My first lathe was a Sieg SC2, which had a DC motor. Its power and speed were controlled by a button and a knob switch. My current lathe is a LD-1216GH, which is a PM1340GT with smaller bed. Of course it has a lever switch and I missed the knob on SC2. So I decided to add an extra spindle switch on the switch panel. Took some time to figure out the circuit, but once done, it was a simple job. Thought someone else might be interested as well.
To add a spindle switch with forward-stop-reverse function you need a 3-position rotary switch and wire it as in the diagram. A 3-pos rotary switch has four posts and the common goes to terminal 3, and two others go to 4 (forward) and 5(reverse) in the control box, and the center post goes to the lever switch. At factory setting the wire to the lever switch is attached on terminal 3 in the control box, so you have to remove the wire and connect it directly to the center post of the rotary switch. This is all you have to do.
The rotary switch has the same safety feature as the lever switch. That is, the motor can be powered only from the stop position of the switch, preventing accidental spinning of the spindle. This safety feature in the lathe is implemented by a relay which is required to be activated to power the motor, and the relay can be activated only when the switch is in the stop position at cold powering the lathe or recovery from E-stop.
To install the rotary switch on the switch panel I removed the lamp and put it in its place as in the picture.
To add a spindle switch with forward-stop-reverse function you need a 3-position rotary switch and wire it as in the diagram. A 3-pos rotary switch has four posts and the common goes to terminal 3, and two others go to 4 (forward) and 5(reverse) in the control box, and the center post goes to the lever switch. At factory setting the wire to the lever switch is attached on terminal 3 in the control box, so you have to remove the wire and connect it directly to the center post of the rotary switch. This is all you have to do.
The rotary switch has the same safety feature as the lever switch. That is, the motor can be powered only from the stop position of the switch, preventing accidental spinning of the spindle. This safety feature in the lathe is implemented by a relay which is required to be activated to power the motor, and the relay can be activated only when the switch is in the stop position at cold powering the lathe or recovery from E-stop.
To install the rotary switch on the switch panel I removed the lamp and put it in its place as in the picture.