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Wayne State University’s Warrior Racing recently needed to machine a sheet of Nomex-honeycomb carbon fiber, a piece of a scratch-built custom steering wheel. It’s a bit of a challenge machining the stuff since it’s an extremely hard fiber suspended in a soft synthetic. After a few experiments, we ran everything at very low feed rates and ridiculous spindle speeds, which is a bit contrary to popular wisdom when machining hard materials.

Carbide is the cutter of choice, in the four-flute flavor, just like machining steel. The same goes for feed rates — right around 2.4 inches per minute seemed to be a sweet spot with a 5/8 in. end mill and maxed-out 3000 RPM spindle speed. Without a CNC system, the feed rate will be hard to match precisely, and there aren’t any chips whose colors can tell you to speed up or slow down.

Speaking of chips, the leftovers from machining carbon are nasty. Fiberglass and carbon weave are nasty enough, but this stuff is coated in epoxy and comes off in unbelievably thin spear-like flakes. The latex gloves the machinists wear are a must, as is a respirator and a vacuum to remove as much dust and as many flakes as possible. Even so, I managed to get a few wicked splinters when cleaning up the part edges. Oh — wash your hands before you use the bathroom afterward.

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8 Responses to Reader Tips: Machining Carbon Fiber

  1. Shopmonger says:

    YEAH gumming up is an issue, but carbon fiber is great…….
    The mast of my father boat is made of this and boy does that make the riggers happy……..

    65 feet of fiber……fun fun

    ShopMonger

  2. Mike47 says:

    Is this increasing or decreasing your carbon footprint?

  3. Mike P. says:

    I machined a few pieces of carbon-Torlon composite, and carbide tooling wears out FAST!

  4. Jaxx says:

    Always best to tape the gap between your gloves and your overalls with masking tape, dont know how you can bear it when sanding otherwise.

  5. Mag Machine says:

    You might try using water as a coolant and PCD index able tooling.
    This is industry standard for Aerospace composites.
    the Poly Crystalline Diamond cutters will last longer than carbide and the water will keep the epoxy from over heating in addition to keeping the dust down.
    if you are using CNC equipment you need to keep that dust away from your electronics! :)
    If your layup is other than vacuum infusion you may need to “cook” off the water before attempting a secondary bond.

    Food for thought. :)
    Brady

  6. jimmy says:

    water jet is still the best for CF/Nomex honey comb.

  7. DocN says:

    “Is this increasing or decreasing your carbon footprint?”

    -Well, since it’s essentially sealing the fibers into an epoxy matrix, it’s a form of carbon sequestration. :)

    Bet’cha you didn’t think all those tuners and tweakers with carbon-fiber hoods and shift knobs were being all eco-friendly, did ya? :)

    Doc.

  8. Shopmonger says:

    Doc = Now that is awsome but so true…..until they crash because they have no idea what they are doing, then they release it into the hillside,

    ShopMonger (i;m still laughing that was awesome DoC)

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