Week 7

★ ★ ★ Computer Controlled Machining ★ ★ ★

This week the focus was set on Computer Controlled Machining, introducing us to CNC* Computer Numerical Control milling, a subtractive manufacturing process that allows for precision cutting and shaping of large materials such as wood, plastics, and some metals. The primary goal was to understand how to design for CNC milling, generate toolpaths, and safely operate a CNC router.

CNC Milling and Types of CNC Machines

CNC milling is a process where a spinning rotary cutter removes material from a workpiece to shape it according to a digital design. This is the anatomy of the a basic CNC:

Anatomy

Different types of CNC machines are used depending on the complexity and scale of the project:

  • CNC Routers: Used for cutting wood, plastics, and soft metals; ideal for 2D and 3D shaping.
  • CNC Milling Machines: More rigid and precise, often used for metalwork.
  • Plasma Cutters: Cut through metal by using a high-temperature plasma arc.
  • Laser Cutters: Used for engraving and cutting thin materials with precision.
  • Water Jet Cutters: High-pressure water and abrasives cut through almost any material, including metals and glass.

Materials

  • Wood (Plywood, MDF, Hardwood) – Affordability and ease of cutting.
  • Plastics (Acrylic, HDPE, Delrin) – Used for more durable projects.
  • Foam – Lightweight, easy to shape.
  • Aluminum – Possible with the right setup and tools but requires careful settings.

Design for Machining

When designing for CNC, considerations must be made for fixtures, cutting strategies, and assembly.

Screw Positions & Bed Positioning

This means ensuring the material is securely placed on the flat surface and does not shift during machining. Some useful fixture strategies include screws, double-side tape, clamps and vacuum beds.

Types of Cuts

  • On: Centered on the path
  • Out: Outside the closed vector
  • In: Inside the closed vector

Types of Cutes

Dog Bone & T-Bone Fillets

This is one the most important aspects of CNC cutting. Because of its very small cutting channel, a laser cutter can produce an inside corner with a sharp angle, whereas a rotary cutter using a physical tool is limited to inside corners rounded at the cutting tool's radius.

Laser vs CNC

See? These round corners represent a problem when designing joints on pieces that fit together, so to make the tool reach those sharp corners, we leave a small margin using Dog Bone and T-Bone strategies.

Dog Bone Dog Bone T-Bone T-Bone


Nesting

Nesting is the process of arranging parts efficiently on a sheet to minimize material waste.

PCB

A very useful open source nesting application I recommend is Deepnest. It supports formats like SVG, DXF, and AI, making it compatible with most design and CNC software.

Toolpath & Cutting Strategies

A toolpath referrs to the programmed movement of the cutting tool. For this specific CNC machine, careful planning is essential to ensure efficiency, precision, and high-quality results.

For that to happen, it is important to understand the main cutting tool; Bit. A CNC bit is the rotating cutter attached to the spindle of a CNC machine. It determines how material is removed, affecting cut quality, speed, and precision. Bits come in different shapes and sizes, each designed for specific types of cuts, materials, and finishes.

Drill Bits vs. End Mills

  • Drill Bits : Only for making vertical holes.
  • End Mills: Can cut in multiple directions, including sideways.

Bit vs Mill

Bit Anatomy:

  • Flutes: Channels that remove material from the cut. More flutes = smoother finish but slower cutting.

Flutes

  • Chip Load: The amount of material removed per flute per revolution.

Chipload

Feeds & Speeds

These parameters control how the cutting tool interacts with the material, affecting cutting efficiency, surface finish, and tool longevity

  • Feed Rate: How fast the tool moves through the material.
  • Spindle Speed: Rotations per minute (RPM) of the cutting tool.

Climb vs. Conventional Cutting

Climb-vs-conventional

  • Climb Cutting: Smoother finish, reduces heat, but requires a rigid machine. -Conventional Cutting: More forgiving but can cause rougher edges. Holding Strategies (Screws & Tabs)

Tabs

Imagine cutting a square, you start from a corner, reach the second, the third, and you are leaving a space where the tool path went through. Now you are reaching the last corner Homerun! HA but the square is loose so the bit starts to move around. This is why you need bridges* to prevent parts from moving. These are small uncut section to be manually removed afterward.

Safety

! Always wear safety glasses, hearing protection, and a dust mask. Keep hands away from the cutting area.Make sure the emergency stop is accessible. Locate the fire extinguisher available.

AND if you are a long haired person like me, tie your valuable hair. Also avoid hanging accesories and scarfs.

꩜꩜꩜ Time to Cut! ꩜꩜꩜

On this week we had to cut a design based on meter-scale dimensions.

RhinoCAM

RhinoCAM is a plugin for Rhino 3D that allows for CNC toolpath generation and simulation. It is particularly useful for complex 3D milling and creating efficient cutting strategies.

Pocketing & Toolpaths

Pocketing is a strategy where material is removed from a defined area without cutting through the entire workpiece. Toolpaths define the movement of the cutting tool, ensuring precision and efficiency. CNC Stock Setup

Before machining, define the size and shape of the raw material (stock) in RhinoCAM. CNC Pocketing

Used to create recessed areas in a workpiece. Depth, tool selection, and step-over settings affect the final quality.