I started by trawling the Pound Shops in my area for anything that looked like it might contain useful parts. It's an odd paradox that many of the most promising items ended up being useless while some of the simplest products proved invaluable. Lateral thinking is essential for this kind of part-hunting. Next, I dismantled everything, being careful to keep all the screws and even the packaging.

After a lot of trial assembly, I finally decided on a satisfactory layout for the front of the reactor (I'm quite tempted to build final versions of some of the alternatives I pieced together during this stage). At the centre is part of the dynamo and from a hand-powered torch. This sits on a disc cut from a shiny metal hanging garden decoration which in turn fits into a translucent blue plastic ring used to store a set of in-ear headphones.

I decided to go for an industrial, manufactured look rather than the prototyped model seen in the first film. With this in mind, I avoided exposed coils of wire, opting instead for a set of enclosed modules surrounding the ring. I made these using sections cut from the guards of disposable razors. I detailed them with strips of ribbed cable ties, which were later painted copper-coloured to suggest internal coils of wire.

I was disappointed not to have found anything with a usable motorised gearbox to power the ejection mechanism, so I had to rethink how that would work. A quick return visit to the Pound Shop produced two lever-action cork screws. After some extensive Dremel surgery I was able to assemble a four-armed Frankenstein cork screw. To my surprise, the mechanism worked quite well with all four levers extending when the central shaft moved, and vice-versa. With the concept proved, I used my angle grinder to chop the arms down to stumps and to remove the screw and handle from the shaft.

The corkscrew mechanism defined the required length of the reactor for me. It was longer than I'd have liked, but I felt it was acceptable since I had decided on a heavy-duty, industrial reactor and the one seen in the movie seemed to go an awfully long way into Stark's chest anyway! A solar decklight with an interesting ribbed body provided the bulk of the cylinder. I cut a hole in its diffuser and fitted the body of a large highlighter pen into it to make an internal shaft which would house the palladium holder.

I used the legs from some mini tripod torches with interesting detailing to extend the cylinder, providing gaps through which the corkscrew arms could protrude. The metal surround for the decklight conveniently matched the diameter of the lantern body I planned to use for the front of the reactor, providing a nice solid rear plate into which I could drill additional mounting holes and fix the main switch.

I stripped the rubber from the handles of some disposable razors and used them as additional detailing on the cylinder. Further skinned razor handles were cut to length, detailed with sections of cable tie and mounted on the stumps of the corkscrew arms. These became the main levers that close around the cylinder and are used to open the unit.

The corkscrew action also defined the space into which I'd need to build the receiver mechanism that accepts the palladium. I used the end of a plastic tent peg as a circular cover for the end of the shaft. A clip-on booklight (which incidentally, my partner spotted being used as a prop in V for Vendetta) donated a useful device with a friction-regulated spring that would move the cover out of the way when it opened. The clip from the battery cover on the booklight made a nice retaining clip for the palladium - which was cut from the plastic body of the light. After some careful measuring and adjustment, I mounted the receiver on the end of the corkscrew shaft so that it aligned correctly. Moving the corkscrew arms now extended the receiver out of the hole, and the circular cover automatically moved to one side allowing access to the palladium strip inside.

I desoldered the LEDs from an inspection light and some small torches and wired them together in parallel before fixing them to a useful circular piece of clear plastic packaging. All additional wiring came from a reel of speaker cable. With a bit of trimming I was able to fit this assembly inside the blue plastic ring and feed the central LED up behind the dynamo part. The blue plastic dimmed the LEDs more than I'd have liked, but I was still quite happy with it. I wanted a battery source that was compact. I considered button cells but doubted they would power the nine LEDs for long. Instead, I cut up the 3 AA battery holder from the inspection light to make one single and one pair holder which I then wired in series. I cut the body of a camping lantern down to the minimum height possible to contain the battery holders, while retaining the thread for its screw-on lid which would allow access to the batteries when needed. The front elements of the reactor were mounted on the lid.

Although I already had a manual power switch from one of the torches, I wanted the LEDs to switch off and on when the reactor was opened or closed, so I experimented with various switches from the other lights and torches without much success - they all required too much pressure to activate. I finally decided on a low-tech solution, braiding some speaker wire to make a brush which would make contact with a piece of metal from a battery clip, mounted on the end of the corkscrew shaft. I fixed the brush inside a ring cut from the bulb holder on the lantern and gripped this inside a part from the booklight. I detailed the parts with yet more invaluable strips of cable tie, as they would be visible from some angles. The brush device was then mounted inside the battery compartment so that the end of the corkscrew shaft passed through the ring and made contact when the unit was closed.

I used a range of metallic laquers to finish the reactor, ranging from dull steel through aluminium to chrome, as well as occasional points of copper. I opted to have several parts in plain black as I felt it made the details stand out and gave the finished piece more depth. For much of the contruction, I painted the individual parts before assembling them.

The complete list of Pound Shop ingredients looks like this:

• 1 x Camping lantern
• 1 x Mini solar decklight
• 1 x Mini earphones set
• 1 x 'Hanging swirly' garden ornament
• 1 x Hand-powered flashlight
• 1 x LED Inspection light with head strap
• 1 x Pack disposable razors
• 1 x Pack cable ties
• 1 x Pack of speaker wire
• 1 x Folding book light
• 2 x Corkscrews
• 4 x Mini tripod torches
• 1 x Highlighter pen
• 1 x Pack lighted tent pegs