Molding Airframes Knowledge Exchange Insider Thread - Page 4 - RC Groups
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Nov 15, 2010, 12:31 PM
Build it again, Sam!
Harpye's Avatar
How many would you like to build ... for one I could support you with another technique which suites your needs... it uses Depron, it bases on a good 3D construction but comes out like the warbirds of FSK or Alfa .. Check out my web site and go for the RC modeling section - go for the tutorial of the Turbo Raven. For your birdy you would have to build the wings in same manner as I did the fuse...

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Nov 15, 2010, 07:03 PM
Crashing with style
deadbird's Avatar
Hi all,

I have to say some of your techniques for molding Depron are producing some fine results.

I'm pretty new to the RC community but have wanted to do something for a long time - just work got in the way. Having been an avid fan of building scale static/display warbirds as a boy I really thought with the advent of the minaturised Rx & servos, kits that I made in my youth would serve well as templates for lightweight, micro or peanut scale as I always used to know it.

This year I bit the bullet & grabbed an aileron & elevator controlled bank & yank micro trainer in the form of a Minium Super Decathlon and taught myself to fly, crash, repair, crash, repair, fly etc. I really cannot describe what pleasure I derived from actually being able to remotely control an aircraft for the first time.

So - flying learnt (how niave I am) I thought it would be a good time to put some ideas I'd been kicking around into practice and with some investigation and sciency type info from Depron I decided to set about molding some of the light stuff to try and create my own 'kit' to build and use the inner working of the Decathlon to power & control it.

I chose to use Plaster of Paris to create the positive and negative molds because it was easy to find, cheap and easy to use - my first subject - rather ambitiously was a 1/32 Hawker Hurricane Mk1 and the slow climb up the learning curve began...

I soon realised that this project would probably turn out to be more of an experiment and was satisfied that it would be extremely unlikely I would get a Hurri flying warbird from it, but I would get a wealth of experience and knowledge on Depron, its characteristics and limitations in this process and learn more about compression or press molding.

Then during a spot of armchair research I then strayed upon threads that Harpye & Heliman420 had posted on some of their builds. You guys are really pressing forward with this stuff which meant I had to sign up to see where it was going.

I'm afraid I left it for a long while as my inexperience in the field of RC didnt exactly give much confidence that I would know what I was talking about but if you dont ask right?

The technique I used was to warm the plaster of paris molds in the oven to 100-110 degs C. I drilled a small hole in each mold so I could insert a temp probe whilst they were still in the oven.

I then take out the 2 sides of the mold and place the sheet of 3mm Depron between the two and slowly apply pressure. The plaster retains plenty of heat for a relatively long time - a bit like a stone. I then G-clamp with protective sheets of MDF either side to spread the pressure from the clamp so it doesnt cause the plaster to crack. Leave it for 15 mins then take it all out.

On the down side the plaster does have a tendancy to crack (due to the heat) and some molds only last for a few shots. The thicker the mold the less likely it is to crack, but it also depends on mix ratios with water too when making the molds initially I think.

I'll post some more as the thread develops - heres some pics of a few of the pieces I have got out of the process. Not the best quality photos - I will try better next time!

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Nov 16, 2010, 01:03 AM
Like a Boss
Heliman420's Avatar
Very nice, excellent job keep at it, and please continue to share your progress here
Nov 16, 2010, 01:06 AM
Addicted to building...
Freddie B's Avatar

Looking pretty good to me, especially using the plaster mold idea. Brings the cost down to where everyone can give it a try, and still get acceptable results for being on a budget.

The high end builds by Heliman and Harpye are true art in motion, and tons of work shows in the quality. I appreciate this very much, and we can all admire their efforts.

I still like when we can bring the tech stuff to the masses and keep teaching building and hands on knowledge to more modelers. The world will be a better place if we can keep interest in using ones head and hands alive. I've done plaster cast molds to make fiberglass parts. Yes it's fragile, but works for cheap and easy one off stuff.

Thanks for sharing and your parts would work out well enough to make most people happy for their efforts.

I'm going to give Polyester All-purpose Filler (Same as Bondo Auto Body filler)a try too, it is superior to plaster in durability, not too expensive, and has worked well in the fiber glass mold department too. Not sure how much heat it can take but worth a try.

Thanks everyone, cool stuff indeed!

Nov 16, 2010, 01:16 AM
Registered User
MUTCAKE's Avatar
I have been using Fix-All and it is working but I think I need to experiment a bit more. I will post when I have a good looking model. I carve all my models from blue foam first then cast them. I've been using vaseline as a release agent. Not even close to heliman/harpye's excellence but good enough for painting! But hey, I would have never known how to even begin with out this help. Heliman you da man!
Nov 16, 2010, 03:03 AM
Like a Boss
Heliman420's Avatar
Thank you guys i really appreciate that i myself was inspired by reading aerogel's original molding threads, the man is a true artist, and the late Bob Hurd who got me started in molding closed cell polystyrene foam, without them id still be rolling my models from flat foam...(not that theres anything wrong with that)...

Im very happy you folks have decided to try molding!!! as i mentioned before this method can produce some of the coolest models, and can be done with affordable common every day materials so everyone can have a go.

The more people that get into this the more the techniques can be refined and new tricks could be learned.

Im looking forward too seeing your creations

All the best.
Nov 16, 2010, 05:27 AM
Crashing with style
deadbird's Avatar
Freddie B, thanks for your words of encouragement. I would really love to work towards the quality that Heliman & Harpye produce though but I'm finding the research and experimenting as enjoyable as the flying at the moment.

Sure there are moments of sheer frustration when a mold that has taken a couple of days to make and a week or so to dry/cure falls apart in your hands when it comes out of the oven (too many bubbles in the plaster mix I speculate) but when you open a mold and you get a piece of Depron thats almost as good as the template it is a real buzz.

I'm fascinated with the surface detail that can be produced from well molded foam too. Using a plaster cast of styrene kit components lifts the detail and it transfers right over to the foam. One of the issues I've found though is if the kit has recessed panel line detail (which is what you want for true representation of scale) as opposed to raised panel lines, if the plaster takes to the template, the resulting detail is very fragile and usually comes of when the template is removed or best case comes off with the first molding process, embeded in the foam.

Other areas of the plaster molds become delicate too after heating. Bits chip off edges when the depron is pulled from the mold. Does anyone know of a way to toughen up the plaster? - I've tried a wash of diluted PVA but that causes severe release issues with the depron - and I tried it with plenty of release agent too. Ideas very welcome!

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Nov 16, 2010, 06:52 AM
Thanks for the Fish!
aerogel's Avatar
Originally Posted by deadbird
Other areas of the plaster molds become delicate too after heating. Bits chip off edges when the depron is pulled from the mold. Does anyone know of a way to toughen up the plaster? - I've tried a wash of diluted PVA but that causes severe release issues with the depron - and I tried it with plenty of release agent too. Ideas very welcome!

Attachment 3601099
Do you seal your plaster molds? Find a very high temp poly or enamel brush on spray when I was doing plaster way back in the day I found that sealing helped with many of the problems with it..

Another low cost way of doing it with plaster is to use a silicone brush on mold method it’s thick and will not drip off use this as the skin. Then use plaster as the mother mold on top of that… I’m doing this for a large cast I’m working on I’m sure it would work with forming depron and give a better pull for sharp edges and some undercuts.. as for a release agent Mans Ease Release 200 you can’t go wrong.
Last edited by aerogel; Nov 16, 2010 at 07:09 AM.
Nov 16, 2010, 11:17 AM
Addicted to building...
Freddie B's Avatar

I just mix up some 5 minute epoxy, thin it well with rubbing alcohol and brush it on very generous, blot off excess and let dry. Next I melt parafin Wax, like for canning food, dip my molds in it several times, bake it awhile until no wax resadue remaings, and polish well when cool and dry. Makes a pretty slick mold to work with.

Nov 16, 2010, 11:52 AM
Scratch building addict
rotagen's Avatar
Thanks harpye, I'm thinking depron is a better way to go than using 2 part foams or that "great stuff" liquid spray foam that is used for insulation? I think I've seen some of your stuff, you use epoxy JBweld for making the mold?

Actually I don't think I will make too many of them, unless I keep crashing, I just want to learn how to mold.

I will check out your website today. I'd like to make a mold for my peregrine even though I think I could make one by hand-bending my depron. Mainly because I don't think I could make a bird with such nice smooth curves like that spanish website had without using a similar method to his. Perhaps he used fiberglass as the fuselage material? I have so much to learn.
Nov 16, 2010, 04:21 PM
Crashing with style
deadbird's Avatar
Aerogel, this sounds like a quick way of protecting the plaster mold (I dont seal them at the moment). Would something like a high temp resistant spray on enamel lacquer do the trick? Seen a black spray in the local car accessories shop thats s'pose to be good to 600 degs.
With the pigment being black this may also help with increasing heat absorption and speeding up the mold heating process too. Definately worth a shot if thats the sort of thing you mean.

Cant seem to find Mann Ease products in the UK I'll keep looking but if any of you know of a source over this corner of the world let me know or suggestions for an alternative. When I do use release agent I have grabbed the silicone spray on the shelf - but I'm sure I read somewhere it eats the depron - which I havent found so far but have been using it sparingly.

And I am liking the epoxy and wax method Freddie B Thats really going to tuff things up and make it slippy. Didnt even know you could thin epoxy. I have plenty to learn. Looks like a few of my molds are going to be made into guinea pigs Thanks guys for the advice.
Nov 16, 2010, 04:36 PM
Build it again, Sam!
Harpye's Avatar
Deadbird! I still dont know the expression by plaster of paris but yor results look neat and for the first attempt its really promising!

Rotagen: When you cut out a piece of plywood with the shape of the wing If you can get 1 K Diisocyanate floor glue ( my favourite Brand is Fermacell) and stir it up with 1 drop of water for 8 ccm of glue ... the material reacts with the water and foams up filling nearly any gap.....

place the top half of the ribs reduced by the dtrength of the skinning materal on this and afterwards pull tape armed Depron over this positive discretizised Mold you will probably get a bird wing structured like those you probably know from the Alfa warbirds

I'm just busy in another size where Ureol molds come too expensive!!!

My 1,4 M A1 Skyraider .... the fuse is made in the same technique I recommended for your wings!!
Nov 16, 2010, 10:31 PM
Addicted to building...
Freddie B's Avatar
Plaster of Paris (In U.S.A.) is a casting plaster, white, mix with water and very inexpensive. Hardens in 10-20 minutes, but takes days to dry out completely if very thick. Hard, but easy to carve, etc. It will form to a mold and very little shrinkage if any when dried.

Kids use it in art class, crafting it is good for small statures casting, fairly fragile but hard. Don't know what they would call it in Europe, but it is just a very common plaster.

If they make plaster walls in Europe homes, similar to what you would buy dry, mix in water, and top coat a wall for finishing work. Although this would be called Gypsum plaster here.

Nov 17, 2010, 12:00 AM
Registered User
MUTCAKE's Avatar
Well here is my first attempt at this. I love Luft "46", so I tried my hand at a Lippisch P-20.
I think I will make the wings larger than scale (like almost every other model Ive seen) to lower wing loading. These came out ok, but I know it can be done better. I can carve any shape I want (well a reasonable lookalike) from blue foam, which is better for me since I can make them to any size I desire. The sharpe lines are just for show as this form is not quite good enough yet.
Nov 17, 2010, 12:04 AM
Registered User
MUTCAKE's Avatar
I have followed your depron tutorials for quite a while, and I must say that you have made some of the most exquisite models from depron that I have ever seen. Your talent is enormous. Thanks for all the great threads.

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