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3d printed fuselage plug for a new moulded F5J

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ThermalBoy

Neil

Wish my first effort had come out as good as this!

Looking at the pics closely it looks like there wasn’t enough ******* put in at the areas in the mould which are almost either right angles or in fact any tight changes of direction however small.  Sploogeis syringed in before you lay up any cloth at all. If you look at the pro made fuselages in areas such as this you will see that there is no cloth at these points merely black coloured epozy-*******. The consistency of this ******* should be thick enough to stay in place but not too thick that it cant smoothly squeeze out of the syringe. The syringe exit tube should be drilled out to as large as you can without losing the outer wall of the tube. (approx2-3mm dia)

Yes to doing a test with the mould dry and inflating the balloon to see if it still fails. This will save you a lot of wasted time/material/frustration and will allow you to see exactly where the balloon is failing. Rubbish bag bladders are certainly another route that can be used and work well but can be time consuming to make/test and get right every time in terms of a 100% sealed edge. I’ve used recycled rubbish bags for this type of bladder and had good success with them.

Hope this helps.

Colin

EDIT
For some reason I cant get the above to accept the word S P L O O G E so that s what the asterisks are!

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CTR

Cheers Colin  and Brett. Keep the ideas coming 🙂

As for temperature, don’t think it is too high because of the very slow cure. Certainly the remainder in the pot only rose by a couple of degrees, not like the tooling resin which reached 55 or so when it was going off! Good logical thought though.

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CTR

OK, so tested the balloons in the empty mould. Conclusive evidence that the 260 balloons burst because the cross section is too big at the leading edge of the wing.

Used a 360 and its been under pressure for 3 hours and holding up well. The unanswered question is ‘why did the 360 fail yesterday?’ I think it must have been to do with the cross section shape of the fuselage. When the balloon touches the resin it sticks in that position; as expansion continues, the next point that touches also sticks. It is left up to the area between these two points to stretch into the corners of the mould rather than the whole circumference of the balloon stretching equally. Well that’s my theory.

Question is, how to overcome it? Any suggestions?

Any way of lubricating the outside of the balloon without it interfering with the resin?

Other ideas?

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Kikapu

I've waited a bit, hoping that someone else would ask, but curiosity got the better of me.  I've looked up the word '*******'.  It seems to mean semen or premature ejaculation.   Then I waited again, still hoping that someone would give a simple explanation, but nothing.  Now I have to ask.  Can someone else explain if there's a connection between the dictionary definition and the word used in this piece, please?

Peter L

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CTR

No specific connection, but keeping on topic It’s an extruded bead of thickened resin to fill the sharp corners in the mould. Using a black pigment in the thickened resin gives a better match to carbon fibre too.

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CTR

Thanks for the various PM’s on this topic.

Suggestions of filling the corners with thickened resin before layup and using a thin smear of Vaseline on the outside of the bladder are worth checking out.

An Idea I had was to use thin PP tape (non sticky) laid in the mould after the layup. If it’s put down both sides, the balloon should slip on it rather than sticking to the resin. Got some on order which should arrive tomorrow.

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Marc RC pilot

 Most probably the stupidest idea ever but how about  putting fuselage in a lathe and spinning it at speed so that centrifugal forces do there thing?  

Or make a solid 3d fuselage mould and wrap/build up the cloth onto it? ( then cut where necessary to release from mould).

 

 

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Stormeflyer
On 08/07/2019 at 16:22, CTR said:

Thanks for the various PM’s on this topic.

Suggestions of filling the corners with thickened resin before layup and using a thin smear of Vaseline on the outside of the bladder are worth checking out.

An Idea I had was to use thin PP tape (non sticky) laid in the mould after the layup. If it’s put down both sides, the balloon should slip on it rather than sticking to the resin. Got some on order which should arrive tomorrow.

I’ve been reading your posts with great interest and wondered if you had read these links? I would definitely say laying a thicker mix at the wing seat area (sharp edges) will resolve those small voids.

http://www.nextcraft.com/fiberglassing.html

http://www.joewoodworker.com/veneering/v2-about.htm

The Joe Woodworker isn’t model specific but has loads of great links and techniques not that I’m saying your technique is lacking! Keep up the great work

 

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CTR

Hi Stormeflyer, glad you have found the thread of interest.

Good links for more general guidance on plugs etc and vacuum  generation.

I hadn’t seen these but appreciate you posting them.  Wasn’t sure how much detail to put in the posts without being too verbose; already quite a tome for the casual reader!

Latest update is not good news.  Despite using over 5 new coats of Easylease as instructed (Easy Comp’s promoted release system) the second moulding severely stuck in the mould and did a lot of damage. Talking with Colin, he told me they have had problems with it too! Shame it hadn’t come up in conversation before. I’ll go back to my old and trusted tin of Meguiar’s Mirror Glaze #8 which has never let me down it the past.

Here we go back to square 1, making another 3D printed plug and mould. I will take the opportunity to incorporate a few small design mods at the same time. Also this time I will make the plug stronger as mentioned in one of my previous posts so it will survive being removed from the mould and live another day (just in case of a repeat of the latest disaster!).

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Brett82

Unlucky mate, bound to run into a snag or two along the way.

I might be teaching you to suck eggs here so if you already know this then at least it might help someone else reading the post. During the many hours of videos I've watched of laying up wings and fuselages, a number of them have mentioned the best solution is multiple layers of wax and then PVA, until the moulds are well used.

The reason why the PVA is so important is because it dissolves completely in water. The PVE forms a very thin layer between the wing/fuzz and the mould so what they do is pull a section of the fuzz/wing (whatever may be stuck) just enough so they can spray water between the gap, just a normal window cleaning spray gun. As the water runs between everything it dissolves the PVA which helps break any bond between the parts. 

There is a very good video of a bloke pulling a wing from a mould. It gets to a point where it is very stuck and he sprays water between the gaps and it pops loose with not too much effort. I will try find it. 

Brett

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Brett82

 

Here is the video. have a look at about 8 min into the video. Will be good to watch all the video so you get a sense of how much he struggles then how easily it pops once he sprays water into it.

 

 

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CTR

Thanks guys for the advice.

I don’t generally like using PVA because you can’t get a good shine like you can with wax; but as you point out, it does give a water soluble contact surface in times of trouble!

As I said in my previous post, I’ll ‘stick’ to using #8 release wax in future rather than these modern chemical methods which are predominantly designed for labour saving, not necessarily better functionality.

Please keep the advice coming, you never know what you don’t know!

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CTR

Just read the link provided by Stormeflyer; very interesting.

Certainly promotes the benefit of PVA release for new moulds. May be worth using it for a few pulls, then revert to wax for the better finish.

Trouble is, I don’t have a gravity spray gun and I hadn’t intended going into mass production 🤔

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Brett82

Hey mate

Most people doing the moulding and on the link advise to use it till the mould has "broken in". Certainly when using the plug to make the mould. So if as you say you use it for a few pulls it might save you some major headache later on.

Brett

Ps, most places advise to put it on with a brush. In fact the link says avoid spray as it leaves too fine a layer. Its needs a single layer but applied "fairly generously". The link gives a lot of really good info.

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CTR

Quote from the link text:

It is imperative to spray PVA in a film thick enough to be peeled off the mold in sample areas. When holding the film up to the light, no pinholes or porosity should be present. Proper PVA application involves using a siphon cup gun and gradually building up a number of thin passes to form a continuous thick film.

This confirms the need for a reasonably thick film. I presume the spray application is to improve surface finish compared to brush application.

My dilemma still remains; the cost -v- only the need for a couple of fuselages, and wanting a good finish!

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Brett82

Just above the quoted section, it states: 

its better to not PVA than to spray thin PVA

I missed the bit about the siphon cup gun. You will be fine doing it with a brush, especially if it's just the first couple to get the mould broken in. Have a look at the video below from East Coast Fibreglass.

 

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CTR

UPDATE:

Finished the new plug and laid up the first half of the new mould. Made it with 40mm sides this time as I had a slight bow in one half of the mould last time, after post-cure, which I had to fix. (Slits in the 25mm wood stiffeners , then a strip of Kevlar applied when clamped flat. This worked).

First pic’s show 3D printed locators and splitter spacers in the box mould prior to layup. I used a piece of melamine covered furniture board (B&Q) for the splitter board this time. To get the reasonably accurate cutout for the plug I used a small 90deg. Engineers square. Held the plug on top of the board with soft fillet wax blobs and ran the square along the fuselage profile, marking the board as I went.

3rd photo is the half mould layup with the new plug still in place ready for the 2nd half to be done. Hope to do that tomorrow. Maybe get the first pull from the mould this weekend all being well.

I used release wax on the plug and PVA release on the board. This was a good solution along with the board material. No warping like seen on the polypropylene sheet used for the first mould. Also the board was less expensive than the PP sheet.

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CTR

Not sure where to post this; but as it is for the Rad1, here seems as good a place as any!

Needed a 31mm spinner so, back to my trusty 3D printer and here we are!

Just an idea, would it be worth having a thread or other deposit place for STL files for 3D printing? I have a collection of spinners, servo mounts,  control horns etc. May be useful to others. I’m sure there are others out there who can add to the library too.

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CTR

OK here we go with a bit of deja vu.

The second mould, reasonably successful. Just needs a bit of remedial work.

First photo is the mould; second one is the small area of gel coat pulled away due to sticking to the plug in the tight corner.

Next photo is the damaged area ground out with a Dremel, followed by filling with a small amount of catalysed gel coat. The gel coat will not fully cure when  exposed to air so I covered it with a small piece of PP tape. PE tape would work too. By excluding the air it will fully cure and the surface will not be sticky. You could mix some wax-in-styrene into the gel coat to do the same thing but I didn’t have any to hand.

Once the gel has gone off I will sand and polish the mould. Hope to get the first pods out in the next few days.

I have read a tip to help ‘condition’ the new mould with minimal risk of sticking. New moulds have microscopic pores in the surface which need filling to avoid the moulding sticking. The tip is to wax the mould as normal then just use gel coat. Leave it to go off, then peel it out of the mould. Repeat wax, gel, remove a second time. Shouldn’t be a problem even if there are some ‘stuck’ areas. This process will help fill any microscopic holes and ensure the following mouldings will release more easily. Obviously release wax needs applying as normal before each new layup.

I’ll let you know how it comes out!

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