Good evening

I was wondering if it is possible to make a part that needs a split mould without the use of a curing oven. The latter is pretty much keeping me from trying prepregs as I can't use my domestic oven because I can't get a vacuum line in there and buying one isn't in the budget. Getting an old domestic oven just for this purpose where I can make a hole would be possible but I also don't really have the space for setting up a second oven...

My idea was to use a very slow curing hardener, i.e 210 or 300 minutes, and then hand lay up the carbon and epoxy inside the two parts before closing them and then add the vacuum bag and just wait until it's cured. I think the curing time would be plenty long enough but the big question is will the hand layup stick well enough to the mould so that it doesn't come loose in the process or how can it be made to stick well enough? Has anyone done this and can share some experiences?

Kind regards
Martin

Ok, that sounds pretty promising. Will spray tack show on the finished part? I guess so as it can't just vanish in the process, but its use would certainly help. The part I think about making is not actually very similar to the airbox made in the split-mould and prepreg tutorials but it has some of the same challenges, the fabric and resin on the upper part of the mould will be hanging like off the ceiling until the vacuum bag is in place and holding it together. Spreading the vacuum bag around the inside will be even more difficult than with the airbox; I'm pretty sure I'd have to lay the separation and breather layers in already before closing the mould, like I've seen it done by other people, so that only the bag remains.

Maybe this will help.. 

https://youtu.be/MAinuf5I_dw

i would like to point out, that in my opinion, hand lamination looses its benefits once you start vacuum bagging. because with the same same tools, you could also do an infusion for the same money, and you will get a far superior part out of it. if you do it right, the risk of failure decreases dramatically, as you have infinite time getting everything down correctly. and most likely you will still end up with significantly less working time, as the surface will be much better.

@Weaponofchoice: This video seems to be about something different than what the question is here. Did you maybe link the wrong one?

@oekmont: Actually the reason I didn't come up with resin infusion is that I haven't seen it done with split moulds. If the fabric has to be put into the parts of the mould before it is closed and screwed tight I think it would take loads of spray tack to hold in place and would probably still get messed up. But maybe I'm wrong...

Maybe I should clarify that I want to make a resonator guitar body in one piece, these have a much larger hole compared to a normal acoustic guitar but it's still a form that is closed all around but where the hole is. I'd bow the side of the guitar a little outwards and split the mould around the circumference. If the resin was hand laid up it would at least be sticking somewhat to the mould already by itself but I'm again not sure if well enough or not to stay in place.

are you experienced in hand laminating with vacuum bagging? If yes, give it a try. for myself, I would consider a resonator guitar body via hand lamination a difficult task. at least, if optic is critical. getting everything done without any distortions and with nice corners is not trivial.

again, for myself I would consider it a fairly easy part when using infusion. my recommendation for difficult multi part infusion: get some 2 component laquer, spray the mold surface,  let it set a bit, and place the first layer onto the still slightly tacky surface. the goal is to just hold it in place, not impregnating the cloth. trim the fabric to the mold flanges, put the mold pieces together, and continue the build up with spray tack. this method results in absolutely perfect finishes, and you part is already painted. if your layup takes to long, a slight laquer mist onto the surface your working on and everything is tacky again.
when joining the mold, you should use some silicone on the outer flange, but not that much, that it reaches the laminate, when your are pressing the molds together. additionally, you might use a whole bag around the mold (keep sure the mold surface ist smooth). some resin will flow around the mold flange, but usually not that much.
I made this part in a 5 piece mold with infusion in one shot. there is a 90° flange all around the outer corner

Well if you did that part you certainly know what you're talking about, nice work! Must be a Super 7 style bonnet isn't it?

No, I don't have experience doing that, just imagined the hand way would be easier but I may easily be wrong.

I hadn't heard about painting the mold first, thanks for sharing this idea! It's somehow like applying gelcoat so makes perfect sense. Do you tape off the flanges before painting?

Your shape is definitely much more complicated thatn what I'm trying to make but the advantage is that you can reach in better to finish the layup.

yes, it's a modified bonnet for a Westfield. as the lamp mounts are integrated, and they are closed from the underside, to get rigidity without high wall thickness, there are sections I can hardly reach, and definitely not look into while my hand is in there.

in my opinion it is much easier to manipulate  a dry fabric in difficult corners without any time pressure, than the wet fabric. the resin usually makes it more difficult.

on smaller parts, I usually brush the laquer, as the inside of the laquer doesn't need do be perfectly flat. so no, I do not tape  the flanges. keep in mind, that it has to be 2 component car laquer. never use 1 component laquer.

Just an additional thought regarding the part that it sounds like you're trying to make (guitar?)

I think that I've seen these made utilising a 'joggle' ring that it placed into one half of the split mould prior to laminating and it sound like it might suit your intended production method more, as it does sound like making a guitar body in a closed mould as you've described would be very difficult to do well via hand lay-up

Basically you'd be making both upper and lower sections separately, but one half would have the narrow joggle (a slight step that matches the intended thickness of your the other half) placed around the top section of one mould prior to laying-up the fabric. Once cured, the joggle ring is removed first to leave you with a flange onto which you can bond the other half of the laminate. You would create the joggle ring by laminating around the top section of one of your mould halves, but the trick is to control carefully its thickness, so that you end up with a flange that closely matches the thickness of the other half of the guitar body (which helps to achieve a neat join in the middle).

Of course, the downside is that you have a visible join of the two parts around the middle, but you could fill and paint over to hide the join or even try to make this a bit of a feature.  If you have a search around YouTube I'm certain that you'll find examples of this technique being employed although, as alluded to already, the use of vacuum pressure (particularly resin infusion) would lead to a more consistent consolidation of the materials and control of thicknesses

Just a thought, as it might be a more realistic approach to achieving a decent-looking end product if you are limited to hand lamination