ROLAND SRM-20

Machine Orientation: Roland SRM-20 (Compact Desktop Subtractive CNC Mill)

This orientation module introduces the Roland SRM-20 precision desktop CNC milling platform featuring a 203.2 \times 152.4 \times 60.5\text{ mm} work envelope, high-speed 7,000\text{ RPM} spindle motor, micro-endmill chuck, and VPanel motion control interface used for high-resolution PCB isolation milling, surface trace routing, wax molding, and custom enclosures.

View 1: Subtractive Mechanical Chip Formation & Substrate Isolation

Conceive

The Roland SRM-20 changes the physical state of flat laminated or solid stock from raw copper-clad FR-1, machinable wax, or polyurethane foam to isolated circuit traces, high-precision surface topographies, and 3D molding masters.

  • Actors: Student operator, Mods / fab modules / FlatCAM CAM generator, VPanel for SRM-20 controller software, 1/64” \ (0.4\text{ mm}) 2-flute flat endmill, 1/32” \ (0.8\text{ mm}) flat endmill, 10\text{ mil} \ (0.25\text{ mm}) \ 30^\circ V-bit, sacrificial sacrificial MDF bed, and double-sided carpet/sacrificial tape.
  • Actions: Z-axis mechanical zeroing, spindle high-RPM rotary engagement, surface isolation pass routing, contour perimeter cutouts, and substrate chip evacuation.

Context

Desktop subtractive milling provides sub-millimeter precision within Unit 2 of the course, enabling rapid fabrication of custom printed circuit boards (PCBs) for smart light microcontrollers and sensors without chemical etching.

  • Course Documentation Link: [Unit 2: Subtractive PCB Milling & Isolation Routing](../../unit-2/pcb-milling.md)
  • Course Documentation Link: [Unit 2: Electronic Production & Soldering Standards](../../unit-2/electronics-assembly.md)
  • Official Manuals: [Roland SRM-20 User Manual & VPanel Guide](https\://www.rolanddga.com)

Comprehend

The Roland SRM-20 generates rotational torque up to 7,000\text{ RPM} through a micro-DC spindle motor. Flying stepper motors drive X, Y, and Z ball screws to move a rotating endmill through solid material stock.
[ VPanel Motion Controller Interface ]
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▼ [G-code / RML-1 Stream]
[ 3-Axis Ball Screw Stepper Motors ]
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▼
[ 7,000 RPM Micro-DC Spindle Motor ]
│
▼
[ 1/8" Collet + Precision Endmill ]
│
▼
=================================================
[ Physical Substrate (FR-1 / Wax / Chemical Foam) ]
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│
▼
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[ Physical Chip Removal / Trace Isolation ]
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  • State Change Mechanics:
  • Mechanical Shear & Chip Formation: Rotating flutes shear off micro-thin layers of solid material. For FR-1 PCB copper stock (1\text{ oz} / 35\mu\text{m} copper thickness), a 1/64” endmill or V-bit cuts 0.10\text{ mm} - 0.15\text{ mm} deep to isolate conductive copper traces from the base phenolic fiber.
  • Trace Isolation vs. Contour Cutout:
    • Traces Pass: Cuts around vector signal traces (1/64” bit or 30^\circ V-bit) at high feed rates (2-4\text{ mm/s}) to clear copper boundaries without snapping fragile tips.
    • Outlines / Holes Pass: Cuts through the full material thickness (1/32” bit) in shallow step-downs (0.2-0.4\text{ mm} per pass) to prevent bit binding.
  • Sacrificial Bed Coupling: Flat double-sided tape binds the substrate to a perfectly surfaced sacrificial bed, preventing structural flex and bit breakage during thin Z-pass cuts.

take Care

  • Human Risk (Hazardous Airborne Dust): NEVER mill FR-4 (fiberglass) copper boards. FR-4 contains glass fibers that produce toxic, carcinogenic airborne dust during milling. Use ONLY FR-1 (phenolic paper base) laminates. Always wear an N95 respirator when vacuuming debris.
  • Machine Risk (Micro-Bit Snap & Spindle Collision): 1/64” carbide endmills are brittle and snap easily if jogged into the bed or subjected to sudden Z-axis drops. Always use low-speed step jogging when approaching the substrate surface.
  • Machine Risk (Spindle Bearing Load): Never take single Z-cuts deeper than 0.4\text{ mm} per pass in solid materials. Excessive lateral force ruins internal spindle bearings and causes trace width inaccuracy.

Calibrate

  1. Sacrificial Bed Surfacing:
  2. Secure a clean MDF block to the aluminum table. Install a 1/4” or 1/8” flat surfacing endmill.
  3. Run a pocketing toolpath (0.2\text{ mm} depth) across the entire bed surface to ensure absolute parallelism with the spindle X/Y travel plane.
  4. Precision Mechanical Z-Zeroing (Gravity Drop Method):
  5. Move carriage over the raw substrate in VPanel.
  6. Loosen the collet set screw while holding the bit gently with finger support.
  7. Lower the bit tip until it lightly touches the copper surface under gravity.
  8. Gently press down on the PCB stock with one finger to ensure zero air gap, then tighten the collet set screw firmly. Zero the Z-axis in VPanel.

Control

  1. CAM Toolpath Generation (Mods / FlatCAM):
  2. Import PNG trace artwork (2000+\text{ DPI}) into Mods (mods.cba.mit.edu).
  3. Select PCB Traces (1/64”): Set cut depth to 0.12\text{ mm}, offset number to 4 passes, and cut speed to 3\text{ mm/s}.
  4. Select PCB Outlines (1/32”): Set cut depth to 1.7\text{ mm}, step-down to 0.35\text{ mm}, and cut speed to 1.5\text{ mm/s}.
  5. Export .rml or .nc driver files.
  6. VPanel Operation:
  7. Secure FR-1 stock to surfaced bed using zero-overlap double-sided tape.
  8. Set X/Y Origin to the bottom-left corner of the workpiece.
  9. Perform gravity drop Z-zeroing.
  10. Load file, verify spindle RPM (7,000), close interlock door, and press Cut.

Create

  • Single-Sided Microcontroller Board: Mill a custom PCB for the Unit 4 smart light controller, featuring isolated surface-mount pads for an ESP32/ATTiny chip, passives, and header connectors on an FR-1 phenolic substrate.

View 2: Tooling Geometry & Material Parameter Tuning

Conceive

Raw substrate materials transition from flat stock to functional circuit boards or 3D molds based on spindle RPM, chip load per tooth, pass depth, and tool bit geometry.

  • Actors: FR-1 Phenolic Board, Machinable Wax, High-Density Polyurethane Foam, 1/64” 2-Flute Endmill, 1/32” 2-Flute Endmill, 30^\circ V-Bit (0.1\text{ mm} tip size).
  • Actions: High-RPM material shear, tool deflection minimization, high-contrast surface finishing.

Context

Understanding chip loads and tool deflection allows students to cut reliable 10\text{ mil} \ (0.25\text{ mm}) trace widths without snapping micro-bits or lifting fine copper pads.

  • Course Documentation Link: [Majik Faktory Tooling & Speeds/Feeds Library](../../unit-2/tooling-library.md)
  • Course Documentation Link: [Unit 2: Modular Toolpath Generation in Mods](../../unit-2/mods-guide.md)

Comprehend

The relationship between spindle speed (RPM), feed rate (F), and chip load (CL) governs milling quality (7,000\text{ RPM} SRM-20 baseline):
\text{Chip Load (mm/tooth)} = \frac{\text{Feed Rate (mm/min)}}{\text{Spindle RPM} \times \text{Number of Flutes}}

Substrate Material Operation / Tool Spindle Speed Cut Speed (mm/s) Max Pass Depth Operational Result & Rules
FR-1 Copper Board Traces (1/64” \ \text{Flat}) 7,000\text{ RPM} 3.0\text{ mm/s} 0.12\text{ mm} Cleans copper layer; run 4 offsets to prevent solder bridging.
FR-1 Copper Board Fine Traces (30^\circ \ \text{V-Bit}) 7,000\text{ RPM} 2.0\text{ mm/s} 0.10\text{ mm} Ultra-fine trace isolation (\<8\text{ mil} clearance); fragile tip.
FR-1 Copper Board Outlines (1/32” \ \text{Flat}) 7,000\text{ RPM} 1.5\text{ mm/s} 0.35\text{ mm} Multi-pass contour cutout; requires tab retention or tape coupling.
Machinable Wax 3D Roughing (1/8” \ \text{Flat}) 7,000\text{ RPM} 20.0\text{ mm/s} 1.50\text{ mm} Rapid material removal for molding masters; no coolant needed.
Machinable Wax 3D Finishing (1/16” \ \text{Ball}) 7,000\text{ RPM} 15.0\text{ mm/s} 0.20\text{ mm} Smooth contoured surfaces; stepover set to 10-15\%.
HDPE Plastic Profiling (1/8” \ \text{Flat}) 7,000\text{ RPM} 8.0\text{ mm/s} 0.50\text{ mm} Low feeds prevent material melting and bit clogging.

take Care

  • Substrate Material Hazard: NEVER mill glass-reinforced epoxy boards (FR-4). FR-4 dulls carbide micro-bits within minutes and releases hazardous glass dust. Use ONLY FR-1 (Phenolic Paper).
  • Tape Overlap Hazard: When taping substrate down, never overlap layers of double-sided tape. Overlapping creates uneven bed height, leading to shallow un-isolated traces on low spots or broken bits on high spots.

Calibrate

  • Trace Isolation Depth Check:
  • Perform a 10\text{ mm} single test line cut on scrap FR-1 stock at Z = -0.10\text{ mm}.
  • Inspect under a magnifying loupe: complete copper removal should show a crisp brown phenolic substrate beneath without excessive gouging into the paper core.
  • Adjust Z-origin down in 0.02\text{ mm} increments if copper remains connected.

Control

  1. Wipe sacrificial bed clean with Isopropyl Alcohol before applying double-sided tape.
  2. Apply double-sided tape strips side-by-side across the back of the FR-1 board with zero gaps and zero overlaps.
  3. Press board down firmly against the bed using a roller or hand block for 15 seconds to ensure full adhesive contact.

Create

  • Reusable Injection Mold Core: Mill a high-resolution 3D mold master out of machinable wax using 1/8” roughing and 1/16” ball-nose finishing passes to cast flexible silicone diffusers for smart light housings.

View 3: Maintenance, Collet Care & Spindle Preservation

Conceive

The Roland SRM-20 transitions from a sub-millimeter precision milling tool to an inaccurate, noisy machine with high runout if spindle collets accumulate dust, ball screws lack lubrication, or set screws slip.

  • Actors: Student operator, lab technician, micro-vacuum hose, brass wire brush, Isopropyl Alcohol, lithium grease, hex key wrenches.
  • Actions: Collet cleaning, spindle runout check, interlock safety check, X/Y/Z lead screw lubrication.

Context

Routine preventive maintenance maintains spindle runout below 0.005\text{ mm}, preserving the delicate edges of micro-endmills.

  • Course Documentation Link: [Lab Maintenance Log & Roland SRM-20 Records](../../lab/srm20-maintenance.md)

Comprehend

Phenolic resin dust from FR-1 milling settles into the spindle collet cone and tool holder set screws. Uncleaned dust creates angular offset (“runout”), causing a 1/64” \ (0.4\text{ mm}) bit to orbit in a wider radius (0.5\text{ mm}+), breaking tool tips and widening trace isolation passes.

take Care

  • Vacuum Protection Hazard: NEVER use high-pressure compressed air nozzles to blow dust out of the SRM-20 enclosure. Compressed air forces abrasive dust into linear guide bearings and lead screw nut threads. Use ONLY a vacuum cleaner with a brush attachment.
  • Spindle Over-Tightening Hazard: Do not over-torque the collet set screws. Over-tightening strips hex head set screws and warps internal spindle threads.

Calibrate

  1. Spindle Runout Verification:
  2. Insert a ground calibration pin into the collet.
  3. Place a dial indicator gauge against the pin side and rotate the spindle manually.
  4. Verify total runout is under 0.01\text{ mm}. Clean collet bore if runout exceeds threshold.
  5. X/Y Home Zero Verification:
  6. Perform homing sequence in VPanel. Verify carriage hits hardware limit switches cleanly without grinding or skipping steps.

Control

  1. Post-Job Cleaning: Vacuum all FR-1 dust from the enclosure after every job using an N95 mask.
  2. Weekly Collet Inspection: Remove 1/8” collet, clean internal taper with IPA and a cotton swab, and inspect set screws for thread wear.
  3. Monthly Lubrication: Apply a light film of lithium grease to X, Y, and Z ball screws.

Create

  • Custom Alignment PCB Bed Jig: Mill a recessed pocket grid directly into an acrylic bed fixture to locate standard 2” \times 3” FR-1 blanks instantly with zero alignment error.