Monoprice Select Mini v2 - Early Impressions

So, as mentioned in my last post I picked up a Monoprice Select Mini v2. I received it on Wednesday, May 3, and got a single print off before I had to stop and try to troubleshoot something... Not a great start, but admittedly what I was expecting.

Lets start with the basics.

Unboxing was somewhat lackluster, or at least exactly what I expected. Light on accessories or pomp, just a couple huge chunks of styrofoam surrounding a dainty 3D printer. After removing the tape that locks a few pieces in place during shipping, and then moving around some stuff on my desk so I could get power to it, I plugged it in and fired it up. Leveling the bed is about as irritating as on the Monoprice Maker Select V2, but overall not terrible. At least since the bed is smaller it's not as annoying to make minor adjustments. The included sample PLA is a somewhat translucent natural PLA tone so I wanted to give it a shot. Loading filament is interesting as I've never used a bowden style extruder, but frankly a bit easier than the Wanhao i3 rebrand. So, time to try printing the model included on the SD card, a little cat.

First attempt at a print and...

Complete adhesion failure by the third layer. The standard gcode for the included model doesn't heat the bed, I wasn't 100% certain I leveled the bed as accurately as I could, and I added no adhesion aids like hair spray or glue stick... so it's not that surprising. I didn't make another attempt because the model includes a raft for some reason, and I have no idea how long it'll take to print the model (note: I've since seen some other users say ~3 hours, so I might try it). I loaded up some gcode (which does heat the bed) to the SD card for a Z Axis limiter clip I want to install so I can switch over to a PrintInZ print surface and tried that instead. I also put down a good amount of glue stick. The model printed decently enough, but one corner did lift off the plate a bit... I'm not sure if there wasn't any glue there or if the bed is warped strangely at that point, but at the end of the day I blame the BuildTak knock off surface. I hate this stuff.

Anything else wrong?

This first problem is apparently a known...thing. For the model I was printing I turned up the infill quite a bit and when it was doing the rapid movements to place infill in the thin areas it sounded like it was shaking screws loose. If I put my hand on the gantry during these moments the noise disappeared, so I clearly was dampening the vibration. A little repeated experimentation in placing my hand in different places showed the noise was mostly coming from closer to the Z axis, on the bottom of the X axis. Apparently, the incredibly thin metal shroud that makes up the X axis gantry has a tendency to make a really nasty rattling sound under certain mechanical movement. It sounds like most people just remove the whole damn thing, which I've now done as well. It requires printing a little mount for the X-Axis endstop, but otherwise it's not too difficult.

I also noticed the bed is definitely warped a bit. In the middle it is bowed up a bit. You can level the corners perfectly but the center will be too close to the nozzle. I've seen a lot of reports of that with this first batch of MPSMv2's, which is ... I dunno, annoying. I mean, look, these things are cheap. There's gonna be something wrong with it. A warped bed is easy enough to work around and most likely caused by picking cheap parts. It's the other stuff that's more frustrating. This rattling X-Axis gantry shows poor engineering and/or QA. Looking at the gantry after having removed it, I'd say the rattle is mostly due to poor welding/folding of the metal, or the fact that it's mounted via "raw" screws that can't sit perfectly flush, so the metal on metal contact just rattles. No matter why, it's silly. First of all, the thing apparently doesn't even need to be there. It's so thin I can't see it providing any real structural integrity to begin with. Second, since it's little more than a facade, why mount it directly to structural pieces? Again, it's cheap, you don't just cut corners by picking cheap parts but also via some shoddy craftsmanship, I get it. Just a bit annoying.

So now?

I went ahead and installed the X-Axis endstop mount and the Z-Axis endstop limiter, threw my PrintInZ bed (note: the 130x160mm fits perfectly) on there, and printed something else. A light coating of AquaNet and adhesion was great. I had some under extrusion at first but that's because when I reloaded the filament I retracted too much, totally my fault. The bed stayed on the platform without binder clips or anything, so that's a nice bonus. That's probably because I got lazy towards the end of removing the BuildTak surface and there's still some of it's adhesive on the platform.

There's still some rattle but it's not nearly as bad. There are also reports that with the V1 some rattle comes from the Z axis due to how it's mounted, but the V2 looks to be very solid in that regard so I'm thinking it's something else. I'll print more this weekend to try to identify it.

The home position of the nozzle is also in what'd I'd call the negative coordinates of the print bed. It was about .5-1mm off the BuildTak surface on the Y axis, and switching to the PrintInZ plate it's similarly off just a bit. I imagine I can adjust the Y axis end stop to "correct" this, but for now it's just as easy to line up the PrintInZ plate "wrong" so it'll catch the nozzle properly. Big advantage of over sized and removable print surfaces is you can do just that.

Still in initial impressions stage or can we make conclusions?

I'm willing to make a couple conclusions, but with the big asterisk that I've only printed 3 items and started changing things after 2.

1. I just hate BuildTak. It's probably not the surface's problem, something about how I'm expecting it to work, but honestly I think anything that might not be perfectly flat shouldn't get the surface. I think it just can't work if there's even a slight warp. Also, it either gets no adhesion or too much, it gets damaged easily and is a hassle to replace, etc, etc.
2. The print quality appears pretty good so far. I haven't broken out the calipers to measure anything, but things look good. The Z Axis limit snapped right into place and worked flawlessly, the X Axis endstop mount was quite snug but the thingiverse post even mentions it's meant to be a tight fit, so yeah, seems solid.
3. The "Magic Numbers" are still a thing? A quick explanation: The MP Select Mini has a slightly "non-standard" Z Axis. Due to the mechanics of the Z Axis, the ideal layer heights are multiples of 0.04375 mm. So, for instance, instead of doing say 0.2mm layer height as you would on most printers, you do 0.175mm layer height. The three objects I've printed used this magic number and they came out pretty decent. Again, I haven't used calipers to check it for accuracy, but it seems good.

So yeah. I think I like it. It's just cheap in the places I was expecting it to be, but at the same time people haven't blown it's surprisingly good print quality out of proportion. Decent piece of kit for $220. That said, we're also going to see Monoprice release a Mini Delta printer very soon, that is mostly feature identical except it has a slightly smaller build volume but also gains auto leveling, for even cheaper (expected price point is $150). I'm going to get one out of sheer curiosity.