Resin Cast LED Vacuum Valve

Sometimes your basic 5mm LED will not cut it for a display, nor will any plain old lens cover. So here I'm going to detail how to make an easy custom LED lens from resin and using a technique similar to lost wax casting to be able to insert the LED right inside the casting without having to cast it in place. For the purpose of this I'm recreating a vacuum valve , suitable for steampunk objects or rayguns. In addition to it being safer than using a glass tube as it wont break, it is also easier to illuminate. You can of course use this method to recreate any type of lens and I have in the past used this to make a runway light lens and you can use it to make anything you want. You can download the files from my thingiverse page, https://www.thingiverse.com/Ajaxjones/designs

First step is to create a master of what you want to make out of whatever you have to hand. In this case I am using an old vacuum valve and a 3D printed base. The valves are glued into the bases and then any gaps filled to make sure that the moulding agent cant creep in. The bases were sanded a little and painted in a filler primer and then varnished. The glass was kept clean and the old ink markings scrapped off the glass so that the surface was smooth. Anything not smooth wont come out clear when you eventually pour the resin.

With the master ready, the next step is to recreate anything that you want to go inside the lens. Here you can see I've made a simulation of a valve interior using 3D printed parts and some dress makers pins. Its at this point I also create a hollow inside the parts that the LED will fit into. So that when you pour the resin it doesn't go into thhis void I fill the void with candle wax. You can then easily scrape this out afterwards and it provides a void inside the resin. This is similar to lost wax casting. The only alternative would be to make a void which is hard to pour around, or actually cast the LED into the resin. Its much simpler this way to have a wax void.

You'll need to make a box around the masters before you pour the silicone mould and this can be easily done with card. You only need to score through the outside to make things easier and then use some hot glue to make sure the edges are all sealed. I've also used leg to build the walls and either technique works. If you had clay or Plasticine you could use that too.

Up until recently I've never bothered with a vacuum chamber when doing normal resin moulding, but with the clear resin I find it almost impossible to get all the bubbles out. So I've gone ahead and bought myself a simple Vacuum chamber setup. These can be obtained quite cheaply nowadays, the pump is a 2.5cfm 1/4HP unit that cost about £40 and came with the oil that you need to put in the pump before you run it, You can also buy compressor oil from hardware shops and I have some ISO 32oil that I use as well for this. The chamber itself can be bought for about £48 and comes with all the necessary pipework, gauges and valves. A 2L container is good enough for making small mixes up although if you have the space to spare a larger one makes things easier if you have larger quantities of silicon and resin that you are using.

Now of course if you have a chamber, you have to put a marshmallow in and remove the air. The marshmallow just grows beyond belief and then when you restore the air pressure it drops back to its original size. Pointless, but fun.

I then mix the silicone and I am using a Polycraft GP3481-F General Purpose RTV and it has a fairly long pot life. I then transfer it to the chamber after mixing and remove the air. All the air expands and it takes up about twice the volume. If you leave it a while the air bubbles all burst and it drops back in volume. Removing the air and it then drops back to the original volume. I do this a few times to really get out as many bubbles as possible and then pour it into the mould. The best way to pour is to do it in a low corner of the mould and let the RTV flow over the master object that you have. Once you have enough silicone in, just leave it to set for 24 hrs and then you can prise out the masters and you are ready to pour some resin.

The resin that I have found best to use is resin that is mixed in a 2:1 ratio and its easy then to end up with something that will set fairly quickly and not end up tacky. I'm currently using clear epoxy resin from swindon composites and they also supply dyes as well that you can use to colour the resin. Again the pot life is pretty long, around 45 mins in fact, so you can take your time to degass it and pour it into the mould. With this resin , it takes at least 24 hours to be hard enough to demould and then probably another day before it really goes hard.

Just to show the advantage of using a vacuum chamber you can see two test pours I did of a small cube. The one on the left has been degassed and the one on the right was poured after mixing. The degassed resin basically has no air trapped inside, and the two valves that came out are pretty clear. Its only a minor point, but really is worth it for clear resins.

I've added these pics to show in a bit more detail the process I'm using to fill the void where the LED will go in the final resin cast. You can see the holder that I use to carry the valve parts and through the middle of this there is a hole. I then use a candle and drip the wax into the hole so that it fills the void. This will then stop the resin filling the hole. Once the resin is cast, i then use a drill to remove the wax, I was going to try some low temperature wax candles and use a heat gun to melt it out. I might try this in future if I was going to make a more complex void. I was also thinking at some point to either carve or make a wax insert without any 3D support to create intricate interior details.

For now this works great as you can feed the LED right up inside the resin without having to cast it in. It gives more flexibility this way if you want to try out different types of LED's I settled for an automatic flickering LED for this project.

So as the resin is poured, this is also when I insert the 3D valve interior. The size of these also allowed me to put them back into the chamber to clear any surface bubbles that might be appear on the 3D piece. You can also see the bottom where the hot wax was dripped in to stop the resin building up inside and is where the LED will go. I just use a 6mm drill bit to scoop the wax out afterwards.

Rather than just leave the lens as clear, it was masked off and the base initially painted in matt black. Then with some burnt umber, raw umber and burnt sienna acrylics it was painted up to give the appearance of old rusted metal. As a finishing touch, I airbrushed molotow chrome on the top and then sealed this with Alcad clear lacquer

With the tube painted , it was now easy to slide a 5mm LED inside and here I use a flickering effect orange LED which gives the impression that it is a real old radio valve.