Originally Posted by JimZinVT

Well you succeeded in not disolving your foam plug with the polyester resin, so I'm guessing you can also isolate the mold from an epoxy layup as well. A healthy coat of PVA? I've never worked with polyester...................

By aging the mould well, weeks not days; months is better. Then do a release test on the mould flange after the usual wax and PVA.

..................... The mac-daddy pro method is to do the wet overlap but with an inflatable bladder in the mold to squeeze everything out tight. I like that method a lot but it requires a really heavily built mold and clamping strategy to withstand the inflation pressure. But you can do it with a much more lightly built mold if you put the whole thing inside of a vacuum bag after doing the layup, with the bladder vented to the outside air. Equal pressure inside and out, so even a very light mold with openings can be used. Works great, I've done a few small fuselages this way.
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+1!

Originally Posted by 3David

how can I add pictures to show you my project?

1. First of all, have your pictures downloaded to your computer and know where to find them.

2. Then click on the window below your text field in the "Reply to Thread" page where it says: "Drag Files here or Click to Browse" and select your pictures from the files offered.

3. You will be able to add comments below each picture after they are uploaded to the page.

4. After all the above, click "Post Reply".

It is also a good idea to fill in some details in your avatar. At least provide your country so that others know what is available to you etc.

Jim.

Bladder setups are great for small slim sailplane fuselages but not for large fuselages with multiple feature changes. The overlap seam won't work for a couple reasons. First by using a core material you need to pressure cure and a bladder as mentioned won't work. The other issue is that it could create asymmetrical flexing of the fuselage which is very bad for an F3A airplane. The best way forward is is do the layup in each mold half with 1/2" excess. Bag the mold and layup so that excess becomes a flange. After cure pull it out of the bag, glue all your formers in place, add a paste of epoxy and cabosil to the bonding edge and clamp them together. Take a acid brush and brush some resin on the inside seam line. Wet out some 1" glass tape and work onto the seam on the inside. Let that cure and remove from molds. Trim off the flange and you have a complete fuselage.

Ahh, yes, if formers and bulkheads are involved then a wet seam done at the same time as the layup probably won't work at all.

Exf3bguy builds these sort of planes professionally, IIRC? Listen to him!

Shawn, what are your thoughts on the polyester mold and epoxy component? I have had mixed results using PVA to block styrene migration. I am almost thinking the best bet would be a semiperm like Freekote.

Scott

Almost 35 years ago I/we built polyester tooling for use in 250F. cure epoxy prepreg processing. Back then we used Frekote 44 as our release agent. Yes it worked but the tooling didn’t last very long under those conditions. Haven’t done things that way in decades now.

Bob

Scott, I was going to wait until he got the plug out of the mold. I think that will be a huge hint. That said, I have done a couple molds out of polyester back in the day and didn't have any issues. Of course it may have had something to do with brushing on the PVA full strength and not reduced and sprayed.

Originally Posted by exf3bguy

Bladder setups are great for small slim sailplane fuselages but not for large fuselages with multiple feature changes. The overlap seam won't work for a couple reasons. First by using a core material you need to pressure cure and a bladder as mentioned won't work. The other issue is that it could create asymmetrical flexing of the fuselage which is very bad for an F3A airplane. The best way forward is is do the layup in each mold half with 1/2" excess. Bag the mold and layup so that excess becomes a flange. After cure pull it out of the bag, glue all your formers in place, add a paste of epoxy and cabosil to the bonding edge and clamp them together. Take a acid brush and brush some resin on the inside seam line. Wet out some 1" glass tape and work onto the seam on the inside. Let that cure and remove from molds. Trim off the flange and you have a complete fuselage.

I completely agree, keep it simple! In many clamshell assemblies like fuselage sides, during the master model build ups I insure that the indexed bagging flanges are 90 degrees to the the trim line and 3” wide. Then I machine an .063” thick 6061 T6 aluminum flange that rest completely on my bag flange, but runs .500” into the layup area. Now I layup the part and onto the aluminum flange, bag and process. After processing I trim the flange to .375” abrade and bond the halves together with a structural adhesive in the assembly fixture or process tooling. Bulkheads, firewalls or whatever can be prepared cast splashed and bonded in at the same time as final assembly. The .375”’internal flange that runs the perimeter of the part ads a great deal of rigidity for very little weight. Here is an example of parts manufactured this way. This was a program of mine in 2017-2018. This is a 100’ fuselage we manufactured for Gulfstream Aerospace.

Bob

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[QUOTE=JimZinVT;47194413]Well you succeeded in not disolving your foam plug with the polyester resin, so I'm guessing you can also isolate the mold from an epoxy layup as well. A healthy coat of PVA? I've never worked with polyester.
Yes, I used 5 coats of mold release wax and two coats of PVA. But before that shaped the foam and covered with a coat of epoxy and micro balloons that then was sanded then filled in the imperfections and used paint primmer many times. The Epoxi, primmer and pva kept the foam from melting. Do you think I will have difficulties releasing my Epoxi part from poliéster mold?
I made my molds out of poliéster to make them heavier thicker without increasing the price since poliéster is lots cheaper than epoxy. My intention is to make the part out of epoxy fiberglass balsa sandwich

Or do the layup with polyester?
It would be imposible to layup set the molds and vacuum. Because polyester cures in 15 minutes.

But you can do it with a much more lightly built mold if you put the whole thing inside of a vacuum bag after doing the layup, with the bladder vented to the outside air. Equal pressure inside and out, so even a very light mold with openings can be used. Works great, I've done a few small fuselages this way.
Thank you so much for these great ideas. This is exactly what I was looking for! I am going to try to make the fuselage in a single part using both molds at the same time. I’ll try to set my resins and fibers inside my fuselage halves, then put a bag inside the fuselage ( bigger than the cavity),then close the mold halves, then bag the outside, then vacum the bags against each other. As long as I don’t damage my molds I can try several times until a good part gets produced.

There is nothing as satisfying as designing, building, and flying your own model!
I agree

Excuse me for sending the same pictures several times. I do not do well with posts blogs pages nor computers. Just barely learning now

Originally Posted by exf3bguy

Scott, I was going to wait until he got the plug out of the mold. I think that will be a huge hint. That said, I have done a couple molds out of polyester back in the day and didn't have any issues. Of course it may have had something to do with brushing on the PVA full strength and not reduced and sprayed.

How can I reduce (thin out) PVA? I have only brushed PVA since all of my thinning tests did not allow for spraying. It would just splatter clumps everywhere and make a mess. The only PVA accesible to me is thicker brush on density

Originally Posted by 3David

How can I reduce (thin out) PVA? I have only brushed PVA since all of my thinning tests did not allow for spraying. It would just splatter clumps everywhere and make a mess. The only PVA accesible to me is thicker brush on density

You thin it with water. I live in southern California where the average humidity is 15% or lower. So I thin it 50/50.

The biggest problem most have with spraying is they don't thin it enough and the don't use the recommended pressure. An HVLP gun needs 22-24psi at the tip. A traditional spray gun needs 60-90PSI.

I've used both and recommend 80psi to both types of spray guns.

The next next thing to do is practice on the mold. If you screw up with runs, air bubbles, or a rough surface you can wash it off and try again.

I do 3 coats. A mist coat 12-16 inches away from the tool. Then 2 med wet coats. The resulting PVA surface should look wet when dry. It should have a mirror image reflection, no orange peel effect, or rough looking surface. Remember that what ever the PVA surface looks like is what the mold or parts surface will look like.

To achieve a med wet coat you overlap by 1/2 and deposit enough material that the resulting surface just attains a mirror finish without runs. 1st attached pic.

When dry after making the mold or part the PVA should peel off like Glad wrap. 2nd pic

Partall PVA #10 directions attached

Originally Posted by 3David

How can I reduce (thin out) PVA? I have only brushed PVA since all of my thinning tests did not allow for spraying. It would just splatter clumps everywhere and make a mess. The only PVA accesible to me is thicker brush on density

I haven't sprayed PVA in 30 years, no need to and it actually works better if applied straight from the bottle. I use a foam craft brush and get great results.


Now on to your bigger issue. You will need to open up the tail post and nose ring of your mold so you have access to join the halves. You are just not going to be able to produce a light enough fuselage without vacuum curing each half and then joining them together.