Cut Star Frame
From PyroGuide
Note that this PAGE WILL BE MODIFIED SOON
Cut star frames are used to prepare uniform slabs of composition to be cut into perfectly cube-shaped pellets of combustable material. Star uniformity is one requirement for artistically pleasing shells.
Making the frame:
This page does not deal with the process of making cut stars. It briefly decribes how to make a very simple cut star frame. The design is self-explanatory to a great extent; however it is neither the only nor the optimum design, but it works if you plan to make small or medium-scale batches of stars per time (say up to 500g of stars).
The tooling consists of a heavy wooden base-plate, which ought to be as straight as possible. You also need a wood lath of the desired dimensions, which is cut to give the four wooden borders. The main requirement is that one beam has to equal the desired cut star dimension. Thus, if we plan to make 10mm cut stars the lath has to be 10mm *let´s say one inch. The width of the borders is not critical but it ought to be possible to fix the borders to the base plate for many times without breaking them apart. The lenght is also not critical, but even if longer borders allow larger batches to be cut they are also more difficult to handle.
The borders are cut in a way to give us a rectangle when fixed to the plate, as seen in the picture. After cutting the borders are placed on the plate as they are desired to stay together when cutting. Each border is fastened to the plate using two brass screws; the resulting frame should represent a perfect rectangle. There should not be any gaps at the junctions or between the removable borders and the plate. Failing which there will always be some damp material which migrates into these gaps. Then we mark their contours with a waterproof pen.
When the frame is to be removed, the screws are only unscrewed to the point where they no longer protrude of the bottom. The borders can also be numbered for future use, to know which side they belong.
Using the frame:
The frame is used as follows: A roughly adequate batch of star composition is dampened, kneaded well and protected with foil or cloth to prevent too rapid drying. Three of the four borders are screwed to the base-plate and their close fit is assured.
The major part of the dough is taken and roughly pressed into the framed area by hand making the plate slightly protrude over the upper egde of the borders. Then the fourth border is screwed to the plate. The idea is to place it close to the edgeways end of the rough plate and fill the remaining framed space with the rest of the dough. This method makes it possible to adjust the framed area to match the amount of available dough.
Alternatively all of the borders can be fastened to the plate before preparing the dough. In the latter case there will most likely be some leftover dough though, which will have to be cut in a second step.
After the framed area is completely filled with dough, we compact the compositon using a wooden hammer or roller. This compaction step is essential, since otherwise the stars lack the desired densitity, show cavities and tend to crumble or break easily. The material protruding over the edge of the borders is then cut off with a very sharp knife. This excess of comp can be reused. Then we carefully remove the borders which will leave an even plate of damp composition. This is followed by star cutting with suitable tools e.g. with scrapers (see pic) and priming (if necessary).
Possible problems:
A crumbly or creamy composition results from improper wetting and this will not be treated here. However some comps may stick to the borders when we try to remove them and this may cause parts of comp to break off the slab. This issue is resolved when we cut around the edges of our slab before removing the borders. This is done with the same tooling used for cutting the stars. Ofca and others like Dan Williams use plastic to make their borders or coat their wood with some layers of polyurethane to prevent both sticking and chemical contamination. This may be a good idea.
Problems of damp compositon intruding into the gaps between two borders or between the border and the plate can be eliminated via the elimination of these gaps. However, there will always be some liquid matter intruding.
Problems of contamination: You should never use the same wooden cut star tools for both sulphur-containing and chlorate compositions. The chemicals migrate into the wood and the tooling is always contaminated to a certain extent even if it looks clean. Therefor we must obey the same strict tool-separation guidelines we follow talking e.g. about mixing screens. Make another frame and stay safe! Always clean your tooling after use. Cleanness is an important part of safety in pyrotechnics. Use water to remove solidified matter, do never scrape stonehard star fragments with metal spatulas etc.!
Larger batches?
More sophisticated designs may be necessary if you´re the notorious cut star maker. The principle is the same but higher and heavier borders are used to allow kilo batches to be made each time. These large cakes are then first cut vertically to give us numerous simple slabs as produced by the above method. Examples how to make large-sized tooling are found in Ofca´s "Technique in fire" Vol.5 or in Shimizu´s classic.