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I think this is a known issue. Something about the installer and security. I think the older versions of Cura (before 4.7 I think) work on any version of the Mac but the newest versions (starting around 4.7 or 4.7.1) need the latest Mac operating system because they are... signed? Something like that? I'm not a Mac person. But if you google around on this forum there is discussion.

A lot of people who have this issue don't actually have an Ultimaker printer. There are some knock offs. Can you take a photo of the print head and maybe a photo of the PCB underneath? Most UM2 owners can tell by seeing only a small area of the printer if it's a knockoff or the real thing. Also is it a UM2+ or UM2 regular, Um2go, or extended? Where did you get the firmware?

Maybe ANET has a forum just like Ultimaker does? Maybe they will know? Maybe it's on facebook? If you look at the range of X values for the "good" gcode versus what cura produces, that would be informative. So in your first post I thought it was hitting the left side. But now you are saying it's hitting the right side. Different issue. Different solution. So check the x width (and depth and height) settings. If you put too large a value there it will print too far to the right. Again - in machine settings.

pva tends to get contaminated on the outer layer first so maybe you just printed larger/faster before? Well it could be the leveling. Do you do manual or auto leveling? I recommend manual. Maybe something was on the print bed where it levelled the 2 nozzles. Or something on the end of the nozzle. But normally it shouldn't matter as it will heat the nozzles before active levelling. And if the leveling is off between left and right core then you should also see issues on the bottom layer. If PVA nozzle is off by 0.5mm (a lot!) then the bottom layer wouldn't even stick. No I suspect it's humidity. Try a fresh spool or try drying this one. When it prints the bottom layer of PVA it should be transparent if it's very dry. Please show a photo part way through the print when the pva is "high".

90% chance the problem is humidity. PVA absorbs water very quickly. Just 24 hours in a 60% humidity can be enough to cause problems. Probably why Ultimaker invented the air handler and material station. Loosen the spool a bit (so air can get at deeper coils) and put the spool on the UM3 heated bed and set to 70C and put at least 200mm of blankets or towels over it. Leave it like this for 10-30 hours. Don't go hotter than 70C or you risk ruining the filament. If you are in a rush and only need a few meters, you can unspool 1 to 5 meters of filament and put it on the bed directly with the spool on top. Still cover with towels but now you only need to heat for maybe 6 hours. After you have dried your PVA, buy some extra large packs of silica. I bought a gallon of color-changing dessicant. I put the dessicant in containers with holes in them and when the dessicant changes color I put in a bowl and microwave until back to the dry color. The dessicant container I put in 2 gallon zip locks with up to 2 spools at a time.

The center is NOT (0,0). The lower left corner is. The only printers that have 0,0 in the center are delta printers. Google what a delta printer is if you are not familiar. They have round build plates, not square or rectangular. go to left side of screen in PREPARE mode. Click on your printer, then do "manage printers" then "machine settings" There is a checkbox about 0,0. Change that and slice again.

Without a sensor, the hotend will get above 700C and melt. You absolutely must have a sensor. To build mariln for UM2, here are detailed instructions. For building Marlin for other printers it is much easier as you can just use arduino IDE.

Your main issue is that the first layer is too high off the bed (I think - would be best if I could see the first few seconds after it starts). Does your printer do autoleveling? Manual leveling? for most printers, manual leveling is better so if that's what you are doing, just move the bed a little closer to the nozzle while it prints the bottom layer until it sticks nicely.

How do you get the gcode to the printer? Are you doing USB printing, octoprint, SD card, USB flash drive or other? If you are doing SD card or flash drive then please check the gcode file on the storage versus the gcode file that was created when you sliced. Look at the bottom of the gcode file on the storage and see what layer it ends on (search backwards from the bottom for the letter Z a few times which typically only appears once per layer). Also do a file comparison - e.g. I think there is a command console program called "diff" you just say "diff file1.gcode file2.gcode" and if even one character is different it will list all the lines of the files that are different.

@Graham-becs did you use a brim? I thought you did but now I'm thinking not. @Mari yeah I have missing glass on both sides of all 5 of the glass of my most commonly used printers. But for the most part the missing slivers are only paper thin. Most of those were from PETG or CPE. I'd say one print in 50 cause that problem (but pretty much never PLA - another reason to love PLA).

Assuming you do have a heated bed (I looked up your printer on google but couldn't tell) then consider getting a chamber for your printer. Or stick with easier plastics like PLA.

It's hard not to get warping without an enclosed chamber to get the air temp up to 35C. But it's possible. People were printing ABS long before heated beds. Does your printer have a heated bed? If not I'd consider giving up now. Know that PETG is a much easier material to print. I assume you don't like PLA because of temperature reasons? ABS is probably the worst material for 3d printing when you look at it's physical properties versus other materials that don't smell so bad and are stronger and tougher. So stick with the PETG. Put a little piece of PETG on your heated bed with a blanket over it and try to find where it starts to get soft (like clay). When it is "soft" and you bend it and let go it will stay in the new position. Below a certain temp if you bend it and let go it will go back. You want the heated bed above that temperature. About 5C hotter. I forget but I think for PETG that is around 80C but I'm not sure. Maybe it's 70C? And squish - you need to squish the first layer really well to get it to stick. And fan - you want very little fan - play with fan settings until you find a setting where it sounds like about 1/3 as loud. That's a good fan speed. It's different for every printer. I talk about more details and show you how much to squish and why prints warp off the bed and the history of things to try (e.g. raft) in my video here. It's a bit long but I expect it will save you lots of time:

Bascially, a slicer like cura, converts an STL file to a gcode file. There are other file formats besides STL for meshes but that's the mesh. Usually the STL file. The mesh is "the object to print" described as a 3 dimensional object using a "mesh" of points. The output of cura is usually a set of slices saved (usually) as a gcode file.

It might have nothing to do with your printer and more to do with your model. Before saving to a gcode file make sure you look at it in PREVIEW mode. Near the top of the screen there is PREPARE PREVIEW and MONITOR. In PREVIEW mode you can slide up and down the layers to see what the print will look like. Maybe it isn't showing that it will print anything there as well? It could be your part is too small or walls too thin to print or maybe it isn't manifold.

Machine settings are usually here: go to left side of screen in PREPARE mode. Click on your printer, then do "manage printers" then "machine settings" Then adjust the x-width and y-depth settings. Cura will pick exactly half of these values for the center of your part. By default. Of course you can move the part around with the move tool on the left side after clicking your part.

Yes! See my post above.

So your walls - even in the main area are too thin for any infill. the model itself has no large solid areas. Am I being clear?

I think the pictures taken with the phone are actually slightly better.

what axis is the one that is the most problem? x,y, or z? What is the expected size and measured size? How far off is it? Typically it's either off by a lot (2X) or a little (0.2mm).

Possible but a huge pain in the neck to do it. You use the feature "per model settings". Basic steps: 1) Set the majority infill for your model (the infill that is more common). If it's half and half then pick either 20% or 40%. 2) Add a cube to the build plate. Select it by clicking. Click "per model settings" icon on left edge. It prompts for mesh type. You can use normal I think but definitely you can use "modify settings for infill of other models". Set the minority infill in the settings (e.g. 20% or 40$). Consider removing all other infill settings from the mesh type. 3) Using scale tool, make the height (z scaling) equal to half your layer height. Make the width and length (X,Y size) larger than your model. 4) Now multiply this part by the number of layers you want to have the minority infill. 5) Now select the "per model" parts one at a time. Select the move tool on the left side, set the Z value by typing in the height for the layer to use the minority infill. e.g. 0.7mm. Repeat for all "per model" cuboids. If you have 50 layers this will take 25 "per model" cuboids. Yikes. It should work though. Once you get good at it you should be able to do this in just 4 seconds per layer. Not too bad if you have less than 100 layers to do. Make sure to do "save" "project" repeatedly as that will save everything including your "per model" cuboids. If you try to follow these instructions and get completely lost, google "cura per model settings" and there are great videos.

What CAD did you make this in? I have a file with different advice for different CAD packages.

90% sure it's the model, not the printer. Tiny changes in printer settings (particularly layer height) can hide problems with a model. So try this: In the upper right corner of Cura click "marketplace" and make sure you are on the "plugins" tab and install "Mesh Tools". Then restart Cura. Now right click on your model, choose "mesh tools" and first choose "check mesh", then "fix model normals" and "fix simple holes" to see if that helps. Cura doesn't fix most issues so... netfabb free repair service is here (you have to create a free account first): https://service.netfabb.com/login.php Here's another service - drag and drop mesh repair service: https://3d-print.jomatik.de/en/index.php There's also an x-ray mode in cura that shows certain problem spots in red but "mesh tools" is better at finding problems.

z-hop works great for delta printers but not recommended for 90% of printers.

Two color printing with a single extruder printer:

How many layers thick is this? You want the first layer to squish quite a bit, otherwise parts tend to come loose during the print or corners "warp" off the bed. But then the second layer isn't fully recovered and also over squishes but not as much. Let's first address Z issues - you suggested maybe it's not moving enough in Z and that makes the second layer bad. This is possible - if it's true then all your prints Z height will be off - this is not that unusual - usually they will be off by exactly 2X because some jumper that controls steps/mm is inserted wrong or removed wrong. So have you ever printed something taller? Try printing something 1cm tall and then measuring it to see if maybe it's off by 2X. Okay that's probably not the issue. Here are some other suggestions. 1) Try making the first layer 0.1mm in Cura. If you have manual leveling and practice you can get small parts to print great at 0.1mm bottom layer. Then have a recovery layer or two and only then print the layer with letters. 2) Print 2 at once as smithy says to insure one cools enough before printing the next layer. 3) Try a smaller nozzle? That helps a lot. 4) Try a more bold font. 5) Make sure "combing" is enabled even in the top layer (often it is disabled in "skin" layers and top layer is a skin layer) 6) Consider having the letters go all the way through (but now many letters like "O" will have an issue with the center of the O falling through so you need a "stencil" font". If you go this route set "initial horizontal expansion" to -0.3mm. 7) Consider going with 2 colors