Z axis "jumps" up at a certain point

[reibuehl]

Hi all,

the Z axis of my Shapeoko 3 shows a strange behavior: If I lower it in 1mm steps, at a certain point, it makes a loud noise and jumps up a few centimeters.
This video shows it twice:

https://www.youtube.com/watch?v=SWVqgriVn98

What could I do to fix this?

Best regards,
Reiner

[RoguePirin]

It looks to me like your set screws are not tight enough on your Z-motor shaft and the pulley gear is slipping when the spring tension gets too high.

Take a look at the Z-Motor shaft; one side of the shaft should be flattened. Your gear/pulley should have 2 tiny set screws, and one of them MUST be screwed against the flat part of the shaft. Make sure that is aligned correctly, and then really tighten both set screws.

[reibuehl]

The shafts of my motors don't have a flat side. Might be a different one - I have the Shapeoko 3 "Sparkfun Edition". But the belt is definitely very loose. I will try to tighten it more and hope this fixes the issue.

[WillAdams]

You can file a flat onto the shaft

Place the motor in a plastic bag, poke the shaft through, clamp the shaft, file a flat carefully then clean up the filings

there's a bit about tension on the wiki:

http://www.shapeoko.com/wiki/index.php/ ... ys#Tension

http://www.shapeoko.com/wiki/index.php/Shapeoko_3#Belts

[reibuehl]

In the second wiki location that you mention, half of the links are dead. It seems that everything that starts with http://docs.carbide3d.com/article/... is not there anymore.

[WillAdams]

Yeah.

Apparently they're reorganizing

[almus]

My newly acquired (~1 month) and assembled shapeoko 3 does this same thing, however in my case
it jumped back to "zero" and in doing so, it destroyed my Z zero/limit/home switch.

So I need a new limit switch.

I will post elsewhere, but since where does one find spare parts (eg limit switch) Does someone have a digikey part number?

Thanks

[WillAdams]

Possibilities:

- belt skipping due to too strong springs --- increase belt tension (careful not to bend motor shaft) and either replace the springs w/ less powerful ones (they're a commodity part from a hardware store) or remove one
- stepper driver is overheating --- shouldn't happen w/ the new board and heat sink
- intermittent wiring connectivity --- check all the connections
- loose pulley set screw (or tight set screw which doesn't mate up fully w/ the flat on the shaft) --- check and tighten

Also see http://www.shapeoko.com/wiki/index.php/ ... rmittently

[RoguePirin]

So I need a new limit switch.

I will post elsewhere, but since where does one find spare parts (eg limit switch) Does someone have a digikey part number?

Thanks

Try this thread:How to order limit switches?

[almus]

I ascertained that it is not the cogged drive pulley on the stepper motor shaft. That
is fixed solid. However I did break the 1.5mm hex ball end off inside the grub screw. ARG!!!!
Not sure how that will resolve itself. But that was not the problem. I marked the pulley
and the shaft and their orientation stays constant.
(Not to self: only use name brand hardened hex tools---the hex tools provided are soft.)
How the hell to get that grub screw out and replaced is a project for future me.

I note that if you have the z axis under spring tension and you turn off
the power------*smack* you will kiss your limit switch goodbye as holding torque--->0

Are the springs there entirely just to counteract the weight of the spindle?

I was surprised that the springs could overcome the stepper motor
torque, as that would mean that under load the z axis would/could slip.... Because face
it the springs are *not that stiff*
And lo-and-behold I discovered that something in the bottom of the z axis is letting go.... I cannot figure it out yet.