My UM2 First Experiences

[dgsharp 0]

I just got my UM2 (Yay Christmas!). I'm fairly new to the hobby/DIY 3D printing community, I've been around it at hackerspaces and even designed the "Hive76 Milled Bolt" for RepRap extruders, but haven't had a machine of my own until now. Until very recently I ran a Stratasys Dimension FDM machine at work for about the last 6-7 years, and I have parts made on pro SLS / PolyJet / FDM machines for work with some regularity. Hopefully my comments will be of some benefit to newbies, and maybe also help with the future documentation. My apologies for such a long message. Here goes:

- There were 2 button head screws loose in the bottom of the box. It's not immediately obvious to me where they go. (They don't look like they go to the extruder.) So far the machine seems to be ok without them, so we'll see!

- There didn't appear to be any documentation about cutting the zip ties that were holding the X/Y stages during shipping. Not a big deal, but in trying to follow all the directions to the T, I saw no mention of it.

- The "getting started" documentation didn't seem to mention attaching the glass plate. Not super tricky, but a quick note in the unpacking docs would have been nice.

- I've got 3 materials, the PLA that came with the machine, some ABS from Makershed, and some Taulman 3D nylon 645. I found that the UM robot model prints fine for me in PLA with no glue stick, but I needed the glue stick for ABS. For the nylon, I used 245C for the hot end with a cold build plate covered in 3M blue painter's tape ("Multi Surface! With EdgeLock!"). The ABS and nylon both have one or two small charred areas but are pretty decent, not much worse than I'd get with white ABS on the Dimension. A little stringy between the two knobs on the tops of the head and a little saggy in the rear-end (in all 3 materials), but overall pretty good.

- I was surprised at how well the PLA seems to stick to the raw glass when the glass is at all warm. I had done several prints and it wasn't until I let it get way down to room temperature that the parts came off the bed with minimal force. I even broke one part removing it after the machine had reported the print was done and the bed was cooled. A razor blade or sharp paint scraper helps if you're impatient like me.

- PLA smells worse than I expected. I've been around DIY machines printing PLA and never noticed any smell at all. I don't know if I was just distracted, or the ventilation in those spaces was better, or if this machine smells more than the others I've seen. I switched to ABS and while it is arguably more objectionable of a smell from close up, for me it's not that much worse, just different and more plastic-y. I needed to run a ceiling fan for an hour or two after a 2-hour print to get the room smelling normal again after PLA. I don't mind the smell but I don't want to bug my family so I'll have to be creative. The nylon seems to have no smell of its own, but the printer still smells like PLA (I assume it's PLA). In general changing material is fairly painless and quick.

- I printed a test cube and it came out about 0.015" too tall (0.381 mm -- I believe in metric but most of my experience is with imperial, sorry!), and about 0.010" (0.254 mm) too small in the X/Y dimensions with PLA.

- I measured the diameter of my UM-supplied PLA with a micrometer and found the average to be about 2.852mm or so. There was a lot of variability but mostly just out-of-round, so that's presumably fine. Pretty close to the specs.

- Bed leveling: it would be nice if these machines could include a limit switch and automatically do the bed leveling the way the Stratasys Dimension machines do. You just plop a build plate in it, and it checks the build plate in 4 places before every print so you never have to think about it. Might require some redesign and a larger machine, I suppose. Anyway, something to think about for the future.

- Customizing material presets on the machine: this seems incomplete or at least undocumented. If you just want to jump between the stock settings for PLA or ABS it works great, but I don't understand the customization interface. Through trial and error I have set up a new preset called "CUSTOM1", which I can't see any way to rename. The UM2 manual has no mention of these presets at all as far as I can tell. Several times while trying to change the values of my new custom preset I have inadvertently changed the values of the stock ABS and PLA settings, and I don't understand why. Is there some way to interface to this stuff from within Cura and send it to the machine over USB or something? I couldn't figure it out.

- I created a 1cm cube, and to test out Cura's support structures I put it at a 45 degree angle. No support structure was created despite having it enabled in software, I guess because of the angle, so it air-printed spaghetti. I tilted it further and it generated support material under one side that did a reasonable job of supporting it and it turned out reasonably.

- While switching material the extruder's stepper motor apparently loses steps when the material goes into the hot end, resulting in a periodic "click....click...click" sound. Seems ok during printing, I'm hoping this isn't anything to worry about. I have seen some posts mentioning that the extruder/hot end doesn't quite have the oomph of the previous one.

How do I think the UM2 compares to my old Dimension machine? The Dimension could only do ABS. It had no smell whatsoever (even if you aborted a print and stuck your head right inside the machine -- nothing), but could only do ABS. I actually find that I like PLA, it's much more rigid than ABS, which can be useful. Nylon is extremely flimsy for thin-walled items but its toughness is awesome and the bonds between layers are impressive. The UM2 can do much finer layer thicknesses (the Dimension's thinnest was 0.010" / 254 microns), which I'm hoping will help me print more void-free thin parts like the trailing edges of prototype prop blades. The Dimension machine will almost never give you a bad print, it just works every time (due to the breakaway support material), but having this machine in my own home is tough to beat. The Dimension machine also cost about 8x as much at the time.

All in all I'm very impressed with this machine. I have some experimentation to do but overall it seems very capable. Thanks for putting all your hard work into it, and keep up the great work!

 

[illuminarti 18]

Welcome to the forum, and thanks for the detailed post. A few points I can address:

1) The firmware is still under active development, and I think a lot of things will be improved quite quickly there. The material presets are still a bit difficult to use, and some of the settings don't get saved correctly when they should.

2) The z height of prints should be fairly accurate, since the height adjustment is fairly precise, but a couple of things can affect it. Firstly, the firmware assumes that after going through the leveling/homing procedure the nozzle is 0.1mm off the bed. If it's any higher than that, that extra height will get added to the print. Secondly, if you print with a thicker first layer, I think you still may get one more layer than you should in the rest of the print, also making it slightly higher than it should be.

3) When generating the support in Cura, it takes into account the overhang angle, but not the need for a base footprint. The printer can happily print 45º overhangs without support. But if you cant a cube over at 45º, then there is not much left to stick the the bed, so the print inevitably falls over. If you print with a brim to widen the base, then the 45º print will probably print ok, although it might still wobble.

4) The 'click-click-click' sound during material change is intentional; the stepper motor current is reduced so that the material can be fed quite quickly, but the motor will slip once the plastic reaches the hot end, rather than risk having the extruder bolt gouge chunks out of the filament.

 

[dgsharp 0]

Thanks for your comments. I was going to post something about aborting print resulting in too much retraction, but I see you beat me to that!

Some updates:

- After printing a bunch of things relatively successfully, all of a sudden anything I would print would lift up after a couple of millimeters. I tried cleaning the bed, adding glue stick, etc. I read over the manual again and it said to try re-leveling the bed, and that seems to have done the trick. Woo! How frequently would you say you have to re-level your bed? Maybe I was pushing too hard when removing some of my earlier prints.

- I think I'll need a combination of more appropriate print settings (and the experience to come up with them), and also some built-in support structures on my models. For some of my parts (like a 3-bladed propeller) I think I'd do better if I just built some supports into the model, designed to be cut away with a hobby knife. I look forward to the day when I can take supports almost for granted like I used to on my Dimension machine. This is a great machine for the price though.

- Lots of my parts seem to come out with the first couple of mm slightly shrunken compared to the higher layers (PLA, 0.1mm layer heights, 2mm shell thickness). My current theory is that this is a combination of large wall thickness, thin parts (perhaps 2-4 mm width), and the heated bed. I think I'll try printing on blue tape without the heated bed to see if that helps at all. Or maybe starting the fan earlier. Any other ideas? Printing objects using the "quick print" options doesn't result in this issue, but the walls are of course thinner.

- The LED strips on the inside of the machine started to separate from the enclosure towards the top. No biggie, I just pressed them back down.

- Now for a bigger issue: I went to print something this morning, and upon clicking the button to initiate a print, the machine started rumbling violently during the homing process. It appears that something has happened to the X axis limit switch (the axis with the linear rail in the back of the machine and the limit switch all the way at the back of the machine). It appears that said limit switch no longer works, presumably after some sort of crash or something resulting in a bent lever (image attached). I tried bending it back briefly and it didn't help. I think I can probably get it working right but there is also a decent chance that the metal snaps after a couple of re-bending attempts. For now I got it printing by carefully waiting with a paint scraper on the limit switch and hitting it when it tried to home (and waiting with my finger on the power switch for when it's done printing), but that's obviously not something I want to do much more of. (I just submitted a ticket about this one just now.)