CNC Spindle Idea

I have a CNC spindle idea, a simple modification to the direct drive 500 series motor. To be precise this is a spindle for the Sainsmart Genmitsu Pro-3018. The spindle will then be belt driven using the current motor.

sainsmart genmitsu spindle play

The reason I’m doing this is down to the play in the spindle. Not surprising really as it uses a cheap 500 series motor with an ER11 chuck mounted directly to the motor shaft. These motors are not really designed for this amount of mass on the end of the shaft. In addition the bearings are simple plain devices.

The ER11 chuck isn’t a very tight fit on the shaft and the slack is made good with a grub screw.

This combination of chuck mass, overhang, poor alignment on the motor and simple bearings is never going to be that great.

Spindle and Bearings

My idea as you can see from the simple sketch and parts in the main page image is to use an ER11 chuck with a plain shaft. This shaft will be supported by ball bearings. The main body will be the same diameter as the motor so it is a simple replacement. The motor will then be rotated 180 degrees and will have a simple belt drive to the shaft.

sketch for a cnc spindle

I’m hoping this CNC spindle idea will give me the following advantages:

  1. accurately aligned shaft
  2. high stiffness with well space ball bearings
  3. low vibration with low runout

The vibration generated by the motor is significant and it does concern me longer term as to the impact on the control board.

spindle for cnc machine with o-ring belt

CNC spindle idea to reality, actually a simple sketch to actual parts.

This is close to the design I had in my head where the motor now points up. Hence it runs in reverse. A simple swapping of the +ve and -ve connections solved this.

The spindle is an ER11 chuck on a straight 10mm shaft. The shaft is supported by bearings at each end.

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