Plunge Moulding Primer: the good and not so good

[Gene K]

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

[CJP]

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.

 

Cheers 

 

Dennis

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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

CJP

[DMC]

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..

 

Cheers

 

Dennis

[DMC]

 

 

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

 

Dennis

 

 

[DMC]

Editing in text

 

 

After reshaping the canopy and windshield moulds and plunging another set I’m satisfied with the shapes.  I plunged the windshield .020 PETG and I think it’ll be okay.  The canopy might be another story, however. The problem with plunging a deep mould into thin styrene is that the stretching of the hot styrene stops at the edge of the female mould.  Only the styrene within the opening is stretched.  Consequently, as with the canopy mould, the first part of the mould to contact the hot styrene remains fairly thick but as the mould is plunged it becomes almost paper thin.  That’s not much of a problem with, say, .040 material, as in the cowling in the photo above, because of the extra thickness.  Forty thou is good for cowlings, spinners and the like but is too thick for canopies.  

 

I have been been unable to find any PETG thicker than .020 anyway but will have another look on the Web.  If I could find .030 PETG I’d give that a try.  Another .010 would make a difference.

 

My my best shot at getting an acceptable canopy is probably to vacuum form one.  When vacuum forming the whole area of the hot styrene is used and is pulled down over the mould so the thickness remains constant instead of thining out as it does with plunge moulding. 

 

Cheers and and thanks for looking

 

Dennis

 

 

Edited July 18, 2018 by DMC
Comments

[DMC]

Greetings loyal followers,

 

Float planes, I've always had an interest in them but, except for an A6M2-N Rufe built many years ago, I've never built one.  Lately my interest has been rekindled by a book I forgot I had.  It had a bright red profile on the cover of a Macchi Castoldi MC72 and an article inside about the Schneider Trophy Cup races.  Further stoking my interest has been Moa's vacuum formed Supermarine float plane build.  And, to seal the deal, I picked up this great book on the Cup racers at Duxford last Saturday.  

 

So, carrying on with the plunge moulding theme of this article, I'm going to have a go at plunge moulding a float for a Macchi M39, the 1926 cup winner,  If that works out I'll mould the other one and then carry on with modelling the rest of the airplane using the techniques outlined in Mr. Woodman's book.  

 

Should be a fairly easy build.  A Spartan cockpit, no wheels or wells to detail and no weapons.  Biggest problem will be the radiators but if I'm successful with the floats I'll deal with that later. 

 

Cheers and thanks for your interest

 

Dennis

 

[Roger Holden]

On 18/07/2018 at 13:54, DMC said:

  

 

I have been been unable to find any PETG thicker than .020 anyway but will have another look on the Web.  If I could find .030 PETG I’d give that a try.  Another .010 would make a difference.

 

 

PETG is available in .020 (0.5mm),  .030 (0.75mm) and .040 (1mm) thicknesses, which can be found easily by Googling or on eBay.  Personally, I wish it was available in thicknesses thinner than .020 (say .015) as .020 is fine for closed canopies but too

thick for open ones in my favoured 1/72 scale.

 

"When vacuum forming the whole area of the hot styrene is used and is pulled down over the mould so the thickness remains constant instead of thinning out as it does with plunge moulding."

 

No, there is still a degree of thinning when vacforming, but it's not as severe as with plunge moulding as the plastic is stretched more uniformly.  

[DMC]

Hi Roger,

 

Yes, so I see, hadn’t looked for any PETG on eBay lately as I had a couple of sheets of ,020.  I’ve ordered a sheet of .030 to see how I get on with that.  Also going to try chamfering the edge again to see if if helps. I used to do that but quit as it didn’t seem to make any difference.  I forgot that Mr. Woodman suggests doing it.  

 

Agreed, some stretching probably with larger or deeper moulds.  I’ve only ever vaced small stuff on my homemade vac former but I note that Moa commented on thinning in his S4 build.

 

Thanks for your reply.  Not many venture over to this part of the BM forums. 

 

[DMC]

Comments in a few minutes

 

Okay, using a set of plans I enlarged to 1:48, I transferred the outlines and templates to thin cardboard and used them to carve out the male mould in a block of laminated balsa.  I had decided to make the float with top and bottom moulds rather than split vertically as a kit manufacturer would probably do. 

 

Top left: balsa male mould with three of the templates.  The block is just a handle and I was able to plinge the top and then the keel by just switching the handle.  Saved me the trouble of carving two moulds.

 

Top right: first plunge.  I was somewhat surprised that it turned out as well as it did.  Needed just a little work on the stern to sharpen it just a little.

 

Bottom left:  the keel, which also turned out pretty good on the first plunge.  Float top and bottom both looking good so I went ahead and plunged another set.  Floats are symmetrical so I only needed one male mould.

 

Bottom right: top and keel trimmed and almost ready to be cemented together.  Balsa bulkheads will be located at the strut attachment points for strength.

 

So, really pleased with the results and it looks like I am committed   After float assembly I’ll tackle the fuselage.  Really getting into these Schneider Trophy racers.

 

Cheers, and thanks for your interest.

 

Dennis

 

[Courageous]

A very interesting thread Dennis, very informative...have bookmarked for the future.

On 7/22/2018 at 4:10 PM, DMC said:

Floats are symmetrical so I only needed one male mould.

Not always the case I believe. I read recently the development of the Supermarine S4-S6 that one of the floats might be larger that the other to cater for extra fuel capacity and torque and stuff...

 

I wonder if their is a tutorial on how to make the wooden formers for molds...

 

Stuart

[greggles.w]

I’ve come in at the tail of this thread, & clearly there is much to learn of merit!  I will wind back to the start ..

 

[DMC]

3 hours ago, Courageous said:

A very interesting thread Dennis, very informative...have bookmarked for the future.

Not always the case I believe. I read recently the development of the Supermarine S4-S6 that one of the floats might be larger that the other to cater for extra fuel capacity and torque and stuff...

 

I wonder if their is a tutorial on how to make the wooden formers for molds...

 

Stuart

Thanks for that, Stuart, and thanks for all the likes.

 

Interesting about the asymmetrical floats.  Apparently the MC 72 overcame the torque program with the contra-rotating props. Also, floats were smaller, lighter and had less frontal area.  MC 72 definitely on the.list.

 

https://www.largescaleplanes.com/articles/article.php?aid=109

 

How can I help, Stuart? Are you talking about plunge moulding the floats, and fuselage?  Or perhaps using another method.

 

Cheers

 

Dennis

 

 

 

 

 

[DMC]

1 hour ago, greggles.w said:

I’ve come in at the tail of this thread, & clearly there is much to learn of merit!  I will wind back to the start ..

 

Thanks, much appreciated.  Not meant to be the last word on the subject just a few things I’ve learned about it over the past few years. 

 

Speedbirds: I’ve held off purchasing the book as I don’t read French.  Are the drawings in the form of plans, sketches or thumbnails of each plane?  I’ve a copy of the Motorbooks edition of the races and it has a few plans that are very small but can be enlarged.

 

Cheers, and thanks again.

 

Dennis

 

 

 

[Courageous]

18 minutes ago, DMC said:

How can I help, Stuart? Are you talking about plunge moulding the floats, and fuselage?  Or perhaps using another method.

Basically I'm clueless on any method as I've never ventured deep into the scratch world. I deal in 1/72, so I don't know what is possible or best in that scale; plunge moulding, vacuforming or any other method. I follow Moa's work a lot which points me in the direction for corrections/ modifications. I also like what Bandsaw is doing with his Avro 504K but the scale is wrong and I haven't touched wood since school.

Basically, any help is good help.

 

Stuart (the Clueless)

[DMC]

1 hour ago, Courageous said:

Basically I'm clueless on any method as I've never ventured deep into the scratch world. I deal in 1/72, so I don't know what is possible or best in that scale; plunge moulding, vacuforming or any other method. I follow Moa's work a lot which points me in the direction for corrections/ modifications. I also like what Bandsaw is doing with his Avro 504K but the scale is wrong and I haven't touched wood since school.

Basically, any help is good help.

 

Stuart (the Clueless)

 

Ok, first thing you need is a plan, obviously, of the airplane you’d like to model.  I’ve chosen one for you as an example, you might chose something else.  The importance thing about this plan are the sectional templates in the upper right corner.  I used similar  templates for the M 39 float(s).  I stuck mine on thin cardboard with a glue stick and cut them out.  Also probably more important are the plan (top) and profile view of the float.  I traced the outlines on to a block of balsa and proceeded to remove the excess with a razor saw, a retractable snap blade and finally a scalpel.  I rough shape it at first and then use the scalpel, and the sectional templates, to finish it off.  That’s more or less how I did the floats for the M 39.

 

Bandsaw is an accomplished woodworker and is comfortable working with harder wood than balsa.  I’d try balsa at first as it’s easy to carve, inexpensive and easy to get.  1/72 is quite small and a slip of the knife might result in a large chunk of your carving, and your thumb, gone in an instant..  Keep several band aids to hand.

 

Not sure what else to tell about getting started.  Practice and experience will soon lead to intuition.  After you start getting the shapes right you can decide whether or not you want to stick with wood ar use your carvings as moulds to work in styrene.

 

Any questions, please ask

 

Cheers

 

Dennis

 

Afterthought:  gluing two pieces of wood together will give you a vertical center line, top and bottom, which will aid you when using the templates.

 

https://www.bing.com/images/search?view=detailV2&ccid=jX64vpgI&id=C9AF175D8F2C9596887B9DAF655491293BFEE6D5&thid=OIP.jX64vpgITQcxwSIwwrXTWQHaKI&q=supermarine+s5&simid=608013968283731064&selectedIndex=34&qpvt=supermarine+s5

[DMC]

Okay, finally managed to get a decent canopy for the Monogram Corsair.  Used .040 PETG this time and because of the depth of the mould it stretched out just about right.  Also cut back on the heat a little as suggested by Mr. Woodman.  Quite a few hours went into getting something useable but there was nothing else for it if I were to have a canopy for the much modified kit.  

 

Posting a photo of the reworked float mould for the Macchi M 39 later today. 

 

Thanks for your interest.

 

Dennis

 

Stumbled onto this while looking for canopy pics on Bing.  John B still around?

 

 

Edited July 25, 2018 by DMC

[DMC]

The stem of the float didn't look quite right to me so I checked it against a good reference image.  Clearly, it didn't have enough "chin".  I carved out the forward bottom of the float and spliced a new piece in place.  After carving it to the correct shape and sanding it, I epoxied a length of brass wire along the keel.  I thought I might get a sharper mould. It didn't make a whole lot of difference but it didn't hurt to try.  

 

Thanks for your interest,

 

Dennis

 

[Courageous]

Good improvement, sharp and well defined.

 

Stuart

[DMC]

One thing that became quickly apparent after plunging the entire float keel was the definition of the step. By cutting the moulding at the step and trimming the stern half I loose 3 0r 4mm that has to be made up.  Better to carve a new male stern half and re-plunge.  New moulding is the correct length and shape.

 

I'm going to carve a new front keel mould and float top also.  I want to get this procedure down pat as it looks as though I might try making more of these diminutive racers.

 

Thanks for your interest.

 

Dennis

 

[DMC]

 

After a lot of experimenting with carving new moulds and yet more plunging I think I've finally got the results I can work with.  This is a float in 1:48 scale for a Macchi M.39.  The M.39 won the 1926 Schneider Cup Trophy.  I had intended to scratch build the M.39 here in this thread but I think I'll move it over to the WIP page later.  

 

However, I'll continue to add any relevant photos and comments on this page as they arise. 

 

Thanks for your interest.

 

Dennis

 

 

[DMC]

Check out the photos for an idea of how much thickness is lost when plunge moulding deep male moulds.  The float in the top half of the photo was plunged using .040 styrene.  The sides along the chine have be reduced to about .020.  The float in the bottom half was plunged using .060.  It's been reduced to about .035.  But, had I vacuum formed the float the thickness would have been pretty consistent, losing maybe only .010 or so.  At lease in my experience.

 

Also, I went back and read Mr. Woodmans paragraphs on plunge moulding and, as he recommended, I have reduced the heat quite a bit and now the styrene doesn't have the really wet, shiny look that I was using before.  When all else fails......

 

Thanks for your interest.

 

Dennis

 

[DMC]

This probably one of those doh!, of course moments but I thought I'd post it anyway.  Having some way of marking the styrene so that the male mould is placed accurately on it is doubly important when there are two pieces that have to match up, like fuselage halves.  The hot styrene will sink into the opening and it will become pretty apparent just where the mould should go.  However, I still use pencil marks to help me get it centred in the mould correctly.  Too much to one side or the other and I get a thick and thin sided shell.

 

This Macchi M.39 fuselage half turned out just about as good as I could expect.

 

Thanks for your interest.

 

Dennis

 

[Marklo]

I'm wondering if you could improve the detail by a post plunge application of a heat gun or a hot hairdryer. I'm presently contemplating my Gamecock fuselage and will probably end up molding the fore decking and the front of the fuselage (if not all of it) and may try this when I get to the molding stage.

 

I find that although Woodman is  pretty the bible for scratchbuilding, I prefer to adapt his methods, e.g. for wings I prefer a plastic core and to CA the blanks to the sheeting rather than use double sided sticky,  Materials have also moved on since the book was published so I suppose that also gives plenty of scope for enhancing his methods ( he wouldn't have had CA for example).

 

Great thread btw.

Edited October 11, 2018 by Marklo
added extra stuff

[DMC]

Hi Mark,

 

Just so I understand, you want to sharpen the detail (such as?) on a plunge mould by using a heat gun of some sorts after you’ve plunged the item in, say, a toaster oven, or, perhaps, instead of a toaster oven?  Not sure, the only time I ever used a heat gun was when I was trying out my homemade vacuum forming rig out in a cold garage.  I couldn’t get the platen and hot styrene  over the rig quick enough so had to reheat the styrene.  I had mixed results but with a little practice it could be useful.  Best, however, to work in a warm place whether plunging or vacuum forming. 

 

I’ll need to look up the Gamecock to so what it looks like.

 

I’m sure that Woodman would agree that his methods were not the last word on technique and could certainly be improved upon.  Good place to start I’m sure you’ll agree. 

 

Thanks for the attaboy.

 

Dennis

 

Edited October 11, 2018 by DMC
Giving a thanks

[Courageous]

In my view, I think that vacforming and heat has its limitations and detail is one of them and the detail needs to be added.

 

Stuart