The chocolate forming device featured in this instructable is used to create strings of chocolate without the need for an external or internal heat source.
Now I here yourself thinking is such a thing possible? Well yes it is possible to shape normal milk chocolate without the need for heat. All you do need is a high pressured squeezing system.
Whats more you don't just need to stick to boring profiles like a circle, you can have the filament come out any number of different shapes, but generally the simpler the better.

When the string is first extruded it is malleable and thus workable, you can use it to do whatever your imagination gives you but if you have trouble, I have included a uses page at the end of the instructable. After a while it turns a bit brittle as though tempered which makes it really tasty.

Step 1: Choc Chamber

The chocolate chamber is where all the chocolate is stored and compressed in.
For my chamber I used a Ø60mm aluminium tube with wall thickness 10mm. the length I decided on is 150mm but could be anything from 50mm up.(Couldn't be much shorter because piston is large). I bought this peice of aluminium from ebay seller forward metals (http://www.ebay.co.uk/itm/Aluminium-Tube-60mm-Diam-x-10mm-Wall-x-250mm-Long?item=150337213831&cmd=ViewItem&_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D1%26po%3DLVI%26ps%3D63%26clkid%3D8273219770097453398)
As you can imagine, (not very clear in picture), this is quite a chunky piece of aluminium. It has to be so chunky so that holes can be drilled in the ends to hold the mounts and extrusion plates. Both sets of holes consist of 4 drilled and tapped M6 holes.
drilling these holes straight proved to be quite tricky for me, as the milling machine I had access too was a bit too small with the vise already on it which is why in the photo there are two vises on the bed(the old one is smaller).
Whenever doing low volume tapping operations after drilling on the milling machine, I start the thread off in the machine as to getit straight from the beggining. I think the photos show this operation clearly but do leave a comment if you have trouble understanding it.

Step 2: Piston

This part pushes the chocolate up the chamber, whilst providing a tight seal to stop chocolate traveling back down.through this design, you can also pull the piston back down . Because there is the potential for thousands of newtons (the weight of a few tonnes) to be going through this part, it needs to be robust. This is one reason that I machined the pston from Delrin, a food safe, self lubricating engineering plastic.
I bought this billet from ebay seller dunk247 (http://www.ebay.co.uk/itm/BLACK-ACETAL-BAR-BILLET-51MM-DIAMETER-DELRIN-2-/370595823756?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item56493b808c)

Step 3: Hydraulics

The system that I am using to move the chocolate out of the extrusion plate is a hydraulic bottle jack. These pumps are usually used for lifting cars and vans, so there should be plenty of available force to extrude a little chocolate. I opted for a large one (5 tonnes) to decrease the probability of dissapointment as I had little idea with which to choose. A 5 tonne jack was a good choice because the higher the amount of cocoa solids, the more difficult it is to extrude.

Step 4: Mounting

Brief
What the mounting has to do is:

Hold the chamber above the jack.
Stop the assembly from falling over.
Give a rigid surface for jack to press against.

Solution

Bolt short bars onto bottom of chamber as close to centre as possible(this will decrease stress in chamber as holes are further apart).
bolt these bars to an offcut of kitchen worktop with threaded rod.
Worktop is long enough to not tip over when jack is pumped.
Flat steel bar is placed underneathe to aid in keeping rigidity and to act as washer for threaded rod. To fit these, slots had to be routed in the worktop bottom.

Step 5: Extrusion Plate

The function of the extrusion plate is to form the chocolate ito the desired shape. The chocolate is forced through a small hole whose shape will become the string's profile.
I started off with a 13mm thick aluminium plate with 2mm and 3mm holes to extrude. Out of these the 3mm hole gave better results. I found that when a large chamfer was put on the in side of the hole.

To make interesting shaped chocolate string you could use any number of cnc machines. eg. laseer cutter, cnc milling machine, 3D printer.
As I only have access to a laser cutter (not a good one), I cut 2x 6mm plates and laminated them together. Due to the brittleness of acrylic I decided to make a cover to reduce the stress acting on plates. Before this cover, all of the plates that I tried cracked before chocolate came through. After, only most cracked. Inspecting the cracked plates, I learned that cracks formed most on sharp internal edges as can be seeen in the pictures. To reduce the likely hood of cracking in the future, corners where the angle<90^o will be filleted with radius 0.5mm or more. This will only be a problem with laser cutting and 3D printing as you will always have the cutter radius when milling.
Of the three options for making plates, I beleive that 3D printing could produce the most interesting plates, perhaps building the profile up helically so that the string spirals.