Plastic. I got one for restriping our boat. I’ve seen them elsewhere too. Some hardware stores have softer rubber ones for wallpapering.
Ok, so this week I’ll try to make my first bit. As I understand it, the process is:
- Wax the mold good, leave it for 8 hours to out gas
- Make a pattern for the cloth, and then cut out the bits of cloth
- Saturate the cloth with resin, then lay the cloth into the mold
- Squeege off any obviously excess resin
- Apply the breathers, perf film etc, and bag the mold
- Vac it up, place it in my ‘oven’
- Wait 24 hours, trim most of the excess
- Pop the part, trim the rest of the excess
- Clean the part with something like prepsol, then spray with urethane clear
- Done!
Anything else I should know?
hmm… make sure your oven is heated to the epoxies recomended curing temperature and follow the directions on the epoxy about how long to leave it in the oven.
What are your molds made out of? I hear Polyester FRP molds can only withstand 120F degrees without warping from heat. Maybe i have heard wrong?
Use bagging materials that can withstand high temperatures ie: peel ply, bagging tape, bag, vacuum connector to the bag, etc. Make sure your vacuum hose can withstand the oven temperature also.
Will he end up with lots of surface bubbles trapped in the resin near the mold surface and the first layer of cloth? I was kind of under the impression that without using a gel coat lots of tiny air/gas bubbles will get trapped in the surface of the part when doing the vacuum bag technique?
malcom, is this part your making fiberglass only or is carbon fiber involved? What type of resin?
Watch out for those plastic squeegies… sometimes they come with rough edges that could potentially hang up on the fabric.
The ‘oven’ is a large (about 600mm x 600mm x 60mm) polystyrene box with a 25W light bulb, keeps it at about 25 degrees celcius. It has been quite cold here recently (winter in the southern hemisphere), and is typically down to about 0-2 degrees C at night, so the ‘oven’ is just to keep things reasonably warm, not to bake anything at high temps 
The resin is a vinylester resin, and the cloth is a 5.8oz dual twill carbon fibre.
Cheers for the tip about watching for snagging with the squeegies
I’ve bagged a few molds up (yeah over kill, but worked really really well and gave me a little experience with vacuum bagging), and all of the stuff seems to be happy with the modest temps I’m using.
Is is common to use a (clear?) gelcoat when doing carbon fibre vacuum bagging? These are cosmetic parts for a motorcycle.
Right, so I’ve rewatched a lot of videos (including that neat one with the carbon fibre cello!), and as far as I can tell, I want to line the mold with resin, let it tack off, then put my wetted out cloth in.
The mold I have it about the size of an A4 piece of paper… I’m guessing I’ll want to mix up about 10-20ml of VER, and then brush that into my mold. Wait about 30 minutes, just long enough for it to tack off, then mix up sufficient resin to wet out the cloth, and then finish the job.
Sounds like a plan?
The carbon fiber cello video is really cool to watch 
The only problem with doing it the way they are … is they have an autoclave or baking oven, and well you don’t. An autoclave elminates all the tiny gas/air bubbles in the laminate and especially on the mold surface side of the part that is going to be what people see.
A lot of people use clear gel coat with carbon fiber part. It makes a really nice looking finished surface. I’m not sure if vinyl ester resin and polyester gel coat are compatible with each other?
Can someone with more experience help this fellow?
Isn’t it just… it’s amazing how every video I watch uses a similar process, but they’re all distinctly different
Ahhh I see 
On the subject of eliminating air bubbles (pretty much my biggest fear at the moment), I found this information:
The main problem I had has been pinholes, imperfections in the laminate surface. After some detective work I decided these were due to air in the resin. When you mix the resin it fills with air bubbles, if you stick the pot of resin in a vacuum chamber it froths up. It takes about 10-15 minutes to pull all the bubbles from Graff SE. So I made up a vacuum mixing pot, the first was mechanical and not successful, I now just have a top for my mixing pot with an ‘o’ ring seal and vacuum fitting. I chuck several stainless bolts in the resin/hardener stick the top on and evacuate, then move the pot around for 5 minutes and I have air free resin, this cured the pinhole problem.
, here: http://www.mci.i12.com/carbon/resins.htm
In your (you experienced guys) opinion, given that I’m going vacuum bagged hand layups into a mold, is it worth going to the trouble of vaccing my resin pot, or is that overkill, and am I just as likely to achieve the result I want by mixing with a round stick in an elliptical motion?
Yeah, I’ve got no idea… I expect my composite supply store will have some idea, I need to guy buy some bits n pieces, so I’ll ask when I’m there.
Well, gave it a go last night… decided on 4.6oz Dual Twill.
Bridging, sure I’ve got a whole heap of it… really hard to eliminate around this bolt hole bit that sticks up. Air would get trapped under the laminate as well, and I really didn’t have a suitable roller… but I couldn’t find a smaller one in the shop, might have to make one. So once I’d chased the air out of under the first layer, then I put the second layer on… more air got trapped… and of course the two layers stick together, in such a way that it created more bridging. So I worked away at it with a roller and a brush for as long as I could, all the time I could tell when I was moving the base laminate… even if I don’t get bridging, I’m sure the weave will be quite askew. One of the problems is that I’m not sure how much the vac bag can go towards rescuing me… I’m very doubtful that it’ll go anywhere near saving this piece.
No matter, I will pop it out when I get home from work, see how the mold stood up, and then try again
Well… it wouldn’t pop. After all that careful waxing, I still fucked it up. I can’t use PVA with carbon fibre, right?
Anyway, settled on brushing the inside of the mold with resin, letting it tack off, then laying into that. Worked pretty well, except for some corner bits where it pooled. Not sure how I’m going to get a thin even coat of resin, but I was really pleased with the finish on the sections that popped ok, so I’m going to persevere.
I figure I’ll use this mold (now that I’ve buggered a small bit of it) to practice brushing in the resin smoothly. I’m thinking about pouring it in thick enough to run, then moving the mold around to chase it around the interior, and letting the excess drip back into the cup. I think that’ll be too think though. I guess I really need to spray it in, but haven’t found a gun yet.
you can use pva with carbon. however you might want to consider using semi permanent release agents instead of wax, much more reliable. also you should spray clear gel coat or infuse your part if you want a nice finish
Might possibly be a good idea to make some simple parts using cheap materials, so you can get some basic understanding of how to do things properly?
This stuff is pretty cheap for the most part… cost me about USD$15 for carbon fibre, plus maybe the same again for misc bits n pieces and resin, so about an hours work to pay for it all 
Of course, most of this stuff is a lot cheaper when buying in bulk, so it’s the price of entry that’s the killer, rather than the single part costs 
This part is less than the size of an A4 piece of paper… it’s about the simplest part I’ve got. I just need to keep chipping away at the job, and learn to solve each problem as I come across it.
I’ve been quite successful with my molds as far as releasing goes, I’m not quite sure how I messed this up.
yes, and it is also a good idea when you first wax your molds is to do a tape test to be sure it is well waxed
Tell me brother, what’s a tape test?
I was sure I’d read on one of these forums that using PVA when vac bagging PVA would result in a residue on the surface? In my mind, that seemed strange… these are just cosmetic parts for my bike, so I’m going to rub them down and clear coat them, surely during the rubbing down process the extremely thin PVA (if any transferred to the part anyway) would be sanded off in record time?
/edit: Found this quote by kb:
The tooling surface is a 2x4’ piece of malamine. 10 coats of release wax later you test it for adhesion with a piece of masking tape. If it sticks at all, more wax.
At all means at all? I mean, it is adhesive tape after all, even if it’s just masking tape… I’m guessing that he means ‘Use your brain, it should be obvious if is adhesing to anything other than wax’?
Yup well pretty much. I just lay a piece on the mold, run my finger over it lightly and pull off. If there’s any significant resistance I wax again.
Tape test seems a great idea, and would save a fair number of people on here a lot of time and trouble.
yea, use 3/4" masking tape tear a piece off and stick it to your mold, have one finger stuck to the end of tape, if the tape pulls off your finger you definetly need to add more. if your mold is well seasoned you should almost be able to slide a piece of tape around on the surface
Appreciate the tips guys
Yeah, I know what you mean… I was 100% sure I’d waxed this up perfect, my technique has been getting better and better… and then this, total failure.
I’ve thinking about that you said, regarding trying some smaller, easier, bits. I know what you’re getting at… I was wondering, is there a common piece that anyone should try and learn to mold? I’ve prepared a few flat panels, as obviously they’re nice n easy, a plug can be just about anything, but that seems a little too easy, if you know what I mean?
True… the only things that I can thing of was not letting it dry enough before buffing, or not letting the layers out gas enough between them.
I’ll get there
I’m sure ya will! Think Edison tried 29,999 times before he found the solution to a practical lightbulb! 