So far I have been injecting the resin into my molds by hand. This works well enough, but isn't ideal. The size opening in the syringe is very important. I started out with some cheap syringes that had an opening that was about 3/16". You could fill the syringe and push it out fairly easily. But the leak because the hole is so big, and it means you have to have a big hole in the mold and large sprues.
Next I tried a syringe with a luer lock fitting. This lets you put multiple size needles. This was great because it made it easy to get the resin in the mold through a tiny hole. I designed my new aluminum mold around 14 gauge needles. These have a inner diameter of 0.067". I wanted to start small because it would be easy enough to drill the hole bigger. You can push the resin through this needle. But it takes a lot of work and it take a long time. The resin comes out slow and by the end of filling my mold my hand hurt. So I started thinking about a better way.
I drilled the hole in my mold to make it fit the luer lock without any tip. This is has an OD of 0.159" and and ID of 0.0995". I didn't drill the hole all the way through though. So my hole has a hole that is 0.159" that goes down halfway, then reduces in size to 0.0995" (or as close as I could get it with normal drill bits). This worked fairly good. It seems to be a good compromise between small sprue and how hard it is to inject. It also has the added benefit of not using a needle at all. So one less part to waste or clean. They sell small luer lock caps, which keep you from dripping anything out while filling up the syringe.
The last step of the puzzle was to avoid pushing the syringe at all. They sell these awesome air powered syringes. I contacted Nordson and they sent me a sample kit. My work has ordered some parts from them before. Here is a picture of the sample kit. I also ordered one on amazon to test out. Now I just need to hook it up to my air compressor and get a solenoid.