. traces are conventionally drawn with positive metal giving an upward movement but when testing experimentally the results can correspond to positive metal either way so it is advisable to check polarity. In the metrology lab this can simplest be done by passing a piece of paper or hair though the mesh. | 20 Chapter 2 Fig Effects of mating two spur gear profiles each with tip relief. . traces are conventionally drawn with positive metal giving an upward movement but when testing experimentally the results can correspond to positive metal either way so it is advisable to check polarity. In the metrology lab this can simplest be done by passing a piece of paper or hair though the mesh. The combined effect of one pair of teeth meshing under no load would be to give a . of the shape shown in Fig. b with about one third of the total span following the involute for both profiles and generating no error. The tip reliefs then give a drop negative metal at both ends. The same effect is obtained if the relief is solely on the pinion at tip and root. However the geometry is more complex at the root as the mating tip does not penetrate to the bottom of the machined flank. Putting several pairs of teeth in mesh in succession gives the effect shown in Fig. a . If there are no pitch or profile errors and no load applied so no elastic deflections the central involute sections will be at the same level of zero . and part way down the tip relief there will be a handover to the next contacting pair of teeth. One base pitch is then the distance from handover to handover. When we measure . under no-load conditions we cannot see the parts shown dashed since handover to the next pair of teeth has occurred. Copyright Marcel Dekker Inc. All rights reserved. Marcel Dekker Inc. 270 Madison Avenue New York New York 10016 Harris Mapping for Spur Gears 21 Fig a Effect on . of handover to successive teeth when there are no elastic deflections. Fig b Effect of pitch error on position of handover and . Fig. b shows the effect of a pitch error which will not only give a raised section but will alter the position at which the handover from one pair to the next occurs Effect of load on . We wish to predict the . under load as this is the excitation .
