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Need help to install 5 axis knematics

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15 Mar 2022 21:42 #237384 by JackRay
Hello everyone.
back to the forum,actually I had a lot of difficulties concerning the 5 TCP setting (type: xyzac-trt) on my machine. It works well but to tell you the truth, nothing is clear to me regarding the Z axis offset values.

which theoretical value should I enter in:

setp xyzac-trt-kins.z-rot-point ...            for 180mm Z-axis travel
and how much for: setp xyzac-trt-kins.z-offset ...        with an  A axis offset of 44.6 mm.

the values ​​I entered work (I adapted them by testing the settings) but I found no logical calculation.(setp xyzac-trt-kins.z-rot-point -127 (mm)???
and (setp xyzac-trt-kins.z-rot-point -44.6  (ok) mm


Do you have a theoretical explanation?

Thanks for your help .

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16 Mar 2022 00:00 #237414 by andypugh
I think that the z-rot-point is the position of the Z axis in machine (absolute) coordinates when the tip of a tool of zero length is in the spindle (and tool length comp is enabled) and the tip of that tool is at the rotation point.
So, to an extent it depends on where you choose to measure your tool length from.

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16 Mar 2022 07:34 #237438 by JackRay
Sorry i made z mistake about "step xyza c-trt-kins.z-rot-point -44.6 " it's setp xyzac-trt-kins.z-offset -44.6 ( in fac it's a raduis of A axe)

To make my zero "Z" I first make a G41h1, then I come tangent to the middle of my axis Pivot AC. and I enter the value "step xyzac-trt-kins.z-rot-point ..." in relation to the machine origin (taking into account the offset of tools). This part is not well documented on the linuxcnc documentation, many people are trying to understand how it works.

Thank you

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16 Mar 2022 12:25 #237464 by JackRay
Hello,
I found the simple but necessary calculation concerning the value of "setp xyzac-trt-kins.z-rot-point ..." .

Here is my procedure : with an axis A of 44.6mm radius
 and tool N°1 of 50 mm length .

- Mount the tool in the spindle (50 mm overhang)
- add this tool and this length in the tool table
- activate the G43h1 (tool length compensation "code G")
- Come tangent to the center of the AC axis (be careful that the A axis is horizontal "A0")
-Read on LinuxCNC the offset in Z ( ex : -222 mm from the origin )

- calculation : 50 ( tool length ) + 44.6 ( A axis pivot point ) - 222 = -127.4 mm

setp xyzac-trt-kins.z-rot-point -127.4

Maybe there are other calculations but on my xyzac-trt machine it works very well.

Sincerely
 

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17 Mar 2022 16:56 #237541 by andypugh
The documentation does rather assume that you can glance at matrix maths and understand exactly what it represents.

I can't.

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