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Manufacturing Techniques

This post aims at showing the methods that were used to produce the fins and the main tube also showing a comparison between the carbon nose cone and the balsa nose cone.
Safety Recommendations

  • When cutting any type of carbon sheet make sure to wear a musk not to inhale any toxic fibre
  • Always place the carbon in a close storage so that it is stored safely 
  • Use gloves when handling resin and hardener


Manufacturing the Tube

 Material Needed
  • Carbon Fibre Sock (Bidirectional Fibre)
  • PVC Tube of external diameter equal to internal diameter of the rocket
  • Wax
  • Resin
  • Hardener
  • Big dimension shrinking tube 
  • Hair dryer/hot air gun
  • Paper Tape
  • Brush

Carbon Sock Sample

Procedure
  1. Wax the PVC tube on the outside over which the carbon fibre sock will be placed. Leave the wax for more than 2 hours and repeat the process at least twice before starting with the lay-up
  2. Create a stand that will allow you to work on the carbon sock over the PVC tube without touching the ground(Eg. fix the ends of the PVC tube with bolts attached to wood walls. This will allow you to rotate the tube as you like)
  3. Lay up the carbon fibre on the PVC tube by sliding the sock over it. Make sure that the end of the fibre sock doesn't ruin too much when opening it up (The fibres tend to separate between one another)
  4. Fix the ends of the fibre with the paper tape allowing the sock for adjustments
  5. Prepare the mixture of resin and hardener (A combination of 40g and 80g of hardener and resin are suggested for one layer of sock of 800mm of length)
  6. Using a brush distribute uniformly the resin and the hardener over the tube. At interval of around 5 minutes use the hot gun to obtain a uniform distribution of the mixture over the sock.
  7. Check that there is no overflow of resin 
  8. Pick up the shrink tube and let the PVC tube with the carbon sock over it slide inside it. 
  9. From inside to outside warm the shrink tube up in order to get rid of the air bubbles. Press firmly on air bubbles trying to let the air escape.
  10. Do not overheat the shrink tube and the carbon or everything will melt together
  11. Let the tube cure for at least one night
  12. Remove the shrink tube by cutting it and the carbon sock from the PVC tube.
Final Product of the Tube


Manufacturing the Fins
When we came up with a method to make the rocket fins, we had to make sure to provide a solid attachment to the rocket body. In fact the loads on the fins could be as high as 10 N. As a consequence we had to provide a large surface to attach them to the body glues strength is effective against shear forces. The fins will have circular sides enclosing the rocket’s body to provide the maximum surface area for the glue to have effect. Eventually 3 carbon layer were used to have enough bending stiffness during flight.

Materials:

  • Wax
  • Resin
  • Hardener
  • Big dimension shrinking tube 
  • Hair dryer/hot air gun
  • Paper Tape
  • Brush
  • Silicon
  • Wooden Tables
  • Bidirectional Carbon Fibre Sheets
  • Clothespins


Preparing the mould:

  1. According to the number of fins and the rocket’s diameter divide equally the circumference of the rocket such that each fins will be with a high surface area of the rocket’s body
  2. Cut the PVC tube in pieces according to point 1.
  3. Make sure the each PVC piece is paired with an equal size one; these ones are going to be used later to close the mould
  4. Prepare 4 silicon sheets of the size of your fins
  5. Wax the silicon sheets and attach them to two separate wooden tables
  6. Get a third wooden mould so that its length is three times the height of the fins
  7. Use the third wooden table to prepare the mould: fix with hot glue two PVC pieces cut previously about 10 cm distant between each other at the center of the wooden table.
  8. Fix with hot glue two silicon sheets on the wooden table making their sides matching with the PVC pieces
  9. Wax the PVC pieces and the silicon sheets

Preparing the fins:


  1. Cut the carbon fibre sheet of a size at least 4/3 compared to the final size they will have to have
  2. “Prepare hardener and resin (use the same amount of resin and hardener)”
  3. Using the brush spread the mixture covering the all surface the carbon sheet will be placed on
  4. Place the carbon sheet on the mould and cover it with the mixture making sure every part is soaked with it.
  5. Repeat the same procedure for 3 layers of carbon fibre
  6. Close the mould by placing each of the wooden tables on the carbon sheet and by pairing the PVC pieces with their correspondent
  7. Fix the apparatus with the clothespins
  8. Make sure not to apply to much pressure on the fin not to squeeze out too much resin
The image shows the first product obtained with the above technique
Comparison Balsa and Carbon Fibre Nose Cones
Manufacturing the Balsa Nose Cone

Manufacturing the Balsa Nose Cone didn't turn out to be really challenging. The hardest part was to find a raw balsa with the dimensions we needed; before starting to work on the balsa cone the team had to cut and glue together a balsa table in order to have a an octagonal prism. The octagonal shape was obtained to be able to shape it on the lathe at a very slow speed using sandpaper to obtain an ogive shape.The fine tuning of the cone was then completed by manually.
Lathing Machine
Obtaining Circular Shape


Manufacturing the Carbon Nose

 Shaping the carbon nose cone was quite challenging. A mould was created and the carbon sock was applied on it and twisted at the tip keeping it tight with a cloth clip. Eventually the tip was sanded and finally resin was applied to it as showed in the figure below.

Twisted tip
Applying final resin layer

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