Comprehensive Group Assignment on Computer-Controlled Machining

Group members

🛠️ Week 7 - Computer-Controlled Machining (Group Work)

This report documents our testing of the Rensi e2-1325 CNC milling machine using OSB (Oriented Strand Board), covering lab safety protocols, machine calibration, material fixturing, toolpath validation, and dimensional accuracy analysis. This guide includes step-by-step instructions to replicate the process.

Rensi CNC Setup
Picture 1: Rensi e2-1325 CNC milling machine setup

🔴 1. Lab Safety Training

Before operating the CNC machine, all team members completed mandatory safety training. Key protocols included:

Personal Protective Equipment (PPE)

  • Safety Glasses: Required at all times to protect against flying debris (OSB produces sharp, jagged chips).
  • Hearing Protection: Noise-canceling headphones or earmuffs (machine noise decibels are not very friendly to the ears on a long period of time).
  • Gloves: Cut-resistant gloves for handling OSB edges were advised to be used, to avoid splinters, especially no touching spindles or wood during operations.

Emergency Procedures

  • Emergency Stop Button: These were located both on the NC studio software and the emergency stop button on the machine.
  • Fire Extinguisher & First Aid Kit: There's always a fire extinguisher positioned at the lab entrance.
  • Buddy System: No solo operation; always have a trained supervisor present (in this case Antti Mäntyniemi, was our supervisor).
  • State of Mind: We were advised never to operate the machine in a fatigued state, as the machine demands our full attention due to it's dangerous consequences if things go wrong.

Machine-Specific Rules

  • Safety Shield: Inspite of our safety gears, there was still a transparent shield placed between operators and the machine before starting the operation on the machine.
  • Loose Clothing/Jewelry: It was noticed that loose clotings are not advised to be worn using this machine.
  • Pre-Operation Checklist:
  • Verify spindle is secure and bit placed in the right order, in order to avoid damaging the spindle permanently.
  • Confirm OSB is properly fixtured.
  • Ensure workspace is clear of obstructions.

Safety Earmuffs
Picture 2: Hearing Protection

Safety Glasses
Picture 3: Safety Glasses

Emergency Controls
Picture 4: Emergency stop and vacuum control knobs

🔴 2. Machine Setup & Calibration

A. Power-Up Sequence

  1. Turn on the CNC machine’s main power switch (below the computer).
  2. Boot the connected computer and launch NC Studio control software.
  3. Enable the dust collector and vacuum pump via the control unit when the board is in place.

B. Tool Installation & Runout Test

Tools Used:
- 10mm and 8mm Mill (10 mm primary tool for OSB milling and 8mm for pockets).
- Caliper (for runout measurement).

Steps:
Install the Tool:
- Click the milling bit holder parts together (Picture 6).
- Slide the 10mm mill bit into the holder to suitable depth (see Picture 7). - Secure using two wrenches (prevents slippage; OSB’s abrasive resin accelerates tool wear).

Milling bit
Picture 5: Milling bit

bit socket
Picture 6: Milling bit socket

Milling bit inserted in socket
Picture 7: Milling bit inserted in socket at correct depth

Milling bit and socket inserted in spindle
Picture 8: Milling bit and socket inserted in spindle

Tightening procedure with spanners
Picture 9: Tightening procedure with spanners

Milling bit in place
Picture 10: Milling bit in place

C. Material Fixturing

Material: 11mm OSB Sheet (1200mm x 2400mm), though we used a left over, estimated at 1200mm x 800mm.

Vacuum Bed Setup:
1. The vacuum table surface was already cleaned. It had a sacrificial MDF attached to it. (OSB dust reduces suction).
2. Place the OSB on the bed, aligning it with the table grid.
3. Activate Zone 1 & 2 (for smaller workpieces) by turning two leftmost levers below the workspace downwards, see Picture 11. 4. Test suction by gently tugging the material, or placing an A4 paper between the vacuum bed and the MDF.

Alternative Fixturing:
- If vacuum suction is weak (common with OSB due to uneven surfaces), use extra wood to cover the full 1200mm x 2400mm surface.

OSB Secured on Vacuum Bedwith vacuum zones 1 & 2 activated (levers at bottom, downwards open).
Picture 11: OSB Secured on Vacuum Bed

D. Axis Calibration

X/Y Alignment:
1. Edge Finding:
- Jog the spindle to the material’s bottom left corner using the handwheel.
- Set X and Y to zero in NC Studio.

Hand_wheel
Picture 12: Jogging spindle with the handwheel

Z-Axis Zeroing:
1. Place the 45mm mobile calibrator on the sacrificial material surface.
2. Align the spindle over the calibrator tool in the x and y directions.
3. In NC Studio, use to Operations > Mobile Calibrator to calibrate the z direction.

Edge_Finder
Picture 13: Mobile Calibrator

🔴 3. Toolpath Configuration & Testing

A. Fusion 360 Design

  • Rectangle: 200mm x 200mm with 5mm-deep pockets.
  • Circle: 200mm diameter (profile cut with 8mm depth).

Toolpath Settings:
| Parameter | 2D Pocket | 2D Contour |
|---------------------|-------------------|------------------|
| Spindle Speed | 18,000 RPM | 18,000 RPM |
| Feed Rate | 250 mm/min | 250 mm/min |
| Stepdown | 3mm (per pass) | Full depth (8mm) |
| Part Count | 1186 | N/A |

Simulation:
- Previewed toolpaths in Fusion 360 to check for collisions.
- Exported G-code and loaded into NC Studio for final verification.

Tool_path_simulation
Picture 14: Toolpath Simulation

B. Machining Process

  1. Dry Run:
  2. Simulated the toolpath without material to confirm paths.
  3. Milling:
  4. Started the spindle and monitored for vibrations (OSB’s uneven texture increases chatter risk).
  5. MIlling was done in two parts 10mm drill for contour milling and 8mm drill for pockets.

Key Observations:
- Pocket Depth: Measured 4.5mm vs. 5mm design (0.5mm undershoot).
- Cause: Assumption of OSB material to be 11mm, upon measuring after milling it was 10.4mm.
- Contour Depth: Measured 8.1mm (within tolerance).
- Dimensional Accuracy:
- Rectangle: 200.4mm x 200.4mm (+0.4mm).
- Circle: Ø200.4mm (+0.4mm).
- Cause: OSB expansion due to internal moisture.

NC_studio_interface
Picture 15: NC Studio Interface while milling

Circular_measurement
Picture 16: Circular artefact after milling - measurement

Tool_path_simulation
Picture 17: Rectangular (inclusive of pocket) artefact after milling - measurement

After_milling_measurement
Picture 18: Clear Caliper after milling measurement

🔴 4. Speed, Feed, and Material Analysis

B. Material Behavior

  • OSB Challenges:
  • Uneven Surface: Requires frequent vacuum checks during fixturing.
  • Moisture Sensitivity: Store OSB in a climate-controlled area pre-milling.

🔴 5. Troubleshooting Guide

Issue Cause Solution
Pocket Depth Error assumption of OSB thickness always measure the thickness (trust no label)
Edge Chipping Dull tool Replace bit immediately
Material Movement Weak vacuum Use extra wood to cover all vacuum bed surfaces
Dust Collector Clog OSB resin Clean environment and preferable inclusive of filter immediately after use

🔴 6. 🎯 Summary

  • Safety Protocols: Non-negotiable for CNC operations, due to it's nonforgiving consequences, especially if your G-code contains negative Z numbers which could damage vacuum bed or sacrificial wood.
  • OSB-Specific Adjustments: Slower feeds, frequent tool checks.
  • Machine Calibration: Critical for dimensional accuracy.
  • Document Everything: Record measurements for iterative improvement.