LED Eye Lens Tutorial

This is my tutorial for placing LEDs inside Space Marine helmets. The photos show this technique applied to a Primaris Marine, but it can equally be applied to regular Marines, or indeed any other model that you feel would benefit from glowing eyes.

I strongly recommend reading through the entire tutorial before starting work, just to make sure you have the necessary skills and tools required and that you’re not going to run into an unexpected barrier halfway through.

I have a separate tutorial about designing LED circuits, basic LED soldering and resin casting. This tutorial assumes you’ve either read these, or are familiar with the techniques discussed (or have settled on an alternative in the case of resin casting).

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1. Start by selecting the type of battery you want to use. I prefer the CR2032 or CR2025 coin cells. These are the lithium memory back-up batteries you find in PC motherboards, among other things. I like these because they last a long time, can power the brighter 3V LEDs and most importantly, because they have a low profile that will fit inside a standard base for a 28mm model.
You’ll also need to select a suitable battery holder. Many types are available and a selection are show below. Again, it’s important to pick one that will fit inside your base (possibly with a bit of trimming).

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2. Personally I like the catchy-named Multicomp Battery Holder SMT, 20mm, CH7410-2032LF (available from Farnell here), since it fits comfortably inside a GW 32mm base (the current standard Space Marine base) without any trimming. This is just personal preference, as long as your battery holder fits inside your base then you should feel free to use any brand.

To cut out the 32mm base, I find the best thing to do is to first drill a number of small circles in the top.

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3. Cut out the top of your base using a craft knife or similar to cut between the holes. I find this is easier than just cutting it with a knife from scratch. Just make sure you leave the rim intact. If you are using a smaller base size, such as 25mm, you may find you have to cut a bit of the rim away so the end of your battery holder can poke out. But you can always disguise this with basing material later.

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4. Insert the battery holder into the base. Make sure the actual battery is inserted into the holder for this step. Position the battery holder so that the side that you insert the battery is face down (this will allow you to change it without disassembling the model) and so that the bottom of the battery holder is flush with the lower edge of the base. This should mean that when you put the base on a flat surface, it is level.

Please note that if you do not have the battery in at this step, you may later find that when you insert it, the battery and holder are not flush with the bottom of the base and your model will be wonky! This is especially true of battery holders with clips.

Once you are happy with the position of the battery holder, secure it to the rim of the base with a couple of small dabs of superglue. Be careful not to get glue on the battery!

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5. Generally I think it’s a good idea to include a switch. This allows you to turn the LED off when not in use without having to take the battery out each time. But if you don’t mind doing that then I guess you can skip the switch and proceed to step 6.

If you do want to include the switch, then you’ll need something very small. PCB slide switches (available from RS here) will normally do the trick, but check the dimensions! A switch with a length of 5-10mm is ideal. These are sometimes called “sub-miniature” switches.

Do not glue the switch to the battery holder! These switches are not sealed against liquids and there’s a high chance the superglue will penetrate the switch and insulate the contacts when it dries, rending the switch non-functional!

To hold the switch in place, simply solder one of the legs to one of the battery contacts.

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6. Next add some wires. You can either use insulated or enamelled wires, but do not use bare metal wires as the wires will end up touching later and you’ll get a short circuit. As you can see in the picture below, one of the wires is soldered directly onto one of the battery holder terminals, while the other is soldered to the switch. If your switch has more than two legs, make sure you have confirmed which two you are using. You can test this with a digital multimeter if necessary.

Polarity is important for LEDs, so make sure you know which wire is positive and which wire is negative. Use different coloured wire to indicate this if you think it will help, or cut them to slightly different lengths as a visual reminder.

You’ll want the two wires to be about a third longer than the intended final height of your miniature, just so you’ve got some slack to work with.

Never short the wires or the battery holder terminals. Lithium-based coin cells can get very hot and potentially explode or start fires if the terminals are connected for extended periods.

At this point I tend to use modelling putty to fix the battery holder to the base, as this is easier than gluing. Milliput is ideal, and cheaper than Green Stuff or Procreate for this application. Don’t cover the terminals at this point, and remember we are not covering the bottom of the base with putty, as you want to leave the battery accessible from underneath so you can change it when it runs out. You can carry on with step 7 and 8 at this point, but make sure you leave the putty to set before proceeding to step 9.

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7. If you’re using a model with a hollow torso, like the Primaris Marine pictured below, then you can go straight to step 8. If you model has a solid torso then you will need to drill a hole through the torso of your model, right down the vertical centre from the neck socket. It’s a good idea for the width of the hole to be slightly greater than the horizontal distance between the outside of the two legs of your LED. If the width is narrower then there is a risk the legs will be pushed together and short circuit.

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8. Now drill a hole through one of the legs of your model. This hole should be wide enough that it can accommodate both of your wires side by side. Ideally the drill will enter through the base of one of the feet and emerge in the centre of the waist, that way it will line up with the hole in the torso. However this can be quite tricky not to break the surface of the leg with the drill, but any mistakes like this can be covered with putty or filler later on.

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9. Make sure the putty you used in step 6 has set. Now feed your wires through the legs and the torso.

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10. If you have been working on a model with a hollow torso that did not require you to drill through it, then you may still need to widen the hole in the neck at this point. As mentioned in step 7, it is best if the hole in the neck is wider than the width of the two legs on the LED, so that the hole does not push the legs together and cause a short circuit.

If you are using Primaris Marines from the Dark Imperium box then the models start with a small hole like this…

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…that you need to drill wider to look like this in the picture below. Don’t glue the torso together to drill the hole, just hold or clamp it tightly.

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11. Next you’ll now need to drill a hole in the base of your Marine’s helmet that is wide enough to accommodate the LED. Don’t worry if your drill is so wide it destroys the ‘neck’ of the helmet, again this is something that can always be fixed with putty later. Remember that you can file down the edges of your LED slightly if you need to make it a bit smaller to fit in correctly, just so long as you don’t file all the way down to the p-n junction (the metal-looking bit inside).

In my designing & ordering tutorial that I mentioned earlier, I explain that I prefer to work with 1.8mm LEDs. Here’s a scale shot next to a helmet for reference; as you can see they’re the ideal size.

If you are duplicating my model exactly, then the red LEDs that I use for my Crimson Fist eye lenses are the TruOpto OSHR7331A-KL 1.8mm Red LED. Also, for reference, the blue LEDs that I use for my Imperial Fist eye lenses are the TruOpto OSUB7331A-KL 1.8mm Blue LED and the green LEDs that I use for my Custodes are the TruOpto OSPG7331A-KL 1.8mm Green LED. Whichever type of LED you are using, make sure they are compatible with the the voltage of your battery – 3V in the case of the coin cells used here.

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12. As I’m working with resin helmets, I’ve drilled the hole to just behind the eyes. As the resin is quite thin this diffuses the light nicely and allows the LEDs to shine through the eye sockets without actually having to drill them out. If you’re working with plastic or metal helmets, then you’re going to have to physically drill out the eye sockets with a miniature drill for the LED to become visible. Why I use resin and what the alternative options are is all explained in more detail in my resin casting tutorial, if you haven’t read that already.

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13. Now insert the LED into the helmet, using a cocktail stick or pair of thin tweezers to help push it in if necessary (push on the LED itself rather than the legs so you don’t bend them too much in the wrong direction). LEDs tend to emit most light vertically rather than horizontally, so you’ll want to bend the top of the legs so the top of the LED points directly towards the eyes of the helmet. The easiest way to achieve this is to hold the legs with a thin pair of pliers or tweezers directly under the base of the LED and bend the legs around that. The optimum angle is shown two pictures above in the image for step 11.

At this point it can be useful to simply hold a spare coin cell battery between the legs of the LED – remembering to observe the polarity – while you position it. Ideally the top of the LED will be between the eyes of the model. That way each eye is illuminated evenly. If the LED is at an angle then you can have one eye brighter than the other.

Once you are happy with the position of the LED, secure it with a tiny dab of superglue. Make sure the superglue does not get between the top of the LED and the helmet’s eyes!

14. Trim the legs of the LED and the wires (although you’ll still want to leave a bit of slack as shown below) and secure them ready for soldering (I use blu tack to hold them in place). Double check you have the polarity correct at this point. Remember, the longer LED leg is always the positive (a.k.a the anode).

Re-read my tutorial on soldering LEDs if you’re not feeling confident at this point, paying particular attention to step 3 of that tutorial.

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15. Now solder the LED legs to the wires! Once you have done this, operate the switch to check that everything works. The LED should now illuminate. It’s always worth checking at this point because there’s nothing worse than having to take an assembled model apart to perform fault finding. In fact it’s worth operating the switch again to check that everything still works after each of the following stages, just to make sure you haven’t caused any accidental damage or short circuits during final assembly.

If you’re working with a resin helmet then you’ll probably notice at this stage that the whole helmet glows rather than just the eyes. Don’t worry though, any areas that are painted will block the light – so obviously paint everything but the eye lenses!

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16. Now pull the slack of the wires through the bottom of the foot and position the legs, torso and head how you want them arranged on the finished model. When you are happy secure them in place with superglue. Any excess wire should be coiled under the feet at this point.

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17. Once the superglue applied in the previous stage has dried, you can now hide the battery holder and any spare slack wire under a layer of putty or filler. Be sure to not get milliput on the battery itself, and to leave the sliding part of the switch exposed so you can still operate it. I tend to position the switches at the back of the base, so it isn’t visible in the picture below. Once the putty covering the battery holder is dry, you can texture it if you wish (I tend to apply a layer of PVA and sand).

This is also the point to use fill in any gaps around the neck with modelling putty, as well as any repairing any accidental damage to the legs and torso that may have occurred during drilling. It can also be handy to turn the LED on at this point and check for any light escaping any gaps around the edge of the torso, for example.

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18. And there we have it, one LED lit miniature! We’re almost there now. The next step is to undercoat the miniature for painting.

During spray undercoating, make sure you cover the helmet eye lenses and the top of the switch with blu tack (or similar) so that they don’t get spray paint on them! If you are spraying from underneath then you will also want to cover the battery itself during the spraying process.

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19. Now apply paint, avoiding the eye lenses, and that’s it! If you find the light is leaking through in any area it shouldn’t, especially from the helmet, then an extra coat of paint will normally sort that out. I hope this tutorial was helpful!

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