The PET bottle trick (step by step instructions here) looked so cool.

I am on my way to working out comfortable and functional interface solution, to get robust and functional arm stump protection. Also I am slowly getting my hand/s dirty in the domain of building some of my own stuff – and if just for testing out some ‘spare parts’. Second last but not least I should also create a feel of ‘amateur’ and ‘enthusiastic’ not as to scare off our ‘professionals’. Also, I always believe in full step by step documentation of stuff, and if only for later referral. Even in instances where it seems that I failed. No one can learn if failures are not available for reviewing.

So trying this one out came naturally.

Required material:

• Alginate (cheap, web order)
• Plaster cast (cheap, supermarket or web order)
• PET bottle (try to get something a bit bigger than the correct size)

Using alginate I first did a stump cast resulting in a wobbly reproduction of my arm:

Here is the resulting shape. The chromatic alginate helps in that its states (‘in solution’, ‘fixing shape’, ‘fixed’) are easily recognizable by its color:

Using a plastic bag (which I did the next time around) helps a lot in getting the finished cast out (see next step):

Using regular model plaster cast (cheap plaster poweder from the supermarket, put some of it in water, mix it and Bob’s your uncle) I filled the alginate imprint:

This now needs to sit for a couple of days. The alginate can simply be peeled off the cast model. The issue is to wait long enough for the plaster cast to dry out and harden.

Then I finished the lemonade contained in that bottle, removed the label sticker from the bottle, sawed off the bottle floor and heat shrank the PET bottle on the plaster cast model of my stump using a cheap heat gun from the local store (not your average hair dryer but almost) (these things are good fun but not everything melts and warps as gracefully as PET bottles do). It did not at all take 15 minutes for the bottle to shrink to the plaster cast shape – that shrinking happened within a few minutes.

Side view of the PET bottle after heat shrinking (as you see my first plaster cast model contracted some fractures but no biggie):

It is extremely easy to mount a tool in the bottle opening but the tool mount was not what I had in mind. Nevertheless just for documentation:

Here is the layer by layer setup using the PET bottle cap:

First I put on a thin sleeve:

Then I place the PET stump protector over that (unused parts of the shrunk bottle got removed in the meantime):

A second sock is put over this and I am ready to carry or push heavy items, to get down to cleaning out stuff, lift around tyres or tons: