Nearly ready for my first attempt, but questions abound!

General Composites Discussions Composites Talk
#1

Hi Guys,

Fastrr put me on to this forum after finding me somewhat alone at the FibreGlast forum, many thanks to him.

I’ve a motorbike, and I thought it would be nice to make some carbon fibre parts for it, some cosmetic, and one minor structural unit (a battery box).

I’ve got as far as completing some molds, they’re made from VER, CSM, and a white gel coat, all vac bagged together. They’ve come out pretty good, so I’m ready for the next steps.

Funnily enough, the methods I’ve used so far are similar to what John Britten used to build bits for his bikes! It’s funny because I live in the same city as he did! (Christchurch, NZ) A 50 degree oven (a friend built it for me from 60mm polystyrene, a 25W light bulb keeps it at about 48-50 degrees C), VER, laid up and vacuum bagged.

What I’ve got available to me is:
92gm plain weave (2.7 oz/sqf)
198gm plain weave (5.8 oz/sqf)
155gm twill weave (4.6 oz/sqf)
196gm plain weave (5.8 oz/sqf)

Ideally I would like all my parts to look that same. The side covers have some tight (5mm radius) corners on them, which is why I had to end up vacuum bagging the molds (but the experience gained was worth the effort imho). For this reason, I’m thinking that the lightest sheet I can get would be better, and that I’ll make the side covers entirely from 92gm.

Questions:

  • If I use 92gm plain weave for the external surfaces (to keep them all looking the same) for parts that I would like to be stronger (like the chain guard), is there any reason why the inner layers can’t be 155 or 196 twill? Will they all laminate together ok?

  • Is twill typically cheaper than plain weave, as it is from my supplier (just a curiosity thing)

  • Considering that I’m an amateur hobbyist, laying up my weave by hand, is there a best technique for ensuring that the weave is adequately saturated with resin before laying it into the mold?

  • Can I use a typical automotive clear coat for finishing my parts?

  • I saw on a video on Google Video a man who did an overlay, which then he essentially poured resin over afterwards, to get a gloss effect all over. This seems wasteful?

  • I have laid up and cured a small piece of carbon tape as an experiment, the effect was quite nice (with the stunning 3D effect that I am working towards), and with clear coat would look better still. If that quality of finish is acceptable to me (I’m a realist), is there any reason why I can’t just run with that?

  • The pump I have is about 150 litres per minute. The documentation I got from the composite supply store mentioned using a pump approximately 150 litres per hour… that would make mine about 60 times too powerful! It seemed to work well enough (it’ an old pump from a friend who is a refrigeration technician), but I’m concerned that perhaps it could suck too well, removing too much resin from the mold. Is that a valid concern? Can I have too much vacuum?

  • For my relatively small purposes, is there any reason why I would want to choose a twill over a weave, assuming that the ‘look’ wasn’t the most important thing to me? Ease of use is probably as important, especially performance around small curves.

#2

Welcome…

It is best to only ask a question or two at a time as it is easier to answer them with volunteer help on here.

Plain weave is cheaper than twill

Twill is what most retial customers want to see

You can wet out material onto some news paper or PE / PP sheeting and then lay it in the mold

Automotive clear coat will work great as it is UV stabized (won’t change colors)

Pouring on the clear coats will work fine but it is a little messy and wasteful

You don’t need to vacuum bag the plug/mold during the making steps…just use thinner reinforcements (like surfacing veil) for the first couple of layers after the gel coat has been applied

#3

Thanks :slight_smile:

I’ve been reading everything on here I can, and I saved all those questions up so as not to annoy :o

This is only for myself. Assuming the same weight, is one more flexible (for going around tighter corners) than the other?

Yep, that’s what I’ve been doing… is there any special technique for ensuring it’s all adequately saturated, or just heap it on, remove the excess, then let the vac extract the rest?

Excellent.

This guy was pouring actual resin on!

Yeah, I figured that my be the case, that vac bagging my mold was overkill, but it gave a 99% perfect mold, and laying it by hand only gave a 90% perfect one, so for this particular application it was worth the extra effort. The chain guard mold that I’ll make on Saturday afternoon, I won’t bag that one though (not enough tight bits to make it worth while). The other thing is that I’ve had no prior experience with vacuum bagging, so it gave me a little :slight_smile:

#4

Anybody care to comment on those two particular questions?

#5

150 litres per minute is about 5 cubic feet per minute. Not too large at all. I use a Robinair 5 CFM vac pump. What I did was build in a vacuum reservoir. This (so I’m told) takes some of the load off the pump at high vacuums. Apparently they can stall and suffer damage starting under high vacuum loads. I didn’t want to ruin a brand new pump.

Resin Trap & Vac Reservoir

#6

I would be surprised if it damaged them… this one I’ve borrowed is from a friend who does refridgeration systems. These pumps are used to pull a vac down to <200 microns (so pretty damn high!) for maybe 4 hours to 2 days, depending on the size of the system. They do this day in, day out.

#7

Most refrigeration systems dont contain uncured resin, which is not likely to do the internal parts of a vac pump a lot of good if it gets inside.

#8

Hey Malcolm

Do those pumps run constantly or cycle on and off? What I’ve read is that starting them under a high vacuum can damage them. Got this from the Joewoodworker site on his vacuum press design.

“The sub-reservoir is a small holding tank of free air that allows the pump to achieve full RPM when starting up without back-pressure against the pump intake port.”

Rick

#9

Quote; “This is only for myself. Assuming the same weight, is one more flexible (for going around tighter corners) than the other?”

Don’t forget, if you cut the fabric at 45degrees, it will drape better.

#10

Quote; “Yep, that’s what I’ve been doing… is there any special technique for ensuring it’s all adequately saturated, or just heap it on, remove the excess, then let the vac extract the rest?”

If you’re using a squeegee or similar to remove the resin, keep passing the squeegee over the fabric until no more resin comes off. this will give you the correct amount. With more experience you will be able to calculate the amount of resin needed for a given area of fabric. For instance, I use .113grams of resin(including hardener) per square inch of 5.7 oz fabric. The trouble with “letting the vac extract the rest” is that the breather might become clogged with resin, making the vacuum not able to reach all the mould.

#11

Ahhh, the ‘on at high vac levels’ might be the clincher. I’ll ask my mate if that’s something he’s aware of. I’ve seen him in action, and I don’t think it’s something that has bothered him, but that could be that he’s unaware of it being a problem! (like me!)

ClassicBikes, the resin getting into the pump is indeed the biggest concern I have, my mate won’t let me use one of the ‘good’ pumps for that reason (but they’ve a dozen odd, so we just use the ‘oldest’ one) :slight_smile:

Cheers for the 45 degree heads up. I’m actually make a triangular side panel, so I’m a bit screwed… at least one edge has to be perpendicular :smiley: No matter, I’ll figure it out :smiley:

Thanks for the tip about the squeege, is there a particular type I should look for that won’t be attacked by the resin, or will most any type work seeing as it won’t see resin on it for much longer than it takes to work the item, and them remove it from the ‘blade’?

Really appreciate your tips guys, I’ve made a number of blunders already, the less I make in the future the better :slight_smile:

#12

@ KnottyBuoyz

That PVC pipe thing is sick… I need to build one of those, I’d feel a whole heap happier having that between my pump and my vac bag :smiley:

#13

I may try and build one of those large pvc resin catch pots.

My question is… Knotty, why do you have one “tank” for vacuum resevior and another for resin catch purposes? Wouldn’t just a good enough colume resin catch do both jobs at the same time?

Malcom, I think the squeegy you want for carbon fiber lay ups is a rubber squeegy, not the plastic ones.

#14

Yup probably. I had the black one from a previous project. A laminating press so I plumbed it in anyways. Found out a few mins ago the resin trap is too tall. Not good having the epoxy running uphill to drop in the top of the trap. It should be below. Well sort of. My vacuum line to the trap was laying up alongside the hot water pipe and it started to kick the resin in the line before the infused part had kicked. Good thing I got a good bag this time. I’ll saw it in two and make it shorter so it’s below the level of the table.

#15

Absolutely Malcolm. It’s not an option. See my other thread on what happens when your trap is too small. You don’t want the resin getting in your pump.

See my previous post on locating the trap. I’ll be cutting that tall trap in two tomorrow. Post some pics of your setup when you’re ready.

#16

My setup is super super ghetto, I’d be embarrassed to post it here :o

#17

Quote; “is there a particular type I should look for that won’t be attacked by the resin, or will most any type work seeing as it won’t see resin on it for much longer than it takes to work the item, and them remove it from the ‘blade’?”

I use a squeege that is intended for applying decals (stickers) as it’s shape makes it easier to pick up when wet than a conventional bondo spreader, which will also work okay. I assume you’re using epoxy, so there should be no reaction with any common plastic.

#18

http://www.harrisdecals.com/tips/tools.asp

#19

Ahhh, I keep thinking like a rubber edge squeege. I’m using vinylester resin if that makes a difference?

That picture KB, is that made of wood like it looks like it is?

#20

Most are made of plastic, I wouldnt have thought wood was flexible enough. Car body filler spreaders will work ok, and are chep and easily available.