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FIRM ODD-LEG CALIPERS (JENNY CALIPERS)
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The two calipers seen here are similar. They are manufactured from tool steel and each scriber / scriber point, has been hardened and tempered. They are for marking out the surface of sheet metal and for checking parallel edges.
 
 
 
 
When marking out metal surfaces, it is recommended that ‘engineer’s blue’ (or layout ink) is applied to the surface first. Engineer’s blue is a paste, that is ‘diluted’ with methylated spirits. This results in a quick drying fluid, that is brushed on to the metal surface. When it is dry, scriber marks show up clearly, making them easy to see.
Engineers blue is also supplied as a ‘felt pen’. Layout fluid is already diluted for use on the surface of the metal.
 
 
  They are easy to use. First set the distance required, using a mm scale on a steel rule. The transfer it to the metal surface, by ensuring the notch is lodged against one edge of the metal, then simply ‘drag’ the scriber, across the surface.
 
 
 
  Odd-leg calipers can also be used to find the centre of a piece of round section material. This is achieved by scribing a number of ‘arcs’, from different points of the circumference. The arcs cross over, revealing the centre.
 
OUTSIDE AND INSIDE CALIPERS
 
The calipers seen below, are for either external or internal measurements and are seen being been used to measure steel tube. In the case of the outside calipers, they are adjusted until each leg touches the outside surface. The caliper is then transferred to a steel rule, so that the measurement can be read from the scale.
 
FIRM OUTSIDE CALIPERS:
Manufactured from polished tool steel. ‘Firm’ calipers are held together by a ‘nut’ type joint and it is the friction of this joint, that allows for adjustment and setting to a specific measurement.
 
 
INSIDE AND OUTSIDE CALIPERS
These inside and outside calipers, each have a spring and an adjusting screw. The adjusting screws allows for fine adjustment, which means they can be set more accurately than a ‘firm’ type caliper, which is simpler in design.
 
 
 
 
MEASURING AGAINST AN ENGINEERS RULE
 
 
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