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Computer-controlled machining

Week 7

DESIGN OF THE MODEL



For this week, I decided to do a rocking chair in plywood. For this I started by drawing in 3D in Rhinoceros the model I wanted for my chair.


To save on the material - plywood, I wanted to optimize the parts of the chair such as: the side pieces, the seat and the back, so that they fit into just one big plywood plate or two small plywood plates, depending on the size of the CNC machine.


To draw the chair in 3d first I made a rectangles with measures 60omm x 80mm which were the measurements of the wooden board. Then as I wished there was no waste of material I thought to use a minimum of wooden board putting the seat and the. Chair weights on the same plate.


With the "pencil" tools I made the contour of the chair, sometimes using the "fillet" and "blend crv" tools to smooth the contour. Then just click on the "extrude" tool to get my piece with the thickness I wanted.



In the pictures and animation you can see the final design of the chair.


All parts of the chair fit by pressfit, without need of nails or tails.

CUTTING





Now is the time to cut the wood and produce my chair!


The FabLab where I am does not have a full size CNC, so we went to a digital workshop to do this part of the process.



In this space there is a large CNC with the size of the platform: 2100mm x 1600mm.As you can see from the figure.



First you need to export your file in vector format dxf.





There are some important notes before you start cutting:

  • Be aware of the work area of the cutter 2120 mm x1600 mm;

  • Exto, holes, areas and shapes cut sketch can be machined separately, generating different NC file codes;

  • In the areas where the grooves will be, it is necessary to keep in mind and to think if the drill is going to cut in the top or the outside of the trait that we designed so that in the end all the pieces fit.





  • Use the machine

    1- First you must choose the type of wood you want to use.


  • I chose plywood with 15mm thick.




  • 2- Then you must hold the wood in the machine.


  • In this case we put a wooden board underneath by clamps and by vacuum
  • And then we put our wood on top studded with screws.
  • In this way our wood will be well fixed, and the cutting of the cutter will not damage the platform of the machine




  • 3- The third step is to select the 0 point of the machine.


  • The point was chosen manually, and it was chosen to set 0 as the center of the wooden board.





  • Use the ArtCam program

    We use the Autodesk program call ArtCam, to open the .dxf file, and define the cutting areas, and CNC machine settings


    If you want more about this program, click here:

  • AutoDesk ArtCam

  • This program is easy to work and is accessible to anyone.



    ArtCam has drawing tools that allow you to make small changes to your drawing, if necessary.





    Before starting to set the cutting tools and settings you need to check:


  • If the drawing is a fully closed drawing
  • If the drawing lines are not overlapping





  • Then you should define in the program settings:


  • Material thickness: 15mm

  • Profile: Outside

  • Do sharp corners

  • Cutting Depths: 16 mm (0.025mm tolerance)

  • Tool: 4mm milling cutter

  • Add.Bridge: 2 (with 5mmx5mm)

  • Save toolpaths





  • Profiting tool:

  • Tool number = 10 (choose the milling machine on the machine that corresponds to the desired one)

  • Feed rate = 5m / min

  • Stepdown = 5mm

  • Steppover = 2mm

  • Punge rate = 1m / min



  • Then you must select the lines whose cut is outside and place them in a layer as an indication "outside"

    And the lines whose cut is inside a layer with the name "interior".




    Then it is to export both layers to a g-code file that will be read by the CNC machine.



    When opening the G-code in the CNC machine opens in the ino.control program, which allows to visualize the path that the machine makes, above the lines of the drawing.



    The code is sent to the machine, which took about 1 hour to finish all the cuts.




    When the pieces were finished, it was necessary to smear the corners to have a better finish.


    I had a problem with the fittings, because I gave the dimension of the fittings equal to the dimension of the thickness of the wood, so it did not fit.

    So I had to sand more in that area so that the pieces fit together.




    Remember that it is necessary to give a tolerance of 1mm for each side in the fittings!

    FINAL PRODUCT


    I'm really pleased with the end result of the rocker chair.





    My Rocking chair is done and swings!!



    :)

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