Making small parts like control horns out of carbon fiber?

[JFarlette]

I have never worked with carbon fiber cloth but it seems it would be hard to cut small parts out the cloth and wet them out without distorting their shape.

Is it better to cut the cloth to the exact shape before laying them up or make them oversize and cut or grind them to the exact shape after they have cured?

I thought I would ask before wasting a bunch of expensive cloth!

Jason

[davidfee]

From my perspective, it's a combination of A and B, but closer to B. Basically, you don't want to waste material or have a big mess on your hands, so usually I will cut the fabric slightly oversize, but still the general shape and size I need. However, this really does depend a lot on what you're making.

What do you mean by "small parts?"

[Tony D.]

USe carbon cloth larger than your needed control horn, use more than 1 layer and lay it up at +/-45 degrees or you can shear it a bit more to 23 or 40 degrees. I use 4 layers of 4.7oz. cloth for control horns.

You can lay up 6"x6" or so carbon plate so that you will have lots of finished material for future projects.

When cured apply masking tape, draw your shape on the masking tape and either use a small band saw or a sander to achieve your final shape. A hack saw blade comes in handy to cut the pieces out before sanding if you do not have a band saw available.

Always wear a resperator when you are cutting or sanding the carbon, the dust is carcinogenic.

Then put it under the drill press and drill a hole for the push rod, you can also drill a couple of holes into the base of the control horn so that when you glue it into the control surface the epoxy will flow through these holes and make for a better glue joint.

I will post some photos' later today of some of the horn I make and also the 45degree carbon V-tail horns I use.


Tony D.

[A6INTRUDER]

I had thought about this before too.
My idea was to build a mold by routing it out of a piece of wood and then
coating the routed out area with epoxy. Polish it up and then lay glass and epoxy or
carbon and epoxy in the little mold. That way you could make them the same evey time. Maybe thats too complicated. I like the sound of Tony D's idea too, seems much easier.
Looking forward to seeing the pics

TIM

[Tony D.]

Here are some photos of the technique I was talking about in my earlier post.

The two pieces of wood are maple but any hardwood will do, I cut the ends to 55 degrees because I generally build V-tails at 110 degrees of dihedral but of course you can table saw then to any angle you want.

When you lay up the carbon on the angled end of the hardwood use sandwhich wrap or wax the boards then put in the vacuum bag and out will come some nice V-tail horns. Then cut the V-tail horns to the desired width and length, glue into your V-tails.

For making the carbon plate I lay the carbon up between the same hardwood boards and either vacuum bag or clamp it together.

The aileron horn in the photo is about 15mm long but you can make it any size or shape you want, the photos' are not so good but you can see the carbon plate under the masking tape if you squint. This technique can also be used to make a carbon fuselage tray with custom servo cutouts or any shape you need for that matter.

I have included a photo of a 2.5 degree wing joiner mould for 3-piece wings that I made out of aluminum channel, this one is 12.5MM wide and about 15MM high and I usually make the joiners about 7.5MM thick and then sand them for a perfect fit.


T.D.

[davidfee]

Oh I see... you said control horns in the thread title. Yes, the methods Tony and Tim mentioned will both work. I've cut lots of horns from flat plate (graphite and fiberglass). I've also molded some. Each method obviously has its advantages.

Something else would be to find someone with a CNC router to cut your horns from plate. That way they would be much quicker to make, and still be identical.

-David

[ORANATOR]

David, Tony D, Tim and Jason

Please PM me with your address and I will send you a couple Carbon Dicscs and some carbon cloth that I have.
The cloth appears to be prepregnated cloth about 4-6 ozs. thick

http://www.rcgroups.com/forums/showthread.php?t=239909


ORANATOR