Thanks a lot, your insight into code really provides some useful info, such
as the pivot point of rotation in the back plot is hardcoded to (0,0,0).
I'm gonna try adding fake axes V and W in my machine config and set
GEOMETRY = VWAXYZ, apply an offset to V and W axes and see what happens.
As for the tilt of the tool you mentioned on your website. My explanation
about the tilted tool is that it seems it's a standard that everything
graphical about multi-axis tool paths, such as in CAM and CNC controller,
is relative to the workpiece.
To be easy to understand, if one is tiny enough to be able to sit on the
workpiece, he will see the tool tilts when A axis rotates. And seems it's a
standard that you are always sitting on the workpiece when viewing a tool
path.
2017-08-25 21:36 GMT+08:00 Kirk Wallace :
> In case it might be handy:
>
>> http://www.wallacecompany.com/machine_shop/LinuxCNC/fourth_axis/
>>
>
> My next task was to try to clearly define what the plot should look like.
> A working example to copy would be nice.
>
>
>
> On 08/25/2017 12:53 AM, 王若溪 wrote:
>
>> Hi forks,
>>
>> I'm using LinuxCNC with my 4 axes (A axis rotate along X axis) mill and I
>> want to make back plot in Axis GUI reflect the path of tool reference
>> point
>> (tool tip) relative to the workpiece correctly.
>>
>> i.e. The tool reference point (tool tip) should rotate about the A axis
>> hinge point, which has a fixed G53 Y, Z coordinate when I'm jogging A
>> axis.
>>
>> If I set "GEOMETRY = XYZA", the tool tip always rotate about the current
>> point, which is not correct.
>> If I set "GEOMETRY = AXYZ", the tool tip rotate about the origin of G53
>> coordinate system. Then I had to offset the min/max/home of YZ axis to
>> make
>> G53 origin coincident to A axis hinge point, which is kinda dangerous
>> because many CAM software defaults to do a "G0 G53 X0 Y0 Z0" in the
>> beginning of an operation, which would crash my spindle into the table.
>>
>> So what's the normal practice when making an NC system for 4,5 axis
>> machine? Do I have to add non-trivial kinematics so that the back plot is
>> correct when "GEOMETRY = XYZA"?
>> Or can I redefine the tool length compensation value to be (Z coordinate
>> of
>> A axis hinge - Z coordinate of tool tip) when machine is at Z home/max,
>> which is normally a negative value, so that I still set Z home/max = G53
>> Z0
>> but get correct back plot when tool length compensation is applied? What
>> is
>> tool length compensation typically defined, BTW?
>>
>> Wow, there are a lot of questions. I'm new to mill with rotary axes, any
>> hint would be appreciated, thanks.
>>
>> --
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>
> --
> Kirk Wallace
> http://www.wallacecompany.com/machine_shop/
> http://www.wallacecompany.com/E45/
>
>
> --
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--
王若溪
清华大学
航天航空学院
航硕161班
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