If you are going to use more than one tool in a part with a CNC lathe, you'll need an accurate tool table.
The tool table tells the controller software where the cutting edge is in space. This is necessary as the G Code tells the controller to move, for example from Z0 to Z10 but doesn't contain any information about where the cutting edge is relative to the lathe. For instance, if you are using a left cutting tool and a right cutting tool, the Z position of the cutting edge will be different (Z offset). Or tools might protrude different distances from the tool post (X offset).
Decide on a system for numbering your tools. Label your tools with these numbers (whiteout correction fluid works well for this).
In LinuxCNC the tool table can be edited manually - either by text file, or more easily via the tool table editor, found in the file menu. You'll need to do some manual entry to set up tool angles for tool display in the preview.
The easy way to set X and Z offsets is using touchoff.
When changing tools you need to call G43 to load the offsets from the tool table. Thus the command to change tools is 'Tn M6 G43'
When changing back and forth from different tools you should see the tool preview move appropriately. For example, if tool 2 is 10mm shorter than tool 1, in the preview you should see the tool move 10mm out from the part display.
Warning: If you've used 'Touch Off' and selected 'Tool Table' in the drop down, the next time you 'Touch off' the drop down will default to 'Tool Table', this can lead to accidently changing your tool table instead of changing the world coordinate system (e.g. G54)
See the following for more info: