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7. Computer-controlled machining

CNC cutting

Overview of week 7 assignment

  1. Group assignment
    1. do your lab’s safety training
  2. Individual assignment
    1. test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

1. Group assignment

For more information, see the Week 07: Group assignment page.

A. Take-Space Fab Lab Hamamatsu

We, the Kannai members, visited to the lab called Take-Space, run by Takemura-san, in Hamamatsu City, Shizuoka Pref., about 2hours from Tokyo. Takemura-san let us use the large CNC router and a number of woodworking tools. Thank you to Takemura-san for allowing us use the lab until late night!

TakeSpace

Name CNC Router ZN1325
Work area 1300 x 2500 mm
End mill (we used) Straight flute, Dia:6mm
Software CUT2D (for making G-code) / Mach3 (for controlling CNC)

largeCNC

B. Safety training

Dangers

  1. Moving Parts: Risk of contact, entanglement, or crushing
  2. Flying Debris: Chips, broken tools, or workpieces can cause injuries
  3. Fire Hazard: Sparks, hot chips and dust

Safety tips

  1. To avoid crashing and entanglement,
    • Make sure the toolpath does not go over the wood fixing screws
    • No loose clothing and no globes
    • Tie up hair if long
  2. To protect from flying debris,
    • Wear safety glasses and a face mask
  3. To prevent potential fire,
    • Do not leave the machine on unattended
    • Check the stop button and emergency stop switch
    • Remove dusts to prevent potential fire

common sense

A sign posted at the door says "No entry for those without common sense"

2. Individual assignment

A. Parametric design with Grasshopper

I wanted to use Grasshopper to create a shelf of 100% parametric hexagonal units. It was unexpectedly inefficient to make with Grasshopper, but it allows changing almost all parameters, including unit size, depth and thickness of wood.

prototype

After testing with 3D printer, I changed design from triangle to hexagon to improve space efficiency and also yield rate of material.

CNC_GH

CNC_GH

Yield rate

I also considered yield rate, so I modified the depth and frame size parameters so that the top and bottom board fit inside the hexagonal frame.

Dog bone

Dogbone fillet
CNC machines use round router bits, making sharp inner corners impossible. This can prevent parts from fitting properly. DogBone Fillets extend outward at corners, ensuring precise joins.

Using Grasshopper, I added a dogbone by offsetting the cutout by the radius * √2 to define the center of the end mill circle to mimize cutout.

CNC_GH

Plywood thickness

The plywood tchickness I used was 12.10mm. I modified a thickness parameter which changes all length related to thickness.

plywood

B. Characterization of the CNC

First, I tested the CNC torelence on the plywood, and found it to be 0.02mm in X direction and 0.03mm in Y direction.

tolerance

C. CNC

CNC details

Collet chuck: By turning the collet nut, the inner diameter of the collet inserted inside narrows and holds end mill. It is important to check whether the collet is installed vertically to ensure accurate machining without wobbling.

Endmill: There are roughly two main types of end mills: straight flute and spiral.

  • Straight flute consists of 2 or 4 "flute" (cutting edge). Compared to spiral end mills, it provides greater stability with less material lift during cutting. Additionally, it can be sharpened like a blade, making it long-lasting, preferred in the Japanese woodworking industry.
  • Spiral end mills (up-cut, down-cut, compression, ball nose, etc.) are specialized for efficiency and specific applications.

Ref.: 6 types of endmill (JP)

D. G-code generation and CNC control

Cut2D (CAM Software – Toolpath Creation)

  1. Import Design
    • Load your DXF, or Ai (did't work) file into Cut2D

  2. Set Material & Job Setup

    • Define material dimensions (X, Y, Z)
    • Set the origin (typically bottom-left) Cut2D 　

    Fixturing material

    In order to fix the screws in a position that does not interfere with the design, I imported the design and then decided on the fixing position.

    • Create a vector > “Circle” with a diameter of 6mm (equal to the tool diameter).
    • Use the Drill profile
    • Cutting depth > Material thickness (in this case, 12.1mm)
    • Export G-code and go to Mach3 and start milling (same as the next Mach3 step.)
    • Fixturing the material by screw

    fixturing

  3. Create Toolpaths

    • Select vectors and assign profile, pocket, or engraving toolpaths
      • Outside
      • Pocket
      • Drill
    • Set cut depth, feed rate, and spindle speed based on material and tool

  4. Add Dogbone Fillets and Tabs (if needed)

    • Use the Fillet tool to add dogbone fillets for interlocking joints
    • Add tab Cut2D_2

    Tab in CNC is a small uncut section that keeps a part attached to the material, preventing movement during machining

  5. Preview & Simulate

    • Run a simulation to check the toolpath and material removal
  6. Export G-Code
    • Select the Mach3 post-processor and save the toolpath as a .nc or .tap file

yield_rate

Mach3 (CNC Controller Software – Machine Operation)

  1. Load G-Code
    • Open Mach3 and load the G-Code file
  2. Set Machine Zero
    • Move the CNC spindle to the desired X, Y, Z zero position
    • Click Zero X, Zero Y and Zero Z in Mach3
  3. Check Feed Rate & Spindle Speed
    • Feed rate: 80% (modified while milling)
    • Spindle speed: 7,000 rpm (For soft plywood, this might be too slow, around 18,000 rpm is recommended.)
  4. Turn on Spindle & Start Cutting
    • Manually start the spindle (if not automated)
    • Click Cycle Start to begin the job
  5. Monitor the Cut
    • Pause or stop if needed for adjustments
  6. Job Completion
    • Once done, raise the spindle, turn off the machine, and remove the part

Although it looks old-fashioned, I found this UI intuitive enough.

I tried to minimize leftover material, but I have packed the pieces too tightly together, causing some parts to become unstable while cutting.

result

E. Post-processing

The plywood I used was very soft, so the machined edges were very jaggy. I used sand papers and an electric sander to process edges.

sanding

Temporary assembly... hex shelf

I quickly disassembled it and returned to Tokyo.

3. Files

Afterthoughts

  • Wood is a good material, and I will pay more attention to the types of plywood and wood.
  • Safety first, especially fire and entanglement.
  • Take-Space Fab Lab Hamamatsu was amazing place, with lovely details. Thank you again, Takemura-san!