smudgersmb
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| posted on 16/2/05 at 05:03 PM |
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Carbon Fibre, Makeing Moulds etc
Hi, I know this has been covered lots of times but... is their any where I can go to learn how to make moulds, lay up and find out more info on
pre-preg and ovens? I want to start off making flat sheets and things like cycle wings before getting into the more complex stuff. Whats achievable in
the garden shed? Who does the best Carbon Fibre Cloth as I have been told their are different grades of cloth. Any help much appricated.
Smudger
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smudgersmb
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| posted on 16/2/05 at 06:05 PM |
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Also is it worth makeing a "warm oven" to help with the curing of the work?
Smudger
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theconrodkid
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| posted on 16/2/05 at 06:23 PM |
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ive got a book on making composite/glass bodywork,yours for £5 plus postie,brand new only read once
who cares who wins
pass the pork pies
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smudgersmb
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| posted on 16/2/05 at 06:49 PM |
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I have just bought today a book called: Competition Car Composites by Simon McBeath. Haynes ISBN 1 85960 624 5.
Will be reading it tonight. Just want a more "practical" view by people who are doing it.
Smudger
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Volvorsport
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| posted on 16/2/05 at 07:46 PM |
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i believe there is a weeks course you can attend at a college nr oxford , basically they go from start to finish .
that book is pretty good , i think youll need to practice first tho !
try to think of lots of different mini projects you can do that give you some experience .
www.dbsmotorsport.co.uk
getting dirty under a bus
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mojo mini
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| posted on 16/2/05 at 10:27 PM |
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is that smudger...of smb composites fame. Who made all the parts for minis. Im confused as to why you need to learn how to make these parts ?
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smart51
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| posted on 17/2/05 at 08:11 AM |
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www.cfsnet.co.uk
CFS sell carbon fibre and epoxy resin.
To make flat sheets, buy a piece of glass from your local glazer and laminate onto this. You will get a nice flat shiny surface to your laminate.
Epoxy will cure at room temperature but takes many hours. every 10°C rise in temperature halves the cure time so in a warm oven (50 - 80°) it will
cure in 10s of minutes.
Epoxy is very viscous and mixing it will add lots of air bubbles to it. these will show in your surface finish as pin holes. these are normally
removed by vacuum. the basic process is to put a perforated PVC film over your wet laminate and a blotting pad over this. the whole thing is put
into a tough plasic bag and all the air sucked out. the atmospheric pressure on the bag squeezes the laminate into the mould and the air is expelled,
in theory.
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Matthew_1
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| posted on 17/2/05 at 09:39 AM |
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I'm half-way through making an carbon body for my seven, I can't fit a standard body and I have a mate who builds race boats in carbon so
I scrounged a load of cloth and thought what the hell. I stopped around november time as the cold weather kills the clear epoxy finish. It's not
even worth starting making ths stuff now until you can guarantee temperatures stay above at least 15C.
Making stuff in the garage is perfectly reasonable, I've made a fair bit now and apart from a few cockups at the start my stuff comes out fine.
It is bloody expensive though, even from someone like CFS who are reasonably cheap a 1M panel is going to set you back around £50.
The air-bubbles problem is one people bang on and on about and you do need to be really careful, but there's no need to vacuum, mix the epoxy
carefully - it goes creamy and looks like you screwed it up - but after a couple of mins it goes clear again. I used the mini-pump dispensers and as
long as you throw away the first 'pump' the epoxy comes out bubble-less. Then if you lay the CF on a sheet of polythene and pour the epoxy
onto that and then lay that lot onto the mould then you shouldnt get bubbles.
Vacuum bagging again isn't strictly necessary but it does give better results for bigger pieces. I got a vacuum pump from Ebay for £20 and then
its just clear poly bags to cover the piece - it's amazing how the poly sheet dosn't stick to the epoxy.
Prepreg and ovens are a non-starter for home use as far as I'm concerned, you could do small bits, so long as you vacuum bag it and don't
mind your oven stinking of epoxy. But it needs pressure and heat which is more difficult to achieve at home?
For curing without an oven the West epoxy I use takes about a day to go 'hard', then it can be removed from the mould and left flat
somewhere, it takes about a week to really cure (at room temperature) and then even my home made stuff is pretty indestructable.
The following link might help with how to make a panel - but wait until its a bit warmer! :
http://www.carcraft.com/techarticles/56999/
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smudgersmb
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| posted on 17/2/05 at 11:50 AM |
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Whilst I am happy making Fibreglass (GRP) panels and parts whenever I do "wet layup" of carbon fibre I get the weave wonky and more
bubbles than an Aero bar. This means relieing on others to do the carbon fibre for me. So I would like to learn how to do higher grade carbon fibre.
Whilst some companys out their seem happy with what they are doing I want to learn more on how to do better/complex moulds so I can offer better
finish/fit/strenth of product.
I am looking at doing vacuum & heat not only for the look but for the strength that can be made by heat cureing the parts. According to the book
makeing a small oven with vacuum takeoff shouldn't be that expensive.
My other problem is getting the right resisn for makeing Carbon Fibre parts which will be used in high heat enviroments. So if anyone knows what
resins are good for heat?
Smudger
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Matthew_1
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| posted on 17/2/05 at 02:09 PM |
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Like I said above I've managed to get panels made with no pinholing and straight weave, they look fine.
I lay up the CF cloth onto a sheet of polythene, straighten the fibres, then pour the epoxy (I use West 105 with 207 Hardener) from there lay the
whole lot, cloth + polythene into the mould and squeegee the lot down, peel off the polythene and then layup the core material etc.
It works just fine, vacuum bagging helps, but you can do it without. and still get no pinholing.
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chrisf
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| posted on 17/2/05 at 02:17 PM |
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Check out this site. They guy made an oven and used prepreg without any
drama. I too considered using it but cannot figure out where to get prepreg in the US.
Ironically, now seems to be the time of year where prepreg would be idea. I would assume you folk have temperatures low enough that the resin would
not go off unless in the oven.
Note that I've never tried this so I could be talking nonsense.
--Chris
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smudgersmb
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| posted on 17/2/05 at 02:47 PM |
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That link helped alot. Think will be buying a garage for the garden and some stuff off ebay before long.
Reading the replies, I can't see any problems other than cost, from this so should be doing flat sheets to start with (using glass/perspex),
then move onto cycle wings etc when I have sorted my life out a bit more.
Running an oven, does that mean I can do "wet layup" and cure in the oven? Would cut down on time. Would cycle wings, flat panels,
bootlids be worth it in Pre-Preg? Or jsut practice with flat sheet and ovens?
What size vacuum pump? Had a look on ebay and their are some LARGE pumps but don't think they would be suitable for home/garage use.
Only one way to find out
Smudger
[Edited on 17/2/05 by smudgersmb]
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krlthms
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| posted on 17/2/05 at 04:46 PM |
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This thread is very informative. While we are at it, could someone who knows about Kevlar tell about the methods, pros, cons, etc. I read in a
recent thread that Kevlar is cheaper but "better" to use.
Cheers
KT
[Edited on 17/2/05 by krlthms]
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smudgersmb
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| posted on 17/2/05 at 05:00 PM |
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Kevlar - very expensive, same "wet layup" as carbon fibre, bitch to cut and when "cured" even harder to cut. Have done bits in
this, had my jigsaw for dinner
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krlthms
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| posted on 17/2/05 at 08:05 PM |
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quote:
Originally posted by smudgersmb
Kevlar - very expensive, same "wet layup" as carbon fibre, bitch to cut and when "cured" even harder to cut. Have done bits in
this, had my jigsaw for dinner
Funny you say that. In a recent thread an interchange between Mix, volvosport, and smart51 here:
http://www.locostbuilders.co.uk/viewthread.php?tid=21609&page=3
I took this to mean that kevlar was cheaper than CF but harder to work with; have I got it wrong?
KT
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smudgersmb
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| posted on 17/2/05 at 08:26 PM |
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Kevlar is more expensive than Carbon Fibre (other than pre-preg), and if not after weave showing, is a bit easier to work with than carbon fibre
because if with stands "rough" handleing with out "fraying". I have used this on some things (I used to make competion seats)
and its a bitch to trim. Would I use it for cycle wings? No, to expensive, to hard to trim, but does look good.
Re-reading the book, checking up on the links above. Think I will be going for an oven and limited choice of moulds.
Smudger
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timf
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| posted on 18/2/05 at 08:23 AM |
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have a look here
for good info also they have a forum with lots of stuff
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nick baker
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| posted on 18/2/05 at 09:00 AM |
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Kevlar: structurally of little use, but looks good and great for impact protection. For mudguards a 50/50 carbon /Kevlar weave might be nice though,
as it'll stop stones from firing clean through it.
Also, as said before: it's a sod to cut. Carbon you can cut with good scissors.
I use vacuum bagging and wet-lay carbon with quality resins to do wings for my planes. Quality resin is more like water, adn wets out the cloth very
well Very easy to get bubble-free finishes.
My vacuum pump is a Compressor from an old fridge. I can get a 92% vacuum with it. Vac-Bags aren't needed with wet lay-ups, but as it's
already been pointed out, you can get better finishes with it.
But... the cost is very prohibitive: only worth it if you really NEEd to save that weight (or if you want it be the sexiest thing on this planet)
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Volvorsport
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| posted on 18/2/05 at 05:46 PM |
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kevlar , structurally of little use ? the high strength of kevlar makes it ideal - you have to design the stiffness into it .
Kevlar can be cheaper and can be used with epoxy resins - as can CSM , it depends how much and where from .
Anyway - ill be using it so if you want some - you know where to come !
www.dbsmotorsport.co.uk
getting dirty under a bus
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nick baker
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| posted on 18/2/05 at 06:14 PM |
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"structurally of little use"
*ahem*
I should probably justify that.... I shall add to it to put it in the correct context.
When building lightweight structures dependant on pure strength, The Carbon fibre that you relinquish in favour of kevlar is not (IMHO) a worthy
sacrifice. If however you need to have a structure that will stay in one piece (when smashed), then having Kevlar in it is a rather good idea. Though
Kevlar's tensile strength is not as high as that of carbon, it can take much higher shear-forces, therefore holds structrues together long after
the Carbon has smashed.
Popping Kevlar in some parts might well be beneficial. I myself wouldn't bother using kevlar apart from in the mudguards, and anything that
might cover driveshafts ETC.
Happier?
have a nice weekend.
N.
EDIT:
I mainly speak from experience of building high-performance RC gliders capable of withstanding 25G... and NOT from car bodywork. (With gliders,
Holding it together after an impact is of little comfort. It's already too late.)
[Edited on 18/2/05 by nick baker]
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smart51
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| posted on 18/2/05 at 07:35 PM |
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Kevlar is cheaper than carbon fibre £12.50 /m2 vs £15.65 at CFS
Kevlar is lighter than carbon (density 1.4 vs 1.75)
kevlar does not quite have the tensile strength of carbon but is less brittle
Kevlar can be cut with shears or a stanley knife where carbon and glass can be cut with scissors
laminated kevlar will be difficult to cut so lay up the kevlar to fall short of the edge of your mould and finish the edges with glass or carbon to
make them easy to trim.
You can use kevlar with polyester where as carbon can only be used with epoxy.
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undecided
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| posted on 19/2/05 at 04:01 PM |
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Polyester resin can and IS used by a lot or people who wet lay carbon fibre.
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Matthew_1
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| posted on 20/2/05 at 12:11 AM |
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quote:
Originally posted by undecided
Polyester resin can and IS used by a lot or people who wet lay carbon fibre.
I'm not convinced you can use polyester resins with carbon cloth. As I said before I scrounged a load of CF fabric on the cheap, and in the
spirit of being cheap, tried it with polyester and I did get a part out of the mould. But even after a weeks cure, if I bent the part, the whole lot
delaminated and split, it broke pretty easily.
If people are using polyester with carbon fabric I'd be genuinely interested to know how - if its true it would make the bodywork a hell of a
lot cheaper?
Maybe its just for cosmetic panelling ? But then I don't see how you would get the polyester to be clear - it dried a horrible yellow/beige
colour - maybe there's a way ?
[Edited on 20/2/05 by Matthew_1]
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smart51
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| posted on 20/2/05 at 10:23 AM |
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polyester doesn't wet out the carbon fibre well enough and the laminates tend to be brittle and prone to delamination. only the surface
filaments and the holes in the weave get wet by the resin, even if rolled properly. The problem is that the filaments of carbon are much finer than
those of glass and so there are smaller gaps between the filaments. Polyester just doesn't penitrate through to the core of the fibre bundles.
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Volvorsport
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| posted on 20/2/05 at 01:07 PM |
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How do you think most carbon appearing nowadays is dead cheap .
We used soley polyester based resins for darrians , and had kevlar and carbon on the chassis , and shown weave for the dash .
If youre carbon is delaminating then im afraid you havent done it right , and probably used to much resin .
the only way to get rid off air bubbles is to use a bristle roller, and have no sharp edges .
tis reason why i dont like offering carbon fibre to people , its a complete PIA to get top quality unless its autoclaved etc
www.dbsmotorsport.co.uk
getting dirty under a bus
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