John, When I set up a machine, I always set the home position for XYZ as just inside the X+ max, Y+ max and Z+max limits. This makes all my tool and XY work piece coordinates always negative values. I set machine XYZ zero as the home position. When I told a machine to go home, the Z position was always as far away from the table (and vises and parts) as possible. I refused to dial in a hole and set XY home as the center of the hole. This always confused the G54 issue as you could use G54 from the center of the hole, but the center of the hole this time was different from the center of the hole next time. I determine what I type of fixture or tool (123 block or 246 block) or whatever. This allows you to use an offline tool setter and match tool lengths for every machine. Tool lengths offsets are always negative and the same value works for every machine. The G54Z (WPC) (Work Piece Coordinate) is then the Z distance from the tool set surface and the WPC in the gcode program. This number can be positive or negative depending on the Z level of the tool set surface. The only "gotcha" is you must not have a WPC Z level active when setting the tool length on the machine. That is also a (mental comfort) feature - you don't have to worry what WPC Z level was previously used to set the tool length as by practice you ONLY set tool lengths with the WPC Z level as ZERO! The tool length value is the distance the Z axis must move to touch the tool tip to the Z level of the tool length set fixture. Shorter tools have a higher negative (absolute) value as the Z axis must move farther to touch the tool set fixture.
This simplified it for my simple mind. ymmv regards Stuart On Sat, Mar 22, 2025 at 7:51 PM John Dammeyer <jo...@autoartisans.com> wrote: > Hi all, > I'm struggling trying to get my head around this. The more sites I visit > and read the more confused I get. > > After I home the machine the knee is all the way down away from the quill. > For the sake of round numbers assume that it's at zero and if it were to > move up to touch the quill the machine Z value would be -12.000" (round > number for this example) > > Now I place a 123Block on the table and insert my T99 Touch Probe which has > a length in the tool table of 4" (another round number for this example) > using M06 T99 G43 > > If I move the table up until the touch probe discovers the 123 block (G38 > command) the G54.Z location changes to the distance the knee has moved up. > So 12" total movement minus 3" 123Block and there's a 4" probe in the quill > so the table can only move up -5.000" and that goes into G54.Z so the DRO > on > the screen now reads 0.000" as that's the now working surface. > > Now I do an M06 T4 G43. Remove probe and Insert the tool with length 2" in > the tool table and click on OK. G54.Z changes. And if I move the knee up > until the tool just scratches the 123Block surface the Z value is now zero. > > How does the system calculate this new G54.Z value? And if I change to a > different tool with 5" in the tool table what does G54.Z become so the tip > of this new tool also scratch the top of the 123Block and the Z value reads > 0.000"? > > Thanks > John > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Addressee is the intended audience. If you are not the addressee then my consent is not given for you to read this email furthermore it is my wish you would close this without saving or reading, and cease and desist from saving or opening my private correspondence. Thank you for honoring my wish. _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
