Plunge Moulding

[Greyhead]

This is a way of producing small plastic mouldings without the need for any vac-forming.


The first stage of the process is to make a hardwood plug, the better the surface finish the better the final moulding will be. If you’re being pedantic make it smaller by the thickness of the plastic, but knowing what the finished thickness of the plastic will be after moulding would certainly tax my brain past the limit!


Then cut a corresponding hole in some plywood. The clearance between the plug and the hole should be about the thickness of the plastic you intend to use but it isn’t that critical.





Cut your plastic leaving plenty of spare and position it centrally over the hole; I find it helpful to pin the plastic in place to stop it curling when the heat is applied.


Heat the plastic using a heat gun; keep the heat gun moving to get as even a spread of heat as possible over the entire area of the plastic then quickly plunge the plug through the hole to the required depth.





Here are 2 tank sumps for my SE5a, one roughly trimmed.





Getting the right amount of heat takes a bit of trial and error and you will almost certainly have a few failures before you get it right but the plastic can be any thermo plastic from pop bottles to ice-cream containers so it costs nothing to experiment.

[Guest]

Another useful idea, especially for doing smaller parts as shown.

Cheers for Posting Grahame.

Regards........Mark

[Greyhead]

This is the first time I've tried this method although I've known about it "for ever"! It really is only for small parts, for anything bigger vac-forming is the way to go and I'll certainly have to get round to making one as per your instructions but at the moment the SE5a is taking precedence.

[Guest]

I can only agree with you there Grahame,

The SE5A must be getting close to completion now and I would do the same in giving that priority before starting anything new, it's always so easy to get sidetracked onto something else.

The Plunge moulding method certainly seems to have worked well for you and as stated, It is probably the better method for small parts where Vac-forming would be wasteful just for a couple of small bits.

The Sumps look good on the Model too.

Regards.......Mark

[Guest]

Thanks for this Grahame - like you I've known about this for a while but never actually tried it. Any idea as to how thick you could go when it comes to forming sheets in this way...would 1mm be out of the question?

[Marudek]

I used similar technique to make canopies for my Hornet and Pitts 1:33 card models. I simply formed canopy with paper parts, then filled paper canopy with Milliput. When it settled I removed paper and polished the “plug” (or matrix). Then I cut off the bottom of 2l Coca-cola plastic bottle and inserted my matrix mounted on a scrap wood block. I heated up the whole thing over the flame of gas cooker and let shrink. After it cooled down I just had to trim the canopy.

I’ll use this technique to make canopies for my 1:33 card Catalina (which is now waiting in a queue).

Regards,

Marudek

[Greyhead]

I've just measured the plastic I used, it's 0.7mm and that moulded easily so I don't think that 1mm would be too thick. It would take more heat to soften but it would "hold" the heat longer; it costs nothing to try so why not give it a go?

[Guest]

This sounds great!.

To be honest Grahame, I was thinking about making a simple vac-former for those parts of my canopy that have a compound curve - however, after reading this thread it would seem that plunge moulding will give me similar results for a lot less effort.

Thanks for the words of encouragement - I'll give it a go just as soon as I can.

[Guest]

Will try this for my M-55 Geophysica..... Thanks

[Guest]

Flying Plastic Bottles

I also have the same plan for this plane which I obtained it as a free gift with an Airplane magizine purchase many years ago. I have blown it up to suit a 120 Enya four stroke and have only got to spliting the cedar and spuce, as a panelbeater I was looking at starting at the easy parts first and making the bonnet and alloy parts.

After reading your articel regading the altrations you had make to your plan, is it possible to have a copy of your alterations. the following scrip may help when making parts from plastic.



Over the years I have modeled with very little money and to that end I have found, used and scavenged any materials to attain an end result.

One of the latest objects I have found is the soft drink bottle, while looking at the base of a bottle and envisaging it as an engine nacelle or an engine cowl for a round motor I commenced to cut it to length and shape when I attempted to match it to the diameter of the fuselage it was so close to the diameter all I needed to do was warm it up and stretch the plastics over the edge and pin it into place. Using a hair dryer I found the bottle began to shrink in diameter … It didn’t work but later I thought about it and found if I carved a plug the shape of a canopy when forced inside the bottle and packed it from underneath so that the plug was tight on one side of the bottle and the packing was no greater in width than the base of the canopy, when the heat was applied the bottle shrunk and pulled down over the plug and gave a perfect reproduction of the plug, all that was needed was a trim around the base.



Later I found if the complete front of a glider from the wing cradle forward was carved several soft drink or cooking oil bottles with their necks and bases cut off could be slid over the plug and heated, as each bottle shrunk the next was slid into place with an over lap of 3/16 “ each segment would locate on each other, when all were heated and locked onto the plug a cut with a box knife from end to end underneath, the parts could be sprung off the plug reassembly by clipping each together and a strip of thin ply the length of the knife cut fixed to each of the segments. I used a staple gun, which shot through the plastic and into the ply. The ply was used to mount the radio gear and to fix the front section to the fuselage, the plastic forward of the radio will remain in place if just clipped on and dispense with the ply backbone as this will break if you hit hard enough. A nose shape was carved from a piece of pine and forced down the first plastic segment and fixed in place by the staple gun. I found that the plastic bottle fuselage was more durably than the other material used as it would bend and buckle on impact but would pop back out again ready for use. Oh! I haven’t spent much time honing my flying skills so my planes need to be resilient, Try breaking a soft drink bottle there is not a lot of selection in colours but if painted the plastic looks good. I can post picture of the method if you are interested

[Greyhead]

I’ve heard of this “shrinking” method for making mouldings but never tried it myself. If it can make complete sections of fuselage as you say it sounds really good and should be able to be used to produce other “large” mouldings, which are not suitable for plunge moulding.

Please post any photos showing the method and the end results, I’m sure they will be of great interest to many of our members.

[Greyhead]

I’ve heard of this “shrinking” method for making mouldings but never tried it myself. If it can make complete sections of fuselage as you say it sounds really good and should be able to be used to produce other “large” mouldings, which are not suitable for plunge moulding.

Please post any photos showing the method and the end results, I’m sure they will be of great interest to many of our members.