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Portable desktop injection machine

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This topic contains 134 replies, has 10 voices, and was last updated by  Plastic Hub 1 hour ago.

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Anonymous

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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dedicated
10/02/2019 at 22:17
6

Just a follow up on the simple wooden mold. I wanted to change the outer profile of the knob I had made earlier to make it more comfortable. So I took the wooden mold (3 layers of flooring) and added 8 pins (about 5mm) to form the indents. I borrowed this from a youtube guy that carefully machined it out of aluminum. Thought I would try it with wood….worked well. I think for quick prototyping, wood and or plaster can make some cheap, usable molds without the CNC or other machining.

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dedicated
04/06/2019 at 22:28
5

So you spend all this time tinkering with that plastic melting gadget in the garage, your spouse looks in every once in a while and just shakes their head..What do you do to salvage some legitimacy to your activities……

Fix something of theirs! (some free gray-haired wisdom here)

This was an otherwise nice cast iron plant stand that was a bit rusty and had a busted wheel. Well, a little spray paint and that clever threaded knob made in the wooden mold in the Feb 10 post, and I achieved temporary hero status. Since we don’t take our plants for walks, the wheel function was less important.

The nice thing about using recycled plastics to make replacement/repair parts is there is no concern about plastic costs so you can make them robust. I’m guessing this solid HDPE part will hold up well, If not, I can make a bigger one.

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dedicated
19/05/2019 at 00:44
4

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.

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dedicated
16/05/2019 at 03:17
4

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.

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dedicated
15/05/2019 at 02:41
4

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

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dedicated
14/05/2019 at 23:50
4

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.

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warrior
10/05/2019 at 19:57
4

@s2019

“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)

 

dedicated
04/02/2019 at 06:12
4

I think for a desktop/home unit the 1 ton arbor press (such as https://www.harborfreight.com/1-ton-arbor-press-3552.html )is a very convenient option. It has a decent stroke and if someone has the capability you can always fabricate a longer rack. It is very quick to actuate and has good leverage. It also provides you with feel for when the mold is full which a hydraulic cylinder may not.

Of course it all depends on the preferred configuration and capacity.

dedicated
30/01/2019 at 19:30
4

For simple molds, I made some clamp plates that can hold different shapes. Since the top and bottom plates (aluminum) handle the heavier load and temperature, the form plate in the middle can be wood or aluminum.

For the narrower forms, I just place them directly under the nozzle with a top washer or plate and then hold them in a C-clamp during cooldown.

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dedicated
27/05/2019 at 21:26
3

@pporg , not sure what you mean. When I chuck up a bar of HDPE, I can take the same cut This Old Tony takes in stainless.

dedicated
27/05/2019 at 18:01
3

I’ve been thinking about having different sized piston hot ends for different types of molds. Making the large clips, I need as much volume as possible. Filling a large cavity through a large diameter nozzle requires less pressure and I can use a larger diameter piston. For small items, with smaller diameter sprue, it needs more pressure, less volume, and potentially a smaller piston. @andyn mentioned that he uses what I think was a bushing in his system to get to a smaller diameter. I’m not sure of the details of his implementation. I think in your design with a little modification, you could have the hot end and a length of the piston be a drop in replacement with the electricals connectorized appropriately. This would give the smaller user (that does not have quite the user-mass advantage I have) a chance to make some smaller items. Actually, in your desktop design, if the middle beam was replaced with a pair of back to back C-beams with a gap in between you could have both hot ends in place and just slide the one you want to use into position. That may also be a way to increase the low throughput of the injection machine.
I’m going to make a mount for my earlier smaller hot end so I can use either in my machine.

warrior
24/05/2019 at 21:37
3

Good advise to drill the screw in and out a couple of times to melt the plastic.

Maybe a V4 version will have a bigger volume, but I’ll keep it in mind.

Thanks for all the info!

dedicated
24/05/2019 at 21:14
3

Yes, even though I’m not quite in windmill country, when it blows, it can be pretty strong, I made the clips long enough that I can put plates across the bottom to fully capture the beam. The clips are chunky with each leg about 12.5 x 38mm. I screw directly into the HDPE with sheet metal screws. I drill an undersized hole and then drive the screw in and out a few times with a cordless. The screw heats up and seems to form a thread in the HDPE.

If you go with the injector, just be aware of the size limitations on the parts. Mine has a cylinder swept volume of about 200cc, I can get maybe 130-140 g of HDPE into a part. The larger bottom clip is about the limit.

warrior
24/05/2019 at 07:34
3

@s2019

Funny how a lot of people here think alike.

I myself am looking to do a solar install in the back of my garden, as this gets a full day of southern sun as opposed to my roof which is south-east and has a tree in front of it…

Would be a bit bigger though, to help power my workshop.

 

In the Netherlands windpower is also an alternative, so I don’t think just a friction fit would be enough, but I guess the clips are big enough to also allow for a bolt through them.

 

“The wood and aluminum tape molds are holding up well” and “just making parts instead of an end item is a good use for the plastic lumber” are music to my ears, and have put an injector back on my shopping list…

 

dedicated
24/05/2019 at 03:19
3

I made more of the large clips in two sizes. The large size (130-140 g) is at the limit of what i can get out of my injector volume.  The wood and aluminum tape molds are holding up well. The parts are very repeatable and provide a nice friction fit onto the bars they are designed for. The plan was to use them for a convenient solar panel mount and they work great. Normally I would have made those out of some wooden or aluminum assembly. Once the wooden molds were made, these were easy to make and I’ll be making more,.

The point of posting them as an example, is that sometimes just making parts instead of an end item is a good use for the plastic lumber.

I would like to claim that the solar panel will help save the planet but in truth it will just power some patio lights and frivolous decorations that i don’t feel like running line power to.

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dedicated
19/05/2019 at 17:42
3

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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warrior
19/05/2019 at 08:55
3

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.

dedicated
18/05/2019 at 16:24
3

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.

warrior
18/05/2019 at 09:58
3

@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!

 

 

dedicated
16/05/2019 at 17:43
3

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.

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dedicated
16/05/2019 at 03:04
3

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.

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dedicated
15/05/2019 at 17:43
3

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/ )

warrior
15/05/2019 at 07:55
3

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!

dedicated
14/05/2019 at 18:52
3

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.

warrior
14/05/2019 at 08:09
3

@s2019

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…

 

dedicated
13/05/2019 at 23:47
3

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.

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dedicated
10/05/2019 at 03:15
3

Thanks @pporg I wanted to post some of the results here so people thinking of what to make broaden the options to making parts that make other things possible. In this case these pergolas are sold through a nationwide chain (Lowes) and there isn’t a good way to mount things without drilling holes and starting a rust spot.

I made a second clip in the mold and it is hard to tell the difference (first image). The wood mold held up well. I use wood screws to hold it together and if I’m careful it re-indexes pretty well on assembly (if only Legos could take the temperature). The second image shows the final install supporting the weather vane. One unplanned feature is that the bottom of the clip is just a bit tighter so it holds very nicely with no fasteners.

I’ll be making more of these…more odd stuff needs to go on top….Though we’ll stop before we reach Gaudi levels

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dedicated
06/05/2019 at 21:20
3

@pporg , Thanks.
This evolving design was never meant to be a specific design worth documenting with drawings but rather an example of a DIY process that takes the necessary off-the-shelf components and links them together using materials and techniques available to the hobbyist. As you’ve noted in the past, this forum is somewhat awkward for documenting a design. If it would be useful, I can put together a PDF with a bill of materials, some detail pictures, and rationale for why I chose that option. I would not expect anyone to duplicate my exact machine.
This design is in the DIY spirit and depends on the builder liking to tinker and hack, and also recognizes that this is hobby labor which does not cost anything. I think for anyone where these don’t apply, your desktop design that you have in the Bazar is a much better and ultimately cheaper way to go.

warrior
21/04/2019 at 13:16
3

in case you have not seen it, here it is again. The guerrilla guide to mold making

 

http://lcamtuf.coredump.cx/gcnc/

 

Steel epoxy sprayed with silicone lube or silicone mold release spray works wonders.  You can mix it with steel wool or chopped strand fiberglass to make it even stronger.  I think a commercial trade epoxy is called kitty hair that has the fiber in it.  Saw a youtube video of someone using it to make custom stereo speakers.

dedicated
21/04/2019 at 06:27
3

Went back to trying to see how useful wood molds could be. I have several small solar panels that run pumps for decorative fountains. The ebay pumps and panels work well but don’t have an easy mounting point. One way to grab them is with a clamping block on the small black block on the back and then drill a mounting hole in the clamping block. The first image shows the arrangement.

I need a handful of these. One option is to make wood blocks but then this is precious plastic not precious lumber. It is not worth making a proper aluminum mold so why not try a wood mold. The second image shows the mold and the resulting part before the flashing is trimmed off. Since for this part only the channel dimensions matter, I used scrap wood without machining the corners tight. Aluminum tape provides a releasable surface and wood screws hold it together. The results came out well for the application (third image). I undersized the channel because I wasn’t sure how much the HDPE would shrink so a light cut  made for a light press fit on the solar panel block.

For something more precise, machine the wood to be true and fill any gaps, Should provide a well shaped part. Not intended for production, but for a handful of parts, it is a viable low cost approach. Next few will try some black PP

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