Z axis "jumps" up at a certain point

Assembly questions and answers for the Shapeoko 3 CNC Mill
reibuehl
Posts: 14
Joined: Thu Aug 11, 2016 11:17 am

Z axis "jumps" up at a certain point

Post by reibuehl » Wed Aug 31, 2016 12:34 pm

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
Posts: 216
Joined: Wed Sep 02, 2015 3:22 pm
Location: Illinois, USA

Re: Z axis "jumps" up at a certain point

Post by RoguePirin » Wed Aug 31, 2016 12:54 pm

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.
Shapeoko 3 #677, Nyloc nuts, ¾" HDPE base with t-nuts, Dewalt 611 w/Super PIDv2

reibuehl
Posts: 14
Joined: Thu Aug 11, 2016 11:17 am

Re: Z axis "jumps" up at a certain point

Post by reibuehl » Wed Aug 31, 2016 7:45 pm

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
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Z axis "jumps" up at a certain point

Post by WillAdams » Wed Aug 31, 2016 7:58 pm

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
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

reibuehl
Posts: 14
Joined: Thu Aug 11, 2016 11:17 am

Re: Z axis "jumps" up at a certain point

Post by reibuehl » Wed Aug 31, 2016 9:14 pm

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
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Z axis "jumps" up at a certain point

Post by WillAdams » Thu Sep 01, 2016 12:37 am

Yeah.

Apparently they're reorganizing
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

almus
Posts: 4
Joined: Mon Sep 12, 2016 7:52 pm

Re: Z axis "jumps" up at a certain point

Post by almus » Mon Sep 12, 2016 8:02 pm

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
Posts: 8618
Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Z axis "jumps" up at a certain point

Post by WillAdams » Mon Sep 12, 2016 8:25 pm

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
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

RoguePirin
Posts: 216
Joined: Wed Sep 02, 2015 3:22 pm
Location: Illinois, USA

Re: Z axis "jumps" up at a certain point

Post by RoguePirin » Mon Sep 12, 2016 9:00 pm

almus wrote: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?
Shapeoko 3 #677, Nyloc nuts, ¾" HDPE base with t-nuts, Dewalt 611 w/Super PIDv2

almus
Posts: 4
Joined: Mon Sep 12, 2016 7:52 pm

Re: Z axis "jumps" up at a certain point

Post by almus » Mon Sep 12, 2016 10:15 pm

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.

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