Foundation Prime Radiant (via 3d Print Assist Casting Workflow)

The Prime Radiant from AppleTV's Foundation Series. 

The Prime Radiant: 

An Archimedean solid, cuboctahedran made of six square faces and eight equilateral triangles.

The internal lattice is created by projecting the edges inward toward the center. A 3d lattice constructed from perspective shifted 2d projection. Thematically satisfying given that the Radiant is supposed to be third dimensional projection of a fourth dimensional quantum computer. Conceptually similar to a tesseract...

I know there are some other models out there but I really wanted to make my own, to explore the geometry a bit more and use it as an introduction to casting workflows.

Up front: this is a challenging build and a good example of a mixed-process make that blends 3d printing, post-processing and casting concepts.  

Instead of reading this thrown-together list of items and description you can also just watch some youtube videos on dice making or resin dice casting.     Exact same process here.

You'll need:


Platinum Silicone, 15A or above; for example:
https://www.amazon.com/dp/B0CXTF535N?ref=ppx_yo2ov_dt_b_fed_asin_title

Transfer Tape:
https://a.co/d/bVCK6Oc

Duck Tape or really sticky packing tape:
https://a.co/d/b5ChHmL

Epoxy Resin, (Deep Pour advised); for example:
https://a.co/d/3FD7D2T

Primer:
https://www.hobbylobby.com/crafts-hobbies/craft-paint-stencils/spray-paint/krylon-colormaxx-spray-primer/p/81039819

Gloss Coat:
https://www.hobbylobby.com/crafts-hobbies/craft-paint-stencils/spray-paint/glossy-krylon-fusion-spray-paint-primer/p/81209783

Gold Leaf or Gold Metallic Paint of your Choice:
https://www.hobbylobby.com/crafts-hobbies/craft-paint-stencils/spray-paint/krylon-premium-metallic-spray-paint/p/1393?srsltid=AfmBOori83Wu446ze0DBsM4z1zQkIjzHimzLna9mDRAOoYvCSU8mDvMD


2k ClearCoat; for example:
https://www.amazon.com/dp/B00W2D83K2?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1

3" Air Polisher; for example:
https://a.co/d/43a544K

A step-sanding / polishing kit; for example:
https://a.co/d/2dxSMZv

You might also want a way to keep all of those discs organized - I got you covered: 
https://www.printables.com/model/1435597-stackable-3in-sanding-disc-trays

Epoxy Polishing Compound and Cleaner:
https://a.co/d/jbY99yW

Petroleum Jelly: https://a.co/d/dpQJICH 
-or-
Mold Release spray: https://a.co/d/7lLczhP


Nitrile Gloves:
https://www.samsclub.com/ip/EQPT-Blue-Powder-Free-Nitrile-Gloves-2-pk-300-ct/13943808234?classType=REGULAR&from=/search

Paint and Body Respirator Kit:
https://www.harborfreight.com/paint-and-body-respirator-kit-large-56983.html

Safety Glasses or Goggles:
https://www.harborfreight.com/safety/vision-protection/safety-glasses/premium-safety-glasses-57503.html

You might also want to make a simple platter to aid in transfers in and out of your pressure pot or leveling area.  I got you covered: https://www.printables.com/model/1435664-casting-tray-casting-bin-liner

Advised but not absolutely required:
A degassing solution, for example:
https://a.co/d/cKOB5KR
 
 

Make Process

The Shell

Print the shell to act as your casting mold master.
I printed mine in PETG..  If you have the ability to print it in resin you might be inclined to do so but just be aware that naked resin doesn't play well with Platinum Silicone and will (still) need to be covered with a high gloss finish first. 




Sand, prime, paint your master. 

This part is key: 
The shinier and more mirror-like this master shape is, the clearer your casting(s) will be and the less post-processing they will require.  

For mine… I printed it in PETG.  Lightly flame polished with a hand torch, then sanded it lightly (800 grit) by hand, primed it, painted several coats of gloss paint, re-sanded until smooth and covered with several applications of the 2k Clear (Activated 2 part Clear Coat) and let it sit until hardened. .   

Then I wet sanded from 800 grit → 1000 grit → 1500 grit →2000 grit →3000 grit →5000 grit → 7500 grit → 10,000 grit

Alternatively, you could print the outer tiles or cut (acryllic, glass) tiles using these as templates, then use the tile jig model to join the tiles.   If you have access to a glass print bed based 3d printer (like an Ultimaker) you could print these tiles face down on the glass to reduce the amount of sanding before casting.

The Lattice

Print the lattice halves.   Make some spares, they are fragile.   If printing on FDM you will likely need to use dissolvable supports like PVA or have magic bridging capabilities on your printer.  I printed mine directly on the build plate in Resin on a Jupiter 6k.  Join the halves (glue them).    Prime them, paint them, clearcoat them.  I recommend the same 2k clear but you can probably get by with a automotive store brand 1k clear like Duplicolor. 

TIP: If you don't let the lattice dry, cure and clear- the heat from the epoxy cure can ablate the finish off of the lattice, making the resin pour cloudy or even introducing gold flakes.

Making the Molds
 

Follow resin dice-making workflows from this point on..

Print some casting keys.  

Print the half mold form. Print the full mold form.  
I used  5" infill, gyroid fill and printed it in PETG but PLA is fine too.

A similar sized PVC pipe for the full mold is also completely doable..  You can also form PVC art sheets into a similar sized tube.   

For the half mold,  I recommend sticking to this half-mold form model though.  It is sized so that you can hide any seams at the hemisphere of the model.

You could split the mold form halfway down the side to make it easier to demold but… the Platinum Silicone is the most expensive ingredient in the make.   Anything that might make it leak seems not worth trying to preserve a $0.20 print :)

I printed some petg platters for the following step but you can use anything really, a crawfish platter, a plate - doesn't really matter it just needs to be level and flat.   The silicone is typically food safe and will come off when it dries.

Onto your plate, platter, whatever you chose: Lay out the transfer tape, sticky side up.  Push the half mold form onto the tape.  Try to make a good seal.  I recommend that you cut corner slits into the excess tape and fold it upwards onto the outside of the mold form and then wrap the whole thing in a loop of duck tape.

At this point you will have the half mold with a transfer tape bottom and the top is wide open. 

Stick two of the key prints to the transfer tape bottom, near the inner wall of the mold form.  Place your master model (triangle tile down) into the half mold.  The triangle side that you stick to the transfer tape here will end up being your top after the second silicone pour is complete.  

Mix your silicone according to instructions.. Pour around the master until the half mold is full, even overflowing a bit.   You can add more 3d printed keys in at the edges on this side, floating at the top or you can cut some later.  

Place it on a level surface for 5-7 hours, according to your silicone instructions. 


After it sets… cut the mold form 3d print off the side of the dried half mold but try not to reposition the master in the mold.

Coat the inside of your full mold with petroleum jelly or a mold release spray. 
(Petroleum Jelly is perfectly fine for this step.)

With the half-mold laying on a flat surface, if you didn't already add 3d printed keys to this side in the previous step you can add them now:

Use a hobby knife to cut a couple triangle or square chunks  in the outer edge,  maybe ½" into the half mold and ½ to ¾" deep.   Just be careful not to go to deep towards the center so as to cut your master.    

If you had added keys to this side (the halfway point of the mold) you can remove them now.  Use a  gloved finger or swab you can now coat the surface around your protruding model with more petroleum jelly.  Get it into those key holes too.  Try not to get it on your master model, if you do - use IPA and a swab to clean the surface.

Add this petroleum-jelly lubricated half-mold into your full-mold form.   

Mix up another batch of silicone and pour over top until the model is covered sufficiently.  Silicone will bind back to dry silicone quite well but the petroleum jelly barriers will prevent these bonds from forming and allow you to split the mold later.     Pour in a thin stream until your master model is covered… I generally covered to about ½" depth.  

After this second half of silicone sets (5-7 hours):

Flip over your full mold.   You should be able to use wooden sticks to separate the mold from the form enough to push the mold out, partially.  With the last pour, now fully set, oriented to the floor you now repeat this process to make a lid.   Remove the lid keys, add petroleum jelly to any silicone:silicone mating surfaces and pour in a bit of silicone to act as a lid. 

Once dry, you can cut away this mold form (or push it out) and separate the mold into into its three parts. Bottom, Top and Lid.   

Since silicone binds well to itself and not much else: Along the way if you messed up, feel free to cut your old attempts into small pieces, clean them in soapy water, let dry and you can introduce these as filler in future builds.

Casting your Radiant

First pour is a spacing floor.   Mix a very small amount of resin and pour.  Pour a small amount of resin into the bottom half.  7-8ml seemed to work for me, as measured through a medical syringe like you use to give babies and pets their meds.  The measuring cups that come with most resin and silicone kits will also suffice here.     Put this into your pressure pot.  Usually about ½-¾ of the stated cure time is the sweet spot. It doesn't have to be fully cured but it needs to be able to support the lattice in the next step.

Second pour is just to lock in the lattice.   Add a small amount of resin to the bottom half again.  Now, position your lattice.



The lattice should rest at about the hemisphere.  This is why we used ½ sized mold form as a starting point. The geometry here plays perspective tricks, try to ensure the lattice is centered fully.  Sometimes 1.88 mm 3d printer filament can be handy to hold the lattice in place.

Set this sit for another ¾ or so of the stated resin cure time. 
(I did about 16 hours for a 24 hour set resin)

After it sets, this is a good time to close up your mold form.  I typically tape the seam with duct tape or really good masking tape.   

At this point you pour 1"-2" pours (I found 3 oz per pour worked well) every (same interval) until full.    It took me about 4 days of pours at this rate but I wasn't diligent.  

Why so many?  Follow your resins directions, specifically but generally more resin equates to more exothermic reaction during curing.  Many pours tended to yield a clearer result and minimize distortions.   It comes with some risk to the full model, though.  Messing up the resin mixture on the last pour.. suuucccckkks so much.  So, take your time.