Cutting carbon fiber - inconsistent results

After having practiced the CAM art and having tuned the machine on wood, I’m finally trying to cut carbon fiber (3k, twill weave, 2mm thick sheet) but cannot get a decent job done. I’m using a 2 mm ball nose, two-flute upcut bit, 1/8" (3.175 mm) shank. My spindle maxes out at ~12.000 RPM but the last 1k makes it whine and shake a little, so I usually run it at 10.000 RPM tops.

I’m cutting 3mm deep to compensate for the ball nose bit - that’s the only 2mm one I have at the moment, I’ll order some PCB/fiberglass milling (diamond pattern) bits soon.

Here are some pictures of my workpiece. The pieces underlined in red belong to the first cut, the ones in yellow to the second; videos of the first cut are included:

Feed Plunge Speed DOC
1st cut 5 mm/s 1 mm/s 9000 RPM 1 mm
2nd cut 2.5 mm/s 0.5 mm/s 10000 RPM 0.5 mm
The first cut broke the bit right at the end of the job, so I thought that I was trying to go too fast. Slowing down made the second cut a little cleaner, but there still are signs of flex/slop and this time the bit did not even make it through the CF. After the cut the bit was cool and the spindle was not overheated.

The material is rather stiff, but it is plausible that it flexes down when the bit plunges and hence the problems with the cut’s depth, especially when restarting after an holding tab - should I come up with a better fastening solution, maybe a support in the center?

Can anybody point me in the right direction to start getting half-decent results?

P.S.: @vicious1, how can Imgur albums be embedded here? I’ve tried by injecting the embed code via bothe the post’s source and media embed dialog, but it won’t work.

CF is durable and flexible. I think you have two issues going on. Your part is flexing. That’s going to cause issues no matter what. You should try to create a slightly smaller wood support to go underneath the CF. Then determine if you are dulling your blades. Carbon Fiber is used in bullet resistant body armor. Its probably dulling your blades. Get a strong, quality magnifying glass and look at the new bit and used bit after a single cut. I think you’ll discover significant wear. Perhaps a good liquid lubricant to cool the bit is needed. Also, I would go with three 1mm passes and see if that helps make a better, cleaner cut. FYI, they make high quality chef’s knives from CF too. It’s just like cutting steel. These machines aren’t designed for cutting steel.

To recap, its your material, not your machine causing problems. I’m guessing you suspect that already. Good luck.

Uhh, no. They don’t make chef’s knives out of carbon fiber. They make them out of ceramic, but not CF.

@Niccolo, you’re using the wrong kind of end mill for CF. You need something like this.!45331!US!-1

Cutting CF should be doable, it is more aggressive on the bits but it shouldn’t (practically) be much harder to cut than fiberglass or pre-made PCB plates. I now think that my problems reside on using the wrong bit and the sheet not being supported in the middle.

Thanks, I’ve ordered some proper bits - I’ll retry the cut in a few days when they’ll arrive. Do you think think kind of bit is also suitable for going ~1mm deep into a wooden spoilboard? What about a 3D-printed one (PLA)? Being forced to work underwater is really pushing my newbie skills with the machine :slight_smile:

With those bits you should be able to do full depth of cut through the CF. I’m not sure on what you should use for a spoil board though. You don’t want to use wood, it will move(swell) when submerged in the water. You could probably hot glue some foam insulation to your pan. Though if those standoffs you have in your video are working, I’d keep doing it that way.

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The situation improved, I’ll post updates on the other thread.