How to Make Ultra Realistic Eyes Using 3D Printing and Casting

In my pursuit to design an effective and reproducible 3D-printed eye mechanism, It became apparent that I would need a reliable system to make realistic eyes. In this instructable I'll show you the process of making these eyes and provide you with the STLs so that you can make your own.

The idea behind this design was to have a component that could easily clip into a holder for painting, then into a a casting chamber and finally into the eye mechanism using the same standardised fitting. I wanted it to be easy to print and accessible to anyone with a 3D printer, yet as realistic as possible within those requirements. I made just about every mistake I could have with this one, so I feel like I'm in a good position to prevent you from doing the same!

I don't think you'll need a particularly expensive or well-tuned 3D printer to do this project (mine is a Geeetech i3), but it would help to be able to reliably print small bridges, use a layer height of around 0.2mm and ideally print in ABS.

• White 3D printing filament - ABS is recommended but PLA is fine.
• Roughly 500ml of casting silicone: https://amzn.to/2JbMYx0
• A very small amount of clear casting resin: https://amzn.to/32CjBvo
• Some small screws - M2 x 10mm-20mm : https://amzn.to/2JcftdQ (but any similar size should work fine)
• Acrylic paints
• Red cotton thread
• Superglue
• Airbrush (optional)

Using the files provided, I'd recommend printing the eyes and "eyeblank" files at a nice low layer height to try and get as smooth of a dome as possible - ideally no larger than 0.2mm. Also, Its best not to use supports (unless you have bridging problems) as the residue left from the supports will typically be more of a pain than the imperfections from the bridge.

For the eyes, PLA is ok to use despite being a pain to sand. However I feel like ABS produces a more realistic eye because of the way it's slightly translucent and produces a sort of subsurface scattering effect - where it seems to light up from the inside. Don't get too hung up on this though, it will be very difficult to tell once the eye is finished.

The other parts should be fine to print at 0.2mm - 0.3mm layer height, in whatever material you like - although generally ABS is a bit better for snap-fits and moving parts.

None of the components need supports, so the post processing shouldn't be too extensive. If your prints are prone to warping on the bottom layers (like mine) you may need to sand around the bottoms of the snap-fit sections so they fit into each other well, on both the eyes and the holder components.

As for the eyes and the casting blank it's super important to get a nice smooth finish - the eyes will likely look good enough after using 240 grit sandpaper if you've used ABS but the blank should be as smooth as possible to try and perfect the mould. I used high-build primer to try and get a very even finish, and polished this to a reasonable shine with some high-grit sandpaper and T-cut polishing compound. Another thing to note is that I didn't sand the concave section of the irises because I thought the rings would add texture and realism, but looking back I think it would have been better if I'd have just sanded it smooth like the rest of the eye.

The two types of holders should go together easily with some 10mm or 20mm M2 screws, as can be seen above. Then, the casting blank should fit on to the casting chamber holder without too much trouble. You'll notice a small gap where the bottom of the eye meets the holder - this can be filled with plasticine or blu-tack to make the assembly water-tight. Also, you'll want to make some channels with the blu-tack or plasticine so that excess resin can escape, just make sure your channels go all the way to the end of the casting holder. If you forget to make the channels like I did, you could always cut them in the mould with a knife once the silicone has set. You'll also need a way to suspend the assembly in the casting chamber - an easy way to achieve this is just to glue or screw some lolly sticks to the casting holder.

Once you're ready and have a suitable container for the silicone, measure it out and mix it thoroughly. One of the biggest problems I faced was trying to get rid of bubbles - ideally you should use a vacuum chamber, but you can avoid them by not mixing too vigorously, pouring the silicone from high up and banging the mould to try and get the bubbles to rise to the top. As you'll see, my container was too big so I had to use some junk to try and raise the level. Also, I used some tape to secure the lollysticks and make sure the blank didn't float to the top.

After a few hours you can remove the blank and see how your mould turned out. I had a lot of tiny bubbles in mine unfortunately, but I decided to stick with it to prove your eyes can still turn out okay if your mould's not perfect.

If you have an airbrush, I'd recommend you start by painting the dark ring that most people's eyes have around their iris. An airbrush is ideal for this because the ring should fade out rather than be a hard border against the white of the eye. That's not to say you can't paint a really realistic eye without an airbrush though, with the right amount of artistry. I also used the airbrush to paint the peachy/red colour that gets darker towards the outer edges of the eye, and by attaching the eye to the paint holder and spinning it in a drill, I was able to ensure that both airbrushed parts were perfectly circular.

As for the painting of the irises, I'd recommend using the finest brush you can get your hands on and look carefully at lots of different reference pictures to get a good idea of the structure of the iris. I also got better results when I focused more on the colour gradient than the details, thats why I feel like my green eyes turned out so much better than the blue ones. The blue eyes were mostly just a mix of different shades of blue, whereas the green eyes had a definite continuum from warm/brownish greens in the centre, then to bright/yellow greens and finally to blueish emerald greens and dark blue around the outside. Also, using transparent yellow, on top of pale greens, transparent red on off-white and transparent blues really seemed to really make a difference in each of the different eye colours. Ultimately its up to you to experiment and get a design that you're happy with.

While it's possible to paint the veins, red cotton thread can give a substantially more realistic effect. I recommend looking at pictures of eyes to get an idea of the structure, but keep in mind that most close-up pictures you're likely to find of eyes on the internet will have the veins photoshopped out. Look at your own eyes or a friend's to get a better idea.

Using short lengths of cotton thread, twist it apart, pull off small bits and stroke with a knife to get a variety of interesting shapes - don't just stick to simple squiggly lines. While you're doing this, you'll want to breathe very shallow to avoid losing your bits of cotton! You can then use superglue to attach the veins, don't worry too much if there are lumps of glue sticking out because the dome you'll cast in the next step with get rid of them.

Once again, the main issue is avoiding bubbles. I recommend mixing very carefully and avoiding any moisture in anything you're using. Its also a good idea to mix up a small amount of resin to fill in the pupils and irises first so bubbles can't get stuck in there later when the eyes are face-down. If you do see any bubbles, you can get them out with a heat gun (be careful not to melt the 3D printed material) or a needle.

Once this dries, only around 10ml is needed to cast the dome over the eye. I dunked the eye in the resin mixture first to get rid of anything on the surface of the eyes, and gave both the resin in the mould and the tiny bit on the eye a quick go-over with a heat gun before carefully plugging the eye into the mould. Wipe up any excess that comes through the vents, and bang the mould a little to force any bubbles out. It took a few tries before I had reasonably bubble-free casts.

The quality of your cast eye will depend largely on how well you were able to eliminate bubbles in both the silicone and resin mixing stages, but even if you do have a lot of bubbles, the eyes will look great at a distance and they look even better under the eyelids I use in my animatronic eye mechanisms. Check the captions to see how different eyes came out differently - some have quite a few bubbles but I love the way they look regardless.

I had a few problems with the resin not having fully cured when I took it out of the mould, which meant it got a bit out of shape - if you have these kind of issues, you can always use a low grit sandpaper and work your way to a finer grit to improve the overall structure. I went to around 600 grit then used T-cut to polish the eyes on some fabric, which gave me a finish I'm really happy with.

Now you can plug your eyes in to whatever you need them for! I'm going to have an instructable out soon on how to build an animatronic eye mechanism which uses these eyes, so check back if that's something your interested in.