Cutting Carbon Consistently

I've been making carbon fiber rings for 3-4 years now as a maker. I've made over 10,000 carbon fiber rings by hand myself. I've taught 4 people to do it and helped give advice to countless others. Carbon fiber rings is what I do. It's all I do. I love it. It's my life. I'm pretty good at it at this point. Okay, you get it, I'll stop hammering that part home that I've got some experience. 

Here's the thing. I know some very experienced ring makers that struggle with machining carbon fiber. It's not the same as metal. It's not like wood or resin. First, I'll explain how to cut it, then I'll explain what to look for and how to know what you're doing wrong if you're still having trouble. I'm going to add some pictures at a later date. 

Here's the bullet pointed version first of how to turn carbon fiber rings but most of the information applies to other machining techniques too. 

  • Turn fast. I spin at 2500 rpm which is as fast as my little mini lathes (I have 4) will go.
  • No autofeed. Don't use autofeed, it cuts too fast. Manual feed.
  • Shallow cuts. I try to never take off more than .5mm. It's more than possible to cut deeper, but start slow. 
  • Use water. Water helps with cooling carbon. If the carbon is too hot to touch, it's too hot. 
  • sharp bits. make sure to use sharp bits.
  • Holesaw. Use diamond holesaws or abrasive holesaws. Use water while cutting
  • Sanding. Wet sand. Wet sand. Wet sand. start with 80-120 grit and end around 1000-2000 grit and use a polish compound. Mother's mag/alum polish works well. Clay bars work well too.

Okay so here's the deal with carbon fiber and why I suggest cutting this way. Carbon fiber is a temperamental material to work with as a maker. Carbon fiber can be made with different resins and different forming techniques that lend itself to a variety of ways to cut it. It's safe to assume that you're turning a plate that was infused or went through a wet layup with epoxy resin that is crystal clear. There's wonderful tooling resins out there that handle heat better, but they tend to look less attractive on the finished product as tooling resin isn't clear. This is why I order from typically. I know a decent amount about his raw plate construction and it's always consistent. I'll talk more about that later. 

Carbon fiber itself acts as an inductor. It absorbs heat. It's black and when you cut, it causes friction that heats the material up. When it gets too hot, the resins start to break down and liquify. The resin soaked up by the individual fibers will be the last to break down so it will retain its shape for a while, but eventually it will completely delaminate and at that point the carbon looks like it has exploded. Before this happens, you can see that between the fibers and layers of tow of carbon fiber, that there are little pockets. Usually like a long diamond shape but only .25mm wide and maybe .5mm long. Usually smaller than that, but with heavier fabric you'll find bigger voids. That is because the resin liquified and is now gone. You've overheated the carbon. It's savable by tinting your resin with carbon dust and reapplying it into those voids, but if it's too bad, it'll never look the same again. This happens when you holesaw with metal cutting blades, or when you use a dull cutter, or dry sanding, or cutting too deep or too fast, or not using water. There's tons of reasons for this to happen. 

Finally is your choice of carbon fiber. Cheap carbon will turn like cheap carbon. If it wasn't infused properly, you may find voids, or the lamination process wasn't effective enough and the carbon will delaminate no matter what you do. I use almost exclusively because of the quality of carbon fiber he offers. It never has voids. Voids are the death of a cosmetic carbon fiber maker and can cause more overheating/delamination problems. Plus, who doesn't like luxury grade, designer carbon fiber that looks better than almost anything out there. 

Reasons your carbon fiber fails from overheating. 

  • dull bits. use sharp bits always. I use the triangle cutters. 
  • no water. the carbon got too hot, use cooling. Lots of water. 
  • holesaw not cutting or getting too hot. Use diamond holesaws or abrasive (60-100 grit) holesaws. Use water. Cut slow. Use a drill press with a strong motor. my drill press is a 15 amp drill press and I have it set to spin at 2250 rpm. 
  • cutting too fast. If you're cutting too deep to fast, it can over heat. Don't cut so aggressively. Cut passively. lol.
  • Autofeed. Turn autofeed off unless you want to do each pass at like .25mm or less. 
  • Sanding. Don't sand dry. Use water and wet sand. Automotive sandpaper does wonders. 
  • Touch your carbon often. Touch your carbon after each pass until you get the hang of it. If it's too hot to touch, it's too hot. 
  • Turning speed. Don't turn slow. I turn at 2500. That's as fast as my lathe goes and I don't ever feel like I need it to go faster and I never slow it down. I actually bypassed the potentiometer on one of my lathes so that it just goes 2500 rpm or it's off. There's no in between. 

Okay next, fiberglass/carbon hybrid fabrics. Designer carbon fiber is fun because it has colors, glow, and other things infused right into the plates. I order a ton of stuff with metallic fiberglass and hybrid carbon/fiberglass. The main difference in using those materials is that those materials tend to heat up quickly, delaminated a tad faster but they cut like butter. You can definitely tell the difference in strength of the fibers between carbon fiber and fiberglass. Fiberglass cuts like a dream. So easy and effortless. Carbon fiber feels like it pushes back. It takes more finesse. It's really fun to feel and it really makes you appreciate the invention of carbon fiber itself even more. That being said, the only thing to worry about with fiberglass variations is that they do delaminate easier, though they don't explode like carbon. They just delaminate. In many situations you can relaminate them back together with some epoxy and a solid vice clamp. When cutting fiberglass and carbon/glass hybrid fabrics, use water and don't cut too quick even though the fiberglass will let you. 

So to recap. cutting carbon is tricky but it's fun. Go slow but turn fast and use water. water for every stage. If you have any questions. Fill out the contact form and give me an ask. Happy to help. Happy turning. 


1 comment

No matter what I do when I turn the carbon fiber on my lathe I can not seem to find that happy medium with heating it up too much. I will always randomly get a puff of smoke even when going very slow and using water..

Stewart Mowery March 02, 2020

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