Mini lathe speed control is broken.... Fixed

Duke

Registered
Registered
Joined
Dec 30, 2018
Messages
73
The other day the variable speed control knob on my mini lathe broke:

I turned the knob to the off position and the click sounded weird. I also could not turn on the lathe using the speed control.

The potentiometer has five connectors - three for the variable speed and another two for the switch. The switch has a small plastic part that is pushed left and right by a pin on the bottom of the pot. Very flimsy design and I am not really surprised it broke.

I made a brass replacement part, but getting the thing reassembled turned out to be more difficult than I thought.

So - replace the whole thing.....

As expected, I could not find a pot with an integrated switch locally so I settled for a 5k pot and a separate on/off switch which I mounted on the lathe's panel.

The lathe works 100% and hopefully this should not mess around with the circuit board.


Potentiometer with the 5 connections:

20190115_170259.jpg

Broken Part:

20190115_171847.jpg
 
Last edited:
Good fix- the pot value isn't critical; anything from around 2K to 50K, linear taper would most likely work- in fact you could have simply kept the original
and just taped over the backside
mark
 
Last edited:
The only thing that I would add is an indicator light (unless your lathe already has one). Some machines the slowest speed is the motor is not turning. So there is a chance of forgetting to shut the machine off. Also, some brushless DC motors are meant to start at the slowest speed, hence the combine on/off speed control.
 
Mine fortunately has the indicator light - a led that goes to the same connector that the switch is connected to.

I was not aware of the slowest speed start for the DC motors. It makes sense why they did it this way.
 
Mine fortunately has the indicator light - a led that goes to the same connector that the switch is connected to.

I was not aware of the slowest speed start for the DC motors. It makes sense why they did it this way.
I have a minimill that has separate on/off switch and speed control. The seller in the owners manual recommended that always turn the pot to the lowest speed before turning it on. I don't know which DC motor that you have in yours, Mine is a brushless motor and this procedure is to protect the electronics. The light is also for safety. I'm glad that you were able to repair lathe. I don't know how good the power is in South Africa, but I would recommend getting a voltage surge protector as insurance for the electronics in your lathe.
 
Our power has been ok so far - apart from the load shedding implemented now and then by the morons at Eskom.

The minister of public enterprises descended on them and it seems that they are cleaning up their act.


In a real **** happens scenario : what are the options if the electronics are fried by something?

Will you have to order the parts or is there a simpler option? I have seen that some guys make use of treadmill motors as well.


The electronics in my mill and lathe should be pretty similar apart from the mill not having a reverse option.
 
Voltage spikes do not have to come from your power company. If you have a refrigerator or air conditioner, every time it kicks on you may have a voltage spike. If the electronics has built voltage surge protectors and quality semiconductors, you should be okay. You can buy a power strip that has a built in surge protection. Just make sure that it can handle the amperage. It's just a little insurance far cheaper than replacing or repairing a circuit board. Maybe I'm being overly cautious, it's just that I've been in electronic repair business for about 40 years and seen this happen.
 
Back
Top