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Mill Z Axis gas lift

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BillTodd:
The mass of the Z axis is necessary to counter the verticle cutting forces  and add preload to bearings and screw. None of  cnc machines I've worked on have any kind of counter balance - all have braking on the z motor to prevent the head falling if the drive fails.

I wonder if you should lash something up as an experiment before you spend too much time on it?

Bill

picclock:
@billtodd
The mill head weighs around 40kg. Downforce needed for drilling/milling is a lot less than this 10kg tops and likely zero or -ve for side milling I would guess. By counterbalancing the head the bending forces on either side of the column are nearly equal. This should result in reduced flexing for different head heights. I'm quite tempted to balance the head such that it is driven down by the motor. Because of the simplicity of the setup and ease of adjustment it will be easy to see if any benefits accrue from this.

@brass_machine
It crossed my mind to do that but I'm happy to leave it outside like this. Its  easy to belt drive the ballscrew from a motor behind the head.

@Philf
The issue with these "benchtop" mills is their lack of rigidity. With larger industrial machines you are not going to see much deflection when the knee is in a different position. With a column mill the bending forces and flexing which occur due to the head weight are significant. This will go a long way to eliminating this.

Best Regards

picclock

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