I bought this small CNC machine to engrave the smokebox door on my miniature traction engine, but the Sainsmart Genmitsu Z-axis accuracy is poor. Poor in a number of ways, but primarily down to the stiffness of the spindle and resultant accuracy of the machining. The movement is allowing the spindle to wander.
The primary issue is down to what must be the very poor quality linear bearings on the z-axis. In the image to the left you can see that the bearing has crept upwards out of the motor clamp. This hasn’t helped.
However, even with this bearing pushed back into place the linear bearings are moving on the two rods. Thus allowing the spindle to move on the two axes as shown by the arrows.
The other issue is the vibration and runout of the ER11 chuck on the end of the motor.
I have a few steps that I’m looking at, in order these are:
- Replace the linear bearings – I’ve order 8x15x45mm bearings to replace the 8x15x35mm originals.
- Replace the direct drive motor with a spindle that is then belt driven with this motor.
The linear bearing replacement should be fairly easy. I have order longer bearings, but the extra 10mm should not be a problem as I tend to use a limited Z-axis motion.
My thoughts around the spindle are to buy an ER11 chuck on a 10mm diameter 100mm long straight shank, add two bearings, make an outer sleeve and add a pulley. I can then offset the motor from the spindle and use a simple belt drive. This should reduce the runout of the cutter and reduce vibration.
Parts are on order and I will and add pages on the Sainsmart Genmitsu Z-axis upgrade as I go about the mods.