View Full Version : "Z" coming down during the night

05-11-2009, 07:10 AM
Is it normal for the spindle to come down from HOME after power down? Mine does this and I read a comment that someone elses does too on another thread.

Mike Westvang
Dryad Bows Inc.

05-11-2009, 08:01 PM
Assuming you are using the spindle with the air balancer, it is normal when you remove the air from the device after shutting down. I use a block to keep it from setting all the way down, and just re-home after each start-up.

05-12-2009, 06:47 PM
In a word...


Right after you lose air pressure. Just remember to take out the tool bit or you'll find a rather heavy spindle resting on a small bit.

05-12-2009, 07:19 PM
Yep mine was a newly chipped 1/2 end mill.

Got a pc of wood in it at night now.


11-11-2010, 01:07 PM
Anybody have the Z drop with the air still connected and the machine powered on?

I have had 3 occasions where I have commanded the Z up with the arrow button on the wincnc interface and after I release the button (after the spindle has raised to the desired height) the Z drops to the table (or whatever else is in the way)- once with the spindle on!
in order to get the machine to respond I have to shut it down and restart the machine and wincnc. Thoughts?

11-11-2010, 09:52 PM

I think the ShopSabre machine is servo, right? And the Z is probably ballscrew. You say when this happens you have to power everything down and restart it. That sounds like your drive is tripping out.

It sounds like the head is falling. That probably couldn't happen if the drive was holding. If it happens again, try turning the ballscrew with your fingers (up or down) if you can turn it, the motor isn't holding.

If that's the case, I'd start looking for some reason for the fault. The drives are designed to trip if they come against something that will not allow movement. It helps to keep them from being damaged. I would check for binding, or the head coming in contact with something when it reaches the top. I would think that there would be a high limit switch to stop it from going too high, but maybe it's not working or something.

Just a few thoughts.


11-11-2010, 11:22 PM
The Z is on a ballscrew and there is an upper limit switch which I know for sure is working. There may be some binding in the Z travel, I have noticed that it studders some times through small Z travel increments (<.125"). I will have to check and see if I can turn the screw by hand if it happens again.

11-16-2010, 03:13 PM
I was in the shop last night and ran into the head falling problem again. I was able to turn the ball screw by hand with the machine still powered so the motor is def. not holding. It is an intermitent problem though, it seems to be random and fortunately happens after I have cut something, spindle is off and I am moving the head up above the work piece to clear it and bring it home. I have check the z travel and it is bind free and well lubed, it also happens well before the head trips the upper limit. I wonder if there is a loose connector or something else that could be causing this. I am going to contact shop sabre today and see what they think. As always any ideas are appreciated.

11-16-2010, 03:33 PM
Calling ShopSabre sounds like a wise choice Ryan. It does seem strange that it doesn't do it when you're cutting. You might have something with the bad connection thing or something, but it's doing it in the air after you finish. I'm sure it raises just as much during a cut sometimes..., especially it's a tool changer.

One more thing that doesn't have too much to do with your problem but does have to do with this original thread, to keep from damaging anything after the machine has been shut down and the air has been turned off, I'd try to find a safe place off the edge of the table to 'park' it. Just lower it down till it bottoms out.


11-18-2010, 02:11 PM
After speaking with the tech support at shopsabre (extremely helpful BTW) it seems that the servos are set with a current limiter to help preserve the motor. If the ball screw has a build up of saw dustwhen it goes through the Z range (or a large portion of it) the nut collects the gunk and the friction is increrased enough to trip the current limiter and shut down the servo. The first solution is to clean the ballscrew and nut by layer the grease on and runningit through the travel range, wiping the dirty grease off with each cycle. Next would be to change the current limiter settings which are set at a min. and there is some room to bump them up.

I cleaned the ball screw/nut assembly thouroughly as well as re-greased the tracks and so far have not had the head drop out on me- Big thanks to the awesome support of Shopsabre!

12-20-2010, 01:07 PM
Just to update the topic, I thought this info might be helpful for other newbs.
I spoke with shop sabre and they explained that there is some sort of sensor that will trip the servos if they are drawing to much current (ie:if the is too much resistance to travel). So we lubed the ball screw, cleaned all the saw dust off and starting running again. We had the problem again a few weeks later and again I call good old tech support. Our conversation revealed that we do not have a air balancer on our machine to help the z motor out when it comes time to lift the big 10 HP spindle. They offer the add on kit but it is a little out of our budget right now so I am going to build one with some constant force springs and some aluminum brackets. This should help a lot and hopefully we'll be cutting again soon.

10-02-2014, 01:54 PM
Hi there! I have the same issue with mine. If you turn off the system and air compressor the head comes barreling down onto the spoil board. After hiring an outside technician and expert to help train me on the CNC he found this to be extremely strange. In all of his years working with different manufacturers, none of them allowed for the Z to bomb down on the bed.

We have a wooden block in place to support the head over night. No need to keep the motor running to burn out early. Now we know to release the air slowly, was definitely shocking at first. Seems like maybe this was overlooked upon being build. Cheers

10-02-2014, 02:59 PM
I'd use a gas strut rather than the CF springs. The springs tend to break under the strain of constant flexing, which they get on a Z axis.

06-01-2015, 03:38 PM
I also have a 4896. Our Z will drop when turning off the machine at seemingly random times. Sometimes it does, sometimes it doesn't. I've never had it come down during the night though.