GCode sends my Z axis beyond my limit switch - Fusion 360

Hi All,
My first build, so am pretty inexperienced. I have just tried sending my first GCode to my machine, but within a few commands the job halts. At first I thought it might be interference from the sindle, so I removed all spindle commands (M3 etc) to try to narrow it down. It still stops at the same place. It appears that the generated GCode is sending my Z axis beyond the limit switch. I get an ALARM 1.

I have a 1m x 1m Ultimatebee with HY VFD and an xPro V5. I am using Fusion360 to model etc and am using CNCjs.

I have set-up a machine in Fusion360 where: Capabilities are set to milling only, Kiematics X, Y and Z home position is set to -2.5mm (that is the coordinate that CNCjs tells me once the machine has homed to the limit switches - X far right, Y back of machine, Z top of travel). Raid feed rate = 2800mm/min, max feedrate = 3200mm/min. Range is set to limited, I put minimum to -2.5 (which for some reason is copied into Maximum - doesn't feel right, but if I change this then the min. is updated to this new number, so I left both at -2.5mm). Post processing is Grbl / grbl 2.

In Fusion360 in MANUFACTURE my setup is as follows: I select my machine (as described above). I set the WCS origin to be on the model body at the back left (close to my machine Home position - which works out to be X -20mm Y -20mm Z -100mm. In my hole milling process (I am just tring to mill a series of screw holes) I have Clearance Height to 10mm above Retract Height, Retract Height is 5mm above Stock Top, Top Height is set to Hole Top, and Bottom Height set to Bottom of Hole.

Settings in my xPro V5:

$0=10
$1 = 255
$2=0
$3=2
$4=0
$5=0
$6=1
$10=1
$11=0.01
$12=0.002
$13=0
$20=0
$21=1
$23=0
$24=200.00
$25=1400.00
$26=250.00
$27=2.5
$30=24000
$31=5000
$32=0
$100=320
$101=3200
$102=800
$103=200
$104=100
$105=100
$110=3200
$111=3200
$112=3200
$113=1000
$114=1000
$115=1000
$130=770
$131=785
$132=$150

Here is the start of the GCode:
(1001)
(Machine)
( vendor: SPAM)
( model: Ultimatebee 1000x1000)
( description: Generic 3-axis)
(T3 D=6 CR=0 - ZMIN=-8 - flat end mill)
G90 G94
G17
G21
(When using Fusion for Personal Use, the feedrate of rapid)
(moves is reduced to match the feedrate of cutting moves,)
(which can increase machining time. Unrestricted rapid moves)
(are available with a Fusion Subscription.)
G28 G91 Z0
G90


G17 G90 G94
G54
G0 X-0.25 Y-0.6
Z15
G1 Z10 F1000
Z0.6
G18 G2 X0.35 Z0 I0.6 K0
G1 X0.65
G17 G3 X1.25 Y0 I0 J0.6
X-1.25 Y0 Z-0.5 I-1.25 J0
X1.25 Y0 Z-1 I1.25 J0
X-1.25 Y0 Z-1.5 I-1.25 J0
X1.25 Y0 Z-2 I1.25 J0
X-1.25 Y0 Z-2.5 I-1.25 J0
X1.25 Y0 Z-3 I1.25 J0
X-1.25 Y0 Z-3.5 I-1.25 J0
X1.25 Y0 Z-4 I1.25 J0
X-1.25 Y0 Z-4.5 I-1.25 J0
X1.25 Y0 Z-5 I1.25 J0
X-1.25 Y0 Z-5.5 I-1.25 J0
X1.25 Y0 Z-6 I1.25 J0
X-1.25 Y0 Z-6.5 I-1.25 J0
X1.25 Y0 Z-7 I1.25 J0
X-1.25 Y0 Z-7.5 I-1.25 J0
X1.25 Y0 Z-8 I1.25 J0
X-1.25 Y0 I-1.25 J0
X1.25 Y0 I1.25 J0
X0.65 Y0.6 I-0.6 J0
G1 X0.35
G18 G3 X-0.25 Z-7.4 I0 K0.6
G1 Z10
X-184.375 Y-0.6
Z0.6
G2 X-183.775 Z0 I0.6 K0
G1 X-183.475
G17 G3 X-182.875 Y0 I0 J0.6
X-185.375 Y0 Z-0.5 I-1.25 J0
X-182.875 Y0 Z-1 I1.25 J0
X-185.375 Y0 Z-1.5 I-1.25 J0
X-182.875 Y0 Z-2 I1.25 J0
X-185.375 Y0 Z-2.5 I-1.25 J0
X-182.875 Y0 Z-3 I1.25 J0
X-185.375 Y0 Z-3.5 I-1.25 J0
X-182.875 Y0 Z-4 I1.25 J0
X-185.375 Y0 Z-4.5 I-1.25 J0
X-182.875 Y0 Z-5 I1.25 J0
X-185.375 Y0 Z-5.5 I-1.25 J0
X-182.875 Y0 Z-6 I1.25 J0
X-185.375 Y0 Z-6.5 I-1.25 J0
X-182.875 Y0 Z-7 I1.25 J0
X-185.375 Y0 Z-7.5 I-1.25 J0
X-182.875 Y0 Z-8 I1.25 J0
X-185.375 Y0 I-1.25 J0
X-182.875 Y0 I1.25 J0
X-183.475 Y0.6 I-0.6 J0
G1 X-183.775
G18 G3 X-184.375 Z-7.4 I0 K0.6
G1 Z10
X-368.5 Y-0.6
Z0.6
G2 X-367.9 Z0 I0.6 K0
G1 X-367.6
G17 G3 X-367 Y0 I0 J0.6
X-369.5 Y0 Z-0.5 I-1.25 J0
X-367 Y0 Z-1 I1.25 J0
X-369.5 Y0 Z-1.5 I-1.25 J0
X-367 Y0 Z-2 I1.25 J0
X-369.5 Y0 Z-2.5 I-1.25 J0
X-367 Y0 Z-3 I1.25 J0
X-369.5 Y0 Z-3.5 I-1.25 J0
X-367 Y0 Z-4 I1.25 J0
X-369.5 Y0 Z-4.5 I-1.25 J0
X-367 Y0 Z-5 I1.25 J0
X-369.5 Y0 Z-5.5 I-1.25 J0
X-367 Y0 Z-6 I1.25 J0
X-369.5 Y0 Z-6.5 I-1.25 J0
X-367 Y0 Z-7 I1.25 J0
X-369.5 Y0 Z-7.5 I-1.25 J0
X-367 Y0 Z-8 I1.25 J0
X-369.5 Y0 I-1.25 J0
X-367 Y0 I1.25 J0
X-367.6 Y0.6 I-0.6 J0
G1 X-367.9
G18 G3 X-368.5 Z-7.4 I0 K0.6
G1 Z10

The job stops at line #25: G1 X0.65. It is stopping because the machine has gone into ALARM 1 and the Z axis has activated the limit switch. I am assuming that the machine itself has not actually reached line 25 because that is not a Z axis command, and is maybe stopping earlier at line 14: G28 G91 Z0, or at line 21: Z15???

I have lots of questions:

Commands such as Z0 in the above GCode, are they in relation to the Machine homing position, or to the job zero position that I have set? My understanding is that G90 means all coordinate values are relative offset to the Work Job zero?

I am assuing that the G28 G91 Z0 command is telling the machine to home in the Z axis, could this be where it is hitting the limit switch?

Is the CGode that is created by Fusion 360 understaning my machine limits and axis orientations correctly? I would assume so because I have values such as X=-369.5. However there seem to be lots of Y=0 values? Is it trying to send my machine beyod the limit switches? Why are some of the X,Y,Z values in the positive, when I would expect all of my values to be in the negative? Machine Home = -2.5 XYZ, machine X Left, Y furthest front, Z lowest position would be X=-770, Y=-785,Z=-150?

Do I have a fundamental misunderstanding the the WCS here?

What do I do to stop my machine hitting the limit switches and alarming?

Thanks in advance for your help. Its been quite a learning curve so far!

 

Hi David, thank you. I will download the OpenBuids post-processor and see what happens! I will let you know.

 

Hi David,

I just wanted to thank you. This has worked a charm. I just ran the job (without a cutting tool installed 'just in case'), and everyting looked perfect.

I owe you a beer. Thank you

 

Hi misterg,

Thank you for this. When you say I need to set a safe position as a once only exercise where exactly do I set this? In Fusion360? In CNCjs?

When I applied the OpenBuilds post processing (through Fusion) I saw the option box to specify the -10, -10, -10 safetymove position. Is this what you are referring to?

 

Great thank you

 

Hi All,

I have just hit a new out-out-of-bounds issue. I am trying to face my spoilboard. I am using the OpenBuilds post processor as suggested above. My spoilboard dimensions are 770x785. I am using a 25mm flattening bit. My machine home = -2.5, -2.5, -25mm. Job zero = -22.4, -28, -114. All other settings on the xPro V5 are the same as above. Here is a snippet of the generated code:

G90 G94 G17
G21

(Operation 1 of 1 : Face5)
G54
(This relies on homing, see Search Results for Query: G53 fusion | OpenBuilds )
G53 G0 Z-10
G0 X-753.713 Y32.658

My issue is that the code is alarming on G0 X-753.713 Y32.658 but I cannot see why the code is being generated like this? I have homed the machine. It appears to be inside my bounds, if I change to X-733 and Y-32 it runs ok. (I am stepping through the job line by line to make sure I catch the correct line).

Does anyone have any pointers for me? What am I doing wrong in Fusion 360 to output X and Y beyond machine limits? Why is -753 out of bounds? WHy is it generating a +Y value?

In Fusion 360 my Machine Library definition states Max X range = -770, Min X range = -770 (fr some reason they always mirror each other?), Max Y range = -785, Min Y range = -785.

 

I have drawn a rectangle that is the same as my limits - 770x785.

The origin is at the work zero. I thought all code was relative to machine zero?

 

Machine limits are 770x785.

I am operating under the assumption that if I specify my machine limits then the code will not exceed that without giving me a warning as it Post Processes, or in fusion when it generates the tool path?

 

Ah! That explains it!! Thank you. All along I was assuming code was relative to Machine Home

 

Good advice. Thank you