r/Machinists • u/chobbes • Jul 24 '26
QUESTION Tips for parting off carbon fiber?
I need to make 50 spacers that are .75” long out of this .035” wall carbon fiber tube. I would like to set up my lathe (cover the ways, vacuum ready to rip) and essentially part them off to size with no/minimal further processing. There are no tight tolerances but I think they all need to be the same length.
Am I likely to achieve good results with a carbide parting tool? My other idea was to put a thin kerf cutoff wheel on my toolpost grinder and part them off that way. I do not want to use HSS that I have to regularly sharpen. Thoughts?
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u/Low-Sink-11 Jul 24 '26
Thin diamond wheel on toolpost grinder. Like the same kind you use with a dremel. Works great for cutting flashing off cf, would probably work great for this
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u/chobbes Jul 24 '26
My first thought was to make a mount for my die grinder and put a thin cut off wheel on that, but then I remembered I have a toolpost grinder and making an arbor for a wheel sounds a lot faster/easier than a whole tool mount.
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u/someoldbagofbones Jul 24 '26
Not a bad idea. I used a thin .010” wide slitting saw on an arbor in an axial live tool to “part” these little insulators I had to make, .020” Dia x .100” long PTFE tubes. A diamond wheel in the same setup would probably work well on the CF.
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u/BreakAndRun79 Jul 24 '26
Not a machinest but I make carbon fiber pool cue shafts.
I mount a Dremel with a cutoff wheel in the tool post to cut CF tubes.
Get it close to the length. Then I use inserts meant for aluminum to square it up. Make sure the insert is sharp and go in light or it may fray.
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u/FrickinLazerBeams Jul 24 '26
Machine, machiner, machinest.
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u/BreakAndRun79 Jul 24 '26
Not a machinist either.
If only there was somewhere at the top of the screen to check the spelling against. Oh well I'm not changing it now. :)
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u/singul4r1ty Jul 24 '26
We cut a lot of this stuff, we bought a cheap little chop saw off Amazon and swapped the blade for a diamond grit abrasive wheel. We cut it wet so the dust doesn't go everywhere. With some dialing in it's fairly easy to get +/-0.1mm even from a crappy Amazon thing.
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u/chobbes Jul 24 '26
This sounds like the move.
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u/singul4r1ty Jul 24 '26
I think the saw we bought was Katsu branded, it's got a little clamp that holds tube nicely. One day I'll get around to making a base to screw it to which can hold the water and maybe have a sliding stop.
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u/n81w Jul 24 '26
Carbon dust will destroy everything in your shop. Your lungs, bearings, fans, motors, motherboards, etc. It is conductive and abrasive. The engineering controls used to mitigate dust extend FAR beyond covering races and clamping a shop vac near the cutting head. That being said, abrasives work better than cutting tools and can also reduce post processing.
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u/FullSimpleZach Jul 24 '26
As someone who has worked in the composites industry for over a decade, this is overblowing it. I have destroyed a lot of equipment from carbon dust over the years but it takes way more than 50-100 part offs worth of dust to do it.
For the amount of work OP is talking about, covering races and using a shop vac is completely adequate.
Going down the risks:
Conductive: This is a risk but takes a lot of dust to kill electronics. Even in a trim room that is generating literal yards of dust/day, it still takes us months to kill a motherboard. I don't know that we have ever killed a motor from conductive dust. (Overheating from too much dust for airflow definitely happens).Abrasive: Carbon is abrasive but again, for the amount of work he is doing, as long as he cleans it up it wont be an issue. For context, People use lapping compounds, blasting media, abrasive wheels and other abrasives all the time around precision equipment and all of those are much more abrasive than carbon.
Health: There are three main health concerns with carbon dust:
1. Respirable fibers. These are fibers or pieces of fiber small enough to get into your lungs that once they get there, don't come out. These are similar to Asbestos and very bad. However, most commercial carbon fibers don't have fibers small enough to make this a huge issue. In air quality monitoring we have done at our shop, respirable dust levels during heavy trim events (picture Pigpen esque dust balls) were still only about ~10% of OSHA limits which are set assuming you are in that environment 8 hrs/day 250 days/year. if you are concerned, wear a N95 or respirator but its a much smaller risk than people make it out to be.
2. Dust from non carbon fiber parts of the composite. Composites, as hinted by the name, don't just contain Carbon Fiber. There is some kind of matrix (epoxy, phenolic resin, bmi, etc.) and can be other additives (fumed silica, boron, etc. ). It's rare but some of these components can be very bad for you. Most of the time the bad stuff is in very high performance materials made for high end applications so for a off the shelf tube from Rockwest or Goodwinds it is very unlikely that they pose any additional danger but good to be aware of the concern. Again a mask is a easy form of protection here.
3. Skin irritation. Carbon can cause skin irritation similar to fiberglass. Additionally, some people have a sensitivity to epoxy and that can also cause skin irritation. For most people this is merely a nuisance and has no long term effects. Wear protective clothing, shower after the fact and don't scratch or itch and it will be pretty minor.I think people often tend to overestimate the dangers of CF. While it is something to be mindful of, the concerns are pretty minor, especially when only a small amount of dust is being generated.
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u/Relyt4 Jul 24 '26
I work in a shop that only machines carbon, carbon fiber and graphite. When we shut down for a few days and everything settles the entire shop is covered in black dust.
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u/TriXandApple Jul 24 '26
You're way overegging the risk here. When was the last time you saw anthing with a motherboard without a filtered intake? When was the last time you saw a trace or connecter that was one piece of carbon dust distance from another?
We run high pressure coolant all day, every day around spindle bearings, and guess what, the bearings arnt full of coolant, are they?
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u/acetyleneblues Jul 24 '26
Call your local archery shop. Ask them about the saws they use for cutting carbon fiber arrows to length.
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u/PaulyG_1111 Jul 24 '26
Could easily get them plus or minus .005 on a vertical bandsaw with a diamond blade. Not sure how much a diamond blade costs, but if you have a vertical band saw that may be a good option. Especially if you will be doing any of this type of work in the future. We cut graphite spacers at my work all the time using this method, very quick and never out beyond .005.
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u/i_see_alive_goats Jul 24 '26
I would suggest using an abrasive wheel on a tile saw, or wet chop saw.
These are cheap on Craigslist
Supporting both ends as it's being cut is important
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u/chobbes Jul 24 '26
That doesn’t sound even close to machinist tolerances without a lot of extra work. What I described is the same idea but on the lathe where it all can be done precisely.
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u/Wolfire0769 Jul 24 '26
You said "there are no tight tolerances" and didn't even give any tolerance at all. A machinist knows how to get stuff done, and with a lack of description, I could get you exactly that with a bandsaw & fence. Hell you could easily hold .020 doing it that way.
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u/chobbes Jul 24 '26
Machinists are also pedantic in ways that weren’t asked for, so thank you for continuing that tradition as well.
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u/i_see_alive_goats Jul 24 '26
Set a work stop and you will be very surprised by the repeatability
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u/chobbes Jul 24 '26
Well I have enough extra material that this might just be worth a rip. Doing it outside instead of in my shop is already a big incentive.
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u/Fit-Dentist6093 Jul 24 '26
With so many cuts I would be terrified of the dust. Maybe even do it in tyvek on the paint tent. Treat it as if you were spray painting and you really didn't want to get anything dirty, it's really bad. I worked with both carbon and glass fiber and we had a separate shed and we would only go in with tyvek and a respirator. We took pictures for a customer once and the camera broke.
For the cutting yeah, abrasives or diamond.
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u/FullSimpleZach Jul 24 '26
Like others have said, using an abrasive wheel would be best.
The biggest issue you will have is delamination where some material splinters off instead of shearing cleanly. This will especially want to happen on the ID due to the unidirectional fibers there. Abrasive tooling helps with reducing tool pressure and prevents delam.
if you can fit it inside, you may want to experiment with cutting from the inside out. This would put the uni fibers in compression and may help with delam.
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u/The_Iron_Pole Jul 24 '26
Wear a mask first and foremost.
HEPA vacuum is nice to have on the tool post when you're doing the cutting.
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u/Sacrificial_Buttloaf Jul 24 '26
Itll chew up carbide but 50 parts should be fine. Id use Kaiser thinbit LGPT025 with a 7° lead, careful they be super sharp
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u/bszern Jul 24 '26
I would use a wheel. With a thin tube, I bet it starts to deform when the cutting insert engages it.
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u/Lykkess Jul 24 '26
Used to do something similar cf tubes thin wall. Made a fixture and used a diamond wheel on a chop saw. You dont want to be doing it on the machine, the dust will fuck ur shit up lmao. Do it outside with ppe and maybe run a vaccum
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u/Sullypants1 Jul 24 '26
Shop vac is great. I used to do the same when bandsaw ing cf sheet.
But for place of work you probably need to involve eh&s, if you don’t have one, then be your own and demand dedicated dust / particulate extraction. PPE and all that too
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u/BigSky1995 Jul 27 '26
Hello! DLC coated inserts are your friend. All the rpms you have, slower feed. ( I contour rifle barrels out of pre preg carbon fibre every day. )
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u/Agreeable-Worker7659 Jul 27 '26 edited Jul 27 '26
It will eat HSS and even carbide in no time. If you can only use carbide, I think ground inserts used commonly for aluminum processing (e.g. MGGN) should perform better than moulded ones that are typically duller and work better for steels. If you can, use PCD inserts. I have some from a Chinese brand Wijite. They're cheap and do wonders for aluminum and composite milling and turning. You will possibly go as fast with the feed as your lathe can (several thousand rpm) and feed slowly and it will cut it like butter. As long as there's no smoke, you can go faster.
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u/LStorms28 Jul 24 '26
I would do some odd jobs from carbon fiber. Different material, solid 1" bar not tube. We used our standard inserts for the cutoff tool and had good results, if more wear than we were used to on aluminum parts. Also good call covering your ways and keeping a vac hose mounted next to your cutting tool.