Prusa Mini+

Prusa Mini+

I’ve ordered this 3D printer in the beginning of 2021, after initial successes with having a few models printed out by my friend. Once I put it together, it was amazing to just watch it materialize models from various sources.

Software

Solvespace has turned out to be a very good program for modelling custom objects, after I had to resolve some of its issues, notably accidental slowness. In general, my relationship with this software can be described as love/hate--it is easy to understand, but limited in features, and has erratic export issues when you inevitably manage to break its NURBS mode and have revert to triangle meshes.

I bought a 3Dconnexion SpaceMouse in an attempt to make it easier for me to work in the CAD, but I’ve eventually learnt how to use the mouse with similar ease--you need to press Ctrl/Shift intermittently as appropriate.

Průša Slicer is a fairly good program as well, though it would be nice if it could also command the printer to print over LAN.

Projects

Future projects:

  • hard and soft EUC attachments

  • battery charger for my laboratory power supply

  • a replacement container for drawers from another, discarded container--I’ve got a rough concept that consists of three kinds of intertwined parts and can be lifted by the top

Favourite models

Knowledge base

Tricks:

  • raising the heatbed temperature can make lifted corners lie back down

  • heated knives easily cut through anything that is stuck

Materials:

  • PLA is really hard and prints very accurately

  • PETG is somewhat softer and can be easily shaved with a knife, but it also strings a lot

  • you can’t really have transparent prints with FDM printers; transparent PETG also likes to stick to the nozzle, get dark brown with heat, and randomly stain the print

Modelling principles:

  • screws can go directly into the plastic, especially with softer materials, and this approach is also used on the printer itself

Průša Mini+ in infrared
Figure 1. Parts of the heatbed can be about 10 degrees C colder

Start of issues

Roughly around the time when I changed the nozzle to the wider 0.6mm, which is much faster at printing and I’d like to use it as the default, I started getting extruder clicks during retraction, and holes appeared at seams when printing PETG as well as PLA. This has remained the case even after returning back to the standard 0.4mm nozzle.

I tried doing these things to make the problem go away:

  • cleaning out the extruder itself, which did have strands of filament in it

  • cold pull, which appeared to be a no-op, and the pulled-out piece of filament looked almost exactly like the example photo

  • replacing the inner PTFE tube in the hotend with the spare one

  • toying around a bit with the idler tensioner screw

  • regreasing the rails, which did at least make it run quieter

  • changing the long PTFE tube

  • realigning extruder gears could rather make it worse, and I got a blister as a bonus

  • changing the nozzle temperature to 230..270 C (PETG)

I’m also not sure why the idler moved so much during retractions:

Bondtech extruder

Desperate, I ordered the Bondtech extruder and heatbreak, as well as some thermal paste. Someone claimed they’re required upgrades for printing from flexible materials, anyway.

Installation of the extruder wasn’t particularly involved, and the official guide was fairly straight-forward--I just used a little screwdriver rather than a hobby knife for the connector adjustment (do they like cutting themselves?) The hardest step was extracting the input PTFE tube that Průša staff inserted fairly violently into their extruder, and has some scuff marks to show for it.

After that, I was immediately met with the first issue of the alternative extruder: it can’t even load the filament right without the proper E-step setting, as it won’t reach the nozzle. Otherwise…​ it hasn’t quite reached my hopes and expectations, but I’m happy with it. The printer is much quieter now, even doing something as simple as loading the filament, which used to be very loud. However, the clicking isn’t gone yet, it just isn’t nearly as annoying. Retractions still appear to cause issues in prints, and in this aspect I’ve managed to get exactly where I was before.

There is one ugly aspect to this extruder as well: the tensioning screw is quite difficult to set up right, and you have to experiment.

Future: Bondtech heatbreak

This is one of the remaining things that I haven’t replaced yet. There is still a possibility that the problem is in my current hotend setup. A random old Internet claims that "only the screw part of the heatbreak should be visible", although it doesn’t seem to be the case in official Průša articles. It’s likely I moved some of the stuff there, and maybe I should reapply thermal paste.

I could also try asking the official support if they have any ideas, which I haven’t tried yet. It’d be unpleasant to screw things up more than they already are.

Resources:

It may be a good idea to get a 1.5 Nm torque wrench they want people to use for the heatbreak replacement, locally e.g. this Yato or for a fancier option our local high-quality Narex, which is sadly much less versatile.

I should also find out where to get replacement PTFE tubes, since they appear to be different here, for some reason.

Future: Tuning

Work on figuring out the best settings. Notably:

  • printing temperature for different kinds of filaments

  • obtain or make a linear advance tuning file for the Mini+ (the i3 one I found was dangerous, but it might be able to fix it by inserting missing G-code for bed levelling), even though Průša claims that everything is already perfect by default

Things to test:

  • one AR-15 speedloader ram print had corners mysteriously curling up, and it happened again later on the death whistle: temperature, fans?

Enclosure

All filaments release measurable volatile organic compounds when printing, as well as nanoparticles, and I plainly felt something wrong with my lungs, even with PLA and PETG. Moreover, I wanted to try ASA, which besides reportedly smelling much more requires stable temperatures. I needed an enclosure.

While thinking about how to go about this, I made a trivial enclosure from an IKEA LACK table and some food wrap. While it prevented dust from falling onto the printer, it was otherwise perfectly useless, what with its impractical size and weight. Also, simply stacking them wouldn’t give me enough room to put things underneath.

Průša Mini+ LACK wrap

After some research, and looking through the IKEA e-shop, I arrived at the decision to formalize my impromptu ugly stack of things in the form of a PLATSA-based build. And I got it right only due to sheer luck--while the 40 cm high glass door I picked was insufficiently high to cover the whole printer, the drawer front had an alternative, lower groove for the bottom, which enabled me to cover exactly the blank space above it. Very little space is wasted.

Průša Mini+ PLATSA enclosure

The quality is sadly appropriate for the low price, in that the door had some resolvable issues with closing flush, because the side walls of the assembly warp outwards under load, and the freely hanging shelf is unable to hold them together.

The bottom part is open intentionally, in order to help dissipate heat from power adapters, and charging devices.

Upgrades

I applied some unused foam tape to seal the huge air gaps around the door at least the tiniest bit better. It even looks nicer that way.

Future: Tuning

First, there is some cable mess that needs tidying up. The printer’s power cable can go through the middle of the shelf (use a milling drill bit), and the UPS power cable through the back (use a hole saw, about ø 5–6 cm). I need to get a USB extension cable (1, 2), USB 2 (theoretical maximum 60 MiB/s) and half a metre will suffice.

The back warps, and there is 16 mm of space to put some support in, ideally rectangular or circular. One could even make a thread on a rod, insert a bolt in a side of the frame (needs to be close to the outer surface), hold the rod in a free-to-spin mount on the other side (need to make a small part of the rod a smaller diameter, may use a drill and a file), and squeeze the sides together. This exists. Another similar option: fix a pipe to one side, and screw a bolt into it from the other side. Both possible, but difficult.

I might want to replace the noisy CyberPower UPS with something better, or even a basic surge protector, though seeing as prints can take a long time to finish, I’m inclined to have that battery in there. Both will fit comfortably.

The enclosure also acts as a large loudspeaker, so I could try placing the printer on a piece of tile and dampening its surface with something like felt pads, which are known to have good sound insulation properties. The minimum required area is 25 by 30 cm, the maximum 35 by 52.5 cm, and the optimum seems to be 30 by 50 cm. With stock Průša feet, the vertical space is exactly 2 cm, though it won’t be desirable to go over 1 cm of thickness. Contestants: 1 (claims 7 mm), 2 (probably similar); the latter needs to be cut to size. If I can’t find a tile cutter, the cheapest one should be sufficient. For felt, e.g. 1, 2, or reuse the random felt-like material I happen to already have, which are about 3 mm in thickness.

My signal white ASA could be used to mask the ugly connecting screws, which are annoyingly almost flush with the surface. Right now I have some prototypes made of translucent PETG installed--these can be pushed out from below.

I’d like to add some LED lighting, and maybe a temperature and humidity sensor with a display (or see how responsive analogue ones are). I’ll need to find a compact 12 V power adapter for this.

Air filter inspiration: 1, 2. People claim something as relatively simple as a HEPA + carbon filter even on low fan speeds gets rid of ABS odours, so there’s probably no need to overengineer.

I could finally make use of my TI MSP 430 dev board, get a temperature sensor, and a humidity sensor from Aliexpress, use my stack of segment displays (I might even find a handy controller for these), do PWM fan control.

In short, this is a time sink, though the experience should be valuable.

Troubleshooting sources

Future: Mini-compatible silicone sock

Apparently these can be ordered from Europe.

Future: Try to print some ASA

Note that it is said to absorb moisture easily, so limit air exposure.

Future: Try to print some flex

I could make use of some attachments to my Ninebot One S2 EUC.

Future: Try drying out my filaments

Put them in the oven at a temperature they don’t warp at, whatever kind they are. Over a long enough period, the moisture should be gone.