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Messages - PeterF

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G-Code, CAD, and CAM discussions / Re: real meaning of G28 ?
« on: March 18, 2010, 05:06:41 PM »
No reason to excuse. Your question was welcome.

I just noticed the release of Mach3 version 3.042.038 and will install it tomorrow in the shop. Actually the spindle (unrelated to this thread) is in the "fixed" list.


G-Code, CAD, and CAM discussions / Re: real meaning of G28 ?
« on: March 18, 2010, 04:17:21 PM »

Now G28.1 gives me a headache.
      Assuming this is all in Mach. coords.
Using the Summary of GCodes in Mach
current position = X10 Y10 (mach. coords)
MDI G28.1 X1 Y1   I would expect the axis's to rapid simultaneously to machine coord x1y1, then commence the normal referencing routine per config. but it doesn't.
Both axis's make a simultaneous INCREMENTAL move in the POS direction of 1 to X11 and Y11 and then the normal referencing routine begins to seek the switches in the proper NEG direction.

Been banging my head on this for 2 weeks ..off and on. lol

The incremental preliminary motion of G28.1 is easy to explain. You are probably in G91 mode (if not, i.e. in G90 mode, then see next absatz).

And please note, the preliminary position in G28 and G28.1 is actually in work+tool coordinates.  (if you have been in G90 mode, then your work [+tool] offset should happen to be (-10,-10,*)  (+10,+10,*) ).

No matter what the NIST-compliant documents say. I just simulated it in Mach3 on my laptop.


The G-Code generator (Mach3-Postprocessor) we are using seems to take Mach3 into account. It clears to home with two lines, and note G91 mode for both lines.
Code: [Select]
N990 G91 G28 Z0.
N992 G28 X0. Y0.

G-Code, CAD, and CAM discussions / Re: real meaning of G28 ?
« on: March 18, 2010, 03:17:14 PM »
You are right. However, the contents of Mach3\Mach3MillGcode.htm seem NIST-compliant (respectively it is the very same text). If there is some more information available, I would be grateful. If not available, we remain grateful and cautious.

edit: I notice the size change by admin, do it myself this time.

G-Code, CAD, and CAM discussions / Re: real meaning of G28 ?
« on: March 18, 2010, 02:20:15 PM »
Life isn't easy, but wonderful.

NIST RS274 specification says: G28 goes to home (home is defined by parameters 5161-5166). Mach3 goes to zero, ignoring parameters 5161-5166.

NIST RS274 says also: G28 goes to home thru the point given, in terms of the absolute coordinate system. Mach3 goes to zero only on the axes given, thru the axes points given and interpreting the latter in work coordinates.

Since I am basically just supporting an engineer, without roots in the shop or in cnc, but used to specs, NISTies or not - what am I really missing? I'm not about the deviations, but about their silency and the possible consequences in the shop. Is this all plain experience?

G-Code, CAD, and CAM discussions / Re: real meaning of G28 ?
« on: March 17, 2010, 06:56:46 PM »

G28 X5. will go to home via the position X5. ( used to avoid obstructions and the like )


 Mach3 R3.042.033 would not go to zero.

Specifically G28 X5. moves horizontally to X5 in work coords+tool offset, then moves horizontally to X0 in mach coordinates. Y and Z are left unmoved.

It is a surprise and I am looking for some confirmation and additional information. (This is admittedly, on my simulation notebook. G91G28Z0 on the real controller moved similarly, XY left unmoved as far as I remember.)

G-Code, CAD, and CAM discussions / Re: risky meaning of G28 ?
« on: March 17, 2010, 03:39:33 PM »
And to find that G28 Z5 moves only Z axis, but G30 Z5 moves z to Z5, then all axes to zero.

(the intermediate value to be handled in work coordinates, in G28 Z0 and G30 Z0).

G-Code, CAD, and CAM discussions / real meaning of G28 ?
« on: March 17, 2010, 03:07:57 PM »
I'm new to G Code and just a computer technician, sort of. Questions relating to G28 going "home".

(a) is G28 going to machine zero, or to the home offset coords given in Config->Homing/Limits? Is "home" meaning machine zero?

(does "ref all home" set the parameters 5161 thru 5166? to zero, or to the offsets given in Config->Homing/Limits, or not touch them?)

(b) is G28 Z0 going to Home/mach zero in all axes, or just in the Z axis (thru abs 0), and why is this so because my docs say otherwise. Why is G28 Z0 not moving the X and Y axes?

I observe that G28 Z5 moves only the Z axis, going to Z5 then Z0. This is of course very sensible, but not so written.

Are these behaviours of Mach3 configureable?

well, I found it myself -

1. I will use MachScreen instead of (unavailable) Mach3ScreenTweak version C1. MachScreen (v1.40a) does list hotkeys.

3. Mach3 looks for the presence of a button with OEMButton Code 103, which means Jog Mode Toggle. Then it enables jog keys.

Sorry for asking in the first place.


1. I would need Mach3ScreenTweak version C1, but the download link http://www.machsupport.com/Downloads/Mach3ScreenTweak.exe on the wiki page http://www.machsupport.com/MachCustomizeWiki/index.php?title=Standard_Hotkeys makes an error. I do have version B1, but there I can't yet see the hot keys.

2. I would need to have hotkeys x y z for mpg#1 axis selection, instead of ALT-A. They should work on all joggeable pages, not just the jog fly-out. (probably I could make global invisible buttons, assign them the hotkeys x y z and do what is needed (OEMbutton 185 thru 187). How to I generate invisible but enabled buttons? or how to handle hot keys without buttons?

3. The global jog hotkeys (up-down-left-right arrows, pageup-pagedown 4up-4down) do work when the "Jog mode button" is on the screen, as I have read in the documentation.  What is the "Jog mode button" (how is its presence recognized by the global jog hotkeys?) Mach3 definitely behaves this way, requiring the presence (and turning-on) of the jog mode button.

Thank you for giving me a helping hand.


I'm going to use Screen4 as a screen editor. This resolves the issue.


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