To measure half-way around a tube, take a piece of paper and wrap it
around the tube, marking the overlap point. Now fold the paper in half
between marked points, and make a mark on the fold crease. Rewrap the
paper and mark the tube at the marked points. Just to be sure, wrap the
paper the other way and check the marking alignment. Very accurate. The
distance from edge or first mark to overlap mark is the circumference.
Use calipers for diameter. For a line of holes, make a wood jig with side
walls as high as the tube diameter, and a width just wide enough to hold
the tube with friction. Now measure a center line between jig walls along
the tube surface (easiest if the walls are equal the tubing diameter).
Also very accurate if care is used in making the jig. With a bit of
finagling, all round measurements can be done with one reliable
straightedge. There are many variations on these themes. The finer your
marks, the more accurate the measurement.
-73-
LB, W4RNL
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