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Above: Hermes 1 nose cone mold (4 layers of 1" thick MDF, sanded and finished with gel coat), manufactured by Raul Largaespada.
Overview of Nose Cone Design
Hypersonic optimum with a 2" straight section for the payload coupler
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What size bolt?
Phenolic washer
Fiberglass Nose Cone Manufacturing Procedure
Overview of Nose Cone Design
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Alignment pins, pry slits
Manufacture Mold
To route the mold we are using the router in Gelb (next to Todd's shop). You will need an STL file of your nose cone mold. Make sure to wear a dust mask while routing and use the vacuum because a LOT of dust will be generated.
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- Program is called "Cut3D" and is a dedicated toolpath for CNC machining
- Make sure to orient part correctly, paying attention to the axis along which you want to cut it. There is usually more than one way to orient the part, just make you set it up on the router according to how you defined it in the software
- Cut3D gives you the ability to scale parts if you need
- The "roughing cut" removes most of the material. For this mold Cut3D says it takes 23 minutes (will vary depending on what you're routing)
- The "smoothing cut" finishes the mold by smoothing the surface. Cut3D says it takes 56 minutes for this mold.
- Make sure you select the proper "feed rate" and "plunge rate." This depends on the material you're using.
- Make sure that the toolpath is correct and save it. Give the file time to download onto the USB
- When routing, make sure that the tool does NOT intersect the table
- Put a foam block under the tool when you turn the power off or it will crash into the table.
- You can either use the vacuum attachment while routing or vacuum periodically while it's routing.
Mold Preparation
Required Materials:
- Sandpaper (400 - 2000 grit)
- Wax
- Epoxy
- PPE: Respirator, gloves
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- Make sure you account for the thickness of ablative/whatever mold prep you're using when you make the mold (for example, if you said you'd use gel coat and increased the size of the mold, you either have to use gel coat or make a new mold because using epoxy to fill it in is not the best/most accurate solution)
- Don't use Fibrelease if you're using wax
- Don't fill cracks in with Bondo- it's difficult to work with and surface of the mold won't sand as easily/epoxy won't permeate the Bondo
- Heat guns are effective in speeding up curing
- Sanding wax is difficult. Make sure you only add wax when you're sure you're ready
- Alignment dowels work well
- Epoxy sides of mold and wax them to ease mold release
- Use smaller squeegees for applying the epoxy because larger ones won't fit the curvature of the mold as well
Nose Cone Layup
Required Materials:
- Fiberglass (5.7 oz S-glass)
- Epoxy (Fibreglast 3000)
- Wax
- Fibrelease
- Phenolic microballoons
- Spray gun
- Squeegees
- Acetone
- Epoxy boats
- Popsicle sticks
- Spear tool
- Scissors
- PPE: gloves
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- Spear tool (two pieces of disposable squeegee attached using 5-minute epoxy to a long rod) works well for smoothing fibers on the inside of the nose cone
- Make sure fiberglass plies are wet enough or you risk delamination
- Do not use Fibrelease, just use wax
- Don't put the ablative layer on the outside --> apply if after the layup
- When vacuum bagging, use cones instead of two separate halves because this will be difficult to apply
- Make sure the outside of the mold is epoxied and waxed so that fiberglass doesn't overhang and stick to either end (makes mold release more difficult)
- Make smaller, and more pry slits so that mold release is easier
- Take the time to vacuum tape WELL so that you aren't looking for leaks later
- Consider using Vaseline for mold release after all (messy but it might help avoid delam)
Nose Cone Tip
Required Materials:
- Steel
- Bolt
- Washer
- Lathe
Thermal Data Collection
We will attach several thermocouples and PRTDs to the inside of the nose cone in order to obtain valuable data about the heating profile of the nose cone during flight.
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