Shapeoko 3 Z-Axis stepper skipping

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WillAdams
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Re: Shapeoko 3 Z-Axis stepper skipping

Post by WillAdams » Fri Dec 02, 2016 8:19 pm

That number is in line with what we have in the wiki:

http://www.shapeoko.com/wiki/index.php/ ... ifications

Normally cutting forces are in the single digits (for pounds), so it's surprising that it fails when cutting, and it being caused by a board fault seems plausible.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

richb
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Joined: Thu Dec 01, 2016 7:08 am
Location: Mechanicsville VA

Re: Shapeoko XXL Z-Axis stepper skipping, spring mod

Post by richb » Sat Dec 03, 2016 4:16 pm

Measured some more data. Using a shipping scale mounted at several heights jogged the spindle down until Z axis stepper skipped. See the plotted data below for the standard springs supplied with Shapeoko XXL machine and replacement Hillman springs from Lowes.
Shapeoko-Zthrust.gif
Plotted Data
Shapeoko-Zthrust.gif (11.3 KiB) Viewed 985 times
This seems to show that the standard springs are too strong and that most of the Z axis thrust is overcome by these springs in the lower spindle positions. That would explain the loss of the Z axis positioning. But using the longer Hillman springs results in a more constant force and available thrust.

Based on these measurements does it look like my machine and controller are operating correctly? For complete data and photos see the attached pdf.
Attachments
Shapeoko-Zthrust.pdf
Complete Data and Pics
(136.29 KiB) Downloaded 41 times

houndel
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Re: Shapeoko 3 Z-Axis stepper skipping

Post by houndel » Sun Dec 04, 2016 6:15 am

I've been having the same issue for months - I stopped using the shapeoko 3 because this inhibits all operations. 0.5mm is the best z depth plunge I can reliably hold in MDF or clear pine (without loosing depth from the stepper skipping).

Recently I gave it a go with a very simple drilling operation using UGS: after several peck drills (each time skipping) UGS threw up a "hard limit hit" warning, and cut all control to the shapoko, dropping the still running spindle into the work piece. Not ideal.

Just as you described - the issue doesn't seem to be mechanical unless it's happening inside the stepper. There's a "thunk" noise when it skips as if it has bottomed out onto something too hard to cut. I have tightened all the belts a number of times a few different ways, and the pulley is definitely not slipping on the shaft.

I am very keen for any new ideas to try.

WillAdams
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Shapeoko 3 Z-Axis stepper skipping

Post by WillAdams » Sun Dec 04, 2016 2:48 pm

For the limit switch hit issue, this is likely why the Carbide 3D homing switch which uses unshielded wires only implements soft limits --- try shielded wires? twisting them doesn't seem to be sufficient for preventing interference. Also review your grounding and ensure that you have a star topology with no ground loops.

I believe the "Thunk" sound inside the stepper motor is the stepper losing position and being forced to the next position which it wants to hold --- try removing or replacing the springs --- I am beginning to suspect that the springs which were well-suited for the original, tall plate, aren't suited for the new shorter one --- probably people who are being successful have added in spoil boards and are mounting the router at the top position, both of which reduce the need for the greater extents of downward travel.

Try removing a spring?

I actually considered and worked up a B.O.M. for changing the machine over to a leadscrew Z-axis: http://www.shapeoko.com/wiki/index.php/ ... Acme_screw
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

richb
Posts: 6
Joined: Thu Dec 01, 2016 7:08 am
Location: Mechanicsville VA

Re: Shapeoko 3 Z-Axis stepper skipping

Post by richb » Mon Dec 05, 2016 5:06 am

The "thunk" sound is definitely what I was hearing when losing Z-axis position.

Interesting... last week when I spoke with Apollo at Carbide3d about these problems he DID say I might have to remove one of the Z-axis strings.

Changing the machine over to a leadscrew Z-axis sounds interesting and (I think) has an advantage of eliminating uncontrolled or run-away plunge when the bit is pulled into the work piece. I had this happen once when switching from a 2-flute to a 3-flute bit without updating the tooling settings. BAD mistake on my part!

WillAdams
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Joined: Mon Apr 09, 2012 6:11 pm
Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Shapeoko 3 Z-Axis stepper skipping

Post by WillAdams » Thu Dec 08, 2016 4:55 pm

After discussing this a bit it seems likely that such problems are caused by insufficient Z-axis belt tension (or maybe a bad motor) --- the stepper motor should be able to overcome the springs and then some. Agree removing a spring is a useful test / technique.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

ajleone11
Posts: 14
Joined: Sat Jan 16, 2016 2:32 pm

Re: Shapeoko 3 Z-Axis stepper skipping

Post by ajleone11 » Thu Mar 02, 2017 1:11 am

I was having the same problem and tried removing one spring. Seemed to work fine after but can the machine run on one spring for an extended time and if not, what would be a good replacement spring?

Tony

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