geert_2

On my printers overhangs work better with thick layer heights: 0.3mm and 0.2mm are more beautiful than 0.1mm (haven't tried 0.06mm with huge overhangs). In 0.1mm layers, the edges of overhangs tend to curl up. Try to optimise the settings and design on *small test pieces* first, so you don't waste too much time and material. And indeed, a round underside might need a brim, or a custom flange designed in CAD, to make it stick. If it has to be a demo-model, I do understand your concerns about elegance: square tubing doesn't look as nice as round tubing. And especially a house-shape (=square with roof) might look ugly due to the unsymmetry. Maybe you could try a couple of small test pieces in different shapes next to each other? A round shape with brim, a house-shape (=square with roof), a true pentagon shape, triangular shape? Although personally I wouldn't use a triangular shape, due to the restricted volume and huge inner surface area, causing more friction to the flow. Then the students can see all the alternatives, and the benefits and disadvantages of each.

Try a couple of these custom supports? They might work for your model. But don't expect miracles, it will allways be ugly. The ribs allow to make the gap smaller, without the support totally fusing with the model. If you provide enough methods for removing the support later (separate parts, holes for hooks and pliers, handles to wiggle things loose,...) you can also reduce the gaps. Making the support extend a bit (see bottom right in first pic) lets the model adhere better. The bridge in the last two pictures uses a separate support-bridge, so the supports don't go all the way down and don't destroy the text. It also has ribs for smaller vertical gaps. Maybe the same results can be achieved with standard supports in Cura nowadays. But I prefer to design my own custom supports, due to my often small or specialised models.

I have no experience with soft 3D-printing materials. But soft plastics do not necessarily handle ink better. There are lots of soft plastics that do repell water, like PP and PE, so they wouldn't work at all. Have you tried treating the surface of PLA-stamps, to accept the ink better? Or try changing the ink, so it adheres better? If you could print in PLA, you would get the best details, I think. For example, try lightly sanding the stamp surface with fine gritt paper, so it is matte? And try adding a little bit of alcohol to the ink, so it spreads easier onto the stamp? The advantage of sanding (or similar treatment) of the print-surface only, would be that the symbol attracts the ink well, while the rest of the stamp repells it. This might give more accurately printed/stamped symbols on paper?

Yes: they change surface tension: soap decreases surface tension (so the water spreads into a very thin layer), and salt increases surface tension (the water tends to pearl). That is how I came to the salt: I reasoned: if soap and oils reduce surface tension *and* bonding, then maybe I need something that increases surface tension, and hopefully bonding too? After googling, I found salt is one of the few things that increases surface tension. And it seems to work, at least for PLA, compared to printing on bare glass. But I am not sure this is the real cause, there could still be another explanation. Also, in manuals on glue, you find that the *glue* should have a very low surface tension to make it spreak easily, so it can easily wet and penetrate the parts to glue. And thus the part to glue needs to have a higher surface tension than the glue. I don't really know the chemics/physics behind it, apart from this simplification. If we would know more about the real mechanism, maybe we could find even better methods. And maybe this principle could also be helpfull for filament-development, to make it stick better to glass.

Changing feeder tension changes the depth of the indents, and thus the effective diameter of the feeder wheel. And it changes the partial slipping of the filament (=filament speed not exactly matching the wheel, due to the indents being stretched by the resistance in the feeding traject). So I can see that both variables (depth of indents, stretching of indents) have an influence. And they will change with material stiffness too. The wheel will bite deeper into a softer material, and it will stretch more. Additionally, speed and temperature are going to play a big role too, because they affect flow-rate, and mechanical accuracy (overshooting, ringing). So I guess there will allways be quite some trial and error for this sort of jobs, especially if you are going to print it in different colors and materials. Which usually is the first requirement of kids, of course. :-) On the Lego-website I once read that the development of "simple" bricks requires quite a lot of precision engineering, to get a good fit.

Does the inside of the tube have to be round? If you would give it a sort of teardrop shape, overhangs on top would be less steep. Then it could be printed in one material without supports. Or maybe you could even try a square tube, with pointed roof, similar to the "home" icon 🏠 in your browser? The tube would look weird, for sure, but it might work? Try this on a very small part first.

An electric fault could of course be the cause, or a ground-wire with high resistance. Let's say you have a ground-resistance of 25 ohms, and a fault current of 4A (=not enough to trip the fuse), then you would get a voltage of 100 Volts on the ground pin of the socket. However, if this would be the cause, then it should happen every time you touch the frame of the printer, and *as long as you keep touching it*. If it is only a short shock and then nothing, it is static charge which is discharged when touching a grounded frame. So I would guess it is the latter? Maybe due to a change in clothes (wool, some synthetics?), or different shoes? Or very dry and cold weather? Or some other equipment that charges up, which transfers its charge to you, and then you discharge it via the printer and ground? For example old monitors with CRT tube were known for this. Try attaching a voltmeter to the ground-pin. If it is static charge, it will be very hard to measure due to the input resistance of the meter being too low and the charge leaking away. However, if it is a fault, it should be very easy to measure (try both AC and DC).

@SandervG: This is weird, because I had the exact opposite experience when printing on bare glass, before I started using the "salt method. When the water spread out into a very thin layer, bonding of PLA would be bad: filament would curl up, the corners would lift, or the whole model would even come off. And vice-versa: when the water would stay in nice round bubbles, bonding would be reasonable. Now, with the salt method, the water also stays in nice round drops. And bonding of PLA is very good, as long as the glass is warm. So my reasoning was that the substrate (=surface to print on, thus the glass) should have a very high surface tension, and the wetting agent (=here the molten filament) should have a low surface tension. So that the molten filament easily attaches to the glass and spreads onto it. This is the concept what glues are based on, if I understood it well? (Correct me if I see this wrong.) Anyway, salt increases surface tension and increases bonding of PLA. And soap and oils reduce surface tension and reduce bonding. But I am no chemist, so I would like to hear the viewpoint of a chemist experienced in glues and bonding, for a better understanding of the basic laws of nature on this.

If you would like to use a more gentle atomic pull, you could try my method here (scroll down a bit): https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/ It lets the nozzle cool down much further than usual, and uses gentle wiggling and turning instead of brutally pulling. This avoids the risk of displacing the teflon coupler or nozzle, or bending rods.

Maybe you should try spraying bright red fluorescent paint in the same way? You would be astonished for far it goes and how wide it spreads. After a few applications, your whole printer and half of your table will have a fine red cast to it. Years ago I used a big cardboard box in which I sprayed silicone oils on moulds, and black conductive paints on electron microscopy samples. Even though there was a strong vacuum flow sucking out the spray from the back of the box, it still went everywhere in front and left and right of the cardboard box. I have seen the same in other spray cabines from collegues. Similar, on old HP inkjet printers, after a year the whole table on which they were sitting, had a black cast around the printer. Just from the ink dust caused by the little sprays. It goes much further than you think. So I would recommend spraying only in a box, with air extraction, and far away from the printer or other sensitive stuff.

I also have noticed that PET and NGEN (which seems to be similar to PET, from colorFabb) are not stronger than PLA. Although for snap-fit lockings, carabiner hooks, and similar things that need some flexibility, PET is much better than PLA, because PLA will crack over time. Also, PET can withstand the heat of the sun, and can be used in a car. PLA can not: it deforms even in mild sunny spring or autumn weather. But for pure strength where flexibility and temperature resistance are not required, PLA can often withstand more than PET. In my PET-models the fracture lines go diagonal through the material, and follow the stress concentrations. They do *not* follow the layer lines. So it has to do with material strength itself, not with layer bonding. However, if in your model the cracks would follow layer lines (=delaminate), there is a bonding problem. This could be due to printing too fast, or using too much cooling fan. So the next layer does not heat up the previous layer well enough, and it does not fuse together. Try turning off the fan, or reduce it to the absolute minimum required for your model. Also, try printing a bit slower: 25...30mm/s. At 20mm/s I can succesfully print PET at 2015°C (recommended range 215...250°C, brand = ICE, from company Trideus in Belgium).

I think your cardboard box is a really great idea: it is very compact, and "part of the printer", sort of. But being of cardboard, it will absorb moisture by itself. It might be better to make it out of transparent plastic (and then you can see what is going on). And add little pieces of teflon tubing from the exit of the box to the feeder-entry. To close the seams between box and printer, maybe you could add soft foam like on window and door seals? I think it is worth developing this further. As Smithy says above, you should add *lots* of silica gel. I use 500 gram packs sold in car shops to de-humidify car interiors. These have a blue indicator turning to pink when saturated. Also, regularly regenerate the silica gel: once saturated it not only loses its function, but makes things worse. Also put dry silica gel in the box/oven while drying the filament. This silica gel bags are clean, easy, and can be regenerated on the central heating, or in a micro-wave.

Maybe you could in CAD model a couple of little dots on the floor, separate from the real model? Then these dots will sit on the glass. All the rest will be at the desired height above it. The idea would be a bit similar to the cross-hairs in printing, to align the different ink colors cyan, magenta, yellow and black.

I like the concept of the longer tubes. But I have a question: don't the red clamps pinch off the tube after some time? And how is unwinding resistance in this setup, compared to the standard spool holder?

Hope you can read a bit of English. This problem is also present in the UM2, but less. It is most visible when using 100% infill and short infill strokes, when the head has to switch direction every few millimeters. This causes visible overextrusion in this area only. As Smithy says, print slow, cool, and with equal speeds (except travel speeds, which may be a lot faster). So that you get a flow that is as smooth and constant as possible, and without excessive pressure-buildup in the nozzle.

Most likely causes, I think: (partially) clogged nozzle, deformed teflon coupler, or little fan not working? After cleaning the nozzle with atomic pulls, make sure you can look through it from above. If you want to use a more gentle atomic pull, instead of brutally pulling, try my method here: https://www.uantwerpen.be/nl/personeel/geert-keteleer/manuals/ Check if the result of the atomic pulls is deformed near the seam of nozzle and teflon? If so, the teflon coupler is worn out. Check if the material is thickened or molten even before entering into the nozzle: if so, the little fan is not working (it tends to accumulate strings and hairs), and heat travels up too high into the filament. Manually heat up the nozzle and feed some material into the nozzle, and feel how much resistance you get, and where.

I think yes and no. People who hope that a 3D-pen will be a cheap but good 3D-printer, are going to be hugely disappointed. (Sometimes it was marketed as such.) However I can see a niche market for it. For example if you want to create custom trees for HO-model train landscapes, then it gives you the freedom and organic irregularities you want. Realistic trees are very hard to model in CAD and print with a normal 3D-printer. Similar for some specialised decorations or juwelry. I am not sure how it would work for adding hairs, eyebrowns, moustaches etc. to 3D-printed models? But I think it could work. The question will be to find a reliable pen that works with an open filament system and with lots of different materials. One that is handy and pleasant to use. Handiness and versatility will be key points.

I saw one in action a couple of years ago, but I don't remember the brand. It was something with "doodler" in the name, but the rest..? Not sure if it still exists. Anyway, I was not impressed with its performance: the art they produced with it, was primitive and clumsy at best. However, later on Youtube I saw others who got better results. So maybe you could do a search on Youtube? Both for getting an impression of pen performance, and of the techniques they use?

What about variations in nozzle-temperature? And thus variations in viscosity and flowrate? Where it would be just a coincidence that they happen at about the same time as a rotation of the gripper wheel? Or for example, if the bed heats up (eating a lot of current) that this would shift the ground-level of the other signals, and thus influencing the measurement of the nozzle-temp? So it would adjust temperature not based on the real temp, but on an error due to shift in ground-level? Or something else along this line of thought? If you swap motors and the problem swaps printers too, then it is related to the motor, of course. But if the problem would stay with the printer, maybe this or something similar could be an issue?

When doing these transparency tests, I also noticed that bubbles do not only occur in the material due to moisture. Even when the filament was very dry, I got exploding bubbles when printing fast and hot at 0.3mm and 0.4mm layer heights. The air which is trapped between the extruded sausages heats up and expands. This causes the still molten plastic to erupt like a micro-volcano, leaving a crater afterwards. Some bubbles don't make it to the surface, but they get big enough to destroy transparency, and to cause an irregular surface. It is clear that they are in the seam-lines between sausages, not in the center of the sausages. This is visible under a binocular microscope (which gives good depth of view), but extremely hard to photograph, so no photos yet. So, even though printing hotter makes the filament flow into all corners easier, it worsens this effect. Thick layers cool slower than thin layers, which again gives trapped bubbles more time to expand and to make it to the surface. Maybe that is one of the reasons why thin layers, printed slow and cool give a better result in my tests here?

Try a small test cube with the same wall thickness, and then while printing adjust settings on the fly: play with temperature, speed, flow-rate,... So you can immediately see what the result is, without wasting too much material. I once read that for ABS you might need to increase the flow rate, since this material is more elastic and thus the feeder wheel might stretch the little indents it creates, making diamond shapes instead of squares. This might result in a lower real flow rate than the feeder wheel's speed would indicate. Maybe try 110% and then adjust as required? (This in combination with the suggestions above: slower speed, higher nozzle temp, and higher environment temp.)

Yes indeed, this is what I also noticed. One of my other test models, not shown in the photos, was a carabiner (snap hook; or in Dutch: karabijnhaak). It stayed soft for several *weeks* after I let it sit in acetone for a couple of hours. And it also had the above cracks. So, once the acetone is deep in there, I don't think we can stop it with superficial methods: the stopper-chemical would have to penetrate deeper and faster... So I am going to stick to one liberal brush-on for my moulds, and then let it thoroughly dry. :-) By the way: the models in these photos are solids, printed with 100% infill (just like almost all of my models).

In Belgium we have big companies Materialise and Melotte, plus another one I don't remember. These are well-known around the world, and they have international factories. Maybe they have one in the US too? But it's not going to be cheap.

Great idea, but make sure it can always be disassembled again afterwards. Because once assembled - if it can't be undone - it would lose much of its magic. :-)

@Cloakfiend: I did some tests to see the effect of an *overdose* of acetone: I left these test pieces in acetone for several hours. Results: models in PLA crack and deform. The cracks often start at layer lines and corners, but then go diagonally through the material. When dry again, the material loses some of its elasticity, and becomes a bit like hard plasticine (=it does not fully return to its original shape after bending). Also, multiple brush-ons with acetone don't have much effect indeed, like you said. Only the first one really works well. So, indeed: after removing/sanding defects, now I just apply one liberal brush-on of acetone, and then leave it at that. It tends to fill the little valleys, without removing the peaks. And then I wipe off the white residu before the model is totally hard again. Works very well for my moulds. You did a really good job in developing that method and balance. Further, smoothing PET does not seem to work: short applications of acetone have no visible effect. Leaving models in acetone for hours, deforms them: square blocks get deformed into a sort of pillow with rounded edges. Ugly bubbles appear below the surface, and keep growing for several days. Pics on top: PLA/PHA (colorFabb Dutch Orange) after sitting in acetone for a couple of hours. This is a small test piece of ca. 10mm x 15mm x 3mm Pic at bottom: block of PET left in acetone (red, pillow-distorted) versus original shape (yellow). Both are the same brand of PET (ICE), but different colors. Notice the rounded edges and the bubbles in the red model.