Setting the start of the machining position

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K0nrad
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Setting the start of the machining position

Post by K0nrad » Sat Sep 24, 2022 6:35 pm

Hi,
Is it possible in CAM module to set the reference point for the start position of the cutter? Usually, the drawing of the detail is not located close to the default reference point. As a results the machine must perform empty movement (sometimes too long, in my case). I tried to modify values in "CAM Configuration -> Home X, Y" but it has no effect. Although a different path in the QCAD window is seen, the generated code is identical and always starts at the reference point. Simulation in CAMotics software also confirmed that there is no difference. Below are screenshots.

Best Regards
Konrad

QCADCAM 3.27.6
Win10
Attachments
code.jpg
code.jpg (78.26 KiB) Viewed 1509 times
Home PosX55_Y130.jpg
Home PosX55_Y130.jpg (44.56 KiB) Viewed 1509 times
Home PosX0_Y0.jpg
Home PosX0_Y0.jpg (46.82 KiB) Viewed 1509 times

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Husky
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Re: Setting the start of the machining position

Post by Husky » Sat Sep 24, 2022 8:22 pm

Hi K0nrad,
K0nrad wrote:
Sat Sep 24, 2022 6:35 pm
Hi,
Is it possible in CAM module to set the reference point for the start position of the cutter?
Yes, that would be the Home position below "CAM Configuration -> Home X, Y"
K0nrad wrote:
Sat Sep 24, 2022 6:35 pm
the generated code is identical and always starts at the reference point. Simulation in CAMotics software also confirmed that there is no difference.
This "Reference point" is the drawing origin at 0/0. Most likely used at your machine as "Maschine Origin". Also called Park Position.

Common praxis is that you have a template drawing for QCAD where the Maschine Origin is at a convenient point which granted short movements to the project.

Let say the machine origin is in the upper right corner (most likely adjustable in the controller) of your machine. A template would look like this example:
The rectangle is your machine work area, the red cross the park position of the laser head (?), the drawings absolute 0/0.
Husky-2022.09.24-01.png
Husky-2022.09.24-01.png (2.45 KiB) Viewed 1496 times

to avoid time wasting empty runs place your part close to the machine origin

Husky-2022.09.24-02.png
Husky-2022.09.24-02.png (7.55 KiB) Viewed 1496 times
If you have already drawings where the absolute zero / machine origin is at an inconvenient point you can select the whole drawing and move it to a more convenient position.
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K0nrad
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Re: Setting the start of the machining position

Post by K0nrad » Sat Sep 24, 2022 9:39 pm

Hi Husky,

1. I understand that since setting "Home X,Y" position has no effect, it should be registered as a bug?

2. Thanks for the idea with the CAM template dedicated to the specific machine. Until now, I usually created a new layer
with the copy of the detail in the right position. Unfortunately - especially when several milling operations were required -
the whole drawing became a mess.

Best Regards
Konrad

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Husky
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Re: Setting the start of the machining position

Post by Husky » Sun Sep 25, 2022 6:31 am

Hi K0nrad,
K0nrad wrote:
Sat Sep 24, 2022 9:39 pm
1. I understand that since setting "Home X,Y" position has no effect, it should be registered as a bug?
No, not a bug. It's working just fine but not the way you thought :wink:
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CVH
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Re: Setting the start of the machining position

Post by CVH » Sun Sep 25, 2022 8:01 am

Similar topic:
https://www.qcad.org/rsforum/viewtopic. ... 635#p33635

This issue resurfaces in several topics.
The homing position is where your machine synchronize itself mechanical.
That does not have to be equal to machine zero position, nor to your working zero positiong.
Please look up 'homing and zeroing'.

The working coordinates and the machine coordinates zero position may differ by a G92 offset.
Machine homing and zeroing various coordinate systems (G54-G59.3) are different aspects.
A working coordinate system can be slanted (G68) in regard with the machine coordinates.
Besides the Home and Zero position, a Parking, Pause and/or a Halting position may be set up differently.
The tool-change position or several distinct positions per tool may also differ from any from the above.

For example, I park just near my homing position so that my limit switches are not activated when I turn on my machine.
Homing, what is done at steady slow pace, then only takes a few seconds.

QCAD/CAM takes the drawing origin to be your working coordinates zero position.
I agree with that a CAM should provide in a way to set a relative origin of a drawing, a UCS for that matter.
Reading https://www.qcad.org/rsforum/viewtopic. ... 635#p33623 and all about USC that will not change in any near future.

Technically, the QCAD/CAM 'Home' is the assumed cutter position before the first toolpath.
Typically the position where you zero your working coordinates.
Remind that there is no feedback about the actual machine or working position at all.
Once a toolpath is started, CAM can foresee where the cutter should be.

Even more complicated is a moving bed machine with a fixed gantry, everything in Y seems to be inverted.
My setup is configured so that I can draw everything in the first quadrant, all positive values.
The drawing origin is where I zero my working coordinates left-near on the workpiece in X-Y, wherever that is clamped on the moving bed.
Still, my homing position is left-far and my machine zero is the left-near corner of my moving bed.

Regards,
CVH

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K0nrad
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Re: Setting the start of the machining position

Post by K0nrad » Sun Sep 25, 2022 1:43 pm

Hi,
Thank you very much for your all explanations.
Does "Home X, Y"settings have any influence on the g-code? In the above example it did nothing.
Nevertheless, an option that allows to set the new origin of milling would be useful.
Regards,
Konrad

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andrew
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Re: Setting the start of the machining position

Post by andrew » Mon Sep 26, 2022 12:28 pm

K0nrad wrote:
Sun Sep 25, 2022 1:43 pm
Does "Home X, Y"settings have any influence on the g-code? In the above example it did nothing.
It depends on the post processor. This position can be used by the post processor in any way imaginable (as starting point, end point, tool change position or not at all).

For the simulation, this is the starting point, i.e. the position of the tool before any movement. The real tool position cannot be known by QCAD/CAM as it might be anywhere before the initial movement.

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K0nrad
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Re: Setting the start of the machining position

Post by K0nrad » Mon Sep 26, 2022 1:18 pm

Hi Andrew,
That is something which is misleading for me. In case of GRBL postprocessor, Home X,Y do not affect the position of the tool before any movement (see the g-code above). Path looks different in the QCAD window but in reality the tool always starts its way from the drawing origin (0,0) position, no matter what Home X, Y values ​​are set. That's why the function of Home X,Y is hard to understand for me. In my machine, I don't really care about initial Home position as it's constant and the machine sets it by itself at the beginning. Later, I always move my spindle to my own "zero position" depending on the material position on the table and the size of my detail. In my opinion, the option called "Zero X, Y" would be more useful (the offset for the origin 0,0 point of the drawing).

Best Regards
Konrad

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andrew
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Re: Setting the start of the machining position

Post by andrew » Mon Sep 26, 2022 1:31 pm

K0nrad wrote:
Mon Sep 26, 2022 1:18 pm
In case of GRBL postprocessor, Home X,Y do not affect the position of the tool before any movement (see the g-code above).
Correct. This post processor (like most others) does not use the home value (variables XH, YH, ZH).
K0nrad wrote:
Mon Sep 26, 2022 1:18 pm
Path looks different in the QCAD window but in reality the tool always starts its way from the drawing origin (0,0) position, no matter what Home X, Y values ​​are set.
That would be an oddity of your controller. As far as I can see, the G-Code you posted does not contain anything that would prompt the tool to move to 0,0 before moving to the first position. I.e. there's no G0 X0 Y0 or similar.
K0nrad wrote:
Mon Sep 26, 2022 1:18 pm
In my opinion, the option called "Zero X, Y" would be more useful (the offset for the origin 0,0 point of the drawing).
You would have to move your drawing to make sure 0,0 is at the location you desire. So far we've avoided an additional zero point as that might be rather confusing (coordinates between CAD and CAM no longer match).

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K0nrad
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Re: Setting the start of the machining position

Post by K0nrad » Mon Sep 26, 2022 2:21 pm

So far we've avoided an additional zero point as that might be rather confusing (coordinates between CAD and CAM no longer match).
As you see, Home X,Y is also confusing :-)
In my opinion, it's just a matter of a proper name. Instead of "Zero" it could be named "machine offset" or something. When g-code is generated
it should be suited to a specific machine and milling conditions anyway. So why not add a new option that will allow it? At the moment I have to do it manually - either create a new layer dedicated to CAM and duplicate my drawing in the desired position or in that way suggested by Husky.

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