M491.1 tests the current stored TLO against a new TLO measurement and halts the machine if the values are more that a tolerance value H off. H defaults to 0.1mm
This function will not test if a tool is broken in the ATC, only if it has broken after the initial calibration that happens when you switch to the tool since TLO are not stored for each tool individually, only the current tool.
The TEST_M491.1ToolBreak.cnc file shows minimal usage and tests for a potential error where the user did not supply an M5 before running M491.1.
After the pause the user should manually simulate a broken tool by running M490.1 to loosen the collet, replacing the tool with a shorter one, and running M490.2 to tighten the collet. After that point, hit continue and the machine will test TLO and halt due to a mismatch.
faecorrigan
commented
7 hours ago 
M491.1 tests the current stored TLO against a new TLO measurement and halts the machine if the values are more that a tolerance value H off. H defaults to 0.1mm
This function will not test if a tool is broken in the ATC, only if it has broken after the initial calibration that happens when you switch to the tool since TLO are not stored for each tool individually, only the current tool.
The TEST_M491.1ToolBreak.cnc file shows minimal usage and tests for a potential error where the user did not supply an M5 before running M491.1.
After the pause the user should manually simulate a broken tool by running M490.1 to loosen the collet, replacing the tool with a shorter one, and running M490.2 to tighten the collet. After that point, hit continue and the machine will test TLO and halt due to a mismatch.