. Electric railway journal . ignment of the fingers with respectto the contact segments on the drum. Where this typeis used care must be taken to make certain that theholes in the contact bases through which the adjustingscrews pass are so large that they do not bind or rubon the screws as the fingers raise and lower. Thesquare nuts on the adjusting screws must also fit closeenough to the lugs on the finger bases so that theycannot turn when in position; but the nuts must not beso close that they will interfere with the slight move-ment which the fingers have as they make and breakcontact with
. Electric railway journal . ignment of the fingers with respectto the contact segments on the drum. Where this typeis used care must be taken to make certain that theholes in the contact bases through which the adjustingscrews pass are so large that they do not bind or rubon the screws as the fingers raise and lower. Thesquare nuts on the adjusting screws must also fit closeenough to the lugs on the finger bases so that theycannot turn when in position; but the nuts must not beso close that they will interfere with the slight move-ment which the fingers have as they make and breakcontact with the contact segments. Finger Springs While investigating controller troubles, I inspectedseveral thousand worn-out controller fingers at variousmaintenance shops, and found that an average of onefinger in every ten was removed for a broken or crackedfinger spring. Most of these breakages occurred justat the edge of the finger where the spring and shuntrest against it. This point is shown in the standardcontact drawing at Elect} ic DEVICE FOR TESTING CONTROLLER FINGER SPRINGS The fingers inspected were of several differenttypes and a further classification of the spring break-ages showed that 90 per cent of the broken springswere on fingers which had no shunts. I first thoughtthat the current carried by the spring might havesomething to do with their breakage, but later testsshowed that this was not the case. The reason thatthe breakages were not as frequent on finger springswith shunts was due to the fact that the soft coppershunt formed a cushion for the spring at the edge ofthe finger so that the bending strain was distributedover a greater area of the spring. By rounding thecontact edge of the finger, the breakages were decreasedsomewhat, but the insertion of a few thin strips of softcopper to act as a cushion proved the best remedy. It isthus seen that shunts are an advantage in another waythan that of helping to carry the current from thefinger to the conta
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