Activity 002: Coordinate Systems & Homing Practice¶
Activity ID: U4M1-ACT-002 Duration: 40 minutes Objective: Students will demonstrate proficiency in homing the CNC router, setting work coordinate origins, and navigating between absolute and incremental positioning modes. Group Size: 2-3 students
Overview¶
This hands-on activity walks students through the complete process of powering on a CNC router, executing a homing sequence, setting work zero using multiple methods, and verifying positions using jog controls. Students will practice on the actual machine with no cutting tool installed.
Materials & Equipment Needed¶
- CNC router (tool removed from spindle)
- Touch plate (Z-axis zero setter)
- Piece of scrap MDF or plywood (12" x 12" minimum)
- Edge finder or dowel pin
- Paper (standard printer paper, ~0.004" thick)
- Control software (UGS, CNCjs, or Mach4)
- Coordinate recording worksheet
- PPE: Safety glasses, hearing protection (if spindle will be run)
Instructions & Procedure¶
Phase 1: Power-Up & Homing (10 minutes) 1. Perform the pre-start checklist: verify work area is clear, no tools left on the bed, E-stop is accessible 2. Power on the machine and controller — observe the startup messages 3. Open the control software and connect to the machine 4. Note the current machine position display — it should show "Unknown" or last-known position 5. Execute the homing sequence — observe the order of axes homing (Z first, then X/Y) 6. After homing, record the machine zero position displayed in the DRO (Digital Readout) 7. Jog each axis manually 1" in the positive direction and note how the DRO updates
Phase 2: Setting Work Zero — Three Methods (20 minutes)
Method A: Manual Jog Method 1. Place the scrap material on the spoilboard 2. Jog the spindle to the front-left corner of the material 3. Align X and Y visually to the corner edges 4. Zero X and Y in the work coordinate system (G54) 5. Record the machine coordinates at this position
Method B: Touch Plate Method (Z-axis) 1. Place the touch plate on top of the material surface 2. Connect the ground clip to the spindle/collet 3. Run the touch plate probing routine in the control software 4. Verify the Z zero is set correctly by jogging to Z=0 — the spindle nose should be at the material surface 5. Record the machine Z coordinate at work Z=0
Method C: Paper Method (Z-axis backup) 1. Place a sheet of paper on the material surface 2. Slowly jog Z down in 0.01" increments 3. Gently try to slide the paper — when it just begins to drag, stop 4. Set Z = 0.004" (paper thickness) in the work coordinate system 5. Compare this Z zero position to the touch plate result — they should agree within ±0.005"
Phase 3: Verification & Coordinate Exercises (10 minutes) 1. Jog to work position X=0, Y=0, Z=1.0 — verify spindle is above the front-left corner 2. Jog to X=6, Y=6 — spindle should be 6" right and 6" back from the corner 3. Switch to incremental mode (G91 equivalent in jog controls) 4. Jog X+2, Y+2 — verify DRO reads X=8, Y=8 5. Switch back to absolute mode and jog to X=0, Y=0 6. Complete the coordinate exercise worksheet: given a set of target positions, predict DRO readings
Discussion Points¶
- What happens if you forget to home the machine before starting a job?
- Why is the paper method less precise than the touch plate method?
- When would you use G55 instead of G54?
- What is the consequence of setting Z zero at the spoilboard surface instead of the material surface?
Expected Outcomes¶
- Students can independently power up and home a CNC router
- Students can set X/Y/Z work zero using at least two methods
- Students understand the relationship between machine coordinates and work coordinates
- Students can navigate using both absolute and incremental jog modes
Assessment Rubric¶
| Criteria | Excellent (4) | Proficient (3) | Developing (2) | Beginning (1) |
|---|---|---|---|---|
| Homing Procedure | Completes homing correctly and explains the process | Completes homing correctly | Completes homing with instructor assistance | Cannot complete homing |
| Work Zero Setting | Sets X/Y/Z zero accurately using multiple methods | Sets work zero using one method accurately | Sets work zero with significant assistance | Cannot set work zero |
| Coordinate Understanding | Predicts positions correctly in both modes | Predicts most positions correctly | Frequently confuses absolute/incremental | Cannot predict positions |
| Safety Protocol | Follows all safety procedures without prompting | Follows safety with occasional reminders | Needs frequent safety reminders | Disregards safety procedures |
Safety Considerations¶
- No cutting tool should be installed in the spindle during this activity
- Always home Z-axis first (upward) before X/Y
- Keep hands clear of the gantry and moving components during jogging
- Use slow jog speeds (10% or less) when approaching the workpiece
- Ensure the E-stop is within reach at all times during powered operation
Last Updated: 2026-03-19