Tool Length Offset TLO

Every tool loaded into the machine is a different length. In fact, if a tool is replaced due to wear or breaking, the length of its replacement will likely change because it is almost impossible to set a new tool in the holder in exactly the same place as the old one. The CNC machine needs some way of knowing how far each tool extends from the spindle to the tip. This is accomplished using a Tool Length Offset (TLO).

The TLO is found by jogging the spindle with tool from the machine home Z-position to the tool setting point on the machine. This can be the top of a tool probe, or as shown in Figure 5.4, the top of a 1-2-3 block resting on the machine table. The distance travelled from home to the top of the block is recorded, and the value entered into the TLO register for that tool (called an H-register, because it is preceded by the letter H in the CNC program).

If a tool wears or breaks, it can be replaced, the H-register reset to the new tool by touching off again on the 1-2-3 block, and the program continued with no other changes.

Leave a Reply