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Portable desktop injection machine


This topic contains 110 replies, has 8 voices, and was last updated by  Stan 3 days ago.


Portable desktop injection machine

27/01/2019 at 19:48

Hey guys,
it was suppose to be an easy thing I thought but I spent then 3 full days on it at the end, lots of hours on the lathe, 1-2 hours welding and a little bit on the mill. I wanted the best result possible, tight tolerances, smooth plunge and an easy to extrude plastic with a flexible nozzle. (btw. I can’t recommend building this without lathe or mill, it really wants it accurate to get a smooth plunge).

In the next iteration I will try to have it spring loaded which is pretty difficult as I noticed.

here you go, full metal desktop injection (some part are hardened to maintain this nice blob sound in the barrel) :

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10/05/2019 at 19:57


“made the worms dizzy” 🙂

True, a good compost heap is better not turned, so it can properly heat up, but I’m sure they’ll find out at Project Kamp, once they start composting their Humanure!


And always aim for succes.

When V4 has gotten rid of all the plastic over 3 years (okay @pporg, probably 5), we have to start working on feeding the world!

(thanks for the links, they look delicious)


10/05/2019 at 20:15

@s2019, thank you soo much, we were pissing in our pants, my pancake supply is secured whilst my wife needs and wants her CNC skills upgraded, lol

11/05/2019 at 00:02

OK, one more idea for things to make. I used the clamped tube tool to produce some square stock. I does have some internal voids, need to work on that, but with a little clean up I made some soft jaws for a vise.

I’ll see how they work, but I could see having a bunch of blanks and then machining reliefs for holding odd shapes.

If they don’t work, well, back into the injector

13/05/2019 at 23:47

I tried a different experiment with the desktop injector…How far can I inject into a tube?
Specifically, I wanted to see if I could make a simple garden stake out of HDPE…Yes I know they are a couple of dollars at the store but those are plain green and are plastic over steel. I could score points at home by providing ones with a more interesting color mix (think laundry bottles).

The image shows the concept. A thin walled steel tube (14.5mm) is held in position and one end has a simple 90 degree entrance port, split for removal.

The goal was to get about 90 cm length the longest I got (not shown) was 64 cm (91gm). It really takes a lot of force to inject. I use the full leverage and a good portion of my … errr .. person weight. Each of the trials shown ended with a leak in the port to tube joint due to motion. I used simple wood tooling and minimized the port block to keep thermal mass down. I will have to enlarge that and rigidize the mount.

On the plus side, the shafts come out very nice. Nice smooth surface and a natural point on the tip. I may do a coupling that would allow using two to get longer lengths.

14/05/2019 at 08:09


If we could get them to 4-5m they would also be ideal for using as frames for polytunnels. The short ones are cheap indeed, but the longer ones are a bit… difficult to transport, so being able to make them on the spot would be really helpful.


Would it work if you only used the tube to ‘shape’ (say 40-50cm (or maybe even less)) and would just leave the extra lenght to cool in the open (or in some kind of halftube guide rail)?

Or maybe cool the tube, as the plastic would shrink, reducing the friction?

Kind of like making filament, only somewhat thicker.


You have the setup, might be worth a test or two, if only to get tot 90cm…

Very curious about the outcome…


14/05/2019 at 18:52

Interesting ideas.
At 4-5m the HDPE may be too soft at this diameter. Since I’m using my injector, I think I can only get about 90-100 cm/shot.

The short forming tube is an interesting idea. I can run the external section in some angle. I did notice a while back how much the HDPE expands after it leaves the nozzle unconstrained. Perhaps with a short tube that would be reduced.

Trying to figure out what is happening in the tube. Not sure if the HDPE is sliding along the wall or if a layer sticks to the wall and the HDPE shears in a layer. Some of the sections that @timslab showed from the larger beam extrusion looked like the material shears internally. Not sure what affect heating, polishing, releasing the tube would have on that.

This leads to the joint options, both mechanical and airgun welding. Also want to make a separate cruciform tip for loose soil.

And I thought I was just going to make a simple garden stake.

14/05/2019 at 23:50

I made a longitudinal cut through one of the shorter fails. To me it looks like there is a wall layer that is established and the resistance to flow is the viscosity within the HDPE (as opposed to friction with the wall), but who knows. It may be that raising the temperature from 200C may reduce the viscosity. I’m not sure that heating the tube would be a strong affect. The black/white HDPE was put into the chamber randomly. Maybe next time I’ll try a specific layering and see what that does in the tube.

This is fertile ground for making up flow theories.

15/05/2019 at 02:41

In case I’m not able to generate longer  HDPE shafts, I took a look at heat welding two pieces together. Nothing new here, the technique is described elsewhere on the forum. I used a simple heatgun approach. The first image shows the result after I sanded down the ridge at the joint. The second image shows a section cut through the part. The weld line is hard to detect and the joint appears strong.

The heatgun approach is a little variable. To do a number of these, it may be better to set up a temperature controlled block of aluminum and then just press each side of the joint against it until it is soft and ready to join.

It is a good technique to have available and I’ll probably go that way to assemble shafts in the .9 – 1.5  m length

15/05/2019 at 07:55

Interesting experiment indeed.

Not just technically, but also some interestig ‘ghosting’. I wonder how many cuts it will take for Jesus to show up 🙂


It almost looks as if the ‘new melt’ is pushing through the centre like a needle, which might also explain the friction. The melt is mainly pushing outwards, not inwards.


I look forward to more colourful longitudinal cuts, including one in which the tube is cooled instead of heated…


I’m preparing some welding experiments myself.

There are actual dedicated plastic-welding-hotguns out there, incl. temperature control etc. (they are used in car/motor repair) and one should arrive next week (from China, I know).

Not much use for these shafts, but I also just happen to have a “a temperature controlled block of aluminum” aka a foil sealer that might just do the trick.


Will dig it up and try some experiments this weekend!

15/05/2019 at 17:43

Yes, the ghosting presents an opportunity, but not knowing which image will show up first makes stocking the gift shop difficult.

The plastic welding is an intriguing topic. It can expand the usefulness of a limited capacity injection machine. It may also allow the use of simpler (non CNC) molds.

I also want to check the plastic typing capability of the welders (see link at the bottom of this page https://davehakkens.nl/community/forums/topic/v4-sheets-joinery/ )

16/05/2019 at 03:04

I tried the short forming tube followed by expansion into open air.The setup is shown in the first image. The aluminum tape was also sprayed with some mold release. Once it leaves the tube the HDPE expanded quickly and does not proceed down the v-trough very far. After the large blob formed the tube slipped in the clamps and the rest came out near the entry block.

I had tried to enhance the color selection and loaded the injector sequentially with black, yellow, and white HDPE in about 20 gm increments, repeating. During compaction there was probably some mixing but that was unavoidable. The second image shows the resulting part. Interestingly, since it was constrained at both ends during cooldown, you can see where it necked down in the middle.

The third image is the section view and provides the requested colorful flow diagram. Now would be a good time to sip some creativity enhancing liquid and let the flow theories form.

Note, I don’t see anything in the ghosting that would justify a pilgrimage.

16/05/2019 at 03:17

I also tried the same approach with my square tube mold. The first image shows the configuration after injection. The tube is 15 cm long.

The second image shows the outside of the section view. There is a skin layer that is predominantly one color. The third image shows the interior of the part. Again some creativity in forming the flow theories is appropriate.

I do need to figure out how to reduce the interior voids for these later parts. Perhaps increase the temperature from 200 to something more.

16/05/2019 at 09:07

@s2019 Re: plastic typing: As long as you use pieces of the original plastic to melt, not much typing is needed, but you indeed still don’t know the right temperature. Isn’t it possible to setup a ‘heating’ needle, with some weight on top, slowly getting hotter and hotter, but switching of once it melts through/into the material.

The temperature reached before ‘switching off’ should give a pretty good idea of the kind of plastic, or at least it’s melting point.


Re: go with the flow:

Looks like this way you create ‘solid’ balloons.

Outer layer becomes solid, but the inner layer still pushes outward in all directions.


I believe the extraction of ‘beams’ with the V4 version went better with a block of wood in the mould, to add some resistance against the ‘needle effect’ .

I still think ‘cooling’ the tube, making sure the plastic is solid (or at least has a thicker outer layer) before leaving the tube (so no balloon-effect) might help.


I keep seeing a ‘heat’ problem in the flow, because the forming tube test look very much like a lit match, which makes sense if you concider every (colour) layer must have had a different temperature when formed.

This might also explain why the square test looks like a car wreck. It’s a ‘hot needle’ that’s folded in on itself, as it had nowhere else to go. The ‘voids’ are a result of this folding.

Cooled down black is reheated by the hotter yellow and white on the ‘inside’ of the needle, but as the outside remains ‘cool’ it does not mix/weld into a solid with the other black, causing voids…

Makes any sense?


Filament becomes round when it is pulled and equally cooled on all sides. The puling might not be needed, but cooling the tube (in water?) might just make the difference (as e.g. the ‘black’ won’t be reheated enough by the ‘needle’), if only to pull off your originally intended 90cm 🙂



16/05/2019 at 17:43

The typing I had in mind was not so much for repair but to identify a large piece of unmarked plastic, something like a trash bin for example. In that case the “does known plastic stick to it” criteria may be worthwhile.

I’ve tried the wooden plug approach in the past. It helped reducing voids in high aspect ratio tubes when I had less injector volume and the nozzle diameter was smaller. For the chilled tube approach, I think there is a difference between the V4 extruder based beam forming and my injector based trial. I think the injector is high pressure and relatively high speed. I’m not sure the cooling of the outer layers would be sufficient enough to separate the plastic from the wall and grow the beam from the middle/rear as opposed to from a fountain at the front. I think the extruder is much slower and lower pressure.

Even in the two different sizes I tried, the 25 mm square tube is easier to inject that the 14.5 mm tube. I think the force pushing the plastic forward goes up with the cross sectional area but the shear stress is applied at a perimeter and increases only linearly with diameter. For this specific sizing, I think the most likely way of achieving the 90 cm shaft is to raise the temperature to drop the viscosity.

One thing that is a disappointment is the exterior of the parts has that bland almost single color skin as opposed to what is happening inside. The attached image was some leftover melt that I injected into a cylindrical mold. It came out with the same dull gray skin on the outside. I then turned it a bit to square it up and the interior popped out. Part of the original motivation was to have some interesting garden stakes (score points with the gardener) as compared to the dull green ones from the store. So maybe make them square and run them through a planer afterwards to remove the outer skin.

I did try the welding approach of pressing both parts against an aluminum block at 200 C. That worked pretty well, need to experiment more with that approach.

16/05/2019 at 23:50

these are coming out great dude, i remember some time when i would have by this for no reason but for the colors, making little cute glass tables to hold my bong collection 🙂
btw. collection, i am still buried under crap but this goes soon into ‘best of PP, 2019’

18/05/2019 at 09:58

@s2019 Only one way to find out: If at first you don’t succeed, try and try again!


A hotter melt could also work, because you might not get the ‘balloon’ effect of a cool outer layer. I am worried however that raising the temperature might ‘burn’ the plastic, making the melt toxic…


Would it be possible to maybe mould vertically to encourage layering of the colours? I agree there is enough gray in the world as it is!



18/05/2019 at 16:24

I think I’ll try slightly higher temperature (210-220) with the full tube to see if I can produce the .9 m, After that, this was mostly an exercise in finding the limit of pushing HDPE in narrow channels.

My setup isn’t really usable for long vertical molds.

The outer skin issue is something to work on. One of the attractive things about using recycled plastic is getting the random bright color patterns. For shaped objects, it is difficult to expose the inner color mix.

19/05/2019 at 00:44

I tried 210 C for the garden stake. It came out well but I could only push out about 65 cm before the nozzle end of the mold leaked under high pressure. To go further I would need to change to more positive connections. Not going to pursue that at this point, but it was a good capability test.

I need to get back to making more of the large black clips for the top of the pergola (from a week ago). There are more things that need to be attached that those will be used for.

19/05/2019 at 08:55

So in conclussion: maximum lenght seems to be 64-65cm, regardless of heat, with this setup.

Would have been nice if it had worked out-of-the-box (so to speak) at any lenghts, but longer stakes need to be welded.


Thanks so much for doing this experiment.

I’m still looking whether or not it would be interesting for my Urban Homestead project* to switch from upcycling to recycling (with machines), but so far upcycling and recycling without machines (for small objects) keeps winning.

But hey, you would not need a V4. if V3. was already perfect!


*in this case: being able to locally produce the materials needed to become self-sufficient(ish), if only through a community (or travelling) “garbage in – buildig materials out” workshop.

19/05/2019 at 17:42

Yes, for that simple mold the next step would be to redesign the aluminum block that forms the 90 degree turn at the entrance to have a more positive seal.

One thing I’ve done both with the injector as well with some press molds is make a collection of stock material that I use on short notice to make some simple items. Yes you can buy Delrin, Nylon, or HDPE bar or rod from a plastic supplier, but it takes time, shipping costs, etc. The other option is to make it out of aluminum, but then I have to go to the metal supplier, dive into their cut-off bin, etc.

For example the test parts I made a few posts ago already got used to repair a glass/LED garden decoration where the original steel support base rusted out and a new solar panel mount was needed as well. I could have made it out of aluminum but why? And the bright yellow color matched.

I think in combination with some simple tooling, it just becomes another tool in the shop.

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