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KOSTAS
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My first print was is HIPS but i cant find a limonene supplier that ships in Greece , Next PVA is semi flexible and very expensive 80 E/Kgr .I have never heard of BVOH its good to know about it but at 160E/Kgr is out of budget for me. I have never print PC sounds promising , i guess you plan to print a mold ... since for core use i don't know any way to dissolve it. Anyway thanks for your insight.
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scottracing
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ABS will be better, but you will need a fair amount of acetone to melt out the print and even then you will probably still have bits stuck inside. Im looking at using PC Polycarbonate filament next as its good for about 120degrees which opens it up to some of the more common prepregs, there are other options like HIPS material that you can use which is dissolved using limonene. Or even BVOH could be a good option as its water soluble. https://www.verbatim.com/prod/3D-printing/bvoh-filament-1.75mm/bvoh-filament-1.75mm-500g-reel-natural-sku-55901/
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KOSTAS
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I FAILED MISERABLY !!! Unfortunately although ambient temperature was 22C-71,5F the exothermic reaction of resin was enough to soften PLA and vacuum pump did its job and squished the whole layup . My mistake was also that i printed my core thin wall (1,6mm ) . I don't want to try PLA one more time with thicker wall , cause if the heat from the resin is high (60C-140F) the core will soften no mater what. So i came to the decision i wanted to avoid in the first place : ABS and dilution with acetone . This time i will print a core with ABS stick a layer of packing tape on its surface and then wrap this frame with CF and vacuum bag it .After curing i will pour acetone in the core to dissolve the core .The packing tape is to unstick the core from the CF shell as soon as possible . Any thoughts? Here some pictures      
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KOSTAS
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+xIf you can find a way of submerging the whole assembly in hot water and keep it hot for an extended period, then it will work. But I daresay that means keeping it at a consistent temperature for at least an hour - possibly longer. Not sure what the convection properties of PLA are, but I would be starting at an hour. Thats a bit hard to do with hot water since it tends to cool quite rapidly out of the insulated tank .BUT My wife told me '' Why don't you place your bike frame in your car and leave the car in the sun '' this might be a good idea worth trying , since it can easily reach 70C at noon .
I had print a phone holder from PLA for my car that had encounter a warped perception of sunlight through my sealed car cabin .It can no longer accommodate any phone 
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Hanaldo
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If you can find a way of submerging the whole assembly in hot water and keep it hot for an extended period, then it will work. But I daresay that means keeping it at a consistent temperature for at least an hour - possibly longer. Not sure what the convection properties of PLA are, but I would be starting at an hour.
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KOSTAS
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+xIf PLA deforms at 55, you might consider a similar approach to what Rob described but at lower temperatures. Most epoxies will take up to 70 without much issue, so if you can get the thing into an oven at 60 or 70 for a few hours then you may have a solution. I dont think hot water would work, it is too localised. You need to heat through the whole core, otherwise you'll be pulling out tiny pieces and it will take hours. I think we have a winner here its PLA plain , easy printed , cost efficient . I have to find a big enough oven since one of my parts doesn't fit my kitchen oven (when my wife is absent of course) . I was thinking about water since the solar heater here in Greece provides big amounts of super hot water around 75C.
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f1rob
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My mistake
Too many forums too little time
Remembered your initial post where you had the picture of the part bagged up an thought you were pre preg
Hence my reply
Just seen your wet lay vac
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Hanaldo
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If PLA deforms at 55, you might consider a similar approach to what Rob described but at lower temperatures. Most epoxies will take up to 70 without much issue, so if you can get the thing into an oven at 60 or 70 for a few hours then you may have a solution.
I dont think hot water would work, it is too localised. You need to heat through the whole core, otherwise you'll be pulling out tiny pieces and it will take hours.
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KOSTAS
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+xRob is talking high end F1 applications, so using pre-pregs. If your max Tg is 90 then you dont want to take it up to 160. Acetone is commonly used for this 'lost core' sort of application, however immersing epoxy in acetone isn't really ideal. If it is the only way, then it probably wont suffer TOO much with only an hour, but I would want to make sure the epoxy is thoroughly cured - which realistically means giving it a post-cure up to your max Tg. Thank you so much Hanaldo for your honest view you really want to help someone like me . Acetone is my last resort solution .I am thinking of test print in PLA that has deform temperature of 55C and then purring some hot water through. I f this doesn't work i print in ABS and dissolve with acetone.
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KOSTAS
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+xHIPS is one route but you can’t get a solvent, then how about PVA. PVA will dissolve in water. I have tried PVA : 1) extremely expensive 80euros per kilo 2) its almost flexible so in order to print a rigid enough core that can stand vacuum then you have to print thicker walls with more infill that comes to no1 the only good thing is that dissolves super easy leaving no residue.if money is no object then is a good solution , but for me is no option .thanks anyway!
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