Abstract
This paper deals with the results of the investigator's own experiment made on the piston stroke of CA-7 type coal pick which is variated by the initial pressure of the spring of the testing machine, that is to say, initial force.
The investigator has made a study of the variation between the two initial forces, one is just zero and the other 34 killogramme. A comparison is made between these two, one is by the compressed air pressure, the other by the number of strokes, length of clearance, forward velocity, backward velocity, and shock velocity.
