Router Z axis drifting down!

[cnctygrys]

Hi all

Today our router table became unusable due to the Z axis rack drifting down by itself. When we powered the machine down to check it we found the ball screw still attached firmly but the DRO was not registering any movement when we maunally spun the motor. All other axes are fine.
We can also lift it up manually but it kind of free falls when you let go of it, slowed only by the spinning ball screw.
Any idea what could be wrong?

The machine is a two year old CNT Motion 900 series.

thanks for any ideas!

Ben

[NEATman]

Sounds like a loose coupling/pulley to me. If the rotary encoder is connected to the motor shaft (as most are) the mechanical connection between the motor and the ballscrew should be suspect.

Another possibility is that the rotary encoder is loose on the shaft. The rotating disk is usually held in place with very tiny setscrews.

Take a close look at the connection between the motor shaft and ballscrew.

NEATman

[MarkT]

Cnctygrys.

I am not familiar with CNT's machinery, however I would recommend not only looking at NEATman's recommendations but also the following;
1.) Check whatever type of brake system the "Z" axis motor is using for funtionality. This may require intervention with CNT.
2.) Some machines have pnuematic cylinders to assist the ballscrew in overcoming the weight of the head assembly. This is especially true if your machine has a boring block or a large router. If your machine is equipped with this it will list it in the manuals as a Z Axis Compensation Cylinder.
3.) During operation, check the axis drives or axis drive cards ( whichever your machine is equipped with), typically you will get errors when an axis is acting abnormally.
If you need any more help do not hesitate to contact me.
Hope this helps!

Mark T.
www.cnccustomservices.com

[cnctygrys]

Thanks to those who replied. It turned out to be that ours does in fact have a pneumatic counterbalance, and that someone had for some reason turned the air pressure down. We tweaked it back up and all's well.