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### Lesson 5: Everything about CNC Tool Length Offsets. Positive and Negaive (G43 g-code, H offset)

October 27, 2015, 9:13 pm

### Did you know there are three ways you can touch off your tools?

Because of how Machine Offsets add up, there are several ways CNC machinists can set their Tool and Work Offsets.

This is especially true Tool Length Offsets.

Tool Offsets can be either Positive or Negative.
Depending on your Machine Shop equipment you should use one or the other.

Regardless of how you set you tool length offset you apply it the same way.
Right after the tool change and after turning on your spindle and moving to your X Y position above the part.
The very first abslute Z movement should be the line where you apply the tool length offset.

Code
T15 M6; (TOOL CHANGE)
G0 G54 G90 X1.0 Y1.5 S1500 M3;(APPLY WORK OFFSET, MOVE TO THE FIRST POSITION, TURN ON THE SPINDLE)
G43 Z2.0 H15; (APPLY TOOL LENGTH OFFSET WHILE MOVING TO 2.0" ABOVE THE PART)
G0 Z0.1 M08;(MOVE TO FEED HEIGHT AND CARRY ON WITH THE PROGRAM..)

### Positive Tool Offsets (gage line tool length offsets)

In case of Positive Tool Offsets, the offset represent the Length of the tool measured as a distance from Gauge Line of the spindle (typically spindle nose) to the tip of the tool. The longer the tool, the larger your Tool Length offset will be.

Attached file: Tool_Length_Offset.PNG

### Lesson 4: Essencial Stuff about Work Offsets, Tool Length Offsets, G54-G59, Part Zero, G43 H

October 3, 2015, 9:03 pm

Before we run any G-Code program, we need to tell the machine where our part zero is.
A Part Zero is simply a bunch of numbers that offset axis to give machine a new coordinate point to work from.

Work Offsets is one of the most basic pieces of knowledge any machinist must have.

Let us account for all the basic coordinate systems and definitions, available in a generic CNC machine

• Machine Home and (Absolute) Machine Coordinates
• Work Offset Coordinates
• Tool Length Offsets

### Machine Home and Machine Coordinates: G53

Machine Coordinates (or Absolute Coordinates) is the absolute and constant representation of machine axis position.
These coordinates never change between Machine Restarts and must remain such. In fact there is often no way for an operator to adjust Absolute Machine Axis Home position.

Machine Home is simply that magical place where all Machine Coordinates should become Zero.

To Home the Machine is to start a machine operation, that will move all Axis to their soft limit position where X,Y and Z axis reading will be set to zero.

Homing must be done every time you restart your machine. Without it machine does not know where is the position of its table or spindle.

When homed your machine coordinates will read X=0 Y=0 and Z=0 and it is going to look like this:

The point where Machine X and Y intersect is called Table Home Position and the one where the Machine Z axis starts from is called Spindle Home.

Now, there is no agreement between machine tool manufacturers on where the machine home should be.