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Author Topic: Noob question on Z Axis setup using soft limits  (Read 476 times)

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Noob question on Z Axis setup using soft limits
« on: January 14, 2019, 12:26:59 PM »
I am setting up a DIY CNC router table using Mach 4 and soft limits. All the axes appear to be working correctly when jogging around the table and clicking on Goto Work Zero returns to the home position correctly.

However, when I run the roadrunner gcode file, I am getting the following error:

Error, Z axis commanded over SoftMaxError

What am I doing wrong? Please point me in the right direction on forum or docs so I can rtfm.  ;D

Attached is my current profile package.

Thanks in advance!
« Last Edit: January 14, 2019, 12:28:57 PM by billskeen62 »
Re: Noob question on Z Axis setup using soft limits
« Reply #1 on: January 14, 2019, 01:58:31 PM »
Hi,
on the Toolpath Tab with the RodRunner Gcode file loaded look at the maximum minimum extents of the Gcode.

Do they exceed the SoftLimit window you set in the SoftLimits page?

Do you have Home switches setup and working?

Craig
My wife left with my best friend...
     and I miss him!

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Re: Noob question on Z Axis setup using soft limits
« Reply #2 on: January 14, 2019, 02:01:50 PM »
Is the tool offset set correctly
Is the WCS set on the machine

Though if I remember correctly the RR does not have the tool offset called out as in g43 hex
Re: Noob question on Z Axis setup using soft limits
« Reply #3 on: January 14, 2019, 02:31:04 PM »
Ah, I have not setup any tools yet. I was trying to test without putting any tools in the spindle.

Active H Offset is 5
Active D Offset is 0

Home/Soft Limits for Z are: Soft Min -4.000, Soft Max 0.000. I also tried Soft Max 1.000

Limit switches are/were setup and working, but my Soft Limits settings are less than the X,Y,Z home positions to keep from going that far. I wanted to go to a soft home position on the table.

Looks like this is the line on RR file where it stops:

G0 X0.000000 Y0.000000 Z5.00000

Guessing that Z5.0000 is the problem?
« Last Edit: January 14, 2019, 02:35:58 PM by billskeen62 »
Re: Noob question on Z Axis setup using soft limits
« Reply #4 on: January 14, 2019, 03:05:35 PM »
Hi,
there is a difference between Limit switches and Home switches.

If you hit the <Ref All Home> button what happens?

Craig
My wife left with my best friend...
     and I miss him!
Re: Noob question on Z Axis setup using soft limits
« Reply #5 on: January 14, 2019, 03:29:48 PM »
If the spindle is sitting at home, nothing happens.

If I have moved it somewhere on the table, it resets the DROs?  from whatever readings they had to 0.

No axes move.



« Last Edit: January 14, 2019, 03:46:01 PM by billskeen62 »
Re: Noob question on Z Axis setup using soft limits
« Reply #6 on: January 14, 2019, 03:44:04 PM »
Hi,
that tells me that you do not have Home switches set up. In absence of Home switches if you ask Mach to
<Ref All Home> it will 'Home in place'....that is to say it will reset the machine coordinates to zero at your
current location.

Sorry to say but that renders your SoftLimts as junk.

Lets say you jog your machine to the center of the table and <Ref All Home>. The machine coordinates of the center
of the table are 0,0.  Lets say you have you soft limits as -12 and +12 for the X axis and -24 and +24 for the Y axis
for a machine of 24 inch movement in X and 48 inch in Y.

If you called a move X30 say Mach would baulk and tell you that move is out-of-bounds.
My wife left with my best friend...
     and I miss him!
Re: Noob question on Z Axis setup using soft limits
« Reply #7 on: January 14, 2019, 03:50:03 PM »
Okay, learning here.

So there is no way to use Soft Limits instead of Home switches?

If I click on Goto Work 0, it moves to where I want it to be. Can the Ref All Home be disabled in a script?
Re: Noob question on Z Axis setup using soft limits
« Reply #8 on: January 14, 2019, 04:01:57 PM »
Hi,
sorry, hit the wrong button and posted before I'd finished....

Now try jogging to the lower left hand corner or close to it and <Ref All Home> again. The machine coordinates of the lower
left hand corner are 0,0. But your soft limit setting have not changed.....they are still -12,+12 for X and -24,+24 for Y.
So if you make a move G0 X-5 Y-5 Mach would say 'Yes that's OK its within the SoftLimit boundaries but in fact the machine
is already at the lower left hand corner and its going to try to go EVEN FURTHER to the left and EVEN LOWER and crash!

The point is that SOFT LIMITS are the extents of the machine FROM SOME DEFINED LOCATION, called the reference point
or home. That point must remain the same every session of Mach. Thus the first thing when you turn Mach on is reference
or home it.

You could jog to some location, like the lower left hand corner and call that home. If you go to exactly that location
and home your machine every time then the Softlimits you set in the table will be consistent.

The more common way is to have home switches so that when you <Ref All Home> the machine will drive, at a programmable
slow speed, in a programmable direction UNTIL the home switch for that axis makes AND THEN reset the machine coordinates
for that axis to zero. It will then do the next axis until all axes are homed.

With good home switches you should be able to get your machine to within a very short distance of 'exactly home' every time
and therefore all your soft limits are consistent.

Craig
My wife left with my best friend...
     and I miss him!
Re: Noob question on Z Axis setup using soft limits
« Reply #9 on: January 14, 2019, 04:06:52 PM »
Hi,

Quote
So there is no way to use Soft Limits instead of Home switches?

No, in order for Soft Limits to be useful and consistent you need to home your machine and that means home switches.

Most people use their limit switches as home switches as well. I personally think its poor practice but having said that
most hobby CNCers do it that way.

If you already have limit switches you could probably make them do double service.

Craig
My wife left with my best friend...
     and I miss him!