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| Step | Estimated Time | Number of People | Notes | ||||||
|---|---|---|---|---|---|---|---|---|---|
| CAD Mold in Solidworks | 1 | Google "Solidworks Mold-making Tutorials" and you can find helpful articles and Youtube videos. | |||||||
| Measure MDF layers | 1 hour | 1 | Make sure to leave enough space on either side of the nose cone (and room for pry slits/alignment holes). Account for thickness of blade when marking lines. | ||||||
| Cut MDF | 2 hours | 2-3 | Cut the lines as straight as you can, because this will give you nice straight edges that will help a lot with alignment during setup for the router. | ||||||
| Epoxy layers together | 2 hours | 2-3 | Epoxy soaks into MDF quickly, so make sure you're using enough epoxy and clamping everything together tightly or you'll get gaps after you start routing. | ||||||
| Prepare CAM | Make sure your step size isn't too big or the tool will be taking off too much material and create a lot of friction/ruin the tool, etc. Quentin Thernize ('21) did this for Hermes 2 so talk to him if you need help. | ||||||||
| Set-up piece on router | |||||||||
| Route | |||||||||
| Sand mold | 5-7 hours | Up to you | Wet sand once you get up to, like, 800 grit. Sanding takes a long time, so prepare for this! Make sure you don't sand the edges to keep them nice and sharp! (protect with some straight edge) | ||||||
| Epoxy mold, sand again | 2-4 hours | 1-2 | Epoxy mold | Apply, let soak for 20 minutes, then wipe away. Don't apply multiple times because epoxy doesn't stick very well to epoxy. Then sand back up to 2000 grit | |||||
| Wax mold (5 layers) | 2-3 hours | 2-3 | Don't apply wax until you're ready because wax is difficult to sand off. Wax the mold, let sit for 15 minutes in between coats. | ||||||
| Apply PVA film | 30 minutes | 1-2 | Use a fine-haired brush (I used a makeup brush). Don't apply acetone to the mold after this or the PVA film will dissolve and mold release will be more difficult. |
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
- Make sure to account for the fact that the mold will have to be clamped down before you glue the MDF layers together
- Make sure your step size is no larger than 1/2 the diameter of the tool you're using (in our case, a step size of 0.25" was fine)
- Don't skimp on glue when gluing the layers of MDF together or you might get cracks in the mold where the layers come together
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- Sand mold to 500-grit. Sanding takes a long time so prepare for this!
- When sanding, make sure to protect the edges of the mold with something straight like a piece of aluminum. If you don't do this, the edges will be curved and when your part comes out of the mold it will have an annoying seam that you later have to sand off.
- Wet sand mold 800-2000 grit
- Add one layer of epoxy
- Mix epoxy (slow-cure)
- Apply thick layer to the inside of the mold, the top, and sides of the mold. Let sit for 20 minutes so that it soaks into the mold. 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 back up 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 the mold
- **Note: wax is difficult to sand off, so make sure you're ready before you apply it. (i.e. you still need to sand more epoxy, etc.)
- Using a shop towel, get a dab of Meguiar's mold release wax (or other suitable mold release wax) and apply a moderate amount to the mold (wherever you applied epoxy, so the inside, top, and sides)
- Rub in circles until there are no more streaks
- Get a fresh shop towel
- Continue to rub in small circles (this is called "buffing") until the mold is really smooth. You'll feel the resistance decrease a lot suddenly, and you'll know it's ready when it's super easy to glide the towel along the mold.
- Let the wax sit for 15 minutes if you're using Meguiar's (read instructions for different wax)
- Repeat this 4 times (so you want 5 layers of wax)
- Apply PVA film
- Using a fine-haired brush, apply PVA film to the inside, top and sides of the mold (everywhere there's epoxy and wax).
- Let sit for 20 minutes.
- **Note: be careful not to wipe any of the surface with acetone as this will dissolve the PVA film and make mold release more difficult.
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