7. GROUP-Computer controlled machining

group assignment
- do your lab’s safety training
- test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

individual assignment
- make (design+mill+assemble) something big (~meter-scale)
- extra credit: don’t use fasteners or glue
- extra credit: include curved surfaces

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group assignment

1. safety training

1.1 Personal Protection

✅ Prepare safety goggles, fitted work clothes, earplugs, and masks
✅ Confirm the position of the emergency stop button
❌ Gloves: Only use during workpiece loading/unloading.
(strictly prohibited during machine operation to avoid entanglement in rotating parts).
❌ Leaving the machine unattended: Continuous monitoring is required throughout the process.

1.2 Machine setting

• We have chosen a CNC equipment made in China, which is cheaper and easier to operate.
  

• Turn on the power of the machine and computer.
  

• For installing the milling head of the machine and cutting wooden boards, we usually choose a flat head milling head with a diameter of 6mm.
  

• fixturing of materials ，No nails or fixtures are needed.
  By turning on the vacuum pump, the material can be firmly attached to the machine tool.
  

• Dust collection system activation, When cutting wooden boards with CNC machines, the blower needs to be turned on, and the crushed wood chips will be sucked into the dust bag.
  

• Machine Specifications

• Voltage: 220V (380V optional)
• Spindle power: 3KW
• Spindle speed: 24,000 RPM
• Max work area: 1300 × 2500 mm
• Z travel: 200 mm
• Controller: Weihong system

1.3 material preparation

• Material selection: I choose 12mm birch wood board, which has a standard size of 1220 × 2440 × 12mm, check and remove burrs or sharp edges before processing.
  

1.4 Check the design drawings

• Export format: .dxf. closed contour check.
  I often have files exported from Fusion 360 that are not closed.
  

• If this problem occurs, it can be fixed through inkscape.
  Path → Object to path → Dynamic offset → Save as “DXF R12” format.
  

2. CNC Machine Testing

2.1 Spindle Runout

Measured with a dial indicator — approx. 0.008 mm (acceptable range)

2.2 Machine Alignment

Flattened spoilboard with a surfacing bit — result was even with no ridges

2.3 Design Test File

• When CNC cutting wood panels, it is not possible to cut 90°.
  Therefore it is necessary to modify the corners, generally a circle is added at right angles (radius ≥ tool radius+0.5mm).
  

• The first time use a CNC machine, design a test file to make sure the boards will engage just right.
  We are using a 12CM multilayer board.
  The estimated cutting error was 1MM, so holes were designed for 11.9CM, 12cm and 12.1cm.
  We also set 2 speeds to test the cutting effect.
  

2.4 Speeds & Feeds Test

• Tool 6mm flat-end mill, feed rate (mm/s): 40, tested 2 speeds (RPM): 18k and 24k respectively. Cut Depth 3 mm/pass.
  

• After testing, the cutting speed of 18k RPM is better. High quality CNC cut powder should curl evenly like dry oatmeal, with a color similar to that of natural wood.
  

• The cutting error of CNC is 0. If you want the board to be easier to assemble, you can widen the gap by 0.1-0.2mm wider than the thickness of the board.