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faklord
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Postby faklord » Fri Jul 20, 2018 8:27 pm
Ok. I’ve made my two part mold (using this as a guide:
http://easycomposites.co.uk/#!/composit ... composites).
Where I’m struggling is understanding.
1. How to determine the required size of each layer of carbon.
2. How to cut carbon cloth to the exactly the right size without edges fraying and falling apart.
3. How to apply the carbon to the mold without the edges fraying, falling apart & getting between the mold mating surfaces or leaving gaps.
For my build I’m considering using 200gm twill (full outer layer), then 1000gm quad (full 2nd layer), one more rough undersize layer of 1000gm quad + (2?) more local layers around the bolt holes and filling the rest with expanding (foaming) epoxy.
Can anyone who has actually done this (tahoedirk ?) offer any tips/tricks/comments on the above?
Thanks
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SaulOhio
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Postby SaulOhio » Sat Jul 21, 2018 2:12 am
The outer layer of carbon needs to be larger than the part you are molding. I am adding recessed areas around the edges of the part so the carbon doesn't hold the mold halves apart.
I am working on more precise wood cores. The cores and molds are cut on a CNC machine, after being designed in Google Sketchup.
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bigcane
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Postby bigcane » Sat Jul 21, 2018 7:41 am
Make some paper templates that fit in the mould. Wet out the carbon on some plastic sheeting. Put more plastic on top then using the templates cut the carbon and plastic with a razor blade. Transfer to the mould and peel off the plastic
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Kevin Brooker
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Postby Kevin Brooker » Thu Jul 26, 2018 10:05 pm
A very light mist of spray adhesive (3m-77) on one side of the cloth before cutting holds it together so the shape will not distort and it keeps the edges together. The mist just dissolves in the epoxy and doesn't change anything.
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tahoedirk
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Postby tahoedirk » Fri Aug 03, 2018 4:14 pm
hey Faklord, your'e on your way!
I'm guessing your'e making a wing...
Don't over think your layup schedule.
If you cut your cloth on a bias(45deg) then it will expand and contract to the curves of your mold nicely. This prevents the edges from being so fragile and is essential for fitting.
Concentrate on saturating the outer layer and then fill your mold. It is easy to disassemble your cloth into tow which is very simple to wet out and fill a mold with.
I used to cut many pieces in descending sizes. I found this is unnecessary . I have not used foaming epoxy but it may be handy for big wings over an inch thick. Now that you have a mold, no core is easiest and strongest
I don't worry about a little spill over in the mold edges , usually this is unavoidably and makes your part an mm thicker , it can easily be trimmed. Your clamping or vacuum bagging method and over/under filling your mold will affect this concern.
Just go for it and fill it up . As long as your part is under 16mm thick or so , nothing should melt. You will quickly develop your own methods
If you are making a Mast or strut then try for minimal epoxy and as many pieces of cloth as will fit, use a roller . I alternate bias twill and unidirectional, No core.
I find 20 oz twill from soller composites very handy for almost everything, it can be easily taken apart into tow and it is cheap. I have also been able to get a good finish occasionally! haha
good luck, have fun!
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SaulOhio
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Postby SaulOhio » Fri Aug 03, 2018 5:56 pm
tahoedirk wrote: ↑Fri Aug 03, 2018 4:14 pm
hey Faklord, your'e on your way!
I'm guessing your'e making a wing...
Don't over think your layup schedule.
If you cut your cloth on a bias(45deg) then it will expand and contract to the curves of your mold nicely. This prevents the edges from being so fragile and is essential for fitting.
Concentrate on saturating the outer layer and then fill your mold. It is easy to disassemble your cloth into tow which is very simple to wet out and fill a mold with.
I used to cut many pieces in descending sizes. I found this is unnecessary . I have not used foaming epoxy but it may be handy for big wings over an inch thick. Now that you have a mold, no core is easiest and strongest
I don't worry about a little spill over in the mold edges , usually this is unavoidably and makes your part an mm thicker , it can easily be trimmed. Your clamping or vacuum bagging method and over/under filling your mold will affect this concern.
Just go for it and fill it up . As long as your part is under 16mm thick or so , nothing should melt. You will quickly develop your own methods
If you are making a Mast or strut then try for minimal epoxy and as many pieces of cloth as will fit, use a roller . I alternate bias twill and unidirectional, No core.
I find 20 oz twill from soller composites very handy for almost everything, it can be easily taken apart into tow and it is cheap. I have also been able to get a good finish occasionally! haha
good luck, have fun!
My next mast is going to have a wood core and 45 degree twill weave wrapped around the core. The recommendation for stiff masts is to have the carbon fibers at a 45 degree angle to the mast, and under tension. I am thinking of actually stapling the carbon to the mast to help maintain that tension.
No core makes a very heavy component, whether it is a wing or a mast, and uses up a LOT of expensive epoxy.
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TomW
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Postby TomW » Sat Aug 04, 2018 6:12 pm
I heard of a trick: put layer of masking tape in the mold. Mark edges, take out and put it on thicker cardboard and cut out as template.
Then do what bigcane said.
I've made a 3D printed wing plug, but not molds yet. I'm still trying to figure out if I can direct 3D print a wing shell halves and then layup carbon on the inside. With thin laminate on outside, to give it some durability.
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