Benchtop (smaller) machines.
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I see some people have created smaller versions of the PP machines, particularly the injection moulder. Myself, I’ve built a smaller shredder and an injection moulder and there’s a lot of advantages to doing this, they are easier and cheaper to build, use less power, heat up more quickly and can be easily transported (even by bicycle).
I’d like to share a bit about the injection moulder I built. I actually built this a couple of years ago and have been using it extensively since. It has a few features I think are a big help. The main reason I built a machine this size is, if you’re making small parts, it’s a lot better to use a small machine. The smaller diameter barrel means you get higher injection pressure (in proportion to the bore diameter^2) which gives you more detail and less failures, which means you can make parts with more ambitious geometry, thinner walls, etc.
The machine I built has a sprung floating nozzle (the nozzle is a regular dome nut) and there’s no need to attach or remove the mould at all. The nozzle is held against it by pressure when you pull the handle. This makes moulding batches of parts much faster and more convenient and also simplifies the design of the mould, I just put a small dimple where the sprue is to locate the nozzle. I see on another thread talk about quite complex ways of attaching the mould to the nozzle, using pressure eliminates the need for that.
I also incorporated a device to hold the handle in the up position to stop the weight of the handle causing plastic to dribble from the nozzle (I used a sprung detent, but after a lot of use it has become slightly unreliable due to wear, a simple counter-acting spring might be better, though it would work against you slightly when pulling the handle).
I also find for moulding batches of parts it helps to have a bed the mould rests on with adjustable stops to locate it exactly under the nozzle and a clamp to hold it in place (not hold the mould shut, I use bolts for that). Then the process becomes simply:
place mould on bed => flip clamp => pull handle => release clamp =>
and then it’s ready for the next one. It takes literally seconds compared to several minutes if you have to thread the mould on and off one handed whilst holding the lever up with the other hand.
Of course the height is adjustable so the nozzle can be positioned correctly for different sized moulds.
I don’t have any drawings/plans for this machine, I tend not to build things that way and only draw what I can’t picture in my head or work out with a calculator, but I did make a fairly comprehensive video showing the construction of it: https://youtu.be/nefLfhUaODM . @davehakkens @katharinaelleke feel free to share this eg. In the community news if you want.
@andyn Thank you that is a great design and a wonderful video.
I think in another thread you mentioned having the option to change the bore diameter with a sleeve and a matched piston. do you do anything to enhance the heat transfer between the sleeve and the outer wall?
Andy’s machine is a work of machining art. If someone does not have those skill/resources, a functional (more Mad Max type ) machine can also be assembled from some off the shelf parts and some garage tool type work. ….Though watching Andy’s video is like eye candy.
Thanks again Andy
Thanks @s2019 Stan,
Ah, yes! That was actually a different machine. I probably didn’t explain it clearly, here’s a picture. There isn’t a sleeve inside the barrel and the bore of the cylinder doesn’t change. There is a plug/bushing in the end of the barrel that can have different sized ID’s for different diameter pistons. The piston doesn’t have to match the bore of the cylinder at all, it just changes the volume inside the cylinder. This was a two stage machine and the plastic was introduced (by a screw) into this cylinder through a valve, and then injected by the piston into the mould. I used this method to vary the pressure/volume as I was using a pneumatic cylinder to push the piston and had a limited range of force available.
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