A simple instrument for finding and marking the center of shafting, etc., can be easily made of three pieces of sheet brass and a small prick punch.

The Point of the Punch is Quickly Adjusted to the Center of the Work

Ill: The Point of the Punch is Quickly Adjusted to the Center of the Work

Take two pieces of stiff sheet brass, 2 1/2by 3 in. in size, and cut two corners, 1/2in. square, out at one end of each piece as shown in the sketch. Bend the metal on the dotted line A, until it stands at an angle of 45 deg. The part B should be bent up in the same direction, but at right angles to the plate, while the part C should be bent out only slightly. A hole should be drilled near each corner for rivets. Be sure that the two plates are bent in-opposite directions, then rivet them firmly together.

Roll one end of a strip of sheet brass, 7/16 in. wide and 2 3/4 in. long, into a tube large enough to firmly hold a small steel prick punch. Place the opposite end of the brass strip in between the two ends C. These ends should spring together slightly in order to hold the punch D at any height it may be placed. If accurately made, the point of the punch will be exactly in the center of the V-shaped trough.

In use, to find and mark the center of a round bar, it is placed in the trough with the end just touching the point of the punch. The brass holding the punch is raised between the parts C until the point of the punch is brought as near to the center of the shaft as can be judged. Press the point of the punch against the end of the shaft and turn the latter in the trough. If the punch marks a circle the center has not been found. This is corrected by slowly moving the punch up or down until the point ceases to make a circle, then the punch is tapped with a hammer to mark the exact center.