Carbon fiber composite fins

PenitantTango

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Hi everyone,

I've got a project in the works that's going to have carbon fiber fins for a high power flight (~10,000 ft on an M COTS motor). I had our school's composites lab lay up 2 sides of unidirectional carbon and sandwich a 1/4" cardboard hexagonal support before putting it in their autoclave. Any tips on ways to precisely cut out our fin shapes? I'll be posting pictures of the sheets when I get back to my lab tomorrow.

Thanks!
 

Steve Shannon

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Make a template out of 3/8” or 1/2” MDF. Do whatever you have to to make it perfect in outline, but don’t bevel it. Use it to mark the CF for rough cutting. Cut the CF about an 1/8 inch larger than needed.
Stick your CF material to the template with double stick tape.
Then use a trim router with a small pattern following bit to trace around the MDF template.
Wear hearing protection, eye protection, and a respirator. Carbon fibers carry with them an element of risk.
 
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pondman

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Make a template out of 3/8” or 1/2” MDF. Do whatever you have to to make it perfect in outline, but don’t bevel it. Use it to mark the CF for rough cutting. Cut the CF about an 1/8 inch larger than needed.
Stick your CF material to the template with double stick tape.
Then use a trim router with a small pattern following bit to trace around the MDF template.
Wear hearing protection and a respirator.

Do not forget safety glasses at a minimum & preferably a full-face shield.
 

manixFan

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And a very good dust collection system, preferably a wet trap. Even a shop vac with some water in it works well to trap the CF particles. CF dust is really hard on things like electric motors in addition to lungs.


Tony
 

PenitantTango

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Our next door carbon lab has a masonry saw with a wet trap setup. Last year with single layer prepreg sheets I used a dremel with a metal cutting bit along an outline I measured from OpenRocket, but couldn't get a very straight line or sharp corners freehanding it. Safety gear was ear muffs and a full face respirator with a teammate holding a vacuum right by the cutting bit (also helped we were outside) Also, and idea how to fillet the ends of the fins? Planning to do a through the wall assembly with another wet layup of CF around the fin can.
 

OverTheTop

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Not sure how the cardboard core would work with the wet methods suggested here.

When cutting CF plate I generally damp things down and do a rough cut with an angle grinder, outside the cut line. I then take it to the line with a belt linisher and vacuum cleaner.

Cutting by hand will raise less dust, but CF really blunts hacksaw blades :(. I did my last set of fins that way but used multiple blades to achieve the outcome.
 

RocketFeller

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We used a Dremel "SawMax" tool with a carbide grit studded blade to cut our carbon fiber parts. It is sort of like a cross between a circular saw and a rotary tool and worked great. we used eye and dust protection and did it outdoors, I certainly wouldn't use it inside except with a quality dust collection system.

To edge the fins you can use hardwood strips, G10 strips, or even thin carbon fiber. We used a .25mm CF veneer to edge our end-grain balsa cored fins.
 

JohnCoker

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The best way to cut out any flat material is a CNC router. Since you have a composites lab with an autoclave, you may also have access to a router. That said, precision isn't really important for fins; slight variations in size won't make a difference.

sustainer-fin-cores.jpg


The fins above were cut from 1/16" CF plate using a 1/8" carbide end mill on a CNC router (ShopBot desktop).
 

amarillo_rocket

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I also like using a CNC router for CF. If you do have access to one make sure it has good dust collection. You will get carbon dust all over the place without one.
 

AlphaHybrids

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The best way to cut out any flat material is a CNC router. Since you have a composites lab with an autoclave, you may also have access to a router. That said, precision isn't really important for fins; slight variations in size won't make a difference.

The fins above were cut from 1/16" CF plate using a 1/8" carbide end mill on a CNC router (ShopBot desktop).

+1 to this method. I cut all the carbon fiber thrust washers I use on a CNC router.

Edward
 
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