Thread sizes for injector

Hey all. I teach at a high school in Minnesota (USA) and one of my students is building an injector (based off the PP one, but modified to use what materials were available in the metals shop). I currently have the nozzle stepping down to a 1/2″ NPT thread fitting, but am curious what others use. I noticed there are little or no molds available on the bazaar. I’d love to be able to get some inexpensive simple molds for my students to start working with! I will make some more elaborate ones this summer, but would be nice to start simple.

I use a metric M10 female thread for the moulds. I find it’s much more convenient to make moulds with a threaded socket than adding a protruding male threaded spigot. Also having the male thread on the injector means you don’t have a female socket that fills with plastic and makes it hard to screw the mould on.

I also try and split the moulds vertically through the threaded socket which makes it much easier to extract the part (not always possible depending on the shape of the part).

I made a custom nozzle that goes straight from the 1″ BSP barrel thread to M10, much better than screwing/welding several plumbing fittings together to get down to this size. The nozzle can also be used on the extruder, I sell these on the Bazar

For my latest injection machine I don’t use a threaded socket at all, I still use the same nozzle with a drilled nut fitted to it and a small dimple on the mould to locate it. The barrel of the machine is floating and is kept held against the mould by pressure as you pull on the handle.

I’ll post a video of it soon, that will show better how the floating nozzle works. The machine is basically a smaller tabletop version of the PP injector, but with a few small improvements.

Hi andyn, I’m very curious to see your injection machine that uses compression to hold on the mold rather than threads. I was trying to imagine something similar because the threads & nozzle keep getting filled with plastic. Would you share a photo of that?