08-02-2013, 01:54 PM
MACHINE SHOP practice
1MACHINE SHOP.doc (Size: 2.23 MB / Downloads: 77)
MEASURING INSTRUMENTS
1) VERNIER CALIPER
The Vernier Caliper is a precision instrument that can be used to measure internal and external distances extremely accurately. The figure shown below is a manual caliper. Measurements are interpreted from the scale by the user. This is more difficult than using a digital Vernier caliper which has an LCD digital display on which the reading appears. The manual version has both an imperial and metric scale. Manually operated Vernier calipers can still be bought and remain popular because they are much cheaper than the digital version. Also, the digital version requires a small battery whereas the manual version does not need any power source.
2) MICROMETER
It consists of a hollow cylinder mounted on a U frame. The hollow cylinder leads to a ratchet which is meant for fine adjustment. The U frame consists of a flat end known as Anvil and a Spindle on the other side. This screw can be moved inside the nut by fitted in the U frame by rotating the hollow cylinder called the thimble. This is called the main scale. The hollow cylinder or the thimble is graduated into 50 or 100 equal parts. This is called the circular scale.
HOW TO TAKE MEASUREMENTS
Total observed reading = Main Scale reading + (Circular Scale Division coinciding the base line of Main Scale) x Least Count
True diameter = observed diameter – zero error
DETERMINATION OF THE DIAMETER OF A WIRE ROD
The wire whose diameter is to be determined is placed between the anvil and spindle end, the thimble is rotated till the wire is firmly held between the anvil and the spindle. The ratchet is provided to avoid excessive pressure on the wire. It prevents the spindle from further movement. The diameter of the wire could be determined from the reading as shown in figure below.