What’s the standard for WCS and offsets?

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10 Jun 2022 23:30 - 10 Jun 2022 23:35 #244920 by Eyecon
I’m completely new to CNC turning and I just got done with my Chinese 7x14 lathe conversion.
I was reading about the procedure for tool touch off on the LinuxCNC lathe page and I realized I have no idea how to setup my tools or WCS. I also watched a couple of videos about setting tool offsets on HAAS lathes and got even more confused :)

Using the touch off methods described on the lathe page, is the standard to set the X on all WCS to zero(e.gG54 X zero = machine X zero) and rely on the tool offsets with G43 so that the offset X position in the current WCS is always spindle center while the Z tool offset is set relative to some reference tool? I guess this way I would only need to set the Z zero for the current WCS by touching off on the part’s face using the reference tool? Obviously this wouldn’t apply to boring bars and tools oriented parallel to the spindle.

what confused me watching the HAAS videos is that their tool table appears to store offsets in machine coordinate systems after doing a “measure radius/diameter” which seems to subtract the current machine coordinates from the test part radius/diameter. Linuxcnc seems to store arbitrary or absolute offsets with no reference to any WCS….at least that’s how I have it setup on my router. 

 
Last edit: 10 Jun 2022 23:35 by Eyecon.

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14 Jun 2022 12:47 #245113 by andypugh
What is commonly done on a lathe is to store tool offsets relative to a "master tool" and then arrange the WCS (G54 for example) to be set such that the end of the part is Z = 0 and the spindle centreline is X = 0. This means that X is sort-of absolute, but that Z is changed frequently (ie, for each part)

It would be possible to keep zero in the G54 X axis and do all diameter comp in the tool table. That might be slightly harder to mess up by touching-off in the wrong way. [1]

But for the Z you probably want to use work offsets, so that all the tools move when you change the absolute position of the Z reference.

After writing this, I am actually considering ceasing to use T1 as a reference tool for diameter and seeing how I get on with referencing tools to the absolute X axis position. I think that it might still make sense to have the Z be referenced to a particular tool (or possibly to a touch-probe)

[1] If you use the "master tool" approach then doing a "tool touch off" with that tool can lead to mis-setting all the other tools. You need to "Work touch off" or "set origin" with the master tool and "set tool" with the other tools.
G10 L1 P1 X0 Z0 in MDI can be useful to recover from accidentally giving the master tool a tool offset.
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15 Jun 2022 00:06 #245153 by Eyecon
Makes sense! After watching the tormach videos I think I prefer the HAAS method which I guess is not based on a master tool but rather absolute offsets for each tool in X. After playing around a little, I think I do prefer your suggestion of using the Z offsets relative to a master tool(a facing tool) this way the WCS offset in Z needs to be setup one relative to the master tool, but the X is always absolute and never need to be changed since the spindle center doesn’t change. So currently all my WCS offsets are zero in X and vary in Z based on the part, tools offsets in X are all relative to machine zero while Z is relative to my facing tool. This also works well for my cross slide drill chuck which always needs to be centered and only needs Z offsets depending on the workpiece and how the bits end up getting mounted.

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28 Jun 2022 02:43 - 28 Jun 2022 02:46 #246046 by smc.collins
this guy covers it in good detail 

Last edit: 28 Jun 2022 02:46 by smc.collins.
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