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7. Computer controlled machining

Assignments in this week

Group Assignment:
- [x] do your lab’s safety training
- [x] test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

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

Group Assignment

In this week’s assignment, we spent more time than usual. The main reason is that the operation of large CNC machine tools is much more difficult than cutting PCBs with small CNC machines. In fact, we all know that the working principles are similar, but the size of the machine still brings some psychological fear to everyone.

Safety Training

  1. Learn the components of CNC machines: The machines in Chaihuo Makerspace are composed of three parts: control computer, machine tool, and air dust processor.
  2. Selection and use of cutting tools: Since the current CNC machine has been equipped with the corresponding cutter head, we used an 8mm wood board milling cutter this time.
  3. There are many safety tips on the machine. During the training process, we also invited a professional machining teacher to guide us in our operations.
  4. Pay attention to dust prevention: During operation, since our equipment is in a city, we must use exhaust emission and dust treatment devices due to municipal air emission requirements. In addition, you need to use a vacuum cleaner to clean the work surface before and after each operation to ensure that the work surface is clean and tidy.
  5. Electricity hazard: During the operation of the machine, it is prohibited to touch the operating surface with your hands to avoid being injured by splashes from tools or processing objects.
  6. Emergency Stop Button: In the event of any emergency during operation of such a large machine, everyone needs to know where to find the machine’s emergency stop button.
  7. Protective measures: Since there will be a lot of dust and noise during CNC processing, protective glasses and noise-cancelling headphones must be worn. At the same time, you must also wear a mask when cutting wood boards and materials with a lot of dust.

About the CNC machine

Regarding the large-scale CNC machining part, we actually delayed it for a long time. The main reason was that we had not used this equipment for a long time and there were some problems with the software and drivers on this equipment. When we wanted to contact the machinery manufacturer, we were told that the brand manufacturer had gone bankrupt. So now we only have the following parameter information to try to repair the device.

Specification of CNC machine

Specification Details
Machinery manufacturer 天成鑫力数控
Machine model 3STX-1325A
Platform size 1450mm * 2900mm
Engraving range 1300mm * 2500mm
Z-axis travel 180mm
Feeding height 200mm
Positioning accuracy ±0.15/300/mm
Spindle speed 0～24000 (r/min)
Engraving instructions G Code, UPP, mmg, nc
Idle speed 0～20000mm/minute
Processing speed 0～15000/minute
Resolution 0.00625/pulse
Tool diameter 3.175mm, 4mm, 6mm, 8mm, 10mm, 12.7mm
Spindle power 3KW water cooling
Cooling system water pump
Actual weight 2200kg
Machine power supply 380V 50Hz (built-in switching power supply)
Body configuration 8mm thick T-shaped steel bracket
Z-axis hanging plate U-shaped cast aluminum, CNC processing
Y-axis side wall all cast iron, CNC processing
Lathe bed 8mm steel structure, CNC processing
X-axis carriage full cast aluminum, CNC processing
Cross beam 8mm steel structure, CNC processing
Bed support 6mm, steel structure

Here is the machine user manual in our Chaihuo makerspace.

Testing the CNC machine

  1. Place and position the processing material: Since the processing size of each CNC processing machine tool is limited, we need to place the test processing material flatly on the processing plane. At this time, we need to keep the processing material the best Keep parallel and consistent with the processing direction of the machine tool.
  2. Use the computer to set the processing origin: Before each processing, you need to check the processing origin of the machine and check the processing origin set in the processing file at the same time. The processing origin contains data in three axes:
    Note: Since the CNC machine in our laboratory has not been used for a long time, the Y-axis limit sensor of the machine tool guide rail failed, which resulted in us being unable to use the zero point setting tool of the machine itself. We can only manually set and adjust the zero point of the machine to ensure the processing size. Do what we want. Special attention needs to be paid to safety at this time.
  3. Set the feed speed of the tool, and using the existing G code, we can see the machine start processing. During the processing, if any emergency occurs, you need to press the emergency stop button.
    During the processing, we can also see the processing progress and tool path on the computer screen.
  4. Inspection after completion of processing.
  5. Processing rules: We found that CNC machines can only process outer right angles, but not inner right angles. This is because the principle of processing cannot be avoided. Therefore, when designing, you should avoid designing internal right angles or drilling and cutting internal right angles.
  6. Processing error: The CNC processing error is relatively small. When our designed processing width is 18.5mm, the final processed product is almost 18.1mm. This error is within the acceptable range of our design.

Make a cabinet

Originally I wanted to design a simple, smaller size design, such as a cat and water basin holder. But I gave up in the end, just because my desktop was messy and I needed a small cabinet for the desktop as my final design..
In the design part, I first designed the support surface of a desk using parametric design. Because I didn’t know the thickness of my CNC-cut board was 18.5mm in the early stage, so I made the board thickness parameter adjustable.

Step 1:Design via Onshape

  1. Through parametric design, subsequent adjustments can be easily made to deal with post-processing fit issues corresponding to different plate thicknesses.
  2. After designing each component, preview the finished product in 3D for installation. In total, my design requires 4 parts, but the number of parts to be processed will be repeated.
  3. Export the design file to step format or dxf format to facilitate subsequent processing.

Step 2:Preparation on Mastercam X6

I briefly learned some basic introduction and functions of Mastercam online. The main process of using it was that we specially invited a teacher to help us with training.
MasterCAM X6 is a version of the MasterCAM software, which is a leading CAD/CAM (Computer-Aided Design/Computer-Aided Manufacturing) program. It is used primarily for designing parts and programming CNC (Computer Numerical Control) machines to manufacture those parts. Here are some key features and capabilities of MasterCAM X6:
Design Tools: MasterCAM X6 offers a suite of design tools that allow users to create complex 2D and 3D models. These tools include wireframe, surface, and solid modeling capabilities.
Toolpath Generation: The software can generate precise toolpaths for CNC machines. These toolpaths dictate the movement of the machine tools to shape the material into the desired form.
Multiaxis Machining: MasterCAM X6 supports multiaxis machining, allowing users to create toolpaths for 4-axis and 5-axis CNC machines, which are essential for manufacturing complex parts.
Simulation: It includes simulation features that allow users to visualize and verify the toolpaths before actual machining, reducing the risk of errors and material waste.
Post Processing: The software has post-processing capabilities to translate the toolpaths into machine-specific code that CNC machines can understand and execute.
Customization and Automation: Users can customize the software to suit specific needs and automate repetitive tasks through scripting and macros.
Compatibility: MasterCAM X6 supports various file formats for importing and exporting designs, ensuring compatibility with other CAD/CAM systems and tools.
MasterCAM is widely used in industries such as aerospace, automotive, medical devices, and consumer products, where precision and efficiency in manufacturing are critical.

1.Cutting methods setting

  • Profile milling
  • 2D grooving
  • Surface milling
  • Milling slots

2.Tool parameter setting:

  • Tool name:xxxx
  • Tool number: 1
  • Tool diameter: 8mm
  • Knife corner radius: 0
  • Length: 10mm
  • Number of blades: 4
  • Type: flat knife

3.Spindle parameter setting:

  • Spindle direction: clockwise
  • Feed rate: 5000
  • Spindle speed: 15000rpm
  • Cutting speed: 500mm/min
  • FPT: 0.0833
  • CS:377.0028

4.Cutting parameter setting:

  • Profile milling method: 2D
  • Correction method: computer
  • Correction direction: right
  • Calibration position: knife tip
  • Maximum processing depth: 0.05mm

5.Margin setting:

  • Wall margin: -0.1mm
  • Bottom margin: 0mm
    In addition to the first time, there are actually Z-axis layered milling, advance/retract parameters, penetration, XY-axis layered milling and other parameter settings.
    These parameters need to be adjusted and set according to different processing materials.

6.Common parameter settings:


- Origin/reference point: X, Y, Z axis origin of the machine tool; position and coordinates of the tool

- Arc filtering/tolerance setting: overall error 0.025mm

- Minimum arc radius: 0.2mm
- Maximum arc radius: 10000mm

Step 3:Import Design file & Output G-code

1.Check and fix design files on CAD

First, you need to check that the processing line segments in the generated DXF/STEP file are continuous and have no breakpoints. Otherwise, you need to repair the file again and complete the breakpoints.

2.Layout processing design files

Arrange the processing files on the computer. In order to save processing materials and improve processing efficiency, we arranged the personal designs of the entire team on three boards. This can be done faster. We chose a 1.2*2.4m piece of 18.5mm thick black density wood board as the processing material. The arrangement process takes a long time and requires a lot of experience. We also invited experienced engineers to help us complete this step.

3.Set drawing zero point

After the arrangement is completed, the processing zero point needs to be set. Because the processing zero point of our machine tool is in the lower left corner, at this time we need to ensure that the processing range can cover the entire board area, and it also tests the installation and positioning of the board.

4.Generate processing drawings

After we check that the processing file is complete and complete the processing software settings according to the previous step, we can generate the processing file in the last step.

5.Set the workpiece processing sequence

Import the files we need to process and place them in order. Because the size of the board we are processing is 1200mm*2400mm, it is best to draw a border to position and place the workpiece.
First, we need to set the processing sequence. Because we have multiple workpieces to process together, we need to arrange the processing sequence.

6.Preview tool machining path

After setting the processing sequence, we can generate the tool path. At this time, we can see on the picture that our workpieces are processed from the first workpiece to the last workpiece in the previously arranged order, and we can clearly see the starting point of the tool being processed. and the path of travel.

7.Last step to confirm

The most important step is that we need to zoom in on the pattern to see that the path of our tool must be around the periphery of the workpiece being processed, because the path of the tool is based on the center axis of the tool.

8.Complete step-by-step video

The full progress wil shown as following video.

Step 4:Milling via CNC machine

1.Place proceesing board

First, place the processing board. We used an oversized black MDF board that required many people to lift and carry to the processing machine.

2.Location the board

Use mounting clamps to secure the board and position the board size at the appropriate location.

3.Adjust processing zero point

Use a computer to manually adjust the mechanical zero point of processing. Since the layout we are processing is relatively large, we need to accurately control the processing of the board within the processing range, otherwise there will be a problem of the tool processing exceeding the range of the board.

4.Turn on air processing machine

Before turning on the machine and starting processing, be sure to turn on the exhaust gas treatment and dust removal device of the CNC machine.

5.Confirm/review processing setting

I started processing after previewing the machining path on the machine, and you can see the tool’s path of cutting progress.
- At the same time, make sure that the machine parameters set are the same as the processing parameters of the previous software.
- This part of the content can be viewed in the G Code window of the computer.

- Machine Cutting Data Parameters - The following are some data parameter settings for the machine when I cut:
- Cutting board size: 1200mm * 2400mm
- Cutting board thickness: 18.5mm
- CNC cutting feed speed: 5000mm/min
- CNC cutting spindle speed: 20000rpm

Below are some photos and videos of the process.

6.CNC cutting

After the processing is completed, be sure to use a vacuum cleaner to clean up excess dust and impurities to ensure that the table is clean before proceeding to the next page processing operation.

Step 5:Assembling the cabinet

Because my board was cut out first, when we got the first board, everyone was excited to discuss it.
The final board I cut is as follows, the final cutting effect is very good. The gap tolerance is just enough to complete assembly and fit.
But since my previous design used internal corners, I had to use a file to do the internal corners after the final cuts were made, otherwise I couldn’t fully assemble the work.
The trimmed boards are hammered together with a rubber hammer to make the finished product.

Hero Shot

The finished product is as follows. I left the partition on the middle layer uninstalled, which helps to place larger items directly, because I originally designed it to prevent my MacBook 13-inch laptop. So the size of this partition is just right.

Group showcase

Design Source

CNC- Assembly by crail.lyu on Sketchfab