8. Computer controlled machining

Assignments and Assessment

Group assignment:
- Complete your lab's safety training
- Test runout, alignment, fixturing, speeds, feeds, materials and toolpaths for your machine
- Document your work to the group work page and reflect on your individual page what you learned

Individual project
- Make (design+mill+assemble) something big

Learning outcomes
- Demonstrate 2D design development for CNC milling production
- Describe workflows for CNC milling production

Have you answered these questions?
- Linked to the group assignment page
- Documented how you designed your object (something big)
- Documented how you made your CAM-toolpath
- Documented how you made something BIG (setting up the machine, using fixings, testing joints, adjusting feeds and speeds, depth of cut etc.)
- Described problems and how you fixed them
- Included your design files and 'hero shot' of your final product

Key Defitions of the CNC

I recommend CNC Cookbook for a practical guide to CNC machining, covering CAD/CAM, speeds, feeds, and G-code. For Siemens users, the Siemens Manuals provide a detailed reference for mastering NC programming and motion control.

• A practical guide for CNC machining, covering essential topics like CAD/CAM software, CNC routers, speeds and feeds, and G-code programming. The book also introduces G-Wizard, a tool for optimizing cutting parameters. Perfect for beginners and professionals looking to improve efficiency and precision in CNC work.

SIEMENS Manuals - Programming guide for Siemens NC Gcode - An official Siemens guide for NC programming, explaining key topics such as geometry settings, tool changes, spindle motion, feed control, coordinate transformations, and tool radius compensation. Essential for engineers and CNC programmers working with Siemens Sinumerik controllers. A detailed reference for writing and optimizing Siemens-based CNC programs.

Kerf, Offset, Runout:

• Kerf: The width of material removed by a cutting process
• Offset: A programmed distance to compensate for tool diameter, ensuring accuracy.​
• Runout: The slight deviation in tool rotation, affecting precision.​

Conventional, Climb Milling:

• Conventional Milling: The cutter rotates against the direction of the workpiece feed, leading to increased tool wear.​
• Climb Milling: The cutter rotates in the same direction as the workpiece feed, resulting in a better surface finish and reduced heat.​

Rough/Finish Cuts:

• Rough Cut: Removes bulk material quickly with less concern for accuracy.​
• Finish Cut: Final pass to achieve precise dimensions and smooth surfaces.​

Advanced Machining Strategies

• High-Speed Machining (HSM): Utilizes higher feed rates and spindle speeds to remove material faster without compromising part quality. ​
• Dry Machining: Cutting without the use of coolant, relying on air blasts or tool coatings to manage heat.​
• Ramping: A technique where the tool enters the material at an angle, reducing stress and tool wear. ​
• Adaptive Clearing: A dynamic toolpath that maintains constant tool engagement to optimize chip load, reducing stress on the tool and speeding up the machining process. ​
• Swarf Cutting: A 5-axis machining technique where the side of the tool is used to cut along tilted surfaces, common in aerospace applications.​
• Rest Machining: A strategy that focuses on removing material left by previous operations, often using smaller tools to access tight areas. ​
• Trochoidal Milling: Involves a looping, rounded path to reduce stress on the cutting tool, used to cut deep slots or narrow areas. ​

Workholding & Fixturing

• One-Sided, Two-Sided Machining:
• One-Sided: Machining performed from a single direction
• Two-Sided: Requires flipping and realignment for machining both sides.​
• Registration: The use of reference points or features to align multiple machining operations accurately.​

Axis Configurations

• 2, 2.5, 3, 4, 3+2, 5 Axis Machining:
• 2-Axis: Movement in X and Y directions only.​
• 2.5-Axis: X and Y movements with stepped Z-axis positions.​
• 3-Axis: Simultaneous movement in X, Y, and Z directions.​
• 4-Axis: Adds rotation around one axis, typically the X or Y axis.​
• 3+2-Axis: 3-axis machining with two additional axes locked in a fixed position.​
• 5-Axis: Simultaneous movement in all three linear axes and two rotational axes, allowing for complex geometries. ​

Cutting Considerations

• Tool Length Compensation: Adjusts the tool’s position to account for variations in tool length, ensuring accurate machining depths.​
• Cut Depth, Clearance, Collisions:
• Cut Depth: The depth of material removed in a single pass.​
• Clearance: The safe distance maintained to avoid collisions between the tool and the workpiece or fixtures.​
• Collisions: Unintended contact between the tool and the workpiece or machine components, which can cause damage.​

Special Cutting Techniques

• T-Bones, Dog-Bones: Relief cuts in internal corners to allow square joints in CNC-cut parts, facilitating assembly.​
• Tabs, Onion Skinning:
• Tabs: Small uncut sections that hold parts in place during machining to prevent movement.​
• Onion Skinning: Leaving a thin layer of material to keep the part attached to the stock, which is removed in the final pass.​
• Nesting: Arranging multiple parts on a single piece of material to maximize material usage and minimize waste.​

Toolpath Control

• Lead-In, Lead-Out: Smooth transitions for the tool to enter and exit the material, reducing tool marks and ensuring a better surface finish.​
• Test Cuts, Cutting Air:
• Test Cuts: Initial cuts made to verify toolpaths and machine settings before full production.​
• Cutting Air: Running the machine through the toolpath above the material to ensure accuracy without engaging the material.​

Verification & Production

• Simulation: Using software to virtually model the machining process, identifying potential issues before actual cutting begins. ​
• Prototyping: Creating a preliminary version of a part to test and validate machining processes and design before full-scale production.

Tool Parameters

In machining, various tools are used, each serving a specific function. The main types include drill bits, which cut axially to create cylindrical holes, and end mill bits, which are designed for lateral cutting and carving.

Differences between Drilling and End Milling

Source: Differences between Drilling and End Milling (Drill Vs End Mill) of Academic Gain Tutorials

Each bit has its key parameters, and the key factors to consider are diameter, tooth design, flute count, and cut direction:

The diameter

• The diameter determines the width of the cut made by the end mill.

Source: The Skinny on End Mills | Make

The tooth

• The tooth refers to the tip shape, with different designs suited for specific cutting purposes.

Source: AUTODESK Instructables

Source: SOLID CARBIDE DRILL MILL| https://www.icscuttingtools.com/

52 Types of Router Bits Explained, Router Bits Charts, Shapes, and Uses | homesthetics gives many types, sizes, and profiles, these bits, from flush trim to chamfer, are the wizards of the woodworking universe.

The flute

• The flute is the sharp cutting edge of the end mill, and each milling bit has a specific number of flutes that affect cutting performance.

Source: AUTODESK Instructables

The cut direction

• The cut direction determines how the tool engages with the material, typically classified as climb milling (moving with the feed direction) or conventional milling (moving against the feed direction).

In CNC, common cutting tools include up-cut, down-cut, and compression spiral router bits, each with different flute directions. Spiral router bits are ideal for plunge routing, as their angled cutting edges slice through material rather than chopping, reducing heat buildup, improving chip evacuation, and producing cleaner cuts.

Source: Choosing the Ultimate Spiral Router Bit: Up-cut vs Down-cut vs Compression | findbuytool.com

I choose the chip load based on the job requirements, which is essential for calculating the router speed. The chart below is an example of a standard chip load reference used in CNC machining.

Chip Load Chart Source: cutter-shop

Feeds and Speeds Feed rate controls how fast the cutter moves across the material, while spindle speed determines the rotation speed of the cutting tool—both need to be balanced to avoid overheating or tool damage.

Feeds and Speeds

• Feed rate and spindle speed The feed rate is the speed at which the cutter moves across the material, while the spindle speed refers to how fast the router or spindle rotates the cutting tool. Both depend on the material being cut, and the goal is to move the tool as fast as possible without compromising the surface finish. Excessive heat buildup can burn the material or shorten tool life. A high spindle speed with a slow feed rate can cause burning or melting, while a slow spindle speed with a fast feed rate can dull or break the cutting tool.

Cutter Selection & Chip Load A good approach is to balance feed rate and spindle speed by making two passes: a roughing pass with a high feed rate to remove material quickly and a finishing pass at a higher speed for a smooth surface. Chip load refers to the size of chips produced during cutting—higher feed rates create larger chips, while higher RPMs produce smaller chips. If chips are too large, the bit may break; if they turn into fine powder, the bit is likely dulling. The key is to start with manufacturer-recommended settings and fine-tune as needed.

Spindle Speed, Feed Rate, and Plunge Rate - Spindle Speed – The rate at which the spindle rotates the cutting tool, measured in RPM (revolutions per minute). - Feed Rate – The speed at which the tool moves through the material, calculated as: - Feed Rate = Spindle Speed × Number of Flutes × Chip Load (inches/min) - Plunge Rate – The speed at which the tool moves vertically into the material, typically set at 50% or less of the feed rate to prevent tool damage.

Calculation for Cutting Speed, Spindle Speed and Feed

Source: ns-tool.com

Milling

In conventional milling, the cutter rotates against the feed for better control, while in climb milling, it moves with the feed, requiring sharper tools due to increased pulling force, though conventional milling can cause chip re-cutting and a rougher finish.

Milling Direction

In conventional milling, the cutter rotates against the feed direction, while in climb milling, it rotates with the feed. Conventional milling is the traditional method, as it helps eliminate backlash, ensuring better control over the cut.

Climb milling puts more strain on the tool due to the pulling force, requiring sharper and stronger tools to reduce deflection. Conventional milling is less demanding but can cause chip re-cutting and a rougher surface finish as the tool wears.

Source: Conventional Milling vs Climb Milling | Redigeringshistorik

Characteristics of CNC Milling Machine

From my experience, the NC 1213 CNC Router is a great entry-to-mid-level machine, ideal for woodworking, signage, and light industrial use, offering a compact working area (1200x1300mm) and reliable NC Studio or Mach3 software for precise control. Its rack and pinion drive system ensures smooth movement, making it a solid choice for small workshops. On the other hand, the Jinan FORSUN CNC Router is a machine with higher spindle power (3.0kW–9.0kW), helical rack and pinion system, and automated tool-changing options, allowing for efficient, high-precision cutting of materials like hardwood, plastic, and even metal. If I had to choose, the NC 1213 is best for small-scale work, while Jinan FORSUN is the go-to for industrial production requiring speed, power, and durability.

Characteristics of the NC 1213 CNC Router

• Work Area (Cutting Size)

  • 1200 mm x 1300 mm (1.2m x 1.3m) – Based on its model number NC 1213, which typically refers to dimensions.

• Frame & Build

  • Heavy-duty steel frame for vibration reduction.
  • Linear guide rails for smooth and precise movement.
  • Gantry-style bridge for rigidity in cutting operations.

• Spindle

  • Air-cooled or Water-cooled Spindle (HQD or similar).
  • Power: 1.5 kW to 3 kW, depending on configuration.

• ER collet system for tool holding.

• Control System

  • NC Studio or Mach3 software (commonly used in Chinese-built CNCs).

• Drive System

  • Ball screw transmission on Z-axis for precision.
  • Rack and pinion drive on X and Y axes for speed and durability.

• Materials it Can Cut

  • Wood, MDF, Plywood
  • Acrylic, Plastics, PVC
  • Aluminum (with proper feed rates and bits)

Characteristics of the ​Jinan FORSUN CNC

• Spindle:

  • Power: Typically equipped with 3.0KW to 9.0KW spindles, depending on the model.​
  • Type: High-frequency air-cooled or water-cooled spindles operating at speeds up to 24,000 RPM.​
  • Collet: ER20, ER25, or ER32 collets to accommodate various tool sizes.​

• Motion System:

  • Drive Mechanism: Helical rack and pinion systems on the X and Y axes, and high-precision ball screws on the Z-axis.​
  • Guide Rails: Equipped with HIWIN or THK linear guide rails for smooth and accurate movement.​
  • Motors: Options for stepper motors or AC servo motors, providing reliable and precise motion control.​

• Control System:

  • Controller: Utilizes DSP handheld controllers, NC Studio, Mach3, Syntec, or Siemens systems, depending on user preference.​
  • Software Compatibility: Supports G Code & M Code; compatible with software like Type3, Ucancam, Artcam, Alphacam, Vectric, Enroute, MasterCAM, and Cabinet Vision.​

• Working Area:

  • Standard Sizes: Models offer working areas such as 1200x1200mm, 1300x2500mm (4x8 ft), 1500x3000mm (5x10 ft), and larger custom sizes.​
  • Z-Axis Travel: Typically 200mm, with options for extended travel up to 600mm

In my experience working with CNC machines and woodworking tools, I’ve come across a variety of equipment that plays a crucial role in fabrication and precision cutting. The combination planer and table saw is a highly versatile tool that combines two essential woodworking functions—planing and cutting. The planer ensures that rough lumber is smooth and of uniform thickness, while the table saw provides clean and accurate straight cuts. What I find most interesting about this machine is its rack and pinion mechanism, which allows precise height adjustments for different material thicknesses, making it a reliable choice for furniture making and carpentry projects.

Combination Planer and Table Saw

Combination Planer and Table Saw - Tool Name: Combination Planer and Table Saw - Function: This is a multi-functional woodworking machine that combines a surface planer (jointer) and a table saw. Characteristics: - Planer: Used for flattening wood surfaces and achieving uniform thickness. - Table Saw: Used for cutting wood and composite materials with precision. - Height Adjustment Mechanism: Uses a rack and pinion system for raising and lowering the planer. - Motorized Operation: Likely driven by a single-phase or three-phase electric motor. - Common Uses: Woodworking, furniture making, and DIY carpentry.

Another indispensable tool in a workshop is the Jet drill press. Unlike handheld drills, this machine ensures perfectly straight and repeatable holes, making it ideal for woodworking, metalworking, and precision engineering. One of the standout features is the adjustable table height, which allows flexibility in drilling different-sized workpieces. It’s a tool I always recommend when accuracy is a priority, especially when working on joinery or fabrication projects.

Jet Bandsaw

- Jet Vertical Bandsaw
- Function: A powerful cutting machine used for precise cutting of wood, metal, and plastics.

Characteristics: - Brand: JET - Blade Type: Continuous loop blade for smooth cutting. - Adjustable Table: Can be tilted for bevel cuts. - Blade Tension Adjustment: Ensures accurate and stable cutting. - Motorized Operation: Typically 1-2 HP motor for efficient cutting. - Common Uses: Cutting curves, resawing wood, and slicing thick materials.

Then there’s the Jet bandsaw, a tool I appreciate for its ability to cut curves, resaw thick materials, and make intricate cuts with ease. Unlike circular saws, which are limited to straight cuts, the continuous loop blade of the bandsaw allows for much greater versatility. What makes this machine particularly useful is its adjustable table, which can be tilted for bevel cuts, expanding its range of applications. Whether for woodworking, metal cutting, or creative shaping, the bandsaw is a go-to tool for anyone serious about precision and efficiency in their workshop.

Jet Drill Press

Jet Bench Drill Press - Function: A precision drilling machine used for making accurate and repeatable holes in wood, metal, and plastic. Characteristics: - Brand: JET - Fixed Vertical Spindle: Provides accurate hole drilling. - Adjustable Table Height: Can be raised or lowered for different workpieces. - Speed Control: Usually has multiple speed settings controlled via pulleys. - Drill Chuck Capacity: Typically 1-16mm. - Common Uses: Metalworking, woodworking, and fabrication.

**Milling Bits and Drill Bits **

Testing Samples