Instructables
Picture of Waste Plastic Injector
It's well known that one of the most commonly thrown away plastics is HDPE (High Density Polyethylene). It is difficult to work with because it shrinks as it cools once formed so it is not generally used in 3D printing, however it's extremely useful in harsh chemical environments, that's why it's commonly used to store chemicals. This instructable will guide you in making a simple hand-crank extruder powered by nothing more than a simple kitchen appliance. No electronics know-how is necessary.

Warning: Wear safety glasses when using tools.
Warning: Use oven mitts when using the injector.
 
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Step 1: Center End Caps

Picture of Center End Caps
01B - Adapter.jpg
01C - Center Cut.jpg
01D - Result.jpg
In this step, you'll need to create pilot points to drill the center holes on the end caps. It's important that this step be done, otherwise the piston may not fit correctly and the injection nozzle will look screwy. To get the most accurate center, we will rely upon the accuracy of the threads, so you'll want to use a nipple as the support.

If you have a lathe, all you'll want to do is to insert a 3/4" non-galvanized nipple into the lathe, put on a cap, and drill the hole. I don't have a lathe since they cost more than I'm willing to pay, so I create an adapter for use with my drill press. Here are the steps:
  1. Find the biggest dowel that your drill press will accept.
  2. Cut a short piece of the dowel off.
  3. Wrap the dowel in masking tape so that it'll fit tightly into a 3/4" nipple.
  4. Insert the dowel into the drill press / hand drill.
  5. Insert the smallest 3/4" nipple you can, on top of the dowel adapter.
  6. Screw a cap onto the nipple-adapter.
  7. Place knife / blade onto cap while spinning.
With respect to step #3, it may require a long piece of tape. Once you finish, you may want to wind it back onto the tape-roll.

With respect to step #7, the rotation tends to push the cutting blade towards the center of rotation. If this doesn't happen, you may need to (roughly) level the cap-tops and try again. A fresh blade from a utility knife works great, though I used some sewing scissors.
twopussez7 months ago

I have absolutely no idea what it is youre describing. I have interest in this cos Im getting a 3d printer, but it looks like you reinvented the bike pedal or a coffee grinder handle. Square metal with a hole in then the corners cut off is - a Nut. What is the balloon bubble witch missing LOL!

I like this idea very much, though I think a jig to use a drill press (powered off) to push on the piston would be more useful, especially for filling molds.

You should change your thread descriptions, however. "NPT" stands for National Pipe Thread, and refers to the tapered threads cut in pipes and fittings. Pretty much identical to MIP, which means Male Iron Pipe according to Wikipedia:
https://en.wikipedia.org/wiki/National_pipe_thread

The bolt uses 3/8-16 UNC threads, as would the tap to cut the female threads for it. I hope this reduces confusion. Also, a similar size for those using metric threads would be M10x1.5.
foobear1 year ago
This is very interesting. A brief video showing the tool in action would be helpful for the uninitiated, like myself. How can the melted plastic be reused? Thank you
vreinkymov (author)  foobear1 year ago
Thanks for the idea. I think I'll add a video soon, I need to make a modification to the back-end cap to strengthen it, but one of my taps snapped so I need to wait a few days to get it in the mail.
I agree with foobear, please PM me when done.