7. 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
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¶
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We have chosen a CNC equipment made in China, which is cheaper and easier to operate.
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Turn on the power of the machine and computer.
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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.
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Use two wrenches to install the milling head, and moving both wrenches inward at the same time can make the milling head more secure.
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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.
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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.
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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¶
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Export format: .dxf. closed contour check. I often have files exported from Fusion 360 that are not closed.
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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¶
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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).
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We are using a 12 MM multilayer board. The estimated cutting error was 0.1 MM, so holes were designed for 11.9 MM, 12 MM and 12.1 MM. We also set 2 speeds to test the cutting effect.
2.4 Speeds & Feeds Test¶
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Tool 6mm flat-end mill, feed rate (mm/s): 40, tested 2 speeds (RPM): 18k and 24k respectively. Cut Depth 3 mm/pass .
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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.
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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.
individual assignment¶
1. Design documents¶
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My final project is small and does not require large CNC machines to cut Marine Plywood, so I want to design a stool for myself. Combining my favorite horse.
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I use Fusion 360 to design my stool. I set the thickness of the board as a variable, and if the thickness of the board changes, I can easily modify my drawings. (The correct result is that by adjusting only a few values, the entire design can be quickly modified. But my design cannot be implemented，and some practice and knowledge are needed in this area.)
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Key point 1: When CNC machines cut boards, the cutting error is 0, which means that a 12mm thick wooden board can just fit into a 12mm wide gap. But I felt it was too tight, so I widened the width of the hole by 2MM. (It turned out that my approach was not a problem)
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Key point 2: Be sure to add arcs (radius ≥ milling cutter radius 0.3MM) to the corners of the file so that CNC can cut 90 °. If you don’t take this step, your product will be a disaster.
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The final step is to convert the entity into a part in Fusion 360, and distribute the file on a plane through the arrangement function. The recommended size range for the plane is 2440mm * 1220mm, and then export .DXF format.
2. Machine manufacturing¶
This CNC machine is easy to operate and does not require complex settings, but requires the replacement of three software. In order to make it easier for beginners to understand, I have compiled a usage flowchart.
2.1 Convert the DXF file to a tool path¶
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Import the items to be processed DXF files, select .dxf file type, and when importing files, you can check the automatic connection breakpoint (0.2mm).
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There are two types of CNC machines when cutting contours. The first type has a tool path that is offset inward to form a hole. The second type of tool path is offset inward while retaining the external contour.
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Select all internal contours, choose tool path - path guide
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Select all internal contours, choose tool path – path guide – curve machining group (contour cutting) – radius compensation (inward offset) – machining depth (material thickness+0.3MM) – Next step
- Select machining tool - taper flat bottom tool (flat bottom JD-6.00) - cutting direction (priority for forward milling) – Next step
- The system material library does not require any changes, simply click next.
- Processing parameters - layering method - limited number of layers - 2 layers
- Processing parameters - cutting method - vertical cutting. (Generally speaking, choosing to cut along the contour can protect the milling cutter head. However, after multiple tests, vertical cutting is also safe and more efficient, so we usually choose vertical cutting).
- If the above operation is completed, we will obtain the processing path of the internal contour, which will display a blue line in the software.
- Next, set the external contour, select all external contours, and repeat the above operation. The only difference is that when cutting the contour, choose to offset outward.
- We have obtained the cutting paths of all the lines, and you will see that all the lines have a blue offset.
- The final step in this software, export the file: Select all lines - Output tool path - Select save location - Change name. Next，Feature point - Path bottom left corner - Confirm. We will obtain a path processing file in .eng format.
2.2 Convert the format of the path file¶
- In this NCConverter software, we need to convert the .eng file format into a machine processed file（.nc）.
2.3 Machine setup, start processing¶
The final step is to adjust the machine, set the XYZ origin of the tool in the Open the NCStudio software, and start machining. The cutting speed has been tested and determined.
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Remove the dust cover so that we can see the position of the milling cutter, in preparation for setting the XYZ origin point.
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In the software, select manual mode and move the milling cutter head to the lower left corner of the material.
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We can also use the keyboard to control the movement of the milling cutter. These keys on the keyboard represent the movement direction of XYZ.
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Next, turn on the vacuum pump to keep the material adsorbed onto the machine tool. Then slowly move the Z-axis to approach the material, while rotating the metal axis. If it can easily rotate, continue adjusting the Z-axis downwards. (Warning: When Z approaches the material, be sure to set its movement to 0.1mm to protect the tool.)
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If the position of XYZ has been determined, we set XYZ to (0,0,0) in the software, then move Z upwards and turn off the vacuum pump.
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Click on the simulation and check the cutting path. The two white lines indicate that the milling cutter will process twice on this path, which is the desired effect. Next, close the simulation.
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Install the dust cover on the cutting tool, turn on the vacuum pump and dust removal of the CNC machine, click on “Start” in the software, and the machine will start working.
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If the machine is cutting materials, please do not leave the machine. Check if the cutting is done in the correct way and monitor for machine malfunctions.
2.4 Polishing and installation of wooden boards¶
- The machine cut perfectly, and it quickly, efficiently, and accurately completed the cutting. But when cutting the remaining material on the second board, we made a mistake: we actually mistook the 15mm board for the 12mm board, but fortunately, it did not affect the assembly of the project. (Anyway, measuring the thickness is very important when cutting any new wooden board!!!)
- Use sandpaper to polish the material and remove burrs from the edges of the board.
- Place the materials in an open area and assemble the wooden boards. You may need a rubber hammer toassemble the boards.
- The stool is almost finished. And surprisingly, it’s even more sturdy than I imagined, and people can sit comfortably on it.
- My unique stool (like a horse) still needs some decoration, which requires using yarn to secure the back of the stool, making it look like a horse. Do you like this stool?
Summarize¶
I used to think that using CNC was very dangerous, it could cut off a person’s arm, and I thought operating it was also very complicated. With the guidance of my teacher Saverio(♥♥♥), I quickly mastered this skill! Then I realized that it was like a laser cutting machine, so there was no need to be too afraid.
When I finished my chair, I was very happy. This practice made me completely fall in love with this big machine.
At first, I designed and made a computer stand, but I thought it was too simple, and I really wanted to make a stool for myself, so I spent a lot of time on it. But this also reminds me to prioritize completing more important things, rather than things that I personally enjoy. The FAB ACADEMY course is not an easy task, and I should manage my time well, which is also an important thing I have learned.
