Prusa-Mini expectations for Prusa i3 users  

  RSS
SeattleDavid
(@seattledavid)
Estimable Member

What are the surprises in the Mini for somebody familiar with the bigger i3?

I presently have and love my Prusa i3s MMU2s. i will soon receive a Prusa Mini. 

I am wondering in what surprises—both good and bad—there are in store. Of course I know the differences from the published features, so those aren’t what I am looking for here. But I am wondering what features, problems, surprises, disappointments, unexpected finicky-ness, or similar may be lurking.

For example, I read about Heat Creep when printing PETG on the Mini. This is worrying, since I only use PETG. If this issue is real, the Mini will be a great disappointment,

I’m mostly wanting to have my expectations set right, so that the Mini isn’t just a huge disappointment, I like the i3 very much, and it is the baseline that I would judge the mini.

What should I be prepared for?

 

Posted : 12/07/2020 11:28 am
SeattleDavid
(@seattledavid)
Estimable Member

Any thoughts on this?

Posted : 14/07/2020 9:03 am
bobstro
(@bobstro)
Illustrious Member

Fewer gummies.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 14/07/2020 2:37 pm
crawlerin
(@crawlerin)
Honorable Member

After some initial SNAFUs with PETG on my MINI (clogged nozzle, underextrusion, filament wrapped around extruder gears), I have since printed LACK enclosure parts, new MINI plastic parts and few other things for household, then like 2 spools worth of mask accessories. Stock R1 version, I did not change plastic parts yet nor installed Bondtech heatbreak. I am in no way PETG expert or even advanced user, I still cannot print PETG with supports properly for example 😀 and my printer is due some maintenance. Things I learned:

0. There are some obvious things to check before you even start first print: lift the heat-block and pre-tension PTFE tube in heatbreak, to avoid getting gaps between nozzle and PTFE tube right from the start. Also just in case check grub screws on motors. There were cases of layer shifting due to loose X and Y pulleys from factory. This single arm design has some weakness - when assembling printer, make sure XZ part is as perpendicular as possible to Y axis and X is parallel to Y. This will avoid issues with inconsistent layer height in various corners of print surface. I use piece of paper under nozzle and I loose and tighten screws and tilt XZ until nozzle is at the same height above the surface (or try as best as I can do that). Right angle tool would be much easier probably 🤣 

1. Dry filament is crucial.

2. Don't overtighten extruder idler. I think that's why I had PETG filament wrapped around gears, it was too tight, while PLA was just fine. Screw head needs to be at plastic part surface level, that worked the best for me.

3. MINI is finicky about first layer with hot vs cold printer. You may need to adjust it back and forth by as much as 0.2 mm ... you start with cold printer, have very nice first layers and everything is OK, then third print in a row you have it too low and solid infill above it totally crumbles. Keep an eye on first layer, MINDA does not have thermistor and firmware does not have temperature compensation. It is set to 170 for probing but first layer calibration uses filament working temperature. Here are some very good observations and tips for starting and end g-code to compensate for some of this stuff: https://sites.google.com/view/newbieprusaminireview/home  

4. As Bobstro mentioned, there is miniature package of gummy bears with MINI.

This post was modified 3 months ago by crawlerin
Posted : 14/07/2020 3:18 pm
bobstro
(@bobstro)
Illustrious Member
Posted by: @crawlerin

[...]

3. MINI is finicky about first layer with hot vs cold printer. You may need to adjust it back and forth by as much as 0.2 mm ... you start with cold printer, have very nice first layers and everything is OK, then third print in a row you have it too low and solid infill above it totally crumbles. Keep an eye on first layer, MINDA does not have thermistor and firmware does not have temperature compensation. It is set to 170 for probing but first layer calibration uses filament working temperature. Here are some very good observations and tips for starting and end g-code to compensate for some of this stuff: https://sites.google.com/view/newbieprusaminireview/home  

Are those your note pages? I don't have access to a Mini, but I'm curious about the MINDA warmup. I notice the example on that page uses an 80 second warmup pause. I've noticed that a COLD nozzle on my Mk3 closely mirrors the PINDA probe temp. I'm wondering if anybody has experimented with an external script -- perhaps something in Octoprint -- to monitor the nozzle temp to make sure the probe is properly warmed before starting probing. This might be more accurate, particularly for folks that live in climates that have large temperature swings.

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 14/07/2020 4:01 pm
crawlerin
(@crawlerin)
Honorable Member

Those are not my notes, it is from some forum user's from here and I for the life of me cannot remember who it was. 

It looks like nice side-effect of probing at constant lower temperature - besides leaving no boogers on plate - is also mitigating biggest issue with MINDA not having thermistor. It just may not be accurate enough in other than cold conditions when printer is starting from other than room temperature, for example when printer is already warmed up or in warm enclosure. The correlation between nozzle temperature and its use as sort of external thermistor for calculations with MINDA had also been suggested in the past, maybe there's still issue opened for it on GitHub. To be honest I am not a programmer and I cannot determine whether any of this is being used at all in firmware. I like the idea of some script monitoring it, but I can tell that even this static 60-80 second warmup in starter g-code improves first layer a lot.

Posted : 16/07/2020 3:19 pm
gordon.w
(@gordon-w)
Reputable Member

@crawlerin

The notes were generated by @marklgoldberg . I totally agree that they are a great source of information.

Posted : 17/07/2020 9:09 am
crawlerin liked
carl.s12
(@carl-s12)
Active Member

I have an I3MK2S and have been working with it for over 2 years, only complaint is that is is loud, but it prints well and I know what to expect.  A level machine in my opinion.  My prusa mini has not been a good experience at all.  I ordered it in December, it arrived in mid May, worked for about 2 days before suffering a pretty nasty jam.  I was able to clear that and then ran into jam after jam.  Support suggested raising the heat block upwards so I did, replaced the PFTE tube with the spare and that seemed to solve the jamming problems.  I then tried to print a number of different items but anything taller than about 5.5 cm or so develops a horrible banding problem.  If I print items near the print arm, that problem goes away but that limits the build space I have to incredibly small for any object over 5.5 cm.  Support has tried giving me some solutions but has been unable to solve that problem and we are in July now.  I've taken the x/z axis off, attached again to the base... replaced the bearings, redone the entire x arm, redone all the belt tensions, undid and redid just about everything humanly possible....No idea if its connected to my already existing problems but I think there is also a ghosting issue at stock speeds and settings, but thats the least of my problems.  So I guess in that sense I still have no idea if this printer is a good printer or not, at this point my conclusion is not but from what I can see its been good for most people.

Posted : 18/07/2020 1:52 am
smoking_rubber
(@smoking_rubber)
Estimable Member

I am not an expert AT ALL, but plenty of experience with big chunks of precision steel.  Banding away from the arm tells me something is loose in the gantry.  Try removing the bolts that hold the X and Z arms, and grind about .04" [1mm] off the tip.  Seems like you could be bottoming out due to shmoo in the hole or something. 

I'm still waiting for my Minis.  Ordered one in May, and another in June.  Hoping to win a MK3S though 🙂  You could help by checking out my entry.  https://www.prusaprinters.org/prints/36508-prusament-organizer   Feedback is appreciated, I still have time to change the design.

Posted : 18/07/2020 2:27 am
carl.s12
(@carl-s12)
Active Member

@smoking_rubber

Some general tower tests, I printed A to show support the problem.  I took off the x/z axis and re-attached mimicking the printer arriving for the first time when I had blissful hopes of printing with it.  I then printed B and was hopeful...but then Print C is the next day after doing absolutely nothing to the printer....just letting it sit overnight turned off.  I have just no ideas 

Posted : 18/07/2020 2:39 am
smoking_rubber
(@smoking_rubber)
Estimable Member

Try printing that tower as a big rectangle stretching to the end of the X axis.  That will show the variation and tell you if your assembly is unstable.

Posted : 18/07/2020 4:35 am
carl.s12
(@carl-s12)
Active Member

I eventually sent the printer back to prusa to have a look at apparently the problem was from the trapazoid nut causing vibrations

Posted : 28/08/2020 4:50 pm
greg-5
(@greg-5)
New Member

Just posting to say the problems people report are not universal - I've had none at all.  I've had my mini for three months now, absolutely stock, haven't touched a thing apart from assembling it. I've printed about a hundred objects,  mostly PLA with a little PETG, and my only quibble is the z-height wanders, so I do a calibration every couple of weeks when my first layer gets a little loose. I haven't bothered with custom gcode or any tweaks, apart from updating the firmware.

I love this machine. It's small enough and quiet enough to sit in a cupboard in my office, so no more running up and down to the garage. It just works.

Posted : 04/09/2020 12:46 am
marklgoldberg
(@marklgoldberg)
Trusted Member

I updated my notes at https://sites.google.com/view/newbieprusaminireview/home and things are still working well after six months. I've gone through almost 20 spools of filament, mostly PETG and printed hundreds of parts. With the gcode tweaks, I just start it up and go.

Regards,

Mark

Posted : 04/09/2020 3:53 am
Share:

Please Login or Register