Nose Cone Mold Manufacturing Guide

Procedure

SUMMARY OF NOSE CONE MOLD MANUFACTURING

Lessons Learned

• 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 but ball bearings are probably better
• Epoxy sides of mold, not just inside the mold, and apply wax to ease mold release
• Use smaller squeegees for applying the epoxy because larger ones won't fit the curvature of the mold as well

Below is the recommended procedure for making a nose cone mold, learned through trial and error and thanks to the advice of Prof. Mark Drela, an leading expert in aerodynamics and composite layups.

1. Obtain necessary supplies
   • Medium-density fiberboard (MDF)
   • Layup supplies (squeegees, acetone + shop towels for cleaning)
   • Clamps
   • Sharpie
   • End mill for router
   • Sandpaper + spray bottle of water
   • Mold release wax
   • PVA film
   • Fine-haired brush
   • Bearings or dowels for alignment holes
2. Get access to necessary technology
   • Router: like a giant mill, drills and moves laterally to route out mold
   • Horizontal bandsaw or tablesaw to cut MDF

   Notes about Gelb router:

   • CAM 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.
3. CAD mold using CAD of nose cone
   • Check out Solidworks mold-making tutorials for help
   • If you want a linear section at the base, determine how long (you want at least 2" for enough engagement with the coupler or things will be bendy/not rigid)
   • Include holes for alignment pins (around three on each side of the mold). Half-spheres work even better because you can put a bearing inside and alignment will be easier/more accurate.
4. Prepare Mold Material (MDF)
   1. Measure: The amount of MDF you need depends on the thickness of MDF you're using, and the dimensions of the nose cone you want to make a mold for. 
   2. Mark the cut lines in Sharpie, accounting for the thickness of the blade that you're using to cut the material.
   1. Cut: Using a bandsaw works, but a table saw might be better. Basically you want the lines to be as straight as possible and the pieces you're cutting might be pretty large, so plan on how you're cutting in advance. Having another person is good because you'll have a lot of pieces to carry and it'll be heavy. 
   2. Epoxy layers together

1. Route mold
   • Prepare CAM
     • Set finishing passes (the step size for the roughing cut should be no greater than 1/2 the diameter of the tool you're using)
     • Make sure the tool is long enough not to collide with the sides of the mold
   • Prepare mold (add brackets so you can attach securely to the table)
   • Route
     • Have vacuum ready
     • Zero the router (zero for router and CAM file will be different so make sure you're zeroing correctly)
     • Do a test pass offset above the mold
     • MAKE SURE THE ROUTING TOOL DOES NOT CUT INTO THE ROUTER BED
     • 
       
2. Post-processing
   • Sand mold to 500-grit
   • Wet sand mold 800-2000 grit
   • Add one layer of epoxy
     • Mix epoxy (slow-cure)
     • Apply thick layer and let sit for 20 minutes. Make sure you get epoxy on the top too, but not in the alignment holes if you have them.
     • Wipe excess epoxy away. If you don't wipe it well, sanding will be more difficult later.
     • At least 24 hours later, sand to 2000 grit. Shouldn't take too long because the mold should have been very smooth before epoxy was applied in the first place.
   • Wax
     • descrbie
   • PVA film