Computer-Controlled Machining

What is CNC Machining?

CNC (Computer Numerical Control) machining is a digital fabrication method that uses coded instructions (G-code) to guide machines like routers or mills to cut and shape materials precisely. It’s ideal for making parts that need consistency, accuracy, and repeatability — especially in wood, metal, and plastic. In this assignment, I used CNC to design and fabricate a functional pinball game table using 12 mm plywood.

Design Process

Step-by-Step Process

Software Used: Fusion 360

I used Autodesk Fusion 360 for the complete design process — from 2D sketches to 3D modeling and preparing CAM-ready geometry. Below is the full design workflow, categorized by operation and tool used:

1. Base Sketch & Extrusion

Tool Used: Sketch → Rectangle, Dimensions, Extrude
Operation: Created a 609.6 mm × 914.4 mm rectangle for the pinball base, placed at the origin.
Extrusion: Used the Extrude feature to pull it up to 12 mm to match the plywood thickness.

2. Pinball Layout Design

New Sketch, Arc, Lines, Circle, Polygon, Mirror

Operation: Created a new sketch on top of the base. I used:

3-Point Arc to make the ball paths
Circle Tool for bumpers and dowel holes
Line Tool for walls and angled corners
Polygon Tool for triangle bumpers
Mirror Tool across the vertical axis to keep both sides symmetrical

3. Extruding Pinball Features

Tool Used: Extrude (multiple profiles)

Operation: Selected different elements from the sketch:

Obstacles like bumpers, rails, and flippers were extruded upwards (6–12 mm) to form raised geometry
These features defined the physical interaction points on the board

4. Creating 2D Slot-Fit Obstacles

Tool Used: Sketch + Extrude, Slot, Cut

Operation: Some pieces (e.g. curved side rails and triangle parts) were modeled to be cut flat and slotted into the base vertically:

I made slots on the base using Extrude → Cut
Matching tabbed parts were kept in separate bodies and cut on the CNC as 2D profiles

5. Dowel Hole Integration

Tool Used: Circle, Dimension, Extrude → Cut

Operation:

Placed 6 mm circles on specific parts and corners
Used Extrude → Cut downwards through the base and components
These holes allow tight-fit dowels for easy alignment and press-fit assembly

6. Edge Finishing – Fillets

Tool Used: Modify → Fillet

Operation:

Applied to sharp edges on flippers and rail guides
Smoothed transitions for better form and safety (less prone to splinters post-cutting)

7. Angled Side Supports (Legs)

Tool Used: Sketch + Extrude, Dimension, Slot, Angle Constraint

Operation:

Created side pieces with slanted geometry (around 5° tilt using Angle constraints)
Added slots using Slot tool and cut using Extrude → Cut
These slots allowed the main board to fit tightly, giving the pinball machine its functional tilt

CAM Setup for CNC Machining

NC Programming in Fusion 360

After completing the full 3D design of my pinball table, the next phase was to prepare it for CNC machining using Fusion 360’s Manufacture workspace. The goal was to convert the modeled components into precise toolpaths that the CNC machine could understand and execute safely.

This process involved creating NC (Numerical Control) programs for drilling holes and cutting out parts from a full 4ft × 8ft plywood sheet.

1. Sheet Layout & Nesting

First, I arranged all the parts (obstacles, side panels, flippers, supports, etc.) flat onto a single plane.
These parts were carefully nested within a 4ft × 8ft rectangle (1220 mm × 2440 mm) — the actual size of one plywood sheet.
I spaced the parts to avoid overlap, reduce tool travel, and ensure material strength around tabs and slots.
This layout planning was critical to maximize material efficiency and prevent post-cut interference.

2. CAM Setup in Fusion 360

Tool Used: Setup (Manufacture Tab)

I created a new Milling setup (2D) and selected all visible bodies for the operation.
Work Coordinate System (WCS) was aligned using:
X & Y axes set from edges
Origin placed at the bottom corner of the plywood (Stock box point)
Stock mode was set to “Relative size box” with 1 mm offsets on X/Y sides and top, and 0 mm at the bottom.
This ensures accurate tool zeroing and efficient machining without risking overcutting.

3. Drill Operation (For Dowel Holes)

Tool Used: Drill Tool Diameter: Ø6 mm Drill Bit Operation:

I created a drilling operation for all 6 mm dowel holes (used for tight-fit assembly).
Hole positions were selected using geometry-based selection.

Feed and speeds were set to:

Spindle speed: 5000 rpm
Plunge feedrate: 300 mm/min
The drill tip was set to go slightly past stock bottom to ensure clean, through-holes.

Simulation: Simulated this file first to verify depth, clearances, and tool paths.

4. 2D Contour Operation (Profile Cutting)

Tool Used: 2D Contour Tool Diameter: Ø6 mm Flat Endmill Operation:

I selected all exterior chains (closed loops) of each part for cutting.
This program was used to cut out the actual pieces from the plywood sheet.

Tabs were added:

Width: 6 mm, Height: 1 mm, Distance: 48 mm
This kept parts in place during cutting and prevented movement.

Cutting Strategy Settings:

Multiple depths enabled:
Step-down: 2 mm per pass (for smooth load)
Finishing step-down: 0.2 mm

“Order by Islands” was checked to ensure small parts are cut first to maintain sheet stability.

CNC Production & Final Assembly

After preparing the CAM toolpaths in Fusion 360, the final stage was to move into CNC production — cutting out all parts from a 12 mm plywood sheet and assembling them into the finished pinball table. This stage involved not just machine execution but also precise technical setup, safety procedures, and careful assembly to maintain fit integrity.

CNC Machine Preparation & Safety

Before starting the cut, the following steps were taken to ensure safe and accurate operation:

1. Safety Protocols

Safety goggles and ear protection were worn during all operations.
Loose clothing, jewelry, and hair were secured away from the machine.
Emergency stop switch was verified to be working before running the job.

2. Material Setup

The 12 mm plywood sheet was placed flat on the CNC bed.
Clamps were tightened firmly on all four corners (and midpoints where necessary) to prevent lifting or shifting during tool movement.
A small sacrificial board underneath ensured clean cuts without damaging the CNC bed.

3. Tool Setup

A 6 mm drill bit was first loaded for the dowel holes.
Later, a 6 mm flat endmill was used for all contour cuts.
Tool tightness was verified using the provided collet wrench, and the spindle was manually rotated to check for alignment.

4. Machine Origin Setting (Zeroing)

Using the handheld controller, I manually jogged the tool head to the bottom-left corner of the plywood.
The X, Y, and Z origins were set using "Set WCS (Work Coordinate System)" in the Fusion 360 setup menu.
For Z-axis zeroing, the bit was gently lowered to just touch the stock surface, then zeroed out using the machine controller.

Cutting Process

Drilling Operation

I executed the Drill NC Program first to make 6 mm holes for dowel joints across the parts.
Drilling depth was set to go slightly below the stock bottom to ensure full clearance.
Drill spindle speed: 5000 RPM
Plunge feed rate: 300 mm/min

2D Contour Cutting

Switched to the 6 mm flat endmill.
The 2D contour file was executed next, cutting the outlines of all parts.
Tabs (6 mm x 1 mm) were generated automatically to hold parts in place.
Used multiple depth passes (2 mm step-downs) for smooth and safe cuts.
Finishing step-down of 0.2 mm ensured clean final edges.

Assembly Process

Part Removal & Finishing

After cutting, I carefully removed each part by breaking tabs with a chisel and sanding the edges lightly.
All holes aligned perfectly due to the accurate WCS and drill setup.

Dry Fit Assembly

All components — obstacles, bumpers, and rails — were fitted using 6 mm dowels with a press-fit method.
The angled legs slid into tight slot joints, providing the correct playing incline.

Final Assembly

No adhesives or fasteners were required.
A rubber mallet was lightly used for pressing dowels in snugly.
The final result was a structurally sound, angled pinball machine made entirely of press-fit plywood parts.

Hero Shots

FILES

Pinball machine F3D

Pinball machine NC Program F3D

NC Programs