Side of head: Hi and Low is a mechanical lever that changes the gearing (simplified). This increases the torque but because of the additional gear train the spindle runs in reverse. Thus comes into play the electrical part of this. In high, the motor runs in one direction. If you leave it in mechanical high and turn on electrical low, the spindle runs in reverse. Not rocket science. Electrical high and low chooses a different contactor where 2 of the 3 phases are reversed thus reversing motor rotation. But put it mechanical low and use electrical low and your spindle runs in the correct direction.
The brake turns on whenever the spindle motor is shut off. This is a production machine. If you were to wait for the spindle to stop by coasting, you would waste a lot of precious time.
There were 2 types of power draw bars. The Lever type where you slap a handle left or right to loosen or tighten the tool into the spindle or the push button type. It helps both types if the spindle does not turn when these devices are used. Another good reason for a brake. The push button type also had a air delay built in so the spindle gets a chance to stop before the mechanism squats down onto the drawbar and does its thing.
George
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(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
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