapes
Veritas Bar Gauge Heads
Wooden Kyougi Pads
Aluminum Sliding Bevel
Heavy-Duty Gate Bracket Kit