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The long jaws on a caliper are used to measure the thickness of a board or other outside dimensions.
3 Check Square ►
It's tempting to assume that framing squares are, in fact, perfectly square. Unfortunately, that's not always the case. It doesn't take much more than a drop off the bench to distort a blade.
Any distortion is magnified down the length of the blade and will result in a loss of accuracy that can ruin a project. The good news is there's an easy way to test your tools. The drawing at right shows you how to determine whether your square is actually square.
FIRST: place your square along the straight edge of a board and draw a perpendicular line
the square over and see if it lines up with the line you just drew
pencil LINE is exaggerated to show problem
Strike the inside corner with a center punch to open the legs or outside (see inset) to close them.
4 Accuracy with Fractional Calipers ▼
If you've ever tried to measure the thickness of a board or the width of a dado with a tape measure, then you know it's a challenge to get accurate results. Even with a good steel rule, it's still tough.
For these measurements, I reach for a caliper. Acaiiperis designed for that kind of job — and it's far more precise than most woodworking tools. But not just any caliper will yield easy-to-read results. Because I use fractional measurements in my projects, I prefer to use a fractional, rather than decimal, caliper. A fractional caliper has marks in Vm" increments. So you don't have to "do the math" to find the dimension you're looking for.
5 Marking Knife
When it comes to laying out marks for cutting joinery, a pencil Line is often too thick. For precision work, 1 reach for a sharp marking knife.
Not only does the knife lay down a fine line, but the mark is durable and won't smudge or fade as you handle the piece. Another benefit for joinery work is the line also provides a handy "groove" for placing a chisel or saw blade. That's especially useful if you're squaring up the sides of a mortise after drilling out the waste. The line keeps your cuts square.