Week 7 - Computer Controlled Machining

CNC Machines

Computer Numerical Control (CNC) is an automated manufacturing process that controls and operates machinery—such as lathes, mills, drills, and more—by way of a computer. It has evolved the manufacturing industry as we know it, streamlining the production process and allowing complex tasks to be done with precision and efficiency.

CNC Machine

CNC stands for Computer Numerical Control, which refers to the computerized operation of machining tools used in manufacturing. CNC machines operate using pre-programmed software and codes, which tell each machine the exact movements and tasks to complete. For example, a CNC machine might cut a piece of material (such as metal or plastic) based on instructions from a computer, meeting the specifications pre-coded into the program—all without a manual machine operator.

A CNC machine is a type of machinery operated by computers and used for the fabrication of different parts and goods. CNC machines might be used to print, cut materials, manipulate parts, create goods from scratch, and more. They eliminate the need for a human operator to control the tools manually, thus improving accuracy and consistency in production.

CNC machines work by carrying out pre-programmed sequences of commands from computer software. These advanced machines do not require manual control (e.g. no hand levers or wheels). Rather, they function using CNC machining language – called G-code and M-code – which gives the machines precise measurements for production, like feed rate, speed, location, and coordination.

Common types of CNC machines include, but are not limited to:

• CNC Lathes: Used for turning operations
• CNC Mills: Used for cutting and drilling operations
• CNC Plasma Cutters: Used for cutting metal using a plasma torch
• CNC Routers: Used for cutting various materials like wood, plastic, and metal
• 3D Printers: Additive manufacturing machines that build objects layer by layer

Cutting Tools

CNC machines can perform various machining procedures due to the different CNC machining tools available. These different CNC tools have various properties that make them suitable for various operations while reducing the need for manual input from machine operators. This eliminates the old problem of machine operators getting tired and ruining the process.

Types of CNC Cutting Tools

1. End Mills

• Flat End Mill – Used for general-purpose cutting, slotting, and contouring.
• Ball Nose End Mill – Ideal for curved surfaces, 3D carving, and detailed cuts.
• Tapered End Mill – Provides finer detail in deep cuts and angled edges.
• Roughing End Mill – Designed for high material removal rates with less vibration.

2. Drill Bits

• Twist Drill – Standard drill bits used for hole-making operations.
• Brad Point Drill – Used for wood and precise drilling without tear-out.
• Countersink Bit – Creates a conical hole to allow screws to sit flush.

3. Router Bits (For CNC Routers)

• Straight Router Bit – General-purpose cutting and shaping.
• V-Bit – Used for engraving, lettering, and chamfering.
• Compression Bit – Prevents tear-out on both sides of plywood or laminate.
• Upcut & Downcut Bits – Controls chip evacuation and surface finish.

4. Face Mills

• Used for large surface machining, often found in metalworking.

5. T-Slot Cutters

• Used for cutting T-shaped slots for fixtures and workholding.

6. Fly Cutters

• Provides smooth finishes on large surfaces with a single-point tool.

[https://waykenrm.com/blogs/cnc-machine-tools/./Images/Week07/https://waykenrm.com/blogs/cnc-machine-tools/)

CNC Router

A CNC router is a computer-controlled cutting machine used for carving, cutting, and engraving materials such as wood, plastic, metal, and composites. It operates by moving a rotating cutting tool along multiple axes, precisely following a digital design.

Unlike traditional manual routers, CNC routers offer automation, repeatability, and high precision, making them ideal for complex designs and large-scale production.

Key Machining Parameters

1. Spindle Speed (RPM)

Spindle speed refers to how fast the cutting tool rotates, measured in revolutions per minute (RPM). The correct spindle speed depends on the material and tool being used. Too high a speed can burn the material, while too low a speed can cause rough cuts.

2. Feed Rate (IPM)

Feed rate is how fast the cutting tool moves through the material, measured in inches per minute (IPM). A higher feed rate speeds up production but requires careful calibration to avoid tool breakage or poor surface finish.

3. Depth of Cut

The depth of cut determines how much material is removed per pass. It is usually equal to or less than the tool diameter to prevent excessive tool stress. A deeper cut may require multiple passes.

4. Step-Over

Step-over is the lateral distance the tool moves between passes when surfacing a material. A smaller step-over results in a smoother finish but takes longer, while a larger step-over removes more material quickly but may leave visible tool marks.

Climb Cutting

In climb cutting, also called down milling, the cutter rotates with the direction of the material feed. This means the cutting tool engages the material at full depth and then gradually thins the chip as it exits. This method is generally preferred in modern CNC machining because it reduces heat buildup and tool wear.

• Advantages:
  • Smoother surface finish
  • Reduced cutting forces, leading to less tool deflection
  • Less heat buildup, increasing tool life
• Disadvantages:
  • Can pull the material into the cutter, requiring secure fixturing
  • Not ideal for machines with backlash issues
  • Can cause tool wear in harder materials

Conventional Cutting

In conventional cutting, also known as up milling, the cutting tool rotates against the direction of the material feed. This means that the cutter starts from a thinner chip and gradually cuts deeper as it moves forward. Conventional cutting is often used in scenarios where machine rigidity is a concern or when working with older machines that might have backlash in the leadscrews.

• Advantages:
  • Less tool deflection, making it better for older machines
  • Reduces tool wear in some materials
  • Less risk of sudden tool engagement
• Disadvantages:
  • Higher heat generation
  • More friction, leading to faster tool wear
  • Can cause material lifting, leading to poor surface finish

In most CNC router operations, climb cutting is preferred for wood, plastic, and softer metals because of its superior finish and efficiency. However, conventional cutting is sometimes used in roughing passes or when machining harder materials to minimize sudden tool engagement.

Shopbot PRSAlpha 96

For our assignment we used a ShopBot PRSalpha 96 CNC router, a powerful machine known for its high-speed, accuracy, and ability to cut full-sized sheets of plywood. It allows for 2D and 3D cutting, enabling intricate joinery and detailed designs.

The ShopBot PRSalpha 96 is a high-performance CNC router designed for precision cutting, carving, and machining of a variety of materials, including wood, plastics, composites, and soft metals. It is widely used in fabrication labs, woodworking shops, and manufacturing facilities for furniture making, prototyping, signage, and custom fabrication.

The PRSalpha series is known for its powerful motors, accuracy, and reliability, making it ideal for both small-scale and industrial applications. The 96 in the name refers to the machine’s cutting bed size, which is 96 inches (8 feet) in length.

Machine Specifications

• Cutting Area: 96” x 48” x 8” (can vary depending on the model and customization)
• Frame: Heavy-duty steel frame for stability and durability
• Drive System: Industrial-grade rack-and-pinion drive for smooth motion
• Spindle/Router Options: Can be equipped with a high-frequency spindle or a standard router
• Speed: Cutting speeds up to 600 inches per minute (varies with material and toolpath settings)
• Software: Compatible with VCarve Pro, Fusion 360, Aspire, and ShopBot’s proprietary software
• Power Requirements: 220V for industrial setups, but varies based on the spindle configuration
• Dust Collection Compatibility: Integrated dust collection system for clean operation

Safety training

Importance of Safety Training

Safety training is essential in any workshop environment, particularly when operating CNC machines like the ShopBot router. A strong focus on safety ensures:

• Awareness of potential hazards and risks associated with machining operations.
• The promotion of a proactive safety culture among all users.
• A significant reduction in accidents, injuries, and equipment damage.
• Compliance with workplace safety regulations and legal standards.
• Increased productivity by minimizing downtime caused by accidents or machine malfunctions.

By adhering to safety protocols, operators can maintain a safe, efficient, and productive working environment.

1. Personal Safety Precautions

1.1 Personal Protective Equipment (PPE)

Proper use of Personal Protective Equipment (PPE) is a fundamental aspect of workshop safety. Every operator should:

• Wear safety glasses at all times, even when using a face shield, to protect against flying debris.
• Use hearing protection, such as earplugs or earmuffs, to reduce exposure to excessive noise levels.
• Wear enclosed, non-slip footwear to prevent slips and injuries from falling objects.
• Use safety gloves when handling sharp materials, but avoid gloves while operating rotating machinery to prevent entanglement.
• Wear a protective mask or respirator to prevent inhalation of dust and airborne particles.
• Avoid loose clothing, hanging jewelry, or accessories that could become entangled in moving parts.
• Tie back long hair securely to prevent it from getting caught in machinery.

1.2 Safe Behavior

Maintaining a safety-conscious attitude is critical when working with CNC machines. Operators should always:

• Stay focused and never operate the ShopBot while fatigued, distracted, or under the influence of medication or alcohol.
• Keep hands and fingers away from moving parts—never attempt to stop a spinning tool or workpiece manually.
• Maintain a safe distance from cutting tools and rotating components to prevent accidental contact.
• Remain vigilant and aware of surroundings to prevent accidents involving other workshop users.

2. Machine Safety Precautions

2.1 Pre-Operation Checks

Before using the ShopBot CNC router, a thorough inspection and setup should be conducted to ensure safe operation:

• Carefully read the manufacturer’s instruction manual to understand proper usage and safety guidelines.
• Inspect cutting tools, including bits and blades, for any signs of wear, cracks, or damage before use.
• Confirm that the work surface is clean and free of dust, debris, or misplaced tools that could interfere with machining.

• Utilize dust collection systems to minimize airborne particles and maintain a clean workspace.

  

• Verify that the emergency stop button is fully functional and within easy reach in case of an emergency.

  

2.2 Operating the ShopBot CNC Router

When using the CNC machine, it is essential to follow these operational safety steps:

• Secure materials firmly using clamps or a vacuum hold-down system to prevent shifting during cutting.
• Conduct a dry run (without material) to verify correct programming and toolpath execution before starting the actual machining process.
• Use appropriate feed rates and cutting speeds based on the material to avoid excessive tool wear or machine damage.
• Never leave the machine unattended while it is running to promptly address any malfunctions.
• Allow the machine to come to a complete stop before making any adjustments or retrieving the finished piece.

3. Workshop Safety Measures

3.1 Housekeeping and Workspace Organization

A clean and organized workspace contributes to overall safety. To maintain an efficient environment:

• Keep floors free of sawdust, metal shavings, or other debris to prevent slips and falls.
• Stabilize workbenches to ensure they do not shift or move unexpectedly under load.
• Use designated workbenches for assembly or adjustments rather than using machine beds as work surfaces.
• Store tools and materials in their designated areas to avoid clutter and potential hazards.

3.2 Fire and First Aid Preparedness

Workshops must be prepared for emergencies to mitigate risks effectively:

• Keep a fire extinguisher in an easily accessible and clearly marked location.
• Maintain a well-stocked first-aid kit nearby to treat minor injuries immediately.
• Ensure proper ventilation to reduce dust accumulation and lower the risk of fire or respiratory hazards.
• Familiarize all workshop users with emergency procedures, including the location of exits and safety equipment.

4. Continuous Safety Improvement

Safety is an ongoing priority that requires regular evaluation and enhancement. To ensure a secure workshop environment:

• Conduct routine inspections of the ShopBot and related equipment for maintenance issues.
• Participate in safety drills and periodic training sessions to stay updated on best practices.
• Encourage open communication and report potential hazards or unsafe conditions to supervisors or team members.
• Continuously assess and improve workshop safety procedures based on feedback and real-world experiences.

By prioritizing safety through education, proper procedures, and continuous improvement, operators can ensure a safe and productive CNC machining environment.

Related article :-http://www.popularmechanics.com/home/skills/yale-students-tragic-death-prompts-a-shop-safety-review

Operating the machine - Tom & Namitha

Operating the Machine:

Operating the ShopBot Machine involves a combination of software and physical movement.

Within software there are 2 essential programs: the ShopBot Control software and Vcarve Pro.

• Shopbot control software controls the movement of the machine in 3 dimensions
• Vcarve is the program which takes your design as input and produces G-Code as output.

1. Overview: machine set-up, layout and parts

Consists of the machine bed, the gantry, vacuum system, and computer. There are 3 main power switches behind the computer. From left to right: vacuum, spindle, gantry-control (3 dimensions).

The vacuum is the loudest part of the system, it’s attached by the spindle which rotates at 12k RPM.

Sometimes we’ll need to change the bit. In this case we’ll need to take off the shoe:

Then use wrenches to release the arbour and collet:

Finally, insert and tighten the bit in place, making sure it extends beyond the brush

2. ShopBot Control Software

Opening ShopBot Control Software immediately bring you to RED panel.

• It gives the position of the spindle head in 3 dimensions.
• It allows the user to calibrate in all dimensions
• It allows the user to define the origin
• Clicking the small yellow box opens the window for manual control:

From the yellow control panel, the user may:

• Move the gantry / spindle in any directions (X,Y,Z)
• Zero the axes.
  • X/Y: To zero the X/Y axes, select them and click “ZERO”. Move them to where you want the origin to be.
  • Z: To zero the Z axis, need to take the

When the user is ready, they may start the project from the Red panel by

• clicking “Cut Part”
• Selecting their file
• Starting the spindle
• Pressing the physical green button “start”

The green “start” button is located on a separate console with blue for “reset” and red for stopping.

3. Operational Workflow - Example

• first we place the board onto the bed above the sacrifical layer
  • it may be necessary to move the gantry
  • use the yellow control box in the shopBot software
  • initially lock the board in place with clamps
• Calibrate and zero the axes in all dimensions”
  • For X and Y dimensions, manually bring the spindle to the appropriate place, set as origin
  • For Z dimension, use the attached plate and metallic clamp.
• In the same project file as your project, place some holes for screws:

• Save the toolpaths for the screw holes, then cut this part; after put in screws.
• Now we are ready to cut the heptagon part (or whatever).
• Be confident that the spindle will not cut into the screws.

Test Piece Design - Noel

CAM Toolpath Creation in VCarve Pro

1. Importing Design

- Imported the DXF file of the test jig into VCarve Pro. - Ensured that the design dimensions matched the plywood sheet size (2440 mm x 1220 mm).

2. Setting Up Job Dimensions

- Job dimensions were set to match the plywood sheet: - Width: 2440 mm - Height: 1220 mm - Material Thickness: 17 mm - The origin was set to the bottom-left corner for consistency with the ShopBot CNC machine.

You could also Design if needed . if no additional designs select the toolpath (2) as in the image.

Use Shift keys for Multiple Selection

3. Toolpath Creation

a. Pocket Toolpath

• Used a pocket toolpath to cut out slots and circular recesses.
• Tool Used: 6 mm Fab end mill. Single flute.
• Settings:
  • Cut Depth: 9 mm (half the material thickness for testing fit).
  • Stepover: 80% of the tool diameter
  • Feed Rate: 16.67 mm/sec
  • Spindle Speed: 12000 RPM.
  • Plunge Rate: 20

b. Profile Toolpath

• Created a profile toolpath for cutting out the perimeter of the jig and slots.
• Tool Used: Same 6 mm end mill.
• Settings:
  • Cut Depth: Full material thickness (17 ).
  • Pass Depth: 4.3 mm per pass (4 passes total).
  • Tabs were added to hold parts in place during cutting.

accept the warning it means the tool would cut through the sacrificial assignment .

4. Toolpath Optimization

• Pocket toolpaths were executed first to clear material efficiently.
• Profile toolpaths were run afterward to ensure clean edges and precise cuts.

5. Preview and Export

- Previewed all toolpaths in VCarve Pro to check for errors or overlaps. - Exported the toolpaths as .sbp files compatible with the ShopBot CNC machine.

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Post- Processing

After routing the wood, we sanded and filed the workpiece to remove splinters and smooth rough edges. Post-processing is essential to improve the finish, ensure safety, and enhance the overall quality of the final piece.

Tools we used for post processing are,

• Chisel
• Mallet
• Reciprocating Sander
• File
• Orbital Sander

Initially the tabs were removed using the Chisel and Mallet.

After removing the tabs, rough sanding is done using the reciprocating sander and the edges were the sander can’t reach was finished using the file.

The orbital sander was used for finishing operation. The sanding block was used to finish the edges were the sander can’t reach.

Results

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Last update: March 12, 2025