Accurately Machine a Motor Spindle

I needed to accurately machine a motor spindle so that I could drive a centrifugal fan at high speed. I actually did this in two stages. First machining a small brass spindle with a shoulder that would fit onto the motor spindle. This part has a shoulder and a thread so that the fan can be easily removed. However, although I machined this brass fitting accurately I was pushing it onto a serrated shaft on the motor.

The end product is to be a steam raising blower. A small fan that sits on top of the chimney of the small vertical boiler and pulls the air through the firebox. Thus giving a faster startup of the boiler.

I pushed the brass fitting onto the motor shaft, being careful to support the other end of the shaft. If you don’t support the other end of the shaft you will either damage the brushes and bearings or push the back out of the motor.

I then needed to mount the motor and very lightly take a fine facing cut of the back flange. You can see in the image below a very sharp carbide tool set up to take this facing cut.

As you can see the easiest set up was to mount the motor in the lathe chuck and then power the motor.

motor mounted in the lathe chuck

In this next image you can see the wires going to a power supply for the motor. Be very careful, you Must Not Switch the Lathe on when you are doing this. This would be very easy to do. So, I pulled the main plug on the lathe so I had a second level of interrupt.

motor spindle machining using motor and power supply

The motor has very little torque. Also, the case of the motor is quite delicate so you need to hold it firm but not too firm.

All of this means you need to take very light cuts with the tool. Remember, this brass fitting was machined very accurately. However, fitting it to the serrated motor shaft would result in a very slight offset. Hence this fine cut was to allow me accurately machine a motor spindle to the next level.

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