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Steve Broad
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+xThe problems with difficult infusions are: It is much harder to get a frayless finish in places where you need to cut the cloth. With painting, this isn't a problem for you. The flow media is much harder to get into complex shapes, than everything used in a prepreg process. on complex 3d shapes the resin front easily flows around some higher or lower shapes, trapping some voids, resulting in pinholes or (In worst case) unimpregnated areas. Split mold infusion is a different topic on its own. If you are careful during the layup, get the bag tight into the corners, and follow the heating instructions, prepreg parts always come out nicely. I never had a failed part. Infusion is in comparison an art. The process allways has to be adapted to the shape of the part. To get it right on first try, you need experience. You have convinced me that prepreg is the way to go, cheers.
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MarkMK
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If your experience with infusion is limited Steve, I'd concur with Oekmont that pre-preg offers, in theory, a more straightforward process in many ways for a first-time user. Key with it is to ensure that the fabric is in intimate contact with the mould, to avoid any bridging that results in a rough, pin-holed or broken surface. Before starting, I'd make up lots of cutting templates to take car of the detailed contours on the front. If done tidily, everything will look great even with loads of joins so time put into planning the simplest ways to achieve coverage without need to pull, push and twist the fabric too much will really pay off. In fact, the trickiest part, unless you're used to making up big envelope bags, will be getting a perfectly sealed bag once everything's laid in. I'd also enlist another pair of hands to help handle any big sections of fabric as it's a pig to deal with in big sections as it just sticks all over the place as you're trying to lay it in. If you've settled upon this route, then put your effort into designing the mould so that, where possible, you'll be releasing it directly away from the part rather than relying on things coming out at an angle or needing to be flexed. This will, hopefully, guide you on where best to create the parting lines.
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Steve Broad
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+xIf your experience with infusion is limited Steve, I'd concur with Oekmont that pre-preg offers, in theory, a more straightforward process in many ways for a first-time user.
Key with it is to ensure that the fabric is in intimate contact with the mould, to avoid any bridging that results in a rough, pin-holed or broken surface. Before starting, I'd make up lots of cutting templates to take car of the detailed contours on the front. If done tidily, everything will look great even with loads of joins so time put into planning the simplest ways to achieve coverage without need to pull, push and twist the fabric too much will really pay off.
In fact, the trickiest part, unless you're used to making up big envelope bags, will be getting a perfectly sealed bag once everything's laid in. I'd also enlist another pair of hands to help handle any big sections of fabric as it's a pig to deal with in big sections as it just sticks all over the place as you're trying to lay it in.
If you've settled upon this route, then put your effort into designing the mould so that, where possible, you'll be releasing it directly away from the part rather than relying on things coming out at an angle or needing to be flexed. This will, hopefully, guide you on where best to create the parting lines.
I have made many items using wet lay vacuum bagging and a fair number of small parts with prepreg but no infusion, although I bought all the stuff many months ago. But, despite the huge extra cost of prepreg, it is probably the way to go. Just need to decide on how to split the mould.
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oekmont
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I drew a few lines into your pic, where I would add flanges. I did not consider any changes, that have to be done, to convert it to a flip front (filling of the bonnet recess, maybe adding a backward edge). As far as I see, this would be the minimum, and you still would need to add the bottom piece afterwards, as it is at 180° to some of your cut offs. And 180° hand formed without mould making in mind are likely somewhat between 175° and 185°.
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Steve Broad
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+xI drew a few lines into your pic, where I would add flanges. I did not consider any changes, that have to be done, to convert it to a flip front (filling of the bonnet recess, maybe adding a backward edge). As far as I see, this would be the minimum, and you still would need to add the bottom piece afterwards, as it is at 180° to some of your cut offs. And 180° hand formed without mould making in mind are likely somewhat between 175° and 185°. Thanks for that. Looking at the photo I reckon that I don't need to take the bonnet all the way down the back of the arch, stop around half way thereby removing the section that curves inwards and negating the requirement of the joint along the wing. I can make the lower section separately, fixing it permanantly to the body. I want to build the splitter into the front in order to add stiffness. As this is a one off part I am quite prepared to, carefully, cut the mould to get it off if necessary :-) Any damage done to the carbon can be repaired. This probably sounds really bodgelike to experts, but with only 20% skill level you have to do what you are capable of. I guess the finished article will prove just how good or bad I am at this stuff.
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oekmont
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But to get to the point, where you can cut the mold to get the carbon piece out, you have to get your pattern out of the mold. This is usually much harder, because of higher thicknesses and the amount of filler used. The fact, that your whole elan body is attached to your pattern won't help either.
You have all ready put that much time into this car, and you are planning to invest about 1000£ worth of prepreg and foam into this, that maybe an additional 20h and 100£ would be worth it. Especially if you keep in mind that cutting out the pattern, cutting off the mould and repairing the actual part easily comes close to 20h labour.
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Steve Broad
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+xBut to get to the point, where you can cut the mold to get the carbon piece out, you have to get your pattern out of the mold. This is usually much harder, because of higher thicknesses and the amount of filler used. The fact, that your whole elan body is attached to your pattern won't help either. You have all ready put that much time into this car, and you are planning to invest about 1000£ worth of prepreg and foam into this, that maybe an additional 20h and 100£ would be worth it. Especially if you keep in mind that cutting out the pattern, cutting off the mould and repairing the actual part easily comes close to 20h labour. Good points, well made as usual. I'm just thinking aloud really. As you say, an extra joint or two is better than hours of struggling.
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oekmont
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Don't be offended by my percentage comparison. You achived more than 80 % of the people who tried making some cf parts. But your current idea leaves out a few steps in the difficulty ladder. You made some fine vacuum compressed parts, even better prepreg parts, but you might need some more experience to sucessfully build half a car in one shot, especially if you are planning to use a method you you have all most no experience with (infusion).
I would consider myself fairly skilled in vacuum infusion, as I am working with this for about 10 years. And it took me quite that long to get to a point, where I am able to do a project like the one attached.
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oekmont
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This is a project I realised for Westfield Deutschland. The bonnet is quite the same "project level" and type than the one you are planning. Half a car, cf sandwich, 4 piece mold, a few difficult areas in the front section, a great plane in the back. I reshaped an original bonnet for the pattern. And your project would contain to convert a car to a flip front, which was not ment to be a flip front. Holy cow, i can't count the problems that this might lead into.
I used resin infusion, mainly because I know ri very well, and because this way I had the freedom of choice when it comes to the used cloth. But even with years of experience this was quite a project. I managed never to fail an attempt, but I learnt from every one.
Your "20% skill level" is not a fixed number, and there are lots of ways to improve it. For example by discussing with people with more experience. But some practice can't be matched with theory.
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oekmont
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Lucky for you, the Westfield grp quality is way beyond what lotus did those days. So your weight saving will be greater than mine. I managed to get the body down to 20kg. Original is about 40-45kg. Bonnet alone was 14kg and is now 3,8kg (near the bottom, you have to keep higher thicknesses against road dirt, so the weight saving of the other parts are lower). I would have been able to get to 3kg, but not with 245g cloth skin, and not within the budged. You don't know 4-5 guys who would invest in a full elan cf conversion?
This would be the project, I was dreaming of since I remember dreaming of anything. I would take one for myself.
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