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Plunge Moulding Tutorial: cowlings

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On 7/9/2018 at 6:32 AM, Troy Smith said:

I also just edited the below to get the captions next to the relevant pics


Thanks, Troy!! Helped tremendously.


Gene K

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On ‎7‎/‎8‎/‎2018 at 3:24 AM, DMC said:




 Yesterday I spent a considerable amount of time on a back story of sorts and then lost it all when this iPad recycled.  I’ve tried copy and paste on my laptop but had no luck. So, II’m going to tray again, quickly, with the iPad and try to get some text in before it recycles again.


Starting right away with the photos:

The first one up is the book that started all this scratch building off.  I found my first copy in a second hand book shop.  Long out of print (‘75) it really opened my eyes as to what could be done with “plastic card”.  Mr Woodman was a genius with the stuff.  Copies are still available on the auction site. A couple at ridiculous prices.  Pity.


Next picture is of an Otaki FW190.  My first real attempt at modifying a model.  Using wooden moulds, I plunged a cowl, cowl ring and canopy.  Took a few tries but I eventually got something I could use.  Thank you Mr Woodman.


Next up is a four-part photo of the clay I use for the male moulds.  The beige is Super Sculpey, the grey is Super Sculpey Firm.  The firm is indeed firm so I mix it about 50/50 with the Firm to make it a little more pliable.  I run it through an old pasta machine several times and then roll it around until it’s well blended.  The photo bottom right is a mould for a Testors U-2 camera bay hatch.  I vacuum formed it but in hindsight I think I could have plunge moulded it.  Bottom left are moulds for the canopy of my P-38 build(s).  I don’t use toothpicks anymore and I’ll get around to the reason why later.


Fourth photos show what can be done if a mould is not quite the right shape.  I use Liquid  Sculpey to fix a thin piece of clay to the already baked mould and then bake it again.   The clay will stand several bakings so additional clay can be added a bit at a time if needed.  


Next photo: balsa wood for the female moulds.  The platform is about 1/4” and the riser about twice that.  If I run out of the 1/4” stuff I glue two thinner pieces together.  The riser has to be thick enough to keep the plunge from bottoming out.  I use bulldog clips to clamp the styrene to the female platform leaving just enough room for the side clips to clear. 


Next, before I epoxy the clay mould to the handle, I take it out on a scrap of plastic and then transfer the outline to the female mould platform and then cut it out.  I discovered that cutting out the shape for the male mould was easier if I split the platform down the middle and then cut the shape(s) out to the pencil lines.  Then I glued the two halves together and,  when set, finished up by shaving thin slivers out until the male mould is a tight fit with no more clearance than the thickness of the styrene then I intend to use.  This is important as to much clearance will produce a sloppy plunge.


The last two photos are of the little Revell Camel that I started as I enlisted in BM.  The cowling, the hump and the “canvas” wheel covers were plunge moulded.  I used a dowel for the cowling mould and a piece of clay for the hump.  I really enjoyed working on the little Camel until I accidentally snapped the lower wing off.  


So, got most of what I wanted to say before I lost it again.  More yet to come.


Please, any criticism,, suggestions or questions have it and thanks for looking.
























This is a really informative article and after studying at the pictures you posted it sparked a memory of that Harry Woodman book - after about an hour of digging around I found my copy of it that I had forgotten about - this is what I like about BM


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2 hours ago, CJP said:

This is a really informative article

Thanks for that, really appreciate it.

2 hours ago, CJP said:

found my copy of it that I had forgotten about

Must have bee a EUREKA! moment.  Good that you were able to find it and I agree about the site..





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Editing in text in a few minutes


Okay,  cowlings are another kit replacement part that are fairly easy to do.  


Top left: this one that I made out of clay but didn’t get quite right.  Good enough for a demonstration, however.  This will be a two step plunge.  Note how sharp the edge is on the opening.  


Top right: first plunge using .040 thick styrene, enough for a little filing or sanding if needs be.


Bottom left:  flipping the assembly over while the styrene is still very hot, and using this length of aluminium tubing, which is conveniently the right size. I pressed into it to get the rolled edge.   


Bottom right: After the second step.  Surprised to get the “spinner” as I hadn’t done this with tubing before.


I first experimented with this method on the intakes for the SH-2G and then used it for the Monogram F4U-4 intakes.  I expect there are other ways it could be useful.


Cheers, and thanks for looking






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