RunRyder - cnc'ing carbon parts for hornet...need hints

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CAD - Engineering - Technical > cnc'ing carbon parts for hornet...need hints

mattijs

Senior Heliman - Location: Keerbergen Belgium -

Okay, here's the deal...i am a complete cnc noobie (i only ever did my own name when I was studying for engineer).

I modeled these parts in autocad and simulated them with cnc viewer mill. (this picture is dated so my models are now somewhat more refined and perfected but that doesn't realy matter)

It is suppose to be 1.5 mm carbon.
The things on the upper right corner are tailblades for my hornet, the other parts are also for the MS hornet.
The blades have a naca profile and should be 1.6 mm back to back.
The machine i am gonna use is a really really big one, but that's about all i know about it...oh yeah , the smallest drill???? i can use is 3mm diameter so my whole drawing is made to accomodate that thickness

IS THERE ANYTHING I NEED TO KNOW ABOUT CNCING CARBON OR WILL IT WORK FOR SURE IF THE DRAWING WORKS ON A TEST BLOCK OF WOOD???

01-29-2004 Over year old.

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JCadwell
Key Veteran
Location: Richland WA/ Morro Bay, CA

Are you cutting tail blades out of flat sheet? I take it all you really need is profile milling. 2.5D, not any contours? Do you have a DXF file for this?

Thanks, John Cadwell

01-29-2004 Over year old.

Rotary Flyer
Senior Heliman
Location: North UK

Looks like you are planning on some contour work there if you are making blades, or did I read it wrong. You can`t really machine a blades aerofoil contour out of carbon sheet, that is why the people who make them mould them. If you start trying to contour (ie. 5 axis) machine then you break through the layers and just make a mess of the fibres. If this is not what you are planning the forget my rambling !

Don`t forget, the dust can be hazardous ! Don`t go licking it or snorting it

01-29-2004 Over year old.

mattijs

Senior Heliman - Location: Keerbergen Belgium -

Wait a minute i did'nt make myself clear i guess.
I DO want to make an airfoil. Because I can obviously only manipulate one side of the carbon you see four pieces, two of them back to back for every tailblade.

Here is a close up

Do you think it will work?

I do know i have to fix the carbon to some scrap wood but i have no clue where to get double sided tape. Will standard household tape, epoxied to a wooden log, be strong enough for the size these parts have?

01-29-2004 Over year old.

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mattijs
Senior Heliman
Location: Keerbergen Belgium

it might not be really clear on the picture...what i did was draw alot of lines in the shape of a somewhat bigger airfoil than the one i plan on making...mmm it's obvious after all now isn't it?

01-29-2004 Over year old.

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Hockeytown
Veteran
Location: Pontiac, Mi. U.S.A.

Looks good, but.....

What they are saying is that once you break thru the layer of resin on the carbon sheet you are essentially destroying the integrity of the mesh.

I think if you were using G10, you might be OK (correct me if I'm wrong anyone), but Carbon sheets must always remain in Sheets.

People will even tell you that if you ding a set of V Blades that you should trash them because you may have 'shattered' the mesh inside, and it's only a matter of time before they let go

Only perpendicular cuts should be done.

Thanks,

Darin[color=red]
Hockeytown[/color]

01-29-2004 Over year old.

mattijs
Senior Heliman
Location: Keerbergen Belgium

seriously ????i thought carbon plates were stacked up and resined cabon cloths. I figured it really didn't matter. Eventough as you can see the blades have holes in them so they do have to get covered with something .That might hold em together but really...Is it really not done this way???

Drawing the blades and making the g code work really took a long time. Would it be ok if I used hardwood for the blades?

01-29-2004 Over year old.

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Rotary Flyer
Senior Heliman
Location: North UK

I think it may be dawning on you that what you want to attempt is a none-starter. I suggest you get some reading matter on how carbon fibre sheet is made.

The blades you buy are laid up in a mould just like glass fibre, then vacuum is added to the sealed mould to extract the air and press the wetted carbon into place. Then it is suck in an autoclave (oven) and cooked. The resin cures, hey presto you have shiny carbon finished curved blades where the fibres are all still intact, just curved and cured to the final shape (basically, and I`m no expert)

You cannot machine laid-up material like carbon, glas-fibre (G10?) etc like it was a piece of alloy.

I think you are actually pulling someones chain, and this is a wind-up, on reflection. Limited knowledge of a cad program does not make an engineer !

01-30-2004 Over year old.

mattijs
Senior Heliman
Location: Keerbergen Belgium

i do know how normal blades are made and am completely aware that this won't produce anything glossy shiny (it can be sanded afterwards though) or even remotely close to a smooth surface BUT i just wanted to know it it would work. In other words, can the cnc produce what the simulator says it will OR will the carbon get delaminated. I am going to coat maybe even fiberglass it anyway....strength really isn't crucial, even the airfoil itself is barely more than an estethic touch because i can just as well use flat surfaces like so many have done with their hornet tailblades.
I just tought it would be nice to try it now I have a cnc machine at my disposal.

what does pulling somebody's chain mean???

"I think you are actually pulling someones chain, and this is a wind-up, on reflection. Limited knowledge of a cad program does not make an engineer !"

Why would I need to know something about cad? I only had autocad lessons for one year and i had to cnc my name on a stupid delrin piece that's about all the experience i had in that field...i am an electronics engineer ...not a mechanical engineer.

01-30-2004 Over year old.

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mattijs
Senior Heliman
Location: Keerbergen Belgium

i guess i'll just try it and see for myself if it works or not

01-30-2004 Over year old.

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shootist
Senior Heliman
Location: New York State, East Coast US

Mattjis,

I have had experience machining both FR4 G10 fiberglass and carbon fiber into airfoils. It does indeed work. With high rotational speeds produced by a router, and multi-fluted carbide router bits, I was able to get smooth (machined) finishes on airfoil tapers in .180" laminates.

This has become a common practice in building high performance high power rockets.

I would certainly advise you to give it a try.

But I would also strongly urge you to use engineering controls on the fibers and dust- a respirator is not sufficient, because the dust remains in the workshop for later inhalation. Carbon fiber dust is bad because it forms very small (metallic) particles that lodge deep in the lungs, much like the bad kinds of asbestos.

01-30-2004 Over year old.

mattijs
Senior Heliman
Location: Keerbergen Belgium

thanks shootist, should i emerge the carbon in oil when cutting ?

01-31-2004 Over year old.

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shootist
Senior Heliman
Location: New York State, East Coast US

I've never tried oil, so I can't comment. My first choice is a strong vacuum that vvents to the outdoors. Next choice would be a strong vacuum through a HEPA filter.
If those aren't available, I think I'd try a water mist. There is a small chance that water will wick into the composite lamins, but I've never seen it.
Sounds like you will be gluing up two sides of each blade. In addition to roughing up the CF to expose raw fiber, use some clamping pressure to get a good mechanical bond. You might want to clamp them to a flat surface, so you don't induce a warp.

I found an old article where an online buddy used a disk sander to bevel the edges of G10 rocket fins:
http://www.info-central.org/index.cgi?construction
Go to the article on Fin Bevels in Construction. I substitued a router in a router jig (for his disk sander) to cut both CF and G10 FRE. The finish was smooth and clean. My article is long gone, however.

01-31-2004 Over year old.

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CAD - Engineering - Technical > cnc'ing carbon parts for hornet...need hints

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