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8. Computer controlled machining

This Weeks’ Task:

Group assignment

  1. Test runout, alignment, speeds, feeds, and toolpaths for your machine.

Individual project

  1. Make something big on a CNC machine.

Group Assignment

Here is the link to our group assignment.

Individual Assignment

To start of this week, the students of FabLab Bahrain participated in an opening of an exhibition which involves showcasing different types of birds found in Bahrain. Therefore, we thought of producing these birds using the CNC machine. Each of us will have to choose a bird and design a 2D sketch of it, to produce a 3D model and cut it in the CNC machine. We visited the Bird of Bahrain website, which includes all the lists of migrated and non-migrated Bahraini birds, and from here, we get to choose one bird and model it. The bird I chose was the ‘Pied Kingfisher’. Here are some images of it:

I combined some of the parts from these images to design my bird. I imported the images in Inkscape and traced them.

Steps to import and trace

  1. File>Import

  2. After importing, select the image and click on Path>Trace Bitmap. The following window will appear.

  3. I played around in the ‘Single scan: creates a path’ settings until i got the best trace out of the image. You can look at the preview whenever you change the settings by clicking on ‘update’ at the bottom of the window. Once you’re happy with the tracing, click OK.

  4. The other way of tracing is just by using the below tool. I found this easier since I just wanted the outline of the bird.

  5. The outline of the bird.

Creating offsets and details

  1. Click on the outline and go to Path>Linked Offset. A node will appear at the top of the sketch. Grab the node downwards or upwards to create offsets from the shape.

  2. I then wanted to create the details of the bird’s face. Click on the line twice and all the nodes will show. Then I grabbed them to the directions that I want to adjust its features.

  3. To join, delete, break any node, hover your mouse along these tools and choose the one you want. You can find them at the top of the page. Just select two nodes by using the shift button and then click on the desired tool.

  4. I broke the path here by using the above mentioned tools and then joined the nodes together since I only want to create an offset for the body.

  5. Select the image and go to Path>Break Apart to break the image in two parts. Delete the unwanted piece.

  6. Create as many offsets as you wish.

  7. For the joint, I drew a rectangle and placed it at the cente of the sketch.

  8. Duplicate the rectangle by selecting it, Edit>Duplicate. The dublicate will be placed exactly on the old rectangle which will hardly be visible.

  9. Select the rectangle and one of the offsets together by using the shift button and then go to Path>Combine. This will combine the two parts into one part.

  10. Move the combined part away. The dublicate will now be shown at the exact same position of the previous one.

  11. Repeat steps 8 to 10 for all the offsets.

  12. I traced the rest of the bird’s body and created the joints the same way as I did. Below are my entire documents in different formats in which I used for CNC/laser cutting.

Download SVG file

Download PDF file

Download DXF file

Laser Cutting

Before cutting with the CNC, we thought of testing how the model will turn out to check whether all the parts will fit in together properly. If not, we adjust the sizes before using the CNC machine. The material for the laser cutting was matboard and below are the settings used.

I faced some issues while trying to assemble the bird with the joints since they were small and weak. The joints were made for 3mm due to the thickness of the matboard. Once slight pressure is applied to them, they immediately break or detoriate. Therefore, I stuck the entire bird with glue gun. However, I did find out that the joints and the other fittings were at right size and the right location. There were only some slight things, which were:

  • The length of the tail: I made it longer
  • Depth of wing fittings on bird body: I increased the depth since the wings are big and I wanted it to fit properly into the body for better stability.

CNC cutting

The material used for CNC is High Density Fibreboard (HDF) and the thickness I used for my bird was 8 mm. Before cutting, we caliberated the machine to set the X,Y,Z origins.

  1. Before starting, we set the sacrifising board.

  2. We placed our desired board on top of it. The thickness board that I used was 8 mm.

  3. This is the bit that we used.

  4. We set the origins of the machine by using the program. This was to set X and Y origins.

  5. This is to set Z origin.

  6. Using the VCarve software, we entered the settings as per the material we are using.

    The speed and the feed rate was chosen according to the datasheet that comes with the machine. Here is the datasheet that we referred to. We also referred to the guide provided by fabacademy.

  7. Then I did auto nesting to fit in all my sketches without wasting as much material and started cutting.