Cutting and Measuring…

Cutting Material

Have you ever noticed that there are two different principles of cutting things?

Cutting By Splitting Things

One way to cut things is the way your scissors or a really sharp exacto knife work: You cut through an object by pushing material apart and splitting it into two pieces:  If you measure the object you start with, then cut it in half with your trusty scissors and then line the two pieces up along the cutting line and re-measure you will get exactly the same measurement.

Cutting By Removing Material

On the other hand, if you cut something using a saw something different happens: Instead of pushing material apart, you remove some material which separates the item you are working on into two pieces: If you take a wooden board and cut it in half using any kind of saw, you get two pieces. But you also get sawdust, which is the material that you removed to separate the board into two pieces.

If you do the same test you did on the object you cut apart with your scissors on that board, you will discover that the aggregate size of the two pieces will be slightly less than the size of your original board: What’s missing is the material that your saw removed. — So how much is missing? An amount equal to the width of the blade of your saw.

Why Does This Matter?

Before you cut something you measure, to figure out where to cut. If you then use a saw to cut, you don’t want to cut at the measured line, but right next to it, on the side that is not part of your carefully measured piece.

I used a pair of calipers to measure the width of the teeth on my hand saw’s saw blade. It turned out to be 1/16th of an inch. — And yes, 1/16th of an inch matters in woodworking. — If you don’t believe me, you’ll learn what coarse-grit sandpaper and expanding wood glue is for later…

However, this makes me wonder if they have metric saw blades outside the States… 🙂

Why All Your Tape Measures are “Broken”

You just spent a lot of money on a really fancy tape measure and you are annoyed that yet again the manufacturer was apparently unable to properly affix the little metal hook at the end of the measuring tape and it just rattles around. — Oh well, nothing that a dab of super-glue can’t fix…

But you better put down that super-glue.

In order for a tape measure to work properly, that metal hook has to be able to move and here is why:

There are two ways you use your tape measure.

Measuring by “Butting Up”

In this case you measure by butting up the little metal hook against your work piece. In this case, your zero-mark is the outside of that hook.

Measuring by “Hooking”

In this case you hook that metal latch onto your work piece. Your zero-mark is the inside of that hook.

So What?

This should make it pretty clear why the hook has to move and by how much: In one case your zero-mark is the inside of the hook, in the other case it is the outside. So the amount by which it has to move in order to give you accurate readings no matter how you use it is equal to the thickness of the hook itself…