G41/G41 Positioning
Code Practice
This chapter supports Lesson 6, page 4
OBJECTIVE
After completing this unit, you should be able to:
- identify the best practices for using Cutter Compensation commands
There are three rules to remember about Cutter Compensation commands–G41/G42.
These rules help operators to use a best practice when using cutter compensation commands.
Rule #1: The tool (or cutter) needs to be in a place away from the measurements of the part
The tool must be positioned “off the part”. The tool must start away from the cutting edge. The measurement of the tool position should be a half of the diameter (the radius) of the tool away from the part. It is a best practice to add 0.100″ to the radius for the tool’s position. For example, the is a 1″ diameter end mill. Its radius is .500. Add .100. The program to starts the cutting action at 0.600″ away from the part. This is called a Safe Position.
Watch approximately 8:00 minutes of this video from 1:29 – 9:34. It provides an example of a CNC code without cutter compensation. Then, it explains the code with cutter compensation. There is a very nice discussion about positioning the tool off of the part before the cut and after the cut.
Why can’t the cutter begin at (0, 0) on the part?
The cutter will begin to rotate to get up to speed. The speed, code S, is set in the program. The edges of the cutter touch the (0, 0) on the part. The cutter could dig into the edge and damage it. The edge could grab the cutter and cause it to go into the material and break the cutter. So, the part could be damaged and/or the tool could be damaged by beginning a cutting operation on the part.
Why is the cutter position off of the part?
The cutter needs a little time and space to build up speed in the program. The cutter should be at full speed when it approaches the part. Likewise, the cutter should be at full speed when it finishes the cut.
It is always a best practice to avoid and remove burrs from the edges and surfaces of a part. Starting and stopping the cutter off the part, allows the cutter to clear any sharp metal fragments or burrs from the edges.
Rule #2: The tool height (Z axis) must be set before cutter compensation (G41/G42) can be used
G41 and G42 only move in the X, Y axes. The program will not understand a Z command when G41/G41 is in operation.
If the Z needs to move, use G40 to cancel cutter compensation. The, move the Z axis.
Rule #3: Check the size of the cutter radius with size of the radius on the part
The radius of the cutter must be less than or equal to the radius on the part that needs to be cut.
Questions
