Week 6

Reference Documentation

Part 1 — Alfonso: Subtractive Manufacturing Fundamentals

Comprehensive overview of subtractive manufacturing processes, from basic 2-axis operations to advanced 5-axis machining capabilities.

Part 2 — Dan: Advanced Manufacturing Techniques

Advanced manufacturing strategies covering design optimization, process control, and quality assurance for large-scale fabrication.

Reference Materials

Source: MIT HTMAA Slack Discussion

Detailed notes from Anthony's training session on CNC router characterization and design rules

Critical Parameters for Characterization

Expert Guidelines from Anthony

EECS Shop CNC Router Design Rules

Succinct guidelines derived from our characterization to ensure predictable outcomes on the EECS shop CNC router.

Runout

Measured at the tool: joints loosen with usage; fresh cuts are tighter.

Metric	Value (in)
Average runout	0.0036
Standard deviation	0.0020
Median (freshly machined)	0.0020

Use average + 1σ (~0.0056 in) as a conservative clearance allowance for press fits that will be tested repeatedly.

💾 Download XLSX 🔗 View on Google Sheets

Dial/runout measurement indicating consistent concentricity with slight loosening after fit tests.

Clearance

Press-fit clearance tests across increments; loosened joints increase effective clearance over time.

Peg length [in]	Hole size [in]	Clearance [in]	Joint type	Fit type
1.995	2	-0.005	Interference	Press
2	2	0	Line-to-line	Transition
2.005	2	0.005	Clearance	Slip

Use 0.005 in clearance for slip fits; interference fits require press assembly.

💾 Download XLSX 🔗 View on Google Sheets

Clearance measurement setup showing press-fit testing across different peg sizes and hole clearances.

Systematic Test Part Design

Designed test part featuring 2-inch slots with 0.005" incremental clearances to systematically evaluate joint tolerances and press-fit characteristics.

Manufacturing Process Documentation

Systematic documentation of the CNC router characterization process from design to measurement, capturing key parameters for design rule establishment.

Demo tabs design featuring 2-inch slots with 0.005" clearance increments for systematic joint tolerance testing

CNC router executing characterization cuts with 3HP spindle at optimized speeds and feeds for OSB material

Completed test part showing three joint clearance variations (1.995", 2.000", 2.005") for press-fit tolerance analysis

Post-machining cleanup using vacuum system to remove OSB dust and debris from work area and test parts

Bandsaw cutting for part separation and precision measurement using calipers to determine actual joint clearances and runout characteristics

Design Files

Demo Tabs v8.f3d: Complete Fusion 360 design file for CNC router characterization test parts with various joint clearances and tab configurations.

Characterization Completion Checklist

Priority Action: Measure runout using calipers based on test part design, then systematically complete all characterization parameters.

Tensegrity Resources

• How to Make Floating Tensegrity Table — Comprehensive guide with step-by-step instructions
• Tensegrity Table Build Video — Visual demonstration of construction process
• Advanced Tensegrity Techniques — Advanced construction methods and tips
• Tensegrity Physics Explanation — Understanding the underlying physics principles
• Basic Tensegrity Table — Fundamental tensegrity table design
• 3D Printed Tensegrity Model — Small-scale 3D printed tensegrity structures
• Tensegrity Table with Swappable Top — Modular tensegrity design with interchangeable surfaces
• Impossible Table Reddit Post — Community discussion and build examples
• Tensegrity Mirror Concept — Specific tensegrity mirror implementation
• MIT Fab Academy Tensegrity Project — Previous MIT student tensegrity work
• Tensegrity Construction Tips — Practical construction advice and techniques
• Tensegrity Table Assembly — Detailed assembly process demonstration
• DIY 3D Printed Tensegrity Tables — Complete DIY guide for 3D printed tensegrity
• MIT HTMAA Week 6 Project — Previous MIT HTMAA student CNC machining project

Hook Alternatives

• Hook Design Video — Hook design and implementation techniques
• 3D Printable Hooks — Various hook designs for 3D printing
• Pattern Holes in Fusion 360 — Creating patterned holes for hardware integration

Note: We decided to go without hooks or screw hooks if needed, focusing on clean design integration.

Design board discussions with Anthony during the floating mirror design process, exploring tensegrity principles and manufacturing considerations

3D design of the floating mirror showing tensegrity structure and mirror integration

Design Process Videos

Nifty Dogbone Configuration

Important: When using Nifty Dogbone in Fusion, click the face, not the tab! Input our tool diameter as 0.25 in and clearance as 0.001 in.

Download: Nifty Dogbone for Fusion 360

Note: If using Mac, you may need to go to Privacy and Security settings to unblock the installation. See Autodesk support article for troubleshooting.

Design Requirements

• No sharp edges: Used modify → fillet for all edges that can be cut
• Meter height: Steep angle 500mm legs for total height of ~800mm
• Integrated legs: Made the legs the tables themselves by cutting them into top and bottom surfaces
• Tension cables: 10mm holes in legs for double loops of 4mm cable, two 7mm holes (minimum size cuts) for surface-to-surface tension cables
• Two-layer surface: Upper layer cuts space for finger adjustment and has channel between holes; bottom layer has two holes per cable

Process Overview

Everything same as in the tutorial video: Anthony's CAM Tutorial

Except for the modifications listed below for our specific project requirements.

Key Modifications

• Create components from bodies: Either in design or manufacturing (nicer workflow)
• 2D contour: Removed lead-in and lead-out for cleaner cuts
• Tab frequency: Reduced to 1 per 5 inches instead of 1 per 3 inches, with manual tabs added where needed
• Arrange setup: Moved to the front to make best use of the stock (instead of center)

Overall Process

1. Go to manufacturing tab
2. Create components from bodies
3. Make a fixed stock manufacturing model with the stock size
4. Click modify → arrange on it
5. Click the components to arrange them on the stock
6. Set up parameters for 2D contours per edge mill (big size and small size, so two tool paths)
7. Generate the .ncl files (numerical control files)
8. Machine takes .tap which is a postprocessed .ncl file

Note: The .tap extension is a historical carryover from the era of tape-driven machinery. Early numerical control (NC) machines used perforated paper or card stock, known as "tape," to store and transfer program data.

3D Printing Process

I 3D printed both altogether which failed and also printed flat as the output of the machining process to test the assembly. I used glow in the dark PLA!

Initial 3D print attempt showing failure mode

Failed print result highlighting design issues

Successfully printed parts for assembly testing

Stratasys Printing

Slice and print on Stratasys software, dissolve support, then remove and wash parts after support is dissolved.

Stratasys print in progress with support material

Dissolving support material in solution

Cleaned parts after support material dissolution

Machining Process

Run the job with care (see training section for details). When removing tabs, use the battery-powered flat drill. For the circles, drill off both sides of the tabs, then use a crow bar gently around the perimeter until it pops off.

CNC machining process showing wood cutting operation

Completed cut parts ready for assembly

Part 1: Assembling 3D Printed for Right Configuration

Testing tension cable ratios and angles using 3D printed components. We used fishing rod line because it's mostly transparent and makes the levitation effect more effective as shown in this Instructables guide, especially when imaged in night mode as glow in the dark assembly!

Prusa CoreOne Assembly

Testing tension cable ratios and angles using 3D printed components with glow-in-the-dark PLA for enhanced levitation effect.

Glow-in-the-dark assembly in night mode showing levitation effect

Color testing of the glow-in-the-dark components

Phone testing of the floating mirror assembly

Wall-mounted floating mirror demonstration

Succulent plant test showing the assembly can hold plants

Kevlar Assembly

Initial threading used a sewing needle; the Kevlar line fractured the needle, so we re‑threaded using a smaller carrier thread. The assembly was completed and wall‑mounted. For rapid iteration we temporarily set tension with tape; for final installations, secure with knots to eliminate slip and creep.

Fully threaded Kevlar assembly with smaller thread

Completed Kevlar tensegrity assembly

Kevlar threading process demonstration

Wall-mounted Kevlar tensegrity assembly

Stratasys Assembly

Assembled with only knots because tape doesn't work on Stratasys printed filament -- works even better than tape anyway.

Stratasys assembly using only knots for tension cable attachment

Part 2: Assembling OSB (Oriented Strand Board)

What is OSB? Oriented Strand Board is an engineered wood product made from layers of wood strands (or wafers) bonded together with resin and high heat. The strands are "oriented" in specific directions, and each layer is aligned in various directions to enhance the board's strength and stability. It is a popular, more affordable alternative to plywood for applications like sheathing and subflooring.

Here we're using 1000ft-rated 4mm paracord from Amazon for the tension cables.

1. Removing Parts After Machining

1. Use a small saw tool to cut through the tabs connecting the machined parts to the stock material
2. Apply full pressure with the saw tool, positioning the blade as close to the part edge as possible for clean cuts
3. For circular parts, cut through both sides of the tab to ensure complete separation
4. After cutting the tabs, use a crow bar to gently pry up the part, working around the perimeter until all plastic nails are released from the stock
5. Carefully remove the part from the CNC bed, ensuring no damage to the machined surfaces

Cutting tabs with saw tool for part removal

Tab removal process demonstration

Cleaning the CNC bed with vacuum after part removal

2. Assembling Without Glue

1. Use a file to refine the press fit joints until they insert smoothly into the dogbone holes with a snug, secure fit
2. Insert the leg components into the circular bottom panels, aligning with the pre-drilled paracord holes
3. Thread the paracord through the edge holes, ensuring proper alignment for the tension system
4. Route the paracord in a straight line across the top surface to the corresponding inner circle hole, then thread back to the leg side
5. Repeat this threading pattern for all four corner holes to establish the complete tension network
6. Insert paracord between the two leg assemblies and adjust tension to achieve the desired vertical or semi-vertical spacing
7. Lift the assembly from the top and adjust paracord tension until achieving a stable, balanced floating configuration
8. Mark the optimal knot positions using a permanent marker or ziptie for reference
9. Lay both subsystems horizontally on a flat surface and tie secure knots at the marked positions
10. Secure each knot with zipties positioned between the knot and hole to prevent slippage and maintain tension integrity
11. Trim excess ziptie material flush with the knot for a clean, professional appearance

Filing joints to achieve proper press fit

Inserting leg into circular bottom panel

Threading paracord through edge holes

Measuring paracord for proper tension

Tightening paracord to marked position

Completed assembly without glue

Horizontal assembly configuration

Holding floating configuration from top

Horizontal assembly without glue showing stability

3. Gluing for Mirror

1. Prepare the work surface with protective paper to prevent glue contamination and ensure easy cleanup
2. Gather an adequate number of clamps to secure all joints during the gluing process
3. Apply wood glue around the press fit joint edges and within the joint interface to reinforce the connection for horizontal wall mounting applications
4. Position clamps at the critical edge locations between the leg and circle perimeter, as this area represents the weakest structural point and is most susceptible to failure under horizontal stress
5. Apply adhesive to the mating surfaces of the upper and lower circles, taking care to minimize contact with paracord channels (any excess glue can be removed and cleaned up later)
6. Carefully position the second layer components onto the upper and lower circles, ensuring paracord routing remains unobstructed through the designated channels
7. Secure the glued layers with clamps, applying even pressure across all joint surfaces
8. For mirror attachment, apply appropriate adhesive (silicone glass adhesive recommended, though wood glue is acceptable) and secure with clamps
9. Allow complete adhesive cure time before applying any stress to the joints to ensure maximum bond strength

Wood gluing mirror with clamps for secure bonding

Cured glue after 24-hour wait period

4. Tightening After Gluing

1. Verify that paracord remains freely movable and is not bonded to the wood surfaces by adhesive
2. If paracord is stuck, apply gentle pulling force or carefully use a utility knife to separate any adhesive bonds between paracord and wood surfaces
3. Execute the tensioning procedure following the same methodology established in step 2, utilizing knots and zipties for secure fastening
4. Apply tension to the paracord until achieving equilibrium where opposing forces are balanced
5. Mark the optimal tension point using a permanent marker or ziptie for precise reference
6. Create a secure knot at the marked position to maintain the desired tension
7. Install zipties between the knot and hole to prevent slippage, continuing until the system reaches a stable, non-adjustable state

Horizontal mirror configuration after gluing

Horizontal mirror side view showing stability

Ziptie tightening for final tension adjustment

Final tight mirror configuration

Final tight assembly with mirror properly mounted

5. Final Assembly

1. Complete the final assembly process and conduct comprehensive stability testing to verify structural integrity
2. Perform load testing with various weights (monitor, laptop, iPad) to validate the assembly's load-bearing capacity and safety margins
3. Verify horizontal stability and confirm the levitation effect is functioning correctly under different load conditions
4. Trim excess ziptie material flush with the assembly for a clean, professional finish

Final working stable assembly

Monitor weight test showing stability

Laptop stability test demonstrating load capacity

iPad stability test showing versatility

Baby for scale showing actual size

Baby happy with the floating mirror assembly

Final trimmed neat assembly ready for use

Scaling Design Steps (Estimated Time: 30-50 minutes)

1. Apply non-uniform scaling to all components using modify → scale → non-uniform, maintaining original thickness (circles: scale x,y axes only; legs: scale x,z axes only)
2. Reposition plate components along the z-axis, then align leg components with their corresponding mounting holes
3. Remove existing joint holes and dogbone features from the design timeline to prepare for recreation
4. Recreate extrusion cuts and apply dogbone modifications to the new scaled geometry
5. Return to CAM workflow using the same procedures outlined in Anthony's CAM Tutorial

Design scale-up timeline showing the scaling process in Fusion 360

Future Parametric Design

In the future, will create parametric design by defining the lengths in terms of other lengths and then can scale by setting values to the base parameters of the design.

Fusion 360 Project

HTMA Team Link: Floating Mirror v12.3mf Project

Download Links

3MF Model: Complete 3D model for 3D printing and visualization.
DXF File: 2D drawing file for CNC machining and laser cutting.
Flat 3MF: Flat configuration for 3D printing assembly testing.

Manufacturing Files

G-Code: For our shop's printer for flat configuration (0.4mm nozzle, 0.2mm layer height, PLA, 1h52m print time).
TAP File: For our shop's CNC router (postprocessed numerical control file).

Demo Tabs Design

Demo Tabs v8.f3d: Complete Fusion 360 design file for CNC router characterization test parts with various joint clearances (1.995", 2.000", 2.005") and tab configurations for testing runout, alignment, and fixturing parameters.