Calipers

a80ve: Internal spring bow calipers

Precision calipers are needed for reliable laving out and for accurate measuring. There are three main types: "outside" calipers, which are used to measure the diameter of solid objects; the "inside" calipers that arc used to measure the diameters inside holes and the "double-sided" calipers that are used by woodturners to pinch the wall thickness of a bowl and to transfer measurements from one rip to the other.

above: External bow above: External firm spring calipers joint calipers left: To measure the outside diameter, hook the arms of the calipers around the workpiece so the workpiece is cradled, then open the arms until the workpiece just slips free.

TIPS BOX

If you want a trammel just for one job, then you can easily get by with an easy-to-make item. All you need is a length of wood with a nail tapped through one end, holes drilled at'/? inch intervals along the wood, and a pencil or large nail to fit the holes.

left: To measure the inside diameter, slide the feet into the hole, undo the screw until the little feet are a snug fit then draw them out of the hole.

Bow spring joint

Split adjusting nut for fast adjustment

a80ve: Internal spring bow calipers

Bow spring joint

Split adjusting nut for fast adjustment

Adjusting nut on threaded rod

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