Nozzle adapter plates

 As I've said in previous posts, we have two plastic injection machines in our shop. Our first machine is the Precious Plastic designed injection machine, built for us by the Sea Monkey project in Malaysia. This is a great organization that we were really proud to support, and we use our machine a lot.

A smooth tapered nozzle. This one was supplied to us from the good folks at Sustainable Design Studios. Amazingly, the threads match those cut into the barrel of our Precious Plastic machine.

While this machine has a host of advantages (for example, a larger shot size and higher manually-controlled pressure), there are some downsides. Mainly ergonomics... the PP design uses a threaded barrel. Molds are screwed onto the barrel, forming a tight, high-pressure seal. This method is simple, cheap, and works fine.

BUT...
It isn't perfect. The threads can wear out over time. This is exactly what has happened with our first square flower pot mold- it no longer attaches to the barrel. Normally it's a simple matter to weld on a new pipe nipple to replace the old one, but this is a stainless mold, and I don't have a TIG welder.

The second problem has to do with us. Our workshop is staffed (if you can call it that) with all retirement-age technicians. Of these, only one of us has the knees/hips that allow getting on your hands and knees in order to screw on the molds. It's further challenging to hold a heavy, stacked steel mold flat while lifting it up to the barrel in order to get the threads to properly catch, and cross-threading is a problem that has to be guarded against.

There is a solution to this problem, and it's partially why we bought our Sustainable Design Studios mini injection machine. It uses a smooth tapered nozzle that fits into a matching recess in the mold. When held under pressure, this forms a seal that doesn't leak. It's self-aligning and quick, and I'm starting to prefer this type of attachment.

So here's the trick: most of our molds use the screw-in type of attachment. What we needed was a way to use both our machines with our existing molds.

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Machining an aluminum rod to accept a smooth tapered nozzle.

What I came up with is a simple- in theory- aluminum nozzle adapter that can be bolted onto a steel plate. I have a supply of  3" x 1/4" aluminum bar that I saved from the trash awhile ago, as well as a few small aluminum rounds that will fit in my small 7 x 14 lathe. 

Machining these little sockets is time consuming, but not too difficult since the aluminum is relatively soft. I suppose it would be theoretically possible to design a cutter similar to a countersink. You could chuck this into a large-ish drill press, to machine this profile in one go. That's probably beyond my machinist skills, though there may be something at Grainger that might work. In the meantime, I cut these manually. As I said, it's time consuming, but it does work. (Note: stay tuned, I may do some more research in this area shortly.)

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A finished adapter plate. This was an early prototype that was oversize, the final version is smaller

​Once these holes are cut to the correct profile, I then solder these onto a small square of 1/4" aluminum with holes drilled in the corners. Some time ago, I purchased some low-temperature aluminum brazing rods similar to these. The resulting "weld" is rather ugly, but it holds well enough for our purposes.

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I'm certain that the folks at Sustainable Design Studios or Easy Molds could fabricate something functionally similar but a lot nicer, but these work for now. ​

The end result is this top plate, mounted on a stack of animal dies. As shown, the die stack is ready for mounting on the Precious Plastic machine. The top plate has four threaded holes, so that by unscrewing the allen bolts, the aluminum plate can be attached and the die stack can be used on the Injection Mini.