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7. Computer Controlled Machining

Week’s Schedule

  • Thursday: Theoretical session, exploring the machine
  • Friday: Design
  • Saturday: Test cut
  • Sunday: Create advanced design
  • Monday: Cut the design

A Hero Shot!

Group Assignment

You can find more details on our lab site: Tech Works - Electronics Design

1. Safety Guidelines

First, the instructor introduced us to safety rules:

  • Eye Protection: Always wear safety goggles.
  • Ear Protection: Protect your ears from the noise generated by the machine.
  • Avoid Accessories: Do not wear watches, rings, or bracelets to prevent entanglement hazards.
  • Avoid Loose Clothing: Oversized or dangling clothes, such as scarves, can get caught in the machine’s moving parts.
  • Wear Closed-Toe Footwear: Protect your feet from potential hazards.

In case of an emergency, press the Emergency Stop (E-stop) Button. Multiple emergency stop buttons are strategically placed around the workshop for quick access.

ShopBot Quick-Start Guide

2. Theoretical Session

The instructor explained essential theoretical concepts and how to use the software.

CNC Milling and Cutting Tools Guide

1. CNC Milling Machine & Its Components

CNC Router vs. CNC Milling Machine
  • CNC Router: Used for wood, plastics, and soft materials; operates at higher speeds.
  • CNC Milling Machine: Designed for harder materials like metals; operates at lower speeds but with higher precision.

The cnc milling machine we are using ShopBot PRS alpha:

Common Milling Operations
  • Face Milling: Cutting flat surfaces.
  • Slot Milling: Creating grooves or slots.
  • Pocket Milling: Removing material inside a defined area.
  • Contour Milling: Following curved or complex paths.
  • Thread Milling: Cutting internal or external threads.
  • Helical Milling: Making spiral features.

6. Cutting Parameters

Feed & Speed
  • Spindle Speed: Tool rotation speed (RPM).
  • Cutting Speed (Vc): constant.


  • Feed Speed: Speed at which the workpiece moves (mm/min).
  • Feed per Tooth “\:f_z”
  • Number of Flutes “z”

Formulas and definitions for milling Formulas and definitions for milling

Depth of Cut & Step Over
  • Depth of Cut: The vertical thickness of material removed per pass.
  • Step Over: The lateral distance between tool passes.

Using CNC Milling Machines

  1. Design Creation: Create your design using CAD software.
  2. Toolpath Generation: Use CAM software (e.g., VCarve) to generate G-code and upload it to ShopBot software.
  3. Machine Setup: Secure the workpiece, install cutting tools, and set the machine’s origin.
  4. Execution: Run the machine, monitor for issues, and ensure smooth operation.

For more details on ShopBot models, refer to their official documentation:
- ShopBot Support & Resources
- ShopBot PRS Alpha Manual

For a visual introduction, check this video:
Intro to the ShopBot Desktop CNC Mill (+ VCarve!)

3. Defining Zero Positions

Lastly, we defined the zero positions of the cutting tool on the X, Y, and Z axes and cleaned the tool holder.

Individual Assignment

After figuring how the machine works and some main concepts now its time to do our special fernature!

Designing Process

  1. I Created a modern circular couch design in SolidWorks (the videos explained the designing workflow).
  2. Focused on designing each part to ensure a proper fit when assembled.
  3. Assembled the design digitally to check for alignment and structural integrity.
  4. Converted each part into a .dxf file to facilitate CNC cutting.
  5. Prepared for cutting by opening the .dxf files in VCarve.

Joint Test in VCarve

Before proceeding with the final design, I created a joint test to ensure proper fit and tolerances:

  1. First we should defined the board dimensions accurately to match the actual material size.

  2. Opened the .dxf file and adjusted its placement within the workspace to optimize material usage.

  3. Added tabs and fillets (dog bone type) to improve assembly and avoid sharp corners:
  4. Ungrouped the design.
  5. Joined elements to enable modifications.
  6. Ensured dog bone fillets were applied correctly to all internal corners.

  1. Selected the appropriate tool and parameters:
  2. Checked spindle speed, feed rate, and plunge rate.
  3. Verified cutting depth to avoid cutting into the spoilboard.

  1. Set the allowance offset to -0.5 mm to ensure a tight fit.
  2. Simulated the toolpath to verify correctness and avoid collisions or excessive material removal.
  3. Reviewed and optimized cutting strategies, such as climb cutting for cleaner edges.
  4. Saved the final toolpath file for use in ShopBot software.




Failed parts to fitting together that was due to the allowanse offset was 0.35 as well I designed the joints in diferent diameter which is wrong, thay should be within the wood board diameter.


Fits Perfectly! I changed the allowanse offset into 0.5 and fixed the design ;)

ShopBot Software

  1. Opened the ShopBot software to load the toolpath file.

  2. Checked the preview settings to ensure proper orientation and scale.

  3. Loaded the file saved from VCarve and verified all toolpaths were correctly assigned.

  4. Ensured correct material placement by aligning the design within the work sheet.
  5. Set up the machine:
  6. Zeroed the X, Y, and Z axes.
  7. Secured the material using clamps to prevent movement during cutting.
  8. Checked tool tightness and bit sharpness.

  9. Positioned the tool at the correct location in the real workspace using the control panel.

  10. Final checks before cutting:

  11. Verified spindle speed and cutting depth.
  12. Ensured the dust collection system was properly set up.
  13. Started the cutting process and monitored the machine closely for any issues.
  14. After cutting, removed the parts carefully and sanded edges for a smooth finish.

This process ensured precision and a successful CNC operation using the ShopBot. By testing joints beforehand and optimizing toolpaths, the final assembly was accurate and required minimal post-processing.

Files