Bridgeport
Heidenhain CNC Mill
Programming & Operating Instructions
Chapter 7
Setting Tool Length Offsets (TLOs)
Definition
Tool length offsets (TLOs) amount to nothing more than the jog distance the Z-axis must travel from its fully retracted position to the position where the cutter makes contact with a Z-zero reference surface (usually the top surface of the workpiece). This is accomplished by "touching off" each cutter on the reference surface (using a feeler gage) and loading the jog distance into the appropriate TLO register. When each tool is "called," the appropriate TLO is accessed and used to offset the Z-axis origin.
Procedures for Setting TLOs
- Make sure the quill is fully retracted and the Z-axis register reads zero at that
position. If necessary, zero out the Z-axis register (in
Chapter 2).
- Load each cutter into a toolholder, making sure it is securely held so it won't slip in
use.
- Adjust the height of the table so that the longest cutter/toolholder assembly can be installed in the spindle without interfering with anything.
- Press the HAND WHEEL OPERATION
key and press Z and 
keys to
make the Z-axis active.
- Hand wheel the cutter to the Z-reference plane, using a feeler gage such as a 0.100" gage block.
- Press the EDIT program
key and move the cursor to highlight the "L"
parameter in the appropriate Tool Definition block.
- Press the DATA TRANSFER
key to transfer the jog distance displayed in the Z-axis
counter into the Tool Definition block. Then press the EOB 
key.
- Retract the quill back to Z = zero.
- Repeat the process for each cutter.
