Router Bit for CF?

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Jan 19, 2009
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I plan to use my router table and a fin template to cut three fins out of CF plate using a 2 flute straight router bit with ball bearing guide. Now I don't expect this bit to last a long time, but I hope long enough to cut 3 fins. Will this bit work ok? Does anyone know where I can get a better bit with ball bearing guide for this purpose?

Depend on the thickness of the CF your cutting.

To be honest I don't think I'd use a router to cut CF because of the Dust/shard problem. I've always had much better dust and fibre control using a fine thickness bi-metal blade and Band saw than anything else. Ya really don't want to be putting Carbon fibre shards in the air. They can float around for much longer then expected and become very harmful.
And they conduct electricity, so if they float into your computer or main electrical panel... :eek:
I'll be doing the cutting outside. Still need to make a little jig to hold the vacuum directly over the work and also a dust collection basket under the table. I have a very nice dust mask also.

Thanks for your replies,
Unless your bit was carbide, I'd expect it to get pretty chewed up pretty quick. Can you use a grinding cutter rather than a blade cutter?
All router bits have carbide in varying amounts. I don't know of any grinding cutters with ball bearing guides for the router. The bit I plan to use is relatively cheap, so I'll easily be able to replace it when it wears out. I thought of getting one of those up cut spiral flush trim bits, but the one I found is $60 for the 1/2" shank. The 1/4" shank version is $30 and I am thinking that that one will result in less CF dust.

We're talking about Solid carbide router bits, Which can be had in just about any configuration and bearing combination needed. MOST HS rotor bits contain only trace amounts of carbide which will be rendered nearly useless in very short order. You attempting to cut an abrasive materal with a material it's ment to remove.
You really need to rethink this. There are so many Better ways to accomplish what your attempting to do that will be SO much better for YOU and everyone around you.
Wear a mask and you'll be ok...except for the splinters you may get in your fingertips. The splinters in your fingers hurt but are otherwise harmless. I would definitly invest in a solid carbide router bit that has helix cutting edges instead of straight flutes. You'd probably be OK with doing just the three fins but if you wanted to do many more you'd want the helix (downcut) bit. Regarding machinery, the dust is hard on it and watch your feedrate as most routers max at about 3K RPM.
I think you mean an upcut spiral bit. In a table mounted router, you want an upcut bit, which is down on a table. I am not going to be cutting a lot of carbon fins, just the three.

I made a test cut in a spare piece of carbon plate I made using two sheets of unidirectional carbon. As you can see in the photo, the edges are a bit frayed from the straight laminate trim bit I used. My question is, would a spiral bit do a better job?


A router will work just fine on carbon; just make sure you're keeping a vaccuum on it to suck up the dust while you're cutting.

In terms of the fuzzies you're getting, I'm not sure why that's happening -- we've cut slots in layups of unidirectional CF with a router without that happening.

I made a little jig to put the vacuum as close as possible to the bit. Maybe my bit is a bit too dull? Should I spring for a spiral bit? The 1/4" version is $30 and the 1/2" is twice that.

It's fuzzing because you are not cutting the fibers. Your particular laminate may be too thin to cut in this fashion or it may not be properly consolidated. The sheet just ahead of the cut is probably bending up and allowing the fibers to fuzz and bend out of the way. If your laminate is not properly consolidated a spiral bit will not help.

Is your sheet fully impregnated? If your laminate is dry, the fibers will bend and fuzz out of the way rather than being sheared off by the cutting edge.

Is your resin compatible with your fiber? If you don't get good bonding between fiber and resin, the fibers will fuzz rather than cut cleanly.

Is it pre-preg material or are you wetting out dry fiber with resin? If it was pre-preg I'd say your consolidation pressure was too low. If it's manual resin impregnation, you might not be getting enough resin in there.

Just looking at that photo, your laminate looks dry.

I don't know if it's properly consolidated or not. Maybe if I described the process I used to make it you could possibly tell me?

The epoxy used was West System 105 epoxy to 207 hardener, which has a 30 minute pot life. The CF sheets have carbon all in one direction on one side and at a 45 degree angle to those on the other side and all held together with what looks like kevlar thread. A 3" paint roller was used to apply the epoxy to the CF on both sides. I made sure the CF was thoroughly saturated. Three sheets of the CF were pressed together between one sheet of release and 2 sheets of breather per side with two 3/8" thick steel plates as the vice. A screw and large wing nut at each of the four corners of the plates was used to tighten the plates just to the point of bending. Any more tightening and the cured CF would have come out curved. The plates, which are painted flat black on one side, was placed in the sun to cure.

The CF in the picture was made with 2 sheets. Also, the frayed carbon is at the surfaces.

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Where are the edges of the plate in relation to the cuts? Was the raw plate much bigger than the fin or were you just trimming it up a little bit? If your clamps are around the outside edges you may have squeezed all the resin out right there and ended up dry around the edges. If you are cutting in the dry zone, then the fuzz.

You said the resin was applied with a roller, so there was resin on the sheets and between the sheets, but was there resin "throughout" the sheets? Did you roll resin on or did you roll the resin up through the sheets?

I'm surprised there aren't more people chiming in with their favorite methods.

Some more photos:

A 3 layer CF plate and the fin template. (Plates are a bit under 1/8" thick.)

The press I used to make the plates. (Steel plates are 12 x 12 x 3/8")

Another view of the press.

The press is made of two 3/8" steel plates.



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With your process, assuming you're wetting out the carbon sufficiently, it should work fine.

I do have a question, regarding temperatures. How warm is it where you're doing this? West Systems epoxy doesn't like to get 120F, so it you're somewhere really warm, and you're setting it out in the sun, it's possible part of your problem is that you're exceeding the Tg of the epoxy, reducing its strength.

Well, looking at the latest closeup it doesn't *look* dry. If you use a spiral bit, the fibers will probably cut cleaner on the top side, but might fuzz worse on the bottom side.

Are you using a bleed ply, peel ply, or smooth release ply? Your surface looks rough and textured. In the composites lab here, that look comes from a silicone-impregnates fiberglass fabric peel ply.

Kevin, are you sure about that temperature? The container says that, if the resin forms crystals, it should be heated to 125 degrees to get rid of the crystals, but that's for just the resin alone. During curing the epoxy probably got to at least 150+. It feels plenty strong when I try to bend it.

I used peel ply, it is white and feels like some kind of plastic. I do not know the exact type. I think I got it from ACP composites. The wavy lines you see in the photo is probably the kevlar thread.

Well, I've got a spiral upcut bit on the way, so we'll see how it turns out with that bit.

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Kevin, are you sure about that temperature? The container says that, if the resin forms crystals, it should be heated to 125 degrees to get rid of the crystals, but that's for just the resin alone. During curing the epoxy probably got to at least 150+. It feels plenty strong when I try to bend it.

I'd have to find the source of that number; can't remember where I found it, in the past.

Resin versus cured epoxy are two very different things, BTW.

If it's not brittle when you try to break it, then it's likely fine.

Well, I've got a spiral upcut bit on the way, so we'll see how it turns out with that bit.

Definitely worth a try!

Well, the spiral bit came apart shortly after starting my cuts with it. The part at the top that holds the bearings on came off. The initial cuts seemed about the same as with the straight bit.

So I went back to the straight bit I was using before. The router stopped working partway through cutting the first fin! I'm not sure what happened, but I'm guessing that the router motor burned out. There was a funny smell coming from it that I can't describe. Could I have been going too fast? Maybe this particular carbon is too strong? Does anyone know what might have happened and how I can avoid it again in the future?

Carbon Fibers are electrically conductive and abrasive. If you got some into the motor of your router, it might have caused your failure. Shielding the router and/or using a vacuum cleaner together with your router should help in this case.

STOP F-ING AROUND WITH THE ROUTERS AND BITS! All I kept thinking as I was reading is why does he keep using a router? I fit all composite panels with a jigsaw or bandsaw. Granted when I cut CF I use a brand new blade it works ALOT better than a router. Trust me, ive tried.

Bandsaws are invaluable for cutting tubes and fins and rings out of composites and woods etc.

For all flat composites with straight line cuts, I use a wet saw with diamond blade. For curved lines, I use a metal bandsaw. Don't try a bandsaw with a wood cutting blade, it will remove all of the teeth in the first second of cutting.

You can use a router with the right bit. You need an endmill with upcut flutes. I've got one on a small home built CNC machine. But the motor is above the part being cut and the dust is being vacuumed away. If you get carbon into the motor, it's toast.

Mike Fisher
Bosch sells an attachment for vacuums that could go under the table. Right now the vacuum is above the table.