05-01-2020, 10:58 AM
I had to renovate the Dewhurst reversing switch on my Myford lathe recently. What I learnt in the process was:
1. Screw on chucks can come loose if run in reverse.
2. The lathe needs to have an on/off switch separate from the forward/reverse switch.
3.If your lathe motor has a centrifugal start winding you will hear the switch make and break as the motor speeds up and slows down.
4. Never switch the earth supply, which as Bob said, needs to be continuous.
5. Ensure the body of the lathe and the body of the motor are both earthed (motors tend to be rubber mounted to prevent vibration).
6.For safety the on/off switch should be a NVR type (no volt release) so that if the mains is cut whilst the lathe is running it will not start up unannounced when the mains comes back on.
7. An emergency stop button is a good idea.
In the end I have left the Dewhurst switch off so my lathe only runs forwards, but I have taken the mains and motor wiring into a separate junction box so that it is easy to reverse the start wiring manually should I need to reverse the lathe at some point, or if I decide to fit a reversing switch in the future.
1. Screw on chucks can come loose if run in reverse.
2. The lathe needs to have an on/off switch separate from the forward/reverse switch.
3.If your lathe motor has a centrifugal start winding you will hear the switch make and break as the motor speeds up and slows down.
4. Never switch the earth supply, which as Bob said, needs to be continuous.
5. Ensure the body of the lathe and the body of the motor are both earthed (motors tend to be rubber mounted to prevent vibration).
6.For safety the on/off switch should be a NVR type (no volt release) so that if the mains is cut whilst the lathe is running it will not start up unannounced when the mains comes back on.
7. An emergency stop button is a good idea.
In the end I have left the Dewhurst switch off so my lathe only runs forwards, but I have taken the mains and motor wiring into a separate junction box so that it is easy to reverse the start wiring manually should I need to reverse the lathe at some point, or if I decide to fit a reversing switch in the future.