Problem 2.6 Loci of Points – The figure given below shows an offset slider crank chain mechanism. The crank OA 40 mm long rotates in clockwise direction about the center O. The connecting rod AB 120 mm long is attached with the crank at the point A and the other end B is fixed in a slider EF 25 mm below the horizontal line passing through the point O, & the connecting rod AB is extended in the direction BA at the point L 35 mm from the point A as shown in the figure. Draw the loci points L & M; which is midpoint of the connecting rod AB for one complete revolution of the crank.
Step-1 First draw a horizontal center line of sufficient length
Step-2 Mark a point O on the horizontal center line and draw a circle of radius 40 mm, which is length of the crank OA, with O as the center.
Step-3 Divide the circle into 12 divisions and give the notations A1, A2, A3 etc. as shown into the figure.
Step-4 Draw a horizontal line parallel to the axis passing through the point O at the distance 25 mm below it. This is offset line of the mechanism.
Step-5 Draw lines starting from the points A1, A2, A3 etc. of the length equal to the length of connecting rod, which is 120 mm in such a way that these lines should intersect on the previously drawn offset line. And at the points of intersections give the notations as B1, B2, B3 etc. as shown in the figure.
Step-6 Now mark the points M1, M2, M3 etc. at the distance 60 mm either from A1 or B1 respectively on the connecting rod AB as shown into the figure. This is midpoint of the connecting rod AB.
Step-7 Connect the points M1, M2, M3etc. into sequence with a medium dark free hand smooth curve.This is the locus of the point M.
Step-8 Now extend the lines B1A1, B2A2, B3A3 etc. up to 35 mm and mark the point L1, L2, L3 etc. as shown in the figure.And connect the points L1, L2, L3 etc. into sequence with a medium dark free hand smooth curve. This is the locus of the point L.
Step-9 Give the dimensions by any one method of dimensions and give the name of the components by leader lines wherever necessary.