The pitch can be represented as; Pitch of the screw- Distance moved by screw No. of full rotations given Least Count of the Screw Gauge The Least count (LC) is the distance moved by the tip of the screw, when the screw is turned through 1 division of the head scale. The least count can be calculated using the formula; Least count = Pitch Total number of divisions on the circular scale Zero Error and Zero Correction To get the correct measurement, the zero error must be taken into account. For this purpose, the screw is rotated forward till the screw just touches the anvil and the edge of cap is on the zero mark of the pitch scale. The Screw gauge is held keeping the pitch scale vertical with its zero down wards. When this is done, anyone of the following three situations can arise: 1. The zero mark of the circular scale comes on the reference line. In this case, the zero error and the zero correction, both are nil. 2. The zero mark of the circular scale remains above the reference line and does not cross it. In this case, the zero error is positive and the zero correction is negative depending on how many divisions it is above the reference line. 3. The zero mark of the head scale is below the reference line. In this case, the zero error is negative and the zero correction is positive depending on how many divisions it is below the reference line. 10 -40 Zero error nil zero error positive Zero error negative Case 1 Case 2 Case 3 Page | 13Part 1. NB: PROCEDURE IS EXPLAINED IN DETAILS DURING CLASS Simulator Procedure (as performed through the Online Labs) 1. Select 0.01mm as the least count (L.C) of the screw gauge from the 'Select screw gauge' drop down list. 2. Choose lead shot from the 'Select object' drop down list and measure four different diameters, do the same for Wire and Glass plate. Record the data in increasing order of diameters in Tables 1 ,2 and 3 respectively. Calculate the radius of each object's diameter. 3. Click on the object to place it between the screw and the anvil to find its measurement. To remove the object, click the object on the left menu once more. 4. Click on the arrows seen on the screw head to tighten it till the screw touches the object. 5. Note the PSR and HSR values. 6. Find the total reading and enter the value in the text box provided. 7. Click on the check button to verify the answer. 8. The 'Reset' button can be used to redo the experiment. Table 1: lead shot diameters Pitch Scale HeadScale Reading Total Reading Object Reading No of circular Radius Placed divisions on reference |Value [n x L.C]mm Observed D,=N+n Corrected mm (N) mm mm D Do + c mm line(n) Lead shot Micro meter zero error =...........mm (a) Calculate the volume of each Lead shot sphere Page | 14EXPERIMENT 1.1 MENSURATION NAVIGATION PATH: http://amrita.olabs.edu.in/?sub=1&brch=5&sim=156&cnt=4 Our Objective Our objective is to use the screw gauge; To measure the diameter of the given lead shot. . To measure the diameter of a given wire and find its volume. To measure the thickness of a given glass plate and find its volume. Theory The screw gauge is an instrument used for measuring accurately the diameter of a thin wire or the thickness of a sheet of metal. It consists of a U-shaped frame fitted with a screwed spindle which is attached to a thimble. Stud Screw Pitch scale Thimble Circular scale Ratchet . Frame Parallel to the axis of the thimble, a scale graduated in mm is engraved. This is called pitch scale. A sleeve is attached to the head of the screw. The head of the screw has a ratchet which avoids undue tightening of the screw. On the thimble there is a circular scale known as head scale which is divided into 50 or 100 equal parts. When the screw is worked, the sleeve moves over the pitch scale. A stud with a plane end surface called the anvil is fixed on the 'U' frame exactly opposite to the tip of the screw. When the tip of the screw is in contact with the anvil, usually, the zero of the head scale coincides with the zero of the pitch scale. Pitch of the Screw Gauge The pitch of the screw is the distance moved by the spindle per revolution. To find this, the distance advanced by the head scale over the pitch scale for a definite number of complete rotation of the screw is determined. Page | 12Table 2: Wire diameter Wire length (1) = 5cm HeadScale Reading Total Reading Object Pitch Scale No of circular Placed Reading Radius Observed Dy=N+n Corrected (N) mm divisions on reference |Value [n x L. C]mm mm mm D Do + cmm line(n) wire Micro meter zero error = ...........mm (b) Calculate the volume of each Wire Table 3: Glass plate thickness Pitch Scale HeadScale Reading Total Reading Object No of circular Radius Placed Reading divisions on reference |Value [n x L.C]mm Observed Do=N+n Corrected mm (N) mm mm D Do+ emm line(n) Glass plate Micro meter zero error =...........mm