For tool and work offsets on my mill I follow the advice given here:  
http://wiki.linuxcnc.org/cgi-bin/wiki.pl?MillSetup 
<http://wiki.linuxcnc.org/cgi-bin/wiki.pl?MillSetup> which in a nutshell says:  
you set one tool (an edge finder perhaps) at a specific point and then 
reference all tools (in length, ie. Z)  to that reference tool.  So settings in 
my mill tool table have Z values that are +/- the difference in length between 
the reference tool and the given tool. 

I am trying to set up the tool table for a lathe and am having problems.  I see 
that the advice for doing this differs from what I am doing above on my mill.  
So, I was trying to follow the advice in section 21.4 of the Linuxcnc User 
Manual: http://www.linuxcnc.org/docs/2.7/pdf/LinuxCNC_User_Manual.pdf 
<http://www.linuxcnc.org/docs/2.7/pdf/LinuxCNC_User_Manual.pdf>

I have the Z offsets in the tool table and that part seems to be working.  
However, I am having problems getting the X offsets to work (even though i 
think i am doing exactly the same thing as Z).   I set the X offset by doing 
this:

In MDI issue: T1 M6 G43
Turned down some stock to 0.55”
Select “Touch off to fixture” in Machine menu
Make sure X is the selected radio button
Select “Touch off Tool” button (This button is new in Axis in 2.7 I think?)  
(Bug? in 2.7.0~pre6 - the dialog for this button refers to Workpiece not 
Fixture)
Enter 0.275 (yes, I entered a positive number even though my tool is above the 
spindle centerline - is that correct?)

In the tool table I get an X value that basically looks like a distance from 
G53 X0 (something like 1.XXXX).

Then to enter a second tool:
In MDI issue: T8 M6 G43 (This is a 0.25” drill)
Bring it down to touch the top of a 0.100” pin which is on top of my 0.55” 
workpiece
Select “Touch off to fixture” in Machine menu
Make sure X is the selected radio button
Select “Touch off Tool” button
Enter 0.275 + 0.100 + 0.125 = 0.5 (yes, I entered a positive number even though 
my tool is above the spindle centerline - is that correct?)

In the tool table, again, I get an X value that basically looks like a distance 
from G53 X0.

When I go back to tool T1 (T1 M6 G43) and then issue a G0 X0 the tool goes to 
the center of the spindle as it should.  

But, if I return to tool T8 (T8 M6 G43) and issue a G0 X0 the drill does not go 
to the center of the spindle.  And it’s distance away is not any of the 
measurements above, in other words I can’t figure out where I went wrong.

Perhaps I should just be following the procedure I used on the mill and just 
forget about “Touch off to fixture” and “Touch off Tool” and enter values +/- 
of the reference tool?

I am quite confused at this point.  I have looked at JT’s tutorials, and all 
the Linuxcnc manuals and other random documents that talk about this, but every 
time I think I understand and try the procedure I get the wrong result.  By the 
way, I have entered the ORIENTATION and the FRONT and BACK ANGLES in the tool 
table for these tools, could those things (if I happened to enter them 
incorrectly) effect the X offset?

-Tom


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