Composites
Fin assemblies
Fin assemblies are a critical part of a rocket's passive stability, and I have made them by bonding plate fins to a tube or by molding them with a 5 part mold.
For bonded fin cans, I made a carbon tube using the convolute wrap method, then bonded fins made from carbon plate onto it with structural epoxy. I've used a variety of alignment jigs to attempt to get the fin plates as parallel with the axis of the tube as possible, but there is always some misalignment.
However, by molding the fin can out of a continuous laminate it can eliminate the misalignment issue as well as create a more stiff attachment between the fins and the tube, which makes the fins stronger to aeroelastic effects. I made the fin can in the picture with a five part mold with four outer quarters and a central cylindrical mandrel. The four quarters each have half of a fin profile cut out, and get the composite laid into them. Then the quarters are closed around the cylinder and compressed. The result is a contiguous laminate with improved outer surface and better alignment than a bonded can.
Nosecone
Nosecones go on the nose of the rocket and are the first parts that hit the airstream, often seeing the highest loading and heating on the rocket. I have made them several different ways.
1. Sleeve over a male mold - the same biaxial sleeve described in the Tubes section can be used to make nosecones because of its ability to varying its diameter. Sleeves along with a male 3d printed plug can be used to make nosecone parts very easily with little upfront cost. However, this results in an uneven wall thickness and a inconsistent OML.
2. Gores/Fabric over a male mold - Fabric can also be used to make nosecones by cutting "gores" or shapes that conform to the mold geometry. This is especially necessary for compound curve shaped nosecones, as a single piece of fabric cannot be wrapped continuously around them. These gores or plies are placed onto a male mold overlapping to build a part. This method often results in a significant seam between the last plies on the OML which must be sanded down.
3. Compression molded with a 3 part mold - By inserting either of the previous layups once they are laid up into a female mold, the OML can be controlled and the surface finish drastically improved. However, the effort to create the female molds is significant.
Tubes
Tubes were the first composite parts I made, and perhaps the most essential. The two methods I have used to make tubes are sleeves and convolute wrap.
Sleeves are biaxal woven "socks" of composite material which expand and contract like a chinese finger trap. This means that a single size of sleeve can make a multitude of sizes of tube, or conform to compound curves such as for tapered layups. I slide these sleeves over a mandrel and add resin for each layer. This results in a tube with tubes with fibers running around the tube, similar to a filament wound tube. Wind angles vary based on sleeve size vs mandrel size, but are generally in the 40-70 degree range.
I convolute wrap tubes in the standard way, by wrapping a continuous ply of fabric around the mandrel and adding resin as each new part of ply is added. This results in tubes which are stronger in bending due to the more axially oriented fibers, but weaker as pressure vessels and in torsion.
Both methods are released from the mandrel with a layer of polypropylene plastic film between the layup and the mandrel. The layer of plastic film acts as a release film, allowing the layup to be separated from the mandrel after curing.