Thermoforming plastic to make landing lights

[npomeroy]

Here's a technique that I use as an alternative to vacuum forming.

This is to make the landing lights for a Funkey 600 size AS350. Here's a view of the type I am making:


I make a male form, usually with wood, and cast a female from the male, using plaster of Paris, mixed with about 20% cement powder. The cement makes a harder material and it sets much faster than the plaster by itself.

Here is a male mould, partly finished:


The male mould is greased, and a cardboard wall is hot-glued around it, into which the creamy-texture plaster-cement mix is poured. Here are the two parts after separation. The grey is primer used to fill and smooth the wooden part.



I have a sheet of 0.5mm PETG but you can cut the same plastic from soda bottles. If you heat a small sheet all over it will just shrivel up. So, you EITHER need to have a sheet a few inches larger in every direction from your casting, and protect most of the area from heating (e.g. with a cardboard or wooden sheet with a hole cut big enough to heat the working area) OR securely fasten the edges of your plastic sheet to a stiff frame e.g. of ply wood.

So, I place the female mould on the floor, place the PETG sheet over it, place a heat shield over the PETG, exposing an area I want to heat, heat the exposed area with a heat gun (paint stripper type, on low) until it softens, then press the male mould into it.
Here is the raw casting:


And here cut out with the lamp lens hole cut:


And here are both landing lights, buffed with bathroom abrasive cleaner, shaped and drilled, ready for priming.


The lamp lens, and reflector are made in a similar way but no female mould is needed. I just rounded the end of a dowel and pressed it into the heated plastic, supported on plywood with a round hole.

As I assemble the parts I'll post more details. I'm using tiny M1 (1mm daim. shaft) machine screws to fasten these to the fuselage.

Nelson

[ssmith512]

Super awesome!!!

Thanks for sharing that process. I learned something!

[Keyrigger]

Well done, Nelson. I need to figure out how to use that technique to make up a lens for my Little Bird build. I used duct seal (what I had on hand) to make a casting mold for a second antenna base on my TOW Defender and when ready to take the epoxy, it looked just like the female portion of your mold. Very cool and simple method and a great tip using a bit of Portland in the plaster of Paris. Take care.

Don

[npomeroy]

Originally Posted by Keyrigger

Well done, Nelson. I need to figure out how to use that technique to make up a lens for my Little Bird build. I used duct seal (what I had on hand) to make a casting mold for a second antenna base on my TOW Defender and when ready to take the epoxy, it looked just like the female portion of your mold. Very cool and simple method and a great tip using a bit of Portland in the plaster of Paris. Take care.

Don

Thanks Don.
The idea to add Portland cement came from an engineer when I was a graduate student at Univ. of Toronto - near your home turf. I've been using that male+female casting system on a semi industrial level recently - casting over 1000 small coffee cup sized units for bumblebees to lay eggs in.
If you just want a convex lens you just need a dowel or broom-stick the the end shaped accordingly, and press it into the softened plastic. One trick that may be interesting, is to press the plastic into woven cloth on a cushioned pad. The weave leaves a matte hatched pattern that look like a lamp lens pattern but it also took away the clarity.

Another tip for this technique:
If there is no gap between the two moulds the plastic may not fit between them. Sometimes I use a layer of flexible tape over the male mould before casting the female - then peel it off and thus create a gap. But if you grease the male first, by the time you've removed the grease later, and sanded the female to a smooth surface there is usually enough gap.

Here's some more images:
Male mould for the recessed light:


With the wall filled with plaster:

[JurassicJet]

That is super awesome! Very nice work. Question though... When you say "grease" are you actually referring to grease that I would pack a wheel bearing or similar with?

[npomeroy]

Originally Posted by JurassicJet

That is super awesome! Very nice work. Question though... When you say "grease" are you actually referring to grease that I would pack a wheel bearing or similar with?

It's just for easy separation of the 2 parts. I use "petroleum jelly" ("Vaseline" in some markets) but I've used bearing grease as well. You need to remove it after if you don't want it on the plastic - problem for painting of course.

Nelson

[gidz25]

Nice work!thanks for sharing

[The_Fox]

Amazing! Your Skills are Top Notch!

I am not skilled well, to try that way. As i need thouse lights, I designed in CAD and printed. It worked nice, i am satisfied.


This is a 470 size fuselage, but as the lights are CAD designed for printing 3D, they can be scaled in any size.

[npomeroy]

They look good. Will you make the transparent "lens" for the front by pressing a dome shape in clear plastic?