Forum Navigation
Forum breadcrumbs - You are here:ForumForums: Questions & AnswersZ axis drift
You need to log in to create posts and topics.

Z axis drift

12

I had a machine crash today when the Z axis machine zero shifted down by about 25mm.

I was air cutting the attached .nc file when suddenly the spindle dived into the table. Fortunately I didn't have a cutter, just a sharpen dowel installed. The WCS was set to X0, Y0, Z-25 this set the point of dowel about 5mm above the true WCS, which is about 18mm above the table. The dowel was driven about 5mm into the table. When the crash occurred I hit the hard wired program stop button, which stopped the program at line 26245, but the crash had occurred in the previous 2D contour. I don't know which line of code drove the spindle into the table.

The job is clearing a 2D adaptive 45mm wide a cross a piece of timber 46mm wide then running a 2D contour down each side of the cleared area, repeated 22 times. The pieces are packed together to form a continuous cut of 1012mm. I am trying out different cutting methods to reduce machining time.

When I jogged the spindle up until it stop at what MASSO thought was the machine Z zero the Z DRO was reading 40mm and the spindle was about 25mm below the limit switch.

MASSO S/N 1801

Running v3.40

Job created in Fusion 360 running MASSO post processor Version: 42267 Changed: 4 days ago.

Regards,

Arie.

For the Bicton Men's Shed.

Uploaded files:

are you running the mill or the plasma version of the MASSO software?

3 axis Mill version.

thanks, is it always drifting downwards?

I wasn't watching it the whole time, didn't notice any drift down.

It just dived into the table and then dragged along the table, then raised up moved across to the other side of the cut and dived into the table again. At this point I was able to stop further movement and shutdown the spindle.

Looking at the g-code and the position that the spindle dived into the table, it was in this portion of code.

(2D CONTOUR3)
N30850 G0 X130.4 Y312.8        This is the point spindle dived into table.
N30855 Z17.
N30860 Z7.
N30865 G1 Z3. F5000.
N30870 Z-6.2
N30875 G18 G3 X129.6 Z-7. I-0.8 K0.
N30880 G1 X128.8
N30885 G17 G3 X128. Y312. I0. J-0.8
N30890 G1 Y267. F10000.
N30895 G3 X128.8 Y266.2 I0.8 J0. F5000.     And travelled to here.
N30900 G1 X129.6
N30905 G18 G2 X130.4 Z-6.2 I0. K0.8
N30910 G0 Z7.
N30915 X162.6
N30920 G1 Z3. F5000.
N30925 Z-6.2
N30930 G2 X163.4 Z-7. I0.8 K0.         Stopped machine on this line of code with spindle buried in table.
N30935 G1 X164.2
N30940 G17 G3 X165. Y267. I0. J0.8
N30945 G1 Y312. F10000.
N30950 G3 X164.2 Y312.8 I-0.8 J0. F5000.
N30955 G1 X163.4
N30960 G18 G3 X162.6 Z-6.2 I0. K0.8
N30965 G0 Z17.
N30970 G17

The physical travel through the table was not the full 46mm so I have to assume that the Y axis lost steps, but I didn't check that.

I don't understand what Fusion is trying to do with the G18, G17, G3 codes, but in the CAM I was requesting a finishing cut with a downcut cutter to remove the 1mm left on the wall of the adaptive clearing that was done with an upcut cutter.

 

If you want the settings file I can obtain it next Monday when I attend the again.

Regards,

Arie.

G17, 18 are for plane selection, details here: https://masso.com.au/masso-documentation/?section=g17-xy-plane-selection

In case of Z axis we have seen that as the Z axis has to work against the gravity, there is more load and it can miss steps, so please first check the mechanical setup. you could also try to reduce the acceleration and max feedrate settings of the Z axis if you are missing steps.

Quote from MASSO Support on March 13, 2019, 6:59 am

In case of Z axis we have seen that as the Z axis has to work against the gravity, there is more load and it can miss steps, so please first check the mechanical setup. you could also try to reduce the acceleration and max feedrate settings of the Z axis if you are missing steps.

We were having instances of the pulley moving on Z acme thread, that has been fixed, filed a flat on the acme rod to enable the grub screws to better engage the rod and added a locknut on top of the pulley.

Will check acceleration and feedrate of Z axis. But I don't think we are missing steps because when we first setup the machine the Z axis was behaving badly, so we adjusted the acceleration and feedrate to a fairly moderate rate.

Also for the crash we had it would have been a massive amount of missed steps, the Z axis dropped about 25mm from the previous 2D contour operation a few seconds earlier.

Regards,

Arie.

Quote from MASSO Support on March 13, 2019, 6:59 am

G17, 18 are for plane selection, details here: https://masso.com.au/masso-documentation/?section=g17-xy-plane-selection

Figured out what Fusion is doing with the G17, G18, G3 code combinations. They are the vertical & horizontal lead in & lead out curves.

I reworked the Fusion CAM last night to get a single 2D contour cut instead of the linear pattern that I was using that resulted in 22 2D contours.

Regards,

Arie.

great, so in your issue resolved?

Quote from MASSO Support on March 13, 2019, 10:13 pm

great, so in your issue resolved?

I won't know until I visit the shed on Monday.

12