Week 07 | Computer Controlled Machining

## Introduction CNC (Computer Numerical Control) is a manufacturing process in which programmed digital instructions control the movement of machines and cutting tools to precisely shape, cut, drill, or form materials. Common types of CNC machining include milling, turning, drilling, routing, and grinding, each suited to specific geometries, material properties, and fabrication requirements. CNC milling was the main focus of this week, where we explored key concepts necessary to understand and operate different milling processes. This included working with various toolpaths, drill bits, and collets, as well as understanding how different materials respond to CNC milling. For this assignment, I chose to design a low-profile chair, reflecting my preference for sitting closer to the ground, while also exploring a strategy of material reuse. The chair is conceived as a system of components that can be assembled from fragments of reclaimed sheet boards, merging fabrication with an intention to recycle through milling.

## Design & Modeling I used fusion 360 to model my chair, with a twist that I combined AI to trace the chair profile, and to get the sketch "Fusion Friendly" , I did some pre-processing to the DXF and then imported it the dxf file into my design space on fusion:

### Sketching the chair profile I started off by drafting a sketch for the chair profile inspired by the pinterest model attached below, the first step was sketching the profile, where i used - **Parameters** in fusion to iterate multiple /slopes/angles/curves - **AutoCAD** : I used spline tool and join functions to fix my sketch to make it model and milling ready.

I used spline tool, Join functions and multiple iterations to get the sketch profile

Defining fusion parameters and a journey of import/exporting dxfs

A preview of CAD imports into fusion , to solve for those multiple centerpoints and multiple line segments, I redrew the file in CAD using spline tool and reimported it as single path/sketch

### 3D Modelling:

Importing the final sketch

Extrude the sketch to 18mm / plywood thickness

Creating Rectangular pattern

Sketching the chair base

Using Combine tool to create the slot fits for the base

Apply fillet to parts

## Toolpath Generation (VCarve/Fusion Manufacturing) To prepare the file for cutting I used Vcarve, which is CAM software compatible with a wide range of brands such as Shopbot. There are two softwares possible to prepare the design for milling, either through Fusion 360 or Vcarve Pro, I chose to work with Vcarve Pro. Below is a step by step workflow:

## CNC Milling In milling, understanding essential parameters, tool geometry, and material composition is critical for achieving desired results and effective troubleshooting. ### Machine Operations There are two distinct operations to distinguish when working with a CNC mill: | Operation | Direction | Characteristics | | :--- | :--- | :--- | | **Drilling** | Axial only (Vertical) | Moves only in the Z-axis; used for one specific hole size; cannot move sideways. | | **Milling** | Multi-directional | Can move in various directions (sideways, helical, etc.) to clear pockets or profiles. | ### Tool Materials & Anatomy A CNC bit is often a hybrid of materials designed to balance **hardness** (for cutting) and **toughness** (to prevent snapping). ### Material Significance: Why They Are Used - **Tungsten Carbide (The Cutting Edge):** - Significance: Extremely hard and heat-resistant. This is our primary cutting material. - Purpose: To maintain a sharp edge at high speeds without dulling. - **Steel (The Shank/Body):** - Significance: Acts as a **metal damper** for vibrations. - Purpose: Carbide is brittle; a steel shank provides the flexibility needed to prevent the tool from shattering under stress. - **HSS / HSSCO (High-Speed Steel / Cobalt):** - Significance: Tougher and less brittle than carbide but less heat-resistant. - Purpose: Generally used for manual milling or where tool "flex" is preferred over hardness. ### Visual Identification Guide | Material | Visual Appearance | Weight/Feel | | :--- | :--- | :--- | | **Tungsten Carbide** | **Dark grey or matte silver.** Lacks a mirror-like shine. | **Heavy.** Noticeably denser than steel. | | **HSS (High-Speed Steel)** | **Bright, shiny silver.** Looks like polished stainless steel. | **Lighter** than carbide. | | **HSSCO (Cobalt)** | **Dull gold or "straw" tint.** Has a distinct yellowish hue. | Similar to HSS. | | **TCT (Carbide Tipped)** | **Two-tone.** Features a dark grey tip brazed onto a shiny steel body. | Weighted toward the tip. | ### Tool Shapes & Functions The shape of the bit determines the geometry and finish of the workpiece. | Tool Type | Primary Functions | Key Details | | :--- | :--- | :--- | | **Flat / Square End Mill** | Pocketing, Contouring | Cuts sideways; cutting depth is correlated to the flat edge. | | **Ball End Mill** | 3D Surfaces, Grooving | Great for plastic runners; can be used as a shoulder mill. | | **V-Shaped End Mill** | Chamfering, Carving | Available in angles like 45°, 90°, and 120°. | | **Tapered Ball Nose** | 3D Surfaces | Ideal for detailed sculptural surfaces and runners. | ### Cutting Physics & Bit Geometry - **Rotation:** Standard cutting is **Clockwise (CW)**. Counter-Clockwise (CCW) is only used for tapping. - **Helix Angle:** Take note of the angle of the flutes as it affects chip evacuation. - **Flutes:** A higher number of flutes increases tool rigidity and diameter. - Note: Avoid single flutes for plastics and aluminum to prevent chip adherence. ### Chip Flow (Up vs. Down) - **Upcut:** Pulls chips up and out. Used for metals and plastics. - **Downcut:** Presses material down. Ideal for wood (fibrous) and pocketing to prevent splintering. - **Straight Cut:** Used for laminated or painted boards; ideal for contouring. - **Compression (Down-Up Combo):** Used for clean finishes on both top and bottom faces. ### Material Interaction & Shop Notes - **Wood:** A forgiving material; lower chances of wearing out the end mill. - **MDF:** Excellent for molding (unlike chipboard). - **Aluminum:** A "gummy" material. Adhesion is avoided by **Grinding** or using **Lubricants**.

Local Sourcing & Budget

A standard 3cm MDF board (1220x2440) in Jordan costs approximately 3 JDS. It is a cost-effective choice for molding compared to chipboard.

### Essential Parameters | Parameter | Value / Definition | | :--- | :--- | | **Spindle Speed** | For wood, use the highest possible setting for the machine. | | **Max RPM (ShopBot)** | 18,000 RPM. | | **Feed Rate** | Travel speed: 15,000 mm/min (15 m/min). | | **Rapid Feed** | Fixed value for movement *outside* the material: 40 m/min. | ## Introduction to Shopbot Gantry The CNC machine available in our lab, and the one we will be working with is a ShopBot Gantry, a robust large-format CNC milling system designed for precise fabrication at scale. It operates through a gantry structure that spans the working bed, allowing the spindle to move seamlessly along the X, Y, and Z axes. This configuration enables accurate cutting, carving, and drilling of sheet materials such as wood, MDF, and plastics, making it especially suitable for furniture prototyping and full-scale production.

Setting up the ShopBot Gantry involves working with three main components:

Measuring the End Tool to define it in the software:

### X,Y Zeroing To set the xy zero points, use the keyboard to position your zero point on the shopbot, the hit zero xy on the shopbot screen to set the zero points.

## Milling,Cutting and Assembly ### Plywood board optimization and re-use I decided to use the residual pieces available to produce the chair components, by measuring and outlining the usable space available to mill from each board piece

### Board mounting

### Setting the Zero point (X,Y and Z)

#### CNC Machine Operation Guide **Startup & Warm-up** Before starting any work, the spindle must be prepared to ensure bearing longevity and accuracy. * **Hardware Interface**: * **Blue Button (RESET)**: Press this first to clear any software faults or E-stop conditions. * **Green Button (START)**: Press this to enable the machine drives and spindle power. * **Software Command**: * Type **`C6`** to initiate the spindle warm-up routine. --- #### Command Reference | Category | Command | Description | | :--- | :---: | :--- | | **Manual Control** | `K` | Opens the movement keypad window | | **Warm-up** | `C6` | Spindle warm-up routine (Run daily) | | **Homing (Auto)** | `C3` | Auto-homes X & Y using proximity switches | | **Z-Zero (Puck)** | `C2` | Runs Z-axis zeroing routine with the blue puck | | **Zero X** | `ZX` | Sets current X position to zero | | **Zero Y** | `ZY` | Sets current Y position to zero | | **Zero Both** | `Z2` | Zeros both X and Y at the current location | --- #### Standard Operating Procedures **X & Y Axes (Auto-Homing)** * Verify the machine bed is clear of all obstructions and clamps. * Ensure the keypad window is closed. * Type **`C3`** to begin the automated homing sequence. **X & Y Axes (Manual Zero)** * Press **`K`** to open the keypad and jog the spindle to your desired origin. * Close the keypad window completely. * Type **`ZX`** for X, **`ZY`** for Y, or **`Z2`** to zero both axes simultaneously. **Z-Axis (With Blue Puck)** * Position the tool bit over the material and place the **Blue Puck** directly underneath. * Ensure the keypad window is closed. * Type **`C2`** to start the touch-off routine. * **CRITICAL**: Remove the puck from the workspace immediately after the spindle retracts. ### Cutting and Assembly After everything was set, I started cutting the first piece and took measurements to see the fit joint tolerances as shown:

Group Assignment

# Group Assignment: Computer-Controlled Machining (17.8mm Plywood) ## 1. Machine Setup & Safety Before any cutting, the following safety and maintenance checks are performed on the ShopBot large-format CNC. ### Safety Checklist * **PPE:** Wear eye protection and ear muffs at all times. * **Attire:** No loose clothing, jewelry, or long hair. Closed-toe shoes are mandatory. * **Emergency:** Identify the location of the E-Stop and the fire extinguisher. * **Dust Collection:** Ensure the vacuum system is active to prevent chip buildup and fire hazards. ### Spindle & Tooling * **Tool:** 6mm Straight 3-Flute Endmill. * **Runout Check:** Use a dial indicator on the tool shank. If runout exceeds 0.05mm, inspect the collet for debris or wear. --- ## 2. Speeds, Feeds, and Chip Load The foundational setup for the 17.8mm actual thickness plywood. ### FSWizard Calculation Based on a 6mm 3-flute bit in plywood: * **Recommended RPM:** 15,500 * **Recommended Feed Rate:** 2,800 mm/min * **Plunge Rate:** 500 mm/min * **Step Down (Pass Depth):** 4.5 mm (Requires 4 passes to clear 17.8mm) ### The Optimization Test We cut a test strip to observe the physical results of different parameters. | Test | RPM | Feed Rate | Observation | | :--- | :--- | :--- | :--- | | **Control** | 15,500 | 2,800 | Check for edge quality and chip size. | | **Fast** | 16,500 | 2,800 | Check for burning/charring on the edges. | | **Slow** | 12,500 | 1,800 | Check for "chatter" or excessive vibration. | --- ## 3. The Comb Test (Material Thickness Validation) **Goal:** Determine the perfect slot width for a sliding or press-fit joint in 17.8mm material. | Slot # | Design Dimension | Clearance (vs 17.8mm) | Intended Fit | | :--- | :--- | :--- | :--- | | 1 | 17.60 mm | -0.20 mm | Interference (Will not fit) | | 2 | 17.80 mm | 0.00 mm | Hammer/Heavy Press Fit | | 3 | 17.90 mm | +0.10 mm | Snug Press Fit | | 4 | 18.00 mm | +0.20 mm | **Ideal General Fit** | | 5 | 18.10 mm | +0.30 mm | Sliding Fit (Shelves) | | 6 | 18.20 mm | +0.40 mm | Loose (Requires glue) | --- ## 4. The Dog Bone Test (Internal Corner Clearance) **Goal:** Ensure square parts can seat fully into internal corners despite the bit's radius. * **Method:** Apply circular "ears" at every internal 90° corner. * **Dog Bone Radius:** 3.10 mm (slightly larger than bit radius to ensure clearance). * **Slot Width:** 18.00 mm (based on the "Ideal Fit" from the Comb Test). * **Test Criteria:** A square test plug must sit flush against the bottom of the slot. --- ## 5. Finger Joint Test (Assembly Friction) **Goal:** Validate a multi-contact joint used for box construction. * **Design Specs:** * **Finger Width:** 18.00 mm (+0.2mm clearance). * **Finger Height:** 17.95 mm (+0.15mm protrusion). * **The Test:** Assemble a 3-sided corner. * **The Logic:** The 17.95mm height ensures the finger slightly protrudes, allowing it to be sanded perfectly flush for a professional finish. --- ## 6. Bone and Hole (Inlay & Accuracy) **Goal:** Measure machine deflection and calculate the required offset for inlays. * **Design:** A 40.00mm Diameter Circle (Bone) and a 40.00mm Pocket (Hole). * **Procedure:** 1. Cut both shapes using the optimized Speed/Feed. 2. Measure the **Plug OD** and the **Hole ID** with calipers. * **Calculation:** The difference between the two measurements defines the "Mechanical Clearance" of the machine. --- ## 7. Runout & Alignment (Gantry Squaring) **Goal:** Confirm the X and Y axes are perpendicular. * **The "L" Test:** Cut an "L" shaped bracket 500mm x 500mm. * **Measurement:** Measure the hypotenuse (diagonal). * **Target:** 707.11 mm ($\sqrt{500^2 + 500^2}$). * **Deviation:** If the diagonal measurement differs significantly, the gantry is "racked" and requires calibration. --- ## Summary Checklist for Documentation - [x] Measured actual material thickness in 3 locations (Result: 17.8mm). - [ ] Photograph the "Chips" from the Speeds/Feeds test (Dust vs. Chips). - [ ] Photograph the successful "Press-Fit" from the Comb Test. - [ ] Measure and record the "Hole vs. Bone" diameters. - [ ] Screenshot VCarve/Fusion 360 Toolpath settings (Bit diameter, Pass depth, RPM).

Resources & Assets

Source Files

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External Refs

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