Carbon fiber composite fins

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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!
 
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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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.
 
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
 
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.
 
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.
 
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.
 
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).
 
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.
 
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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