Creating the Coupon (Composite Sample)


Partnered with Fab Lab veteran, Adesola Holmes to create a composite. We planned to make a hard-case shell for small, flat electronics. We created a coupon first by cutting out linen corners to wrap the shape of the foam block.


Vacuum Bag Workflow:
  • cut mastic tape and bent in folds to form corner seams
  • cut out breather in the complete square to cover the linen
  • cut out release film to match breather
  • cut plastic to cover the surface of work table
  • cut out top layer of plastic larger than the bottom layer to accomodate creases for vacuuming
  • insert valve inside of bag before sealing; carefully poke a small hole matching the valve hole to insert tubing connected to the vacuum generator; wrap tightly each connection with mastic tape to make airtight; wrap the tape around some of the plastic bag leading up to the tubing securely
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    Laid out all materials to be used for coupon creation:

  • epoxy mix
  • nitrate gloves
  • linen sheets cut to fit material (fiber) - also: fiber layers need to increase in size overall to cover the object during the vacuum process, an example would be if you wanted to use 3 layers of linen; your 1st layer might be 15 square inches, the 2nd layer would be 16 and the 3rd layer 17inches
  • release film
  • mastic tape
  • shears (really sharp scissors)
  • breather material to go under suction valve for vacuum hose
  • 2 plastic squeegees
  • 2-3 plastic cups
  • 2-3 wooden paint mixing sticks
  • extra hands for help!
  • giant zip-lock plastic cut to cover table work surface
  • 2 aprons to protect clothing
  • watched short video on making seams in plastic for complete vacuum suction on objects
  • This link shows how the coupon workspace was prepared BEFORE we started the wet layup process.

    We also rehearsed (acted out how to actually go through the wet layup process, using the dry supplies)) at least 3 times before actually mixing the resin, applying it to the fabric, folding it around the foam, placing it in the bag, and finally using the generator. Lots of thorough communication is needed to get this done in less than 90 minutes, so if you have a large piece and you're working with a partner, COMMUNICATE.

    Hero Shots

    Completed Coupon: Bottom and Top

    Designing the Composite:

    Following Holmes' lead, I had to figure out OpenSCAD. We reviewed images of hard-case shells via Google and proceeded to use the Minkowski script to combine a cylinder and rectangle:

    I found an Instructables link to help us get started in the design process, because I have no experience with scripting design programs, except for the time I taught myself how to use AutoCAD 10* while still in high school (that book was bigger than the dictionary!).

    We exported the OpenSCAD file into Partworks v.3 to create a toolpath for the Shopbot to follow when machining (cutting) the insulation foam we were to use for our composite:

    Here we had to create a toolpath and select our bit for the foam. Again I took to Google to look up an online forum stating what settings to use for machining house insulation foam (purple):

    1. Cut Depth: 1/2 inch
    2. Feed Rate: 6Ips
    3. RPM: 9000
    4. Plunge Depth: 6
    5. Bit chosen, named and saved: 1/2 Bit with 4 flutes
    6. Tips:

    7. Use a bigger bit, or drill, to move faster.
    8. If the bit gets clogged with foam, dip it into acetone to clean it, then dry it with a soft, dry cloth (use gloves!).
    9. Plunge depth matters more when carving or engraving.
    10. Make sure your file name is saved with the extension .sbp, or the Shopbot won't cut your file.
    11. After calculating the toolpath, be sure to preview your settings to view how your object will be cut out of your material:

      Shopbot Workflow:

      Due to my inexperience with this machine, I had to run back and forth between editing my Partworks file and the Shopbot to make sure the my part of the case (the top) would machine out:

      1. Pass depth needed to be adjusted, as a previous cut drilled slightly into the base layer (the sacrificial board).
      2. The Shopbot must be zeroed on top of the base layer then moved up, I couldn't just edit the settings in my design file.
      3. My piece had to be re-saved into a new file and moved closer to the origin of the material in Partworks.
      4. 2 C-clamps were used to hold the insulation board in place towards the end of the bed.
      5. Where my piece was to be machined out, carpet tape was used on the side that would meet the base layer to hold it in place while being machined, as was with Holmes' piece:
      6. Laser Cutting the Fiber (Linen):

        I designed paper patterns to reinforce the corners for both our pieces in CorelDraw v.5 (now that I finally know how to use it without turning into an ogre) and corner flaps for my piece (the top).

        I used the laser cut settings that were recommended for linen with the Epilog Legend 75watts, but discovered that conditions weren't exactly correct for precise application to my piece. I simply ran the same job to cut the linen until it cut all the way through as the work day was ending and I was running out of time:

        Preparing the Composite Wet layup:

        We followed the same steps as we did in preparing the coupon composite. The only difference was that we almost used the entire 90 minutes (the potlife time for the resin to be applied and used in the vacuum before it's no good) to get through the wet layup process for both our pieces. We used 3 layers for the sides that mattered and an additional 3 layers per corner, using our linen fabric tabs.

        This video shows how I applied resin to my piece.

        This video shows how Holmes and I finished assembling the valve while placed inside of the bag and how quickly the generator works when turned on:
        We had a few leaks that we were able to find and seal, so our composites can out great - especially Holmes' piece. I need more practice. A very special thanks to our lab coordinator, Zuberi Moore, whose extra hands definitely were needed when making the vacuum bag for the coupon, and helping to find and seal the air leaks for the final composite!