Z axis problems while milling PCB

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vulcan
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Joined: Tue Jul 14, 2015 12:55 am

Z axis problems while milling PCB

Post by vulcan » Wed Jul 15, 2015 5:05 am

I have a Shapeoko 2 that I am using to mill a PCB. The PCB is designed in Eagle, converted to Gcode with PCB-GCODE, and sent to the mill with UGS.

My problem is that the tool does not move nearly as far along the Z axis as it's supposed to, probably by at least a factor of 50. If I step the Z direction 100 (mm, in UGS), it moves a less than a cm. By contrast, if I step it 100 in the X or Y direction, it correctly moves about 10 cm. When I make drilling Gcode, rather than drilling through the board as it's supposed to, it only makes a tiny indent on the top.

The threaded rod appears to have roughly the correct pitch, and could not account for such a discrepancy. But, the Z axis motor rotates very slowly--about 10 s per turn, or 6 RPM. I've seen videos on youtube where it appears to rotate much faster than that, and I think only some of those videos were sped up after recording! But, to be clear, the problem is not just a slow feed rate--even moving slowly, the tool stops, reverses, and moves on while never reaching its destination depth (or height).

Has anyone ever encountered this problem before or have ideas? Sorry if this isn't quite the right place to post it; I couldn't find a category that fit exactly. Thanks for any help!

CastIrony
Posts: 650
Joined: Mon Jul 21, 2014 10:21 pm
Location: Portland, OR

Re: Z axis problems while milling PCB

Post by CastIrony » Wed Jul 15, 2015 6:00 am

Whoever replies first is going to ask you to post your GRBL settings, so it might as well be me. :D

I'm not super knowledgeable about UGS, but I think it should be pretty straightforward to send a $$ command and copy the results.
Shapeoko 3 #192 - Complete! Needs limit switches.

RobCee
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Location: Birmingham, UK

Re: Z axis problems while milling PCB

Post by RobCee » Wed Jul 15, 2015 10:08 am

It sounds like you missed the Tuning, the GRBL Configuration or the Calibration section of the build process (assuming that this behaviour is not a new thing).

You probably have an incorrect value in your $102 setting in GRBL 0.9 (If you are using an earlier version of GRBL than 0.9i, you would be advised to upgrade it).
For a stock SO2 the Z-Step value, used as a starting point for calibration, is about 320 step/mm
ShapeOko2 #3400 - Chinese 800W AC Spindle - Stiffened X-Axis - TR10 Z-Axis - Inverted Z Motor - Hall Effect Limits - Drag Chains & Custom Brackets

vulcan
Posts: 4
Joined: Tue Jul 14, 2015 12:55 am

Re: Z axis problems while milling PCB

Post by vulcan » Wed Jul 15, 2015 11:55 pm

Thanks for your responses! I just updated my grbl from 0.8 to 0.9. I loaded it with the arduino IDE and used the defaults for Shapeoko 2, then made a few changes to the step/mm and z max rate (to reflect advice I've seen elsewhere) and to the max travels (to be careful).

The X and Y are still correct, and the Z still has the same issue: penetrated maybe 0.5 mm instead of the requested drill depth of 3.81 mm.

Do any of these look wrong?

Grbl 0.9i ['$' for help]

$0=10 (step pulse, usec)
$1=25 (step idle delay, msec)
$2=0 (step port invert mask:00000000)
$3=0 (dir port invert mask:00000000)
$4=0 (step enable invert, bool)
$5=0 (limit pins invert, bool)
$6=0 (probe pin invert, bool)
$10=3 (status report mask:00000011)
$11=0.010 (junction deviation, mm)
$12=0.002 (arc tolerance, mm)
$13=0 (report inches, bool)
$20=0 (soft limits, bool)
$21=0 (hard limits, bool)
$22=0 (homing cycle, bool)
$23=0 (homing dir invert mask:00000000)
$24=25.000 (homing feed, mm/min)
$25=500.000 (homing seek, mm/min)
$26=250 (homing debounce, msec)
$27=1.000 (homing pull-off, mm)
$100=40.000 (x, step/mm)
$101=40.000 (y, step/mm)
$102=320.000 (z, step/mm)
$110=500.000 (x max rate, mm/min)
$111=500.000 (y max rate, mm/min)
$112=250.000 (z max rate, mm/min)
$120=10.000 (x accel, mm/sec^2)
$121=10.000 (y accel, mm/sec^2)
$122=10.000 (z accel, mm/sec^2)
$130=150.000 (x max travel, mm)
$131=150.000 (y max travel, mm)
$132=50.000 (z max travel, mm)

WillAdams
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Re: Z axis problems while milling PCB

Post by WillAdams » Thu Jul 16, 2015 12:11 am

Sure you're not losing steps due to thermal shutdown?
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

vulcan
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Joined: Tue Jul 14, 2015 12:55 am

Re: Z axis problems while milling PCB

Post by vulcan » Thu Jul 16, 2015 2:01 am

I'm definitely not an expert here (at about day 4 of trying to work with this mill), but I just looked up thermal shutdown and it doesn't seem to describe what's happening. The motors aren't cycling on and off--at least not at a perceptible rate. They just don't move as far as they're supposed to. Am I misunderstanding what thermal shutdown can do?

By the way, I didn't mention in my previous post but my Z step/mm value was originally 40. Setting it to 320 changed the rate the motor turned (now about 1 rev/sec) but not the distance the tool traveled up and down.

WillAdams
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Re: Z axis problems while milling PCB

Post by WillAdams » Thu Jul 16, 2015 2:35 am

Mystified here.

There was a run of bad gShields ― perhaps you have one of those?

The other question is what are the microstepping jumpers on the gShield set to?

Check the latter, and if possible, add active cooling and adjust the current, striving to make it lower, while keeping the machine moving.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

jarretl
Posts: 135
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Location: Edmonton, AB

Re: Z axis problems while milling PCB

Post by jarretl » Thu Jul 16, 2015 4:01 pm

Your settings look ok to me as well.

As Will said, check what your microstepping is set to on the Z axis. I have mine set at 8x microstepping (no jumper on the Z axis pin header), and I think my $102 value is 1280 steps/mm, instead of the typical 320 steps/mm for 2x microstepping.
Also make sure your Z axis coupler that connects the motor to the screw is tight on both sides, so there is no slipping.

Details on how to tell what your microstepping is set to can be found here

-J.
Shapeoko 2 #4043; DW660

vulcan
Posts: 4
Joined: Tue Jul 14, 2015 12:55 am

Re: Z axis problems while milling PCB

Post by vulcan » Sat Jul 18, 2015 4:41 am

It was the microstepping. They were all set to 8x. When I jumpered the Z axis to make it 2x microstepping, it worked correctly.

Thank you for all this help! Very much appreciated.

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