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ok, on Wards request heres what i can share with you on fabricating carbon fiber parts for use on our garden tractors.
Hello Chris,
Could you start another thread to give a quick CF primer? Could you answer the questions such as:
- Where do you order your CF?
I order all my composite goods from Applied Vehicle Technology. Link: http://www.avtcomposites.com/cgi-bin/commerce.cgi?display=home
- What grade?
I use 2x2 twill weave 3K 5.9 oz. i understand the 2x2 twill is more flexible for compound curves and shapes than plain weave. I think it looks better than plain weave, but thats a personal choice.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?search=action&category=0900
- What do you use for resin?
Resin i order from Aircraft Spruce, or Jamestown Distributors. price is the same, at least it was last time i ordered it. if i have an order going into ACS ill get it there, otherwise ill get it from Jamestown..... share the wealth. I use West Systems epoxy products. epoxy resin is recommended for carbon fiber, vinylester resin is acceptable, and polyester is not compatible with carbon fiber. I get their 105 resin and 206 slow hardener. you need slow setting time for the vac bagging. it sets up overnight at 70*. the trick is only to mix up enough and not too much and work fast. a cup full of it will kick off real fast because of the heat created during the chemical reaction. if you could spread it out it the working time would be better. i never had that problem, you just have to work fast and carefully. west system 105 epoxy resin is mixed 1:5 by weight, so a good accurate scale is necessary. also, when applying the resin, you hardly ever need a brush. you need squeegees. pour a bit of resin on the fabric and squeegee it in. at least on the first layer bail it on, and push it through throughly so you dont have any air pockets. you dont want to rely on the vac bag to squeeze it against the mold. spend most of your time on this first layer getting it as perfect as you can. then add each additional layer pouring and squeegeeing as you go. you know if you have enough resin in it, if you can hold the squeegee 90 degrees to the work, push down and drag it along. if it pulls resin up, its wet enough. more is better than dry though, it will get sucked up in the bleeder. depending on the size of the part i usually make a separate batch for each layer, unless its a small part. this keeps the cup amount low and less likely to kick in the cup. just be accurate with your measuring.
- What do you use for mold release compound?
I use Partall wax, and wax a new plug or mold at least 5 times. once a mold is seasoned, or made several parts, i will only wax it once before making a part. once it is waxed (applied just like you wax your car or airplane) then you spray in the PVA mold release. we have a ton of it at work so i never bought it. ill check tomorrow on the brand and edit this.
- How many layers? How do you decide?
This one kind of comes from experience. in my turtle deck fabrication i talked to someone else who made one similar to mine and i used what they did. worked out well. have learned since how many layers it takes to build something up to a required stiffness. my turtle deck is only 3 layers. there are 2 layers down in the mold, which would put them on the outside, then a layer of 1/8 foam, then the final layer creating a sandwich. this is the secret to creating stiff carbon parts. my glareshield is stiff, but its 6 layers with no foam, the turtle deck is stiffer at 3. once you make something you really get a handle on whats required and can base other parts on what you already made. the floor for my turtledeck is 2 layers of carbon, one layer of 1/8 foam and 2 more layers of carbon for a sandwich. it weighs less than a pound and is stiffer than 1/4 plywood. but again, experience comes from experimenting with it.
- What do you use for vacuum source?
I have a compressed air vacuum source. its a regulator and vac source you hook up to your air hose. you want to be able to pull at least 25" of mercury. i would like an electric vac pump so my compressor doesnt run all night, but i have what i have and the air one works pretty good.
- What plastic do you use for bagging?
High elongation vac bagging film.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=HEBAGFILM
also, ive experimented on what seales it best around the "bag" i started with double sided sticky tape with poor results. then switched to window calking, that sticky clay stuff they sell in a roll at the hardware store. then i found that super sticky black round stuff they hold car windshields in with! that works outstanding! im sure you can find that at the local auto parts store.
after you get your carbon laid up in the mold, and youre happy, you lay down a layer of peel ply. which is basically lightweight dacron fabric.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=PEELPLY
this peelply doesnt stick to the carbon once the resin sets up. next you put down a layer of bleeder material:
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=BREATHER
this does 2 things, it soaks up the extra resin in the carbon through the peelply as the vac bag is squeezing down on it, and second goes into the next question.......
- What method to distribute the vacuum around the entire assembly?
the bleeder material lets the vacuum in the bag suck throughout the entire part and pull the bag down into it. thats it. if its a compound part, make sure there is enough slack in the bag so it can get in all corners and seal it up. turn the vac on and dont worry, if its sealed perfectly it will suck down the entire thing. thats the gravy part, watching it suck down and squeeze all that extra resin (weight) out into the bleeder.
when its all set up the next day, you turn off your vac, and cut off the bag. pull off the peel ply..... which sometimes puts up a little fight, then pop your part out of the mold, wash off the mold release, trim and fit.
- All the other questions I don't know enough to ask....
There is no black magic (pun intended) in carbon fiber work, it just takes time and practice. like anything skill will come with experience. the main trick is to plan ahead, go over the entire job in your head from start to finish, have all your carbon pre cut and everything ready to go because once you start you are committed. you need to work very fast and carefully. on anything larger than 2 square feet, when youre starting out it really helps to have a knowledgeable helper. doesnt have to be someone skilled in cf work although that would really help, but they have to have an idea on what youre doing so you dont spend half the time explaining it to them while the resin is setting up! one huge point is, your part is only going to be as nice as your mold, and your mold is only going to be as nice as your plug. you start out making a plug of what you want it to look like and spend a bunch of time making it nice, real nice. then pull a mold off of it. if theres ANY imperfections in the mold, fix them then. you want to pull your part out, and install it.
which leads to another point. i usually make a fiberglass part in my mold before making a cf one. the reason is 2 fold. one, it allows you to try out the mold and see how you will lay your laminates in, and another is it allows you a blank to fit to whatever your building. in my turtle deck and seat, i made glass ones and fit them to the airplane. trimmed them all up and drilled the mounting holes. then put them back in the mold, and scribed all the lines into the gelcoat in the mold. then when you vac bag the cf part, the lines are pressed into the part and you simply trim and install.
heres the thread on my turtledeck for review:
http://www.biplaneforum.com/f22/cf-turtle-deck-fabrication-acrosport-2s-6107/
of course, any questions feel free to ask. or if anyone can add anything please do........
Disclaimer: all advice given in the preceding shalt only be used on garden and lawn tractors and not on aircraft.
Hello Chris,
Could you start another thread to give a quick CF primer? Could you answer the questions such as:
- Where do you order your CF?
I order all my composite goods from Applied Vehicle Technology. Link: http://www.avtcomposites.com/cgi-bin/commerce.cgi?display=home
- What grade?
I use 2x2 twill weave 3K 5.9 oz. i understand the 2x2 twill is more flexible for compound curves and shapes than plain weave. I think it looks better than plain weave, but thats a personal choice.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?search=action&category=0900
- What do you use for resin?
Resin i order from Aircraft Spruce, or Jamestown Distributors. price is the same, at least it was last time i ordered it. if i have an order going into ACS ill get it there, otherwise ill get it from Jamestown..... share the wealth. I use West Systems epoxy products. epoxy resin is recommended for carbon fiber, vinylester resin is acceptable, and polyester is not compatible with carbon fiber. I get their 105 resin and 206 slow hardener. you need slow setting time for the vac bagging. it sets up overnight at 70*. the trick is only to mix up enough and not too much and work fast. a cup full of it will kick off real fast because of the heat created during the chemical reaction. if you could spread it out it the working time would be better. i never had that problem, you just have to work fast and carefully. west system 105 epoxy resin is mixed 1:5 by weight, so a good accurate scale is necessary. also, when applying the resin, you hardly ever need a brush. you need squeegees. pour a bit of resin on the fabric and squeegee it in. at least on the first layer bail it on, and push it through throughly so you dont have any air pockets. you dont want to rely on the vac bag to squeeze it against the mold. spend most of your time on this first layer getting it as perfect as you can. then add each additional layer pouring and squeegeeing as you go. you know if you have enough resin in it, if you can hold the squeegee 90 degrees to the work, push down and drag it along. if it pulls resin up, its wet enough. more is better than dry though, it will get sucked up in the bleeder. depending on the size of the part i usually make a separate batch for each layer, unless its a small part. this keeps the cup amount low and less likely to kick in the cup. just be accurate with your measuring.
- What do you use for mold release compound?
I use Partall wax, and wax a new plug or mold at least 5 times. once a mold is seasoned, or made several parts, i will only wax it once before making a part. once it is waxed (applied just like you wax your car or airplane) then you spray in the PVA mold release. we have a ton of it at work so i never bought it. ill check tomorrow on the brand and edit this.
- How many layers? How do you decide?
This one kind of comes from experience. in my turtle deck fabrication i talked to someone else who made one similar to mine and i used what they did. worked out well. have learned since how many layers it takes to build something up to a required stiffness. my turtle deck is only 3 layers. there are 2 layers down in the mold, which would put them on the outside, then a layer of 1/8 foam, then the final layer creating a sandwich. this is the secret to creating stiff carbon parts. my glareshield is stiff, but its 6 layers with no foam, the turtle deck is stiffer at 3. once you make something you really get a handle on whats required and can base other parts on what you already made. the floor for my turtledeck is 2 layers of carbon, one layer of 1/8 foam and 2 more layers of carbon for a sandwich. it weighs less than a pound and is stiffer than 1/4 plywood. but again, experience comes from experimenting with it.
- What do you use for vacuum source?
I have a compressed air vacuum source. its a regulator and vac source you hook up to your air hose. you want to be able to pull at least 25" of mercury. i would like an electric vac pump so my compressor doesnt run all night, but i have what i have and the air one works pretty good.
- What plastic do you use for bagging?
High elongation vac bagging film.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=HEBAGFILM
also, ive experimented on what seales it best around the "bag" i started with double sided sticky tape with poor results. then switched to window calking, that sticky clay stuff they sell in a roll at the hardware store. then i found that super sticky black round stuff they hold car windshields in with! that works outstanding! im sure you can find that at the local auto parts store.
after you get your carbon laid up in the mold, and youre happy, you lay down a layer of peel ply. which is basically lightweight dacron fabric.
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=PEELPLY
this peelply doesnt stick to the carbon once the resin sets up. next you put down a layer of bleeder material:
http://www.avtcomposites.com/cgi-bin/commerce.cgi?preadd=action&key=BREATHER
this does 2 things, it soaks up the extra resin in the carbon through the peelply as the vac bag is squeezing down on it, and second goes into the next question.......
- What method to distribute the vacuum around the entire assembly?
the bleeder material lets the vacuum in the bag suck throughout the entire part and pull the bag down into it. thats it. if its a compound part, make sure there is enough slack in the bag so it can get in all corners and seal it up. turn the vac on and dont worry, if its sealed perfectly it will suck down the entire thing. thats the gravy part, watching it suck down and squeeze all that extra resin (weight) out into the bleeder.
when its all set up the next day, you turn off your vac, and cut off the bag. pull off the peel ply..... which sometimes puts up a little fight, then pop your part out of the mold, wash off the mold release, trim and fit.
- All the other questions I don't know enough to ask....
There is no black magic (pun intended) in carbon fiber work, it just takes time and practice. like anything skill will come with experience. the main trick is to plan ahead, go over the entire job in your head from start to finish, have all your carbon pre cut and everything ready to go because once you start you are committed. you need to work very fast and carefully. on anything larger than 2 square feet, when youre starting out it really helps to have a knowledgeable helper. doesnt have to be someone skilled in cf work although that would really help, but they have to have an idea on what youre doing so you dont spend half the time explaining it to them while the resin is setting up! one huge point is, your part is only going to be as nice as your mold, and your mold is only going to be as nice as your plug. you start out making a plug of what you want it to look like and spend a bunch of time making it nice, real nice. then pull a mold off of it. if theres ANY imperfections in the mold, fix them then. you want to pull your part out, and install it.
which leads to another point. i usually make a fiberglass part in my mold before making a cf one. the reason is 2 fold. one, it allows you to try out the mold and see how you will lay your laminates in, and another is it allows you a blank to fit to whatever your building. in my turtle deck and seat, i made glass ones and fit them to the airplane. trimmed them all up and drilled the mounting holes. then put them back in the mold, and scribed all the lines into the gelcoat in the mold. then when you vac bag the cf part, the lines are pressed into the part and you simply trim and install.
heres the thread on my turtledeck for review:
http://www.biplaneforum.com/f22/cf-turtle-deck-fabrication-acrosport-2s-6107/
of course, any questions feel free to ask. or if anyone can add anything please do........
Disclaimer: all advice given in the preceding shalt only be used on garden and lawn tractors and not on aircraft.
Last edited:
