Carbon Fiber Feeds and Speeds and more

How To Machining
1

I have just been presented with a small project to cut a 5 mil piece of carbon fiber. Flat piece about 8"x14" or so.

What would be the best:

  1. Feed and Speed rate?
  2. Endmill?
  3. Depth of cut?
  4. Anything else to consider?

I know that I should make sure I have respiratory protection.
Is a water bath really needed?

2

See:

which is listed at:

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You can get by without a water bath IF you are really dang sure you have a powerful vacuum that is HEPA rated. However, having additional ventilation/filtration in the shop doesn’t hurt. And if you want to be extra safe, wearing a respirator while cutting isn’t a bad idea.

Joe @ BPS Space has probably cut the chunkiest piece of CF I’ve ever seen on a Shapeoko, and he takes full precautions with regards to respiratory hazards.

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I know that carbon fiber dust is hazardous but what makes it so hazardous. Is it the fine dust or the carbon or both? Is carbon fiber also a fire hazard?

5

BPS’s project is cool, but I think I got them beat…and on a 4Pro. :crazy_face: The material was 24"x24"x0.5" and is a headrest extension for a $4,500,000 cancer zapping machine.

I also did the clamps for the extension to the table on the HDM. The material was 7"x3.5"x1".

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Preface: I worked at Boeing for a decade in CNC and the 787 composite fabrication and assembly areas. So we got plenty of training on composite hazards.

From a health perspective carbon fiber and fiberglass dust are akin to asbestos. The tiny fibers get in your lungs and they get encapsulated in the tissue. They then become an absolute breeding ground for cancer.

When I cut composites here’s what I do:

  • Well ventilate the area. At work we have a huge vent I run to get airflow. At home I open the window and garage door, have fans running, and turn on the shop air filter with a 1 micron filter.
  • I have a 3M P95/OV rated respirator.
  • Run the Sweepy at as much an optimum height as possible.
  • Have a cyclone dust separator that is well sealed.
  • I have a shop vac that was tested to be well sealed. It has a HEPA cartridge filter and a HEPA collection bag. So it is double HEPA filtered.
  • After I’m done I leave the shop open and ventilating for an hour or so.
  • I really should get air quality monitors in my shop and the basement where I have 3D printers. :slight_smile:
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According to this NASA report, not as bad as asbestos, see page 2-10. Still, not healthy to breath in the dust.

https://www.google.com/url?sa=t&source=web&rct=j&opi=89978449&url=https://ntrs.nasa.gov/api/citations/20150012180/downloads/20150012180.pdf&ved=2ahUKEwi9hMWPmdCLAxX2DHkGHbT9ADEQFnoECB8QAQ&usg=AOvVaw2UdOBqxDLatqshbTPrHQcI

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Thus my use of the term “akin”. :slight_smile: It’s in the same category, and has most of the same engineering, control, and PPE requirements. I’d rather people think of the specter of asbestos than them thinking something benign.

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I have been cutting carbon fiber plates for the last 3 years on my SO4 XL. I use 1.5 or 2mm carbide burr bits for a variety of thickness material. Usually cut between 1-6mm carbon 3k carbon sheets. Cyclonic dust separator with a shop vac using hepa filters and a bag. I’ll wear a basic mask when handling the carbon after the job but when it’s cutting, I don’t usually wear a mask. The dust collection does it’s job well.

1.5mm Bit:
1.5mm DOC
300mm/m
24k RPM (go higher if you can)

2mm Bit:
2mm DOC
400mm/m
24k RPM

You can do the typical 1/2 of the diameter of the bit for your DOC and increase your feeds but I find I lose some accuracy as I go faster on the machine. Might be the small diameter bits flexing. Slow and steady with a minimum of 2 passes seems to yield the cleanest cuts for me.

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