Back in the old days, with tube televisions and radios a temperature dependent resistor was placed in series with the transformer primary to prevent a large current surge that happened as the transformer power supply charged up.? As the current flowed the resistor warmed and the value of the resistance dropped to a value that reduced the voltage drop and the TV/Radio behaved as if it wasn't there.

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That worked well for those types of equipment because they weren't repeatedly switched on and off.? While hot they wouldn't do what they were supposed.? But for Motor Control systems they don't work because system may be switched off due to an estop or limit switch (or a spindle motor) and while hot you no longer get that soft start.

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That's why I added a small 8 pin PIC micro-controller to switch the relay in/out based on when AC is applied.? Now each ESTOP causes the same sort of inrush current suppression.

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Now about the spindle motor.? Putting a inrush resistor on a simple DC brushed motor would probably work.?

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But a speed controlled motor like on the mini-lathes may not like an inrush limiter on the AC input.? If the motor is a two wire DC brushed motor then something like that might limit the motor current but only when it's cold.? It stays hot while running so if the motor is switched off and then on again there is no benefit.

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Another possibility, is switching a resistor in series with the motor for a short time and then removing it may work.? But again I'm not sure it will work with the types of motors on these lathes.

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If you changed to a switch that was momentary in one direction and ON in the other.? Or had two ON positions you could perhaps switch a resistor in series in the one position and then remove it in the second. ?So for the small chucks flip the switch directly to ON.? For heavy chucks and work held in the chuck, switch to the start position which limits the current into the motor and then as the motor picks up speed switch it the rest of the way onto the ON position.

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Or alternatively switch the motor driver to one that can actually ramp up the motor speed at whatever rate you program.? Especially if it's got an encoder that lets it close the loop and maintain exact spindle speeds at slow RPM.? Useful for threading with a 1PPR spindle sensor and MACH3.

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John

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