Every woodworker has one. Every woodworker uses it every time they work on a project. And yet not everyone knows how to use it to its full advantage. Yes, we are talking of the lowly measuring tape.
Though measuring tapes come in all shapes and sizes, for the purpose of this article I am referring to retractable metal or fiberglass tape measures that have a hook (also called a tang) at the end.
A simple example can demonstrate almost every feature of the measuring tape. This example is the simple "L", where the vertical "I" is joined with the horizontal "_".
If you hook the end on one end of the "I" and draw the tape to the other end, let us say it measures an exact 10" in length. If you measure the width of the "I", say it measures 3/4".
If you hook the end on one end of the "_" and draw the tape to the other end, let us say it measures an exact 5" in length. If you measure the height of the "_", say it measures 3/4". This example uses 3/4" stock, of course!
If you place the "_" against the long edge of the "I" to form an "L", logic says that the height should be exactly 10" and the width from the left of the "L" to the point farthest to the right will be exactly 5-3/4". Go ahead and measure it. See, I told you so! Now say you were in a situation when you could not measure from the outside. If you press the hook against the inside corner of the "L" and draw the tape out to the point farthest to the right, you will see it measures exactly 5".
"Wait a minute," you say, "The hook is 1/16" wide. Why wasn't the last measurement 1/16" shy of 5 inches?"
The answer is because the hook floats. When you press the hook in, the scale on the tape measures the length from the end of the hook. When you pull the hook out, it measures the length from the inside of the hook.
I've seen many woodworkers "tighten" the rivets holding the hook to keep the hook from floating, in a misguided belief that the sliding hook is inaccurate. This does fix the hook's accuracy, but only for on circumstance, and not the other.
Because of all this, it is very important to treat your measuring tapes with a fair amount of care! Never let your measuring tape retract at high speed, with the hook slamming against the body as the tape finishes its retraction, since this will extend the rivet's hole and introduce inaccuracies. Never step on your tape's hook, or allow it to be pinched between other pieces of wood since this may change the angle of the hook, and also ruin the accuracy of the tape.
Want more of a lesson? Look at the hook of your tape measure. You might notice a small notch taken out of the bottom of the hook. This notch is to help with measuring point-to-point instead of the normal flat-to-flat. Take the example of the "L" again. If you measure from the top-left to the bottom-right, the notch helps keep the hook firmly hooked to the point, freeing your attention to read the sale instead of trying to keep the hook in place.
Something that is of use to construction workers but of little use to average woodworkers is the amount of standout the ruler provides. This is the amount of tape you can pull out horizontally without having it snap or bend downwards. This is useful when you have to span a large distance with your tape and you do not have an assistant to hold the far end for you. This standout is actually a disadvantage to fine woodworkers because to achieve this standout the blade of the tape must have a large amount of curve. The blade on the tapes with the largest standouts looks like a garden hose sliced in two. This makes the edge of the tape standoff from the wood by nearly 1/2", and makes the measurements and markings you make less accurate since you have to roll the tape to one side or another to make the markings flush with the wood. Tapes with less of a standout tend to have flatter blades, thereby making measuring and marking more accurate. This accuracy is what you, as a woodworker, are truly striving for.
So the next time you go shopping for a tape measure, keep some of these uses in mind, and maybe you can get more use out of your tape measure.