Mechanism to Generate Spiral Shape

There are many variations...

http://en.wikipedia.org/wiki/Spiral

CAD software...

http://www.freedownloadmanager.org/download/archimedean-spiral-cad-3906867.html

http://jwilson.coe.uga.edu/emt668/emt668.folders.f97/anderson/writeup11/writeup11.html

A rack and pinion could be rigged up for this, with the pinion's pitch circumference equal to the spacing between successive wraps of the spiral.

If material is "fragile" it cannot be bend thus no system to form it as a spiral. If the material is "ductile" and presents a yield limit then you may use same technology as for spiral coils (springs used as energy accumulators in mechanical motors as for clocks).

Good point, it would help for the poster to better define "fragile" wouldn't it?

Whata bout curlers, works on fragile hair...

If you need to fabricate the spiral, you might need to make a cone and mark the pattern on the cone corresponding to the desired spiral spacing and number of revolutions needed.

The fragile strands could be held in place with clips, pieces of tape or even a low-tactile strength adhesive. To remove the spiral from the cone, invert the cone. Or you could make the cone from a rubbery material and remove the central axis to let the rubber sheet go flat once the spiral is formed.

Fabricate a cone like this and mark the pattern you need to position the strands.

Fragile material cannot be bend this is the main problem. As for what you suggest the devices I mentioned are used in spring manufacturing and are extremely simple in fact the wire/flat is pushed against a knife and directed with two ther which can be changed as radial position thus generating different and programmable radii.

For me for instance ceramic is fragile since it can afford only a small elastic deformation and then breakes since it has NOT any yield.

Maybe the fragility is dimensional in nature...

You may be right -- But it depends on how fragile, doesn't it? The material needs to be bent to go into a spiral shape; if it can't be bent then the problem is moot.

Well... consider a thin piece of straw that is partly dried. It can be bent somewhat, but is still fragile, in the sense of being easily broken. Nick Name makes a good point, obviously what is fragile will break instead of bending - we can only assume that the material in question can be bent but is at risk of breaking, like a partly dry straw.

Usbport's approach of using a mandrel is a good way to form it - but something will have to be added to support the fragile strands, or they will not form a free standing spiral. If they can be formed into the desired shape on a mandrel for support, and then strengthened and hardened with glue or resin, this might be sufficient. Or incorporate wire for support.

"Fragile" is an insufficient description of those strands for you to receive a meaningful answer. If the contributors to this forum were given more information about their physical properties, someone with the requisite theoretical and practical knowledge of the material might give you exactly what you are looking for. Otherwise, probably not.

Thanx for suggestions. The fragile description beg a paradon was too fragile. I am looking at forming a dough (with no gluten as in wheat dough) which generally has a tendency to break. Wrapping around a cone as an option was tried with limited success as upon inverting and tapping the cone the dough loses its spiral form. Coiling on an inverted plate (more like thread wound about the bobbin) was also quite ok. Still remains unresolved as this has to be done continuously and every time the dough breaks, continuity of the shaping process gets affected calling for re-initiation manually

It sounds like you need a baking cone - to wrap the dough, bake it in place, and then remove from the form. Or I should say, enough custom baking cones to do the work continuously. Assuming that dough will be baked, and will harden sufficiently to be self supporting.

So the dough is in preformed fixed lengths....

Can you not extrude the dough and wind it as it lays a cable?

Can the dough strand have a flat bottom?

Will you be applying icing on top?

A simple guiding principle would be to unwind a wire or cable from a central post or spool. Here's an example of one that comes in toward the center, but others, including a patented kit (Tethering device kit - Patent # 3963192 - PatentGenius), worked outward. Usually, there would be a kill switch of some form either at maximum or minimum radius, whichever represented the end of the job. http://www.youtube.com/watch?v=DpQBHyfx7O4 . This may help you form the pattern but we could almost certainly provide better help from a more detailed knowledge of the problem.