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Mill slot in carbon Fiber Tube

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  • Mill slot in carbon Fiber Tube

    I need to mill a 9" long x .312" wide slot in a Roll wrapped Carbon Fiber Twill tube. The tube is 1.250" x 1.00" ID.

    Actual one I purchased:

    https://dragonplate.com/carbon-fiber...4-gloss-finish


    Not sure How to go about this without destroying it. Carbide, HSS, single pass to size, multi pass with small endmill?

    Or should I be looking to cut with a thin cut off wheel on a grinder by hand?

  • #2
    I would go for 5/16" carbide end cutting mill if you can tolerate a few thousandths oversize with the slot. A test slot on a surplice length of 1" long would be a good idea if possible. Depth increments of 1/16" at a time rather than full penetration at once. Your greatest problem is holding the tube without distorting it over at least 15".
    For an exact width, a 1/4" cutter down the centre followed by 1/32" extra each side (measured from the centre line).
    I forgot, use a vacuum cleaner to suck up the dust as you make it.
    Last edited by old mart; 10-23-2018, 12:40 PM.

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    • #3
      The big problem is to cut it without pulling the fibers away from their bond around the edges. I think you're looking at a small solid carbide end mill running very fast for the best results. Like 1/8" or at most 3/16" and spin that puppy up to max speed. Solid carbide instead of HSS just because what I've read about carbon fiber and my results from cutting arrow shaft size pieces with a razor saw tells me that it's hellishly abrasive to the cutting edges. I ruined a razor saw blade in just the few cuts needed for a project. Took the set right off the teeth. And the last of the 8 or 10 cuts I made the blade was more or less wearing its way through instead of properly cutting.

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      • #4
        Check out router bits for carbon fiber. You will find they look a lot like rotary files. https://www.amazon.com/fiberglass-ro...20router%20bit

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        • #5
          Originally posted by Illinoyance View Post
          Check out router bits for carbon fiber. You will find they look a lot like rotary files. https://www.amazon.com/fiberglass-ro...20router%20bit
          That's a great find ! ! ! ! I'm going to order up a pack of the 3.175mm (1/8") rotary files to use on my Dremel for various things.

          I can see where these rotary files would also limit or avoid the fiber tearout too.

          Note too that there's lots of information out there on the toxicity of both carbon fiber dust as well as epoxy dust. And the file teeth will try to fill up. So a small air jet to keep the carbon tube cool at the cutting point and to clear the dust from the cutter teeth would be a good idea. But at the same time a good strong vacuum with a HEPA filter pulling away that cooling air and dust would be just as good.

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          • #6
            I ride a carbon bike, but that's the extent of my experience. I was under the impression that cutting through the fibers nearly eliminates the strength. Whenever I see structures with holes or slots the fibers always seem to be wound around that feature. What's the truth?

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            • #7
              In addition to the above comments, I would add to put a 1" wood, delrin, or aluminum bar on the inside for support, maybe with a premachined slot for tube cutter clearance.

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              • #8
                Originally posted by Toolguy View Post
                In addition to the above comments, I would add to put a 1" wood, delrin, or aluminum bar on the inside for support, maybe with a premachined slot for tube cutter clearance.
                Even a slightly larger force fit plug of blue or pink styrofoam that needs to be pushed in through a flared mouth fitting or some slight bell mouthing of the actual carbon tube. A slip cover of parchment paper or old style wax paper would allow such a firm force fit plug to be easily pushed along the tube to the location of the slot to be cut. Not sure how much larger than the ID to make the foam but a bit of playing around would quickly tell you. Anything that pushes out against the fibers firmly to aid in their support during the cut would be a good option.

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                • #9
                  I was recently considering carbon fiber plate for a project, and it was around the same time I saw some photos on Instagram of parts Robin Renzetti was making for his repeat-o-meter out of CF, so I e-mailed him to ask his advice. He talked me out of it for my project, but perhaps his response will be helpful here:

                  Quoth he: "I have very little experience with it but here is what I think I know so far. It's abrasive but seems not as bad as G10 epoxy glass. There are cutters designed specifically for it but a good carbide end mill will work ok for a while. I surface ground most of what you saw on instagram using diamond wheels. you have to watch for delamination from cutter forces. IMO don't use it unless you really need to and use a good vac right at the cut."

                  EDIT: My mistake, it was not parts for his repeat-o-meter he was making from CF, it was parts for what he calls his "Renzometer".
                  Last edited by mars-red; 10-24-2018, 09:04 AM.
                  Max
                  http://joyofprecision.com/

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                  • #10
                    As the others said.
                    I was at a plant where our 3-4 biggish VF4/6 machines were machining CF 16/day for years.

                    My feel is similar to router cutters for finishing .. but might be 100% wrong.
                    I really, really do not know.

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                    • #11
                      I had to slot a piece of carbon fiber tubing for a friend a few months ago, used the carbon fiber router bits mentioned above after plugging one end of the tube, filling it with water, standing it upright in the freezer for a couple of days until it was frozen solid then milling it.

                      The ice supported the tube nicely, and kept the fibers from breaking out on the inside of the tube, after the milling was done, just let it sit in the sun until the ice melted out.
                      Steve
                      NRA Life Member

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                      • #12
                        Originally posted by chipmaker4130 View Post
                        I ride a carbon bike, but that's the extent of my experience. I was under the impression that cutting through the fibers nearly eliminates the strength. Whenever I see structures with holes or slots the fibers always seem to be wound around that feature. What's the truth?
                        I love my bikes too. Hence my username.

                        Carbon bikes are a bit of a different animal. We're talking a highly stressed frame that uses the least possible amount of material in very smart ways. And that's why almost any damage to the frame... and ESPECIALLY to the fork.... can cause a catastrophic failure.

                        To illustrate... there's an old trick of standing on a pop or beer can. If the can has no dents at all and you put your weight on the can very evenly it will hold you up. Then while you're on the can have someone lightly tap the side of the can with a pencil. Be ready for the big let down... . And that can is like the legs of your carbon fork. And that scratch that goes through the clear coat is like that tap from the pencil. And you crashing is like you crashing.... but face first instead of feet first.

                        But I'm guessing that sen2two is not using this tube in a way that the major load will be supported by the portion of the tube that has the slot cut into it. Or that it will be stressed to that sort of high load for the tube in question.

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                        • #13
                          Originally posted by RetiredFAE View Post
                          I had to slot a piece of carbon fiber tubing for a friend a few months ago, used the carbon fiber router bits mentioned above after plugging one end of the tube, filling it with water, standing it upright in the freezer for a couple of days until it was frozen solid then milling it.

                          The ice supported the tube nicely, and kept the fibers from breaking out on the inside of the tube, after the milling was done, just let it sit in the sun until the ice melted out.
                          A superb idea! I'm going to put that in the back of my head for some time in the future.

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                          • #14
                            You can "wire" EDM carbon fibre plate. Maybe sink type EDM also works. There are some simple homemade sink type systems around.
                            Helder Ferreira
                            SetŮ’bal, Portugal

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