Lesson 2: G90 vs. G91—Absolute and Incremental Logic
Duration of Days: 2
Lesson Objective
SWBAT: Calculate a tool path using Absolute Positioning (relative to a fixed work origin).
Calculate a tool path using Incremental Positioning (relative to the tool's current location).
What is the danger of confusing where you are with where you are going?
When would it be faster to use incremental moves instead of absolute moves?
Absolute positioning (G90), Incremental positioning (G91), reference position, absolute zero, tool path, vector, absolute positioning.
CTE.MFG.C.13 (Describe CNC machine movements)
CCSS.Math.7.NS.A.1 (Addition/Subtraction of rational numbers).
Students learn the two ways a machine calculates movement. The purpose is to master the difference between moving to a specific "address" (G90) versus moving a specific "distance" from the current spot (G91).
DOK Level: 3 (Strategic Thinking)
Support: "Human CNC" Activity – One student acts as the "spindle" and must move based on instructions given by another student using only G90 or G91 logic.
Extension: Students take an existing absolute coordinate list and "translate" the entire sequence into incremental coordinates.
"The Tool Path Quiz" – Given a starting point, students must provide the next 5 moves in both absolute and incremental formats.