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  • Carbon fiber

    Anyone had any experience milling carbon fiber? What type of tooling to use etc?
    I have a leg brace that is really causing me pain to the point that I can't wear it but about 15 minutes at a time, and I really need it all the time.
    What I think I need to do is mill a slot in the front of the brace to relieve the pressure on my shinbone, I know carbon fiber is formed and cured under heat and pressure, but I don't know if milling on it will reduce it's strength,
    or if it will break in use after milling it.
    I know I shouldn't be asking for medical advice on a machinist's forum, but I've been back to the orthodist 2 or 3 times and all he does is put a small foam pad on it, and it still hurts after 15 minutes or so.
    olcop

  • #2
    haven't done it myself, but seen it.....its very abrasive and don't breath the dust....very high speeds and a carbide cutter. Should be lots of expert advice a google away. OT will be here in a minute and save the day.
    .

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    • #3
      your not asking for medical advice your asking how to mill CF --- it's not like your coming on here telling everyone your balls hurt or something

      anyways - Carbon Fiber is tricky and can "catch" too depending on the piece thickness and the ability to hang on to it and stuff,,, but if you want a safe bet then use a little abrasive wheel,,, and yes use a mask of some kind...

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      • #4
        Originally posted by olcop View Post
        Anyone had any experience milling carbon fiber?
        Yes, I have had excellent results with single flute carbide cutters using a ramped profile cut, I used the feed & speed data for GRP from HSM Advisor as a starting point,

        - Nick
        If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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        • #5
          If your going to slot the thing to get relief would a bridge peice stabilise the now cut moulding? I've only ever cut the stuff with a grinding wheel, was very untidy btw
          Sorry your knee is playing up, one guy in work had the same he used the leg off a wet suit for support, seemed to work better than the elastic things you buy
          Mark

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          • #6
            I haven't cut it. But I'd lean toward a diamond pattern cutter. A seller I buy from has a good variety and reasonable prices. If you can't wait, then use whatever you've got - you don't need to maximize pieces per tool bit, etc. Other tool forms will also work, and may be better.

            http://stores.ebay.com/CARBIDE-PLUS/...0&_sid=2877033

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            • #7
              Originally posted by boslab View Post
              If your going to slot the thing to get relief would a bridge peice stabilise the now cut moulding? I've only ever cut the stuff with a grinding wheel, was very untidy btw
              Sorry your knee is playing up, one guy in work had the same he used the leg off a wet suit for support, seemed to work better than the elastic things you buy
              Mark
              It isn't my knee unfortunately, I had about half my right foot amputated a few years ago due to bone cancer, and this a new prosthesis that I can't wear due to the pain it causes.
              And I've been back to the orthodist a few times but he can't or won't fix it.
              olcop

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              • #8
                The carbon products I've worked with played very nicely with regular wood working hand tools. The carbon doesn't wear the saw teeth terribly fast. And it sands well with regular sandpaper. Regular fine to medium TPI hacksaw blades used either in a frame or with a pulling cut by themselves or in a half blade handle also cut carbon composites easily and cleanly with little fuss.

                What can occur quite easily is that the teeth exiting the cut on the back side can catch and rip fibers out of the matrix when near the surface. This ripping or running can extend onto the part you don't want damaged. So a "stop groove" on the line you want and then making the actual thru cut on the waste side of your stop groove is a safe way to proceed. The stop groove can be cut with a Dremel cut off wheel or narrow grinding wheel easily. But because high speed will make the epoxy of the matrix melt into the grinding surface I'm going to suggest a slow speed operation for the wheel or narrow wheel. I think it could also be done with the corner of a flat file or with the edge of a "D" shaped "half round" file nicely. It only needs to be around .01 to .02 deep to avoid the catch and run issue.

                I know that the cut off wheel and high speed is often offered on model airplane forums. But the one time I tried it the results were smelly and nasty to look at and I had to file and sand quite a lot away to leave me with a presentable edge. Using hand tools only on subsequent jobs with carbon worked far better for my tastes.

                The dust isn't good for you so do this outdoors and even then wear a decent dust mask. It's not only the carbon dust. The epoxy dust has equally bad if not worse concerns.

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                • #9
                  Depending on how it is constructed, you can severely weaken it.
                  Normally you would use pcd coated cutters.

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                  • #10
                    I concur with bc riders suggestions. I have worked with carbon fibre and epoxy layups for many years on custom boats and low speed with a foredom or dremel and cutoff wheels work well for slotting. A bit of sanding with fine emery paper and a touch of epoxy on each edge with some clear packing tape applied over the wet epoxy will leave a smooth finish.
                    Have fun with the brace.
                    steve

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                    • #11
                      Originally posted by Magicniner View Post
                      Yes, I have had excellent results with single flute carbide cutters using a ramped profile cut, I used the feed & speed data for GRP from HSM Advisor as a starting point,

                      - Nick
                      Please explain what you mean by "ramped profile cut".
                      Any products mentioned in my posts have been endorsed by their manufacturer.

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                      • #12
                        Originally posted by olcop View Post
                        It isn't my knee unfortunately, I had about half my right foot amputated a few years ago due to bone cancer, and this a new prosthesis that I can't wear due to the pain it causes.
                        And I've been back to the orthodist a few times but he can't or won't fix it.
                        olcop
                        Ah I understand, my sympathy for what must have been traumatic, there's not much flesh on a shin, particularly when your older, the leading edge is very sensitive I know, the socket of the prosthesis must be tubular so I can see as the calf muscle flexes it's going to tighten on the shinbone, rather than cut the thing I'd be tempted to take it to a different prothetic engineer, if that's what they are, and see if it can be modified or reworked as everyone has said it can be cut with conventional tools, abrasive disks, water jet, but it would loose its integrity or hoop strength, so may flex in ways not helpful, I know the socket is bias laid to give strength so how cutting that works I have no idea, but instinctively it doesn't sound good!
                        Mark

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                        • #13
                          Originally posted by winchman View Post
                          Please explain what you mean by "ramped profile cut".
                          A profile cut is one which follows a profile.
                          A ramped cut is one where the tool is lowered further into the work as the tool moves in X and/or Y
                          If you benefit from the Dunning-Kruger Effect you may not even know it ;-)

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                          • #14
                            You might try sending an inquiry to these people: http://dragonplate.com

                            I've machined a very little bit of the stuff -- I put a couple of strips into a mandolin neck for stiffening -- and didn't have any particular trouble. I found it cut readily with a hacksaw. It machined well with a carbide end mill. It's sort of like very splintery wood. Fibers may pull out on the exit side of cuts unless they are backed up with a piece of scrap aluminum or something for support.

                            It does make a mess, and apparently it's bad to breathe. I had a vacuum cleaner going when I machined it under power, and wore a dust mask.
                            ----------
                            Try to make a living, not a killing. -- Utah Phillips
                            Don't believe everything you know. -- Bumper sticker
                            Everybody is ignorant, only on different subjects. -- Will Rogers
                            There are lots of people who mistake their imagination for their memory. - Josh Billings
                            Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                            Don't own anything you have to feed or paint. - Hood River Blackie

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                            • #15
                              It also does depend what type of CF it is - for instance certain tubular CF is actually very fragile stuff and designed for strength in just one direction yet can split very easy - cross linked tubular CF on the other hand is very durable stuff and will resist this.

                              layered cloth type is pretty good at being able to take some abuse from multiple directions but can de-laminate where the layers stack.
                              besides the difference in the material itself fiberglass is very similar with all the different structures and linking processes involved,,, how much do you need to remove?

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