7. Computer-Controlled Machining¶

Group Assignment Overview¶

This is the group assignment of the week.

  - Do your lab’s safety training;
  - Test runout, alignment, fixturing, speeds, feeds, materials, and toolpaths for your machine

Machine and Software¶

Because our lab, FabLab Kannai, dgitidn’t have a large CNC router, our instructor consulted with the manager of FabLab Hamamatsu and made an arrangement for us to have a hands-on local session in Hamamatsu in one day on Saturday, March 9.

Here is the details of the CNC machine and the software we used at FabLab Hamamatsu:

 Machine: CNC Router ZN1325                                                  
 End Mill: Straight, 6mm
 Software: CUT2D (for making G-code) / Mach3 (for controlling CNC)

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Safty Tips¶

Before we travelled to Hamamatsu, we took a local session online and were briefed about the general rules to protect ourselves from any risk of injuries and health hazards:

  - Eye protection 
  - Shoes
  - Clothes
  - Hair
  - Gloves
  - Facemasks

Besides, as soon as we arrived at the lab, we were briefed about the following safety tips:

Clearance of the Gantry: We will use many tools besides the CNC router. They include chargeable impact drill, screws, calipers, vacuum cleaner, PPE, and so on. Some of them are big enough to interfare with the X-axis or Y-axis movement of the gantry. We should return those tools to their original place as soon as we finish our work witho those tools.
Clearance of the CNC Bed: Similarly there is a high risk that we leave screws in the ditches created on the CNC bed. They should be removed as they may damage the bit.
Path Interfarence: We usually drill screws for work-holding. Those guide holes should be placed as near as possible to the work, but we also have to make sure that the toolpaths for profile cutting would not interfare with those screws. Otherwise the bit will be damaged by the screws.
We should always keep an eye on the progress of CNC cutting.

Workflow¶

The workflow from CAD data preparation to CNC milling in the FabLab Hamamatsu is described in the following figure.

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Translation of the workflow of FabLab Hamamatsu written in Japanese

Cut2D could read not only AI files, but also SVG and DXF files. However, when we tried to import the SVG files to Cut2D, the outlines of the CAD data missed the original size. This unexpected error seemed to have been reported by other Cut2D users and it had not been rectified yet. When we made the data in terms of AI file with Adobe Illustrator, the outline data was placed on the work plane without losing the size information.

Another point to note is that when we save the AI file, we should select the file version as “CS”.

Materials¶

There are a few DIY stores in our neighborhood in Japan such as Cainz, Kohnan and Valor. Some shops even offer extra services to cut the board on the spot so that the materials could be accommodated and brought back home in the customers’ vehicle. Or they offer a rental service of their pickup track for transportation. There were a few varieties of the boards in the shop. For the sake of individual assignments as well as group assignments, we picked up the falcata board. It’s one of the lightest wood materials.

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The two photos in the bottom were provided by Masato Takemura of FabLab Hamamatsu.

This is details of the material for our group and individual assignments:

 Material: Falcata
 Thickness: 12mm                                   
 Size: 910mm x 1,820mm x 2 pieces

Test Cutting¶

1. CAM on Cut2D¶

Here are the steps we have taken to make g-code data.

  1. Launch the Cut2D program;

  2. Select "Create a new file" as a start-up task in the first dialogue window;

  3. In the new dialogue window for "Material Setup" on the left, input the data:
      - Width: X-axis length of the board we brought (910mm);
      - Height: Y-axis length of the board we brought (1,820mm);
      - Thickness: Thickness of the board we brought (12mm). Put the top serface of the board as a zero point in the Z-axis;
      - XY Origin Position: Be sure to appoint the front left corner of the board as an origin on XY plane;

  4. In the new dialogue window for "Drawing" on the left, click "Import vectors from a file" icon and import the AI file;

  5. Be sure to have the design data on the workplane;

  6. Click the "Toolpaths" tab on the righthand side of the workspace, and then the new "Toolpaths" dialogue will be popped up;

  7. Select the toolpath type (hole, pocket or drills) in  the "Toolpath Operations" dialogue;

  8. Set the parameters in the "Toolpaths" window, and then click "Calculate";
      - Cut Depth: 12mm (for cutting) / less than 12 mm (for pockets)
      - Tool Diameter: 6mm
      - Machine Vectors: Outside / Inside / On the toolpath

  9. The workplane will automatically be switched to 3D View. By clickng the 2D tab, return to the "Toolpaths" window.

  10. Select the toolpaths for the cutting profile and for drilling pockets, and save each file one by one in terms of G-code.

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If the profile for cutting is very small, the cutout may start bouncing as the milling process reaches the final stage. This bouncing may cause us to miss the accuracy of the board size. To avoid this, you could add “Tab” to the last sequence of the toolpath. In the “Toolpath” dialogue, click “Add tabs to toolpaths” in the 2D profile toolpath. After recalculate, save the g-code data for the revised 2D toolpath.

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2. Cutting with Mach3¶

Once we completed creating the g-code data for all the toolpaths, we moved to the milling operations on the Mach3 program. First, we placed the board, work in CNC’s terminology, on the CNC bed. Then on the desktop PC, we took the following steps:

  1. Turn on Mach3;

  2. Set the XY origin:                                                                     
     - By pressing up, down, left and right keys, move the spindle to the front-left corner of the material;
     - By clicking the "Zero X" and "Zero Y" on the control panel, XY origin is set;

  3. Set the Z origin: 
     - By pressing up and down keys, move the endmill down to the material. Plase a sheet of paper to check;
     - By clicking the "Zero Z" button on the control panel, Z origin is set;

  4. Load G-code: Click the "Load G-code" on the control panel and select the target g-code file;

  5. Click "Cycle Start" (Green Button) on the control panel to start the machine operation.

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Safety Tip: While the CNC router is on operation, keep pointing the mouse cursor to the “Stop” (Red Button) on the control panel to be ready to stop the operations as soon as the trouble is detected. We could shut down the operations by pressing the red button, too. But in this case, all the information about the origin will be deleted and you have to start with setting the origin.

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3. Tips for Work-Holding¶

For 2D woodworking, we have to ensure that the material, or work, should be laid flat. But the work is always bent and we should make it as flat as possible. There are many ways for work-holding: pasting them with double-sided tape, clamps and screws. Among these different measures, screws are likely to be the most effective measure for work-holding. Even if the work is bent in the middle of the width, we could make it flat.

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However, if we drive the screws at random placing, there is a risk of the screws interfaring with the toolpath of the profile. To ensure that the screws are placed in the neutral positions, we were advised to drill a screw hole in advance.

    1. On the Cut2D, we first draw center-diameter circles for drilling; 
        - Select the drawing tool and draw circles on the workplain:
        - The circles should be placed outside the profiles, but near to them;
        - Select all the profiles;

    2. On the Cut2D, we click the "Toolpaths" tab and open the dialogue;
        - Select the toolpath type as drills;
        - Then calculate;
        - Select this toolpath and save the g-code.

    3. On Mach3, set the XYZ origin and initiate the drilling operation.

During this first drilling, we don’t have to hold the work onto the CNC bed. Once all the holes are created, then we drive a screw at each of the holes.

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4. Test Cutting¶

Now we drew 50mm x 50mm square on Cut2D and went for test cutting. We followed all the procedures described above. We set the machine vector to go along the outside of the square.

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On the next trial, we set the machine vector to go along the inside of the square, and confirmd that the width of the square was around 38mm x 38mm, 12mm (double the diameter of the endmill) smaller than 50mm.

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Tab and Pocket Test¶

During the local session, we were briefed about the Dogbone and T-Bone Fillets that will help the tab and pocket perfectly fit without any glue. For the detailed description of the fillets and how to add fillets to each corner of the tab and pocket, please see Koji Yamada’s individual assignment page.

We cut out the components of our design for individual assignement and applied both Dogbone and T-Bone Fillets on Fusion360. After making SVG data for all the components, we placed all of them on the artboard of the Adobe Illustrator and made an AI file for Cut2D.

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SVG files: Dogbone Tab / Dogbone Pocket / T-Bone Tab / T-Bone Pocket