Creating Something Big with The CNC Router

  • Document the process for CNC Machining
  • Make something BIG.
  • The CNC machine that I am using is a PrintRBot Crawlbot. The Crawlbot can cut a piece of 4 x 8 plywood(or similiar) material. The Crawlbot is portable which requires setting up. The setup is a pair of saw horses and two 2x4's. A base piece of plywood is placed down on the 2x4. The belt of the machine is bolted across the board and goes. The plywood for cutting is then screwed down to the lower plywood. The machine is connected to the power and the computer. The computer sends the gcode to the router and then we have our piece.

    Test Cuts/ Design Rules

    Two pieces were cut as test pieces:
    1) A circle
    2) A square

    The circle was cut at 23.5". Within the margin of error of finding the diameter, it was exactly 23.5".

    The square was 18.5" x 18 15/16". It too was within a 1/16th of an inch in accuracy(i.e to the precision to which I can rad the tape measure."

    The setup is about 5 minutes.
    The machine requires GCODE, I will use Fusion 360 to generate.
    The router bit can be changed to fit your need.

    Creating Something Big To Cut On The CNC Router

    For this week's assignment, Fusion 360 was used to model the project, a shelf.
    Opening a blank Fusion360 design. Selecting Sketch. A Sketch is a 2-D drawing.
    A script was created using python. The script generates a cosine wave.Python Script
    Double check the axis direction.
    Completeing the sketch by drawing a line from the end points of the wave to the x and y axis.
    A notch was added for the vertical supports at each edge and the middle. The notch was a sketch Rectangle positioned 5 cm from edge and the width of a 1/2" board.
    The shelf was Extruded. It was stretched by 1/2".
    Made three copies of the wave shelf. Made another sketch on the vertical surface.
    Extruded the vertical shelf just as we did the horizontal shelf.
    Made extra copies of the horizontal shelf. Subtracted the horizontal shelves from the one vertical shelf so that the notches would match up.
    Copied the shelf to create three vertical shelves. Aligned each with the slots on the horizontal shelf.
    A completed shelf!


    Modeling a shelf had several difficulties. It took time to figure out the process to get a script to work. Deciding how to model is tricky and takes experience. I subtracted one shelf from the other because I wanted to try a boolean operation(cutting). I am more comfortable with Fusion 360 because of this process.

    Building a Shelf

    Fusion Process:
  • Select the piece to cut from Fusion.
  • Switch to CAM mode
  • Setup the axis under setup. Proper X and Y axis is essential for cutting.
  • Select the type of cut(2D Contour). Select Toolhead and Cutting Depth.
  • Generate/Process the GCode.

  • Setup the Router following design rules.

    Screw down the board to be cut to the wasteboard.
    Open CNC App and set the origin of the system just as it was in Fusion setup.
    Run the Code. Wait.
    Cut 3 Vertical and 3 Horizontal shelfs.
    Mockup the position of boards.
    After a little sanding. A Functional Shelf!

    Lessons Learned:

    My first cut, I forgot to lock down the wheel edge. This resulted in a misalignment on the second pass.
    The depth seemed to be inconsistent. Some of this is from slight warping in the board. Some due to the bed not being level.
    After several pieces, the process is faster and very consistent.

    Fusion 360 File

    Link to Shared Fusion 360 file

    Wave Shelf STL

    The CAM tool

    After using the CAM tool and CNC router for several projects throughout the class, I had numerous learning lessons on getting the tool set right.
    It is important to get the right speed.(I mistakenly choose a mill tool setting aimed at Aluminum once, and it was way too slow.)
    Here is the basics. It is pretty simple.
  • Switch from model view to CAM.
  • Choose setup. Position the axis where you want. The tool cuts in the XY plane. Ensure your contour is in the XY plane. Clicking the arrows changes the direction.
  • Choose 2D-Contour. Click on the bottom edge of the piece.
  • In the dialoge box, check the settings. I made a new 1/4" tool and choose the RPM to be 5000. Changing this changed the speed. When cutting, my tool cut about 1m per minute. I could adjust the RPM to make it cover more. Also need to check the speed of the router. You can increase the speed, on the knob. The spindle speed is not controlled by the program.
  • Click OK on the diaglog. Select Post-Process. Coose Generic TinyG. Your G-Code is generated.
  • I inspected the code with Brackets to make sure the dimenstions made physical since.
  • I opened Printrbot App from chrome. I positioned the router in the same location that I instructed CAM tool. At this point, I zeroed the axis. Because of fluctuations in size.
  • The depth of the machine is another issue. I zero the machine at the top of the board. I prefer to make my model larger(more depth) than the actualpiece of board. Due to warping and variations, if I cut straight there tends to be about 10% not cut through. I fix this several ways.
    1.)Instructing the board to cut deeper, by making the wood thickness greater. Some of the cut is into my wasteboard, but that is what its for.
    2.)Setting the z-axis zero in the wood.(About 0.1" below on a 0.75" board.)
    3.)After finishing the contour, it is easy to see whether or not the cut completed. Run the contour again, but manually move the router position to cut into the wasteboard.

  • Resources

    Fusion 360 tutorial:
    Fusion 360 Shelf
    Manual Nesting Tutorial:
    Patrick Rainsberry Tutorail
    GitHub Repository for Nesting Script

    Code sample adapted from:
    Autodesk Fusion 360 Forum
    Setup instructions from:
    Printrbot Crawlbot