gr5

14 is a lot. You could try zero. Or do the XY calibration. Doing the XY calibration is the proper way. Do you have the calibration sheet? After it lays down material from both cores you are supposed to remove the glass and place on a piece of paper so you know which lines are +1,+2,+3, etc for each axis. See these instructions https://support.makerbot.com/s/article/1667410778876?utm_id=UMa1709000000F48h

yay! I'm going to stop following this thread. Good news.

Don't tune on the bottom layer though. The bottom layer depends too much on your leveling. So you can play with tuning on the bottom layer but think of that as practice. The real tuning happens on a higher layer.

So you are printing a bit fast. 0.28mm layer height 0.55mm line width and printing speeds at 30,40,55 mm/sec. If you mulitply the speed by the other two you get 4.6mm^3/sec for the 30mm/sec and 8.5mm^3/sec for the faster speeds. I mean a UM2+ should be able to do that. Not a UM2. That's too fast for a UM2. And your temp is pretty good. Are you absolutely certain you have a 0.6mm nozzle on there and not a 0.4mm nozzle? If it's a 0.4mm nozzle that would explain everything perfectly. That "top" (not really the top but the topmost flat area) layer is about 50% underextruded. And is printed at 30mm/sec. I mean the quick fix, since it is underextruding by about 50%, is to print at about half speed. I mean change *only* layer height from 0.28mm to 0.14mm will drop the volume in half. It will give you a nicer looking print as well. But will take twice as long to print (twice as many layers. I would do some cold pulls on the nozzle. Google "atomic pull" or "cold pull" and read about it or watch one of many many videos explaining it. That will clean out the tip of the nozzle in case you have some caramelized grunge on the inside surface of the nozzle. You could also test the feeder. Go into the MOVE command and back the filament out so you see it in the bowden. Then move it forward and fight it with your other hand just below the feeder. You should be able to barely get the feeder to skip backwards at your full strength. About 10 pounds or 5kg force should be required before the feeder skips where the only resistance is you (filament not in the print head but merely in the bowden). You can grip a weigth in one hand against the filament to use the weight as the pull amount. Or you can lift a weight and then in your mind apply a similar force. Finally if the feeder seems fine and the nozzle seems fine the next most likely thing is the teflon part. Have you change the teflon part lately? It needs to be switched out every 500 hours of printing or so. It's a "consumable" just like filament (but much cheaper). One more thing - never print with flow > 110%. You risk grinding the filament to dust and you don't get any extra extrusion after around 110 or 120%. In fact if it's underextruding as bad as you showed us, you might even be better at 90% as you won't grind the filament as much. Here is the complete list of things that can cause underextrusion on the UM2 (or UM2+): CAUSES FOR UNDEREXTRUSION UM2 AND HOW TO TEST FOR THEM AND REMEDY THEM One can quickly check the feeder (it takes seconds) so I would always do that first. The feeder on UM2+ and UM2 can push with 10 pounds (5kg) force easily so first thing is to lift that lever (if um2+, if um2 regular do move material) and insert filament so it is only part way into the bowden (e.g. half way). Then move the filament with "move material" command in menu so the feeder is energized and then pull down on the filament under the feeder. You should be able to pull with 5 to 10 pounds force without it slipping. Then have it move the material up while you pull down. 5 pounds force (2kg) is enough to make decent prints at moderate speeds listed below but you need 10 pounds (5kg) to print fast (e.g. 0.2mm layers and 60mm/sec) As far as underextrusion causes - there's just so damn many. none of the issues seem to cause more than 20% of problems so you need to know the top 5 issues to cover 75% of the possibilities and 1/4 people still won't have the right issue. Some of the top issues: 1) Print slower and hotter! Here are top recommended speeds for .2mm layers (twice as fast for .1mm layers) and .4mm nozzle: 20mm/sec at 200C 30mm/sec at 210C 40mm/sec at 225C 50mm/sec at 240C The printer can do double these speeds but with huge difficulty and usually with a loss in part quality due to underextrusion. Different colors print best at quite different temperatures and due to imperfect temp sensors, some printers print 10C cool so use these values as an initial starting guideline and if you are still underextruding try raising the temp. But don't go over 240C with PLA. 2) Shell width confusion. Shell width must be a multiple of nozzle size (in cura 15.X. In cura 2.X it doesn't matter as much but still makes a difference). For example if nozzle size is .4mm and shell width is 1mm cura will make the printer do 2 passes with .5mm line width which is possible but requires you to slow down much more to make a .5mm line out of a .4mm nozzle. If you really want this then set nozzle size to .5mm so it's clear what you are asking Cura to do for you. 3) Isolator - this is most common if you've printed extra hot (>240C) for a few hours or regular temps (220C) for 500 hours. It gets soft and compresses the filament under pressure. It's the white part touching the heater block. It's very hard to test when not under full pressure (spring and bowden) so sometimes it's best to just replace it. Also if you notice parts of it are very soft (the blacker end where it touches higher heat) then it's too old and needs replacing. 4) Curved filament at end of spool - if you are past half way on spool, try a fresh spool as a test. 5) curved angle feeding into feeder - put the filament on the floor -makes a MASSIVE difference. 6) UM2 only: Head too tight? Bizarrely MANY people loosen the 4 screws on the head by just a bit maybe 1/2 mm and suddenly they can print just fine! Has to do with pressure on the white teflon isolator. 6b) UM2 only: Bowden pushing too hard - for the same reason you don't want the bowden pushing too hard on the isolator. 6c) Um2 only: Spring pushing too hard. Although you want a gap you want as small as possible a gap between teflon isolator and steel isolator nut such that the spring is compressed as little as possible. 7) clogged nozzle - the number one problem of course - even if it seems clear. There can be build up on the inside of the nozzle that only burning with a flame can turn to ash and remove. Sometimes a grain of sand gets in there but that's more obvious (it just won't print). Atomic method (cold pull) helps but occasionally you need to remove the entire heater block/nozzle assembly and use flame. I found soaking with acetone does not help with caramelized pla. Even overnight. Maybe it works on ABS though. Simpler cold pull: https://www.youtube.com/watch?v=u07m3HTNyEg 😎 Temp Sensor bad - even the good ones vary by +/- 5C and bad ones can be any amount off - they usually read high and a working sensor can (rarely) fail high slowly over time. Meaning the sensor thinks you are at 220C but actually you are at 170C. At 170C the plastic is so viscous it can barely get out of the nozzle. You can verify your temp sensor using this simple video at youtube - on you tube search for this: mrZbX-SfftU 9) feeder spring issues - too tight, too loose. On the black UM2 feeder you want the tension such that you can clearly see the diamond pattern biting into the filament. You want to see at least 2 columns of diamonds. 4 columns is too much. On the white UM2 plus and UM3 feeders you usually want the tension set in the center. 10) Other feeder issues, one of the nuts holding UM2 and UM3 together often interferes with the feeder motor tilting it enough so that it still works but not very well. Other things that tilt the feeder motor, sleeve misaligned so it doesn't get a good grip. Gunk clogging the mechanism in there. 11) Filament diameter too big - 3mm is too much. 3mm filament is usually 2.85mm nominal or sometimes 2.9mm +/- .05. But some manufacturers (especially in china) make true 3.0mm filament with a tolerance of .1mm which is useless in an Ultimaker. It will print for a few meters and then clog so tight in the bowden you will have to remove the bowden from both ends to get the filament out. Throw that filament in the trash! It will save you weeks of pain 11b) Something wedged in with the filament. I was setting up 5 printers at once and ran filament change on all of them. One was slowly moving the filament through the tube and was almost to the head when I pushed the button and it sped up and ground the filament badly. I didn't think it was a problem and went ahead and printed something but there was a ground up spot followed by a flap of filament that got jammed in the bowden tube. Having the "plus" upgrade or using the IRobertI feeder helps you feel this with your hand by sliding the filament through the bowden a bit to see if it is stuck. 12) Hot weather. If air is above 30C or even possibly 25C, the air temperature combined with the extruder temperature can soften the filament inside the feeder such that it is getting squeezed flat as it passes through the feeder - this is obvious as you can see the problem in the bowden. The fix is to add a desk fan blowing on the back of the printer. Not an issue on the UM3 or UM2 "plus" series. 13) Crimped bowden. At least one person had an issue where the bowden was crimped a bit too much at the feeder end although the printer worked fine when new it eventually got worse and had underextrusion on random layers. it's easy to pull the bowden out of the feeder end and examine it. 14) Worn Bowden. After a lot of printing (or a little printing with abrasive filaments) the bowden resistance can be significant. It's easy to test by removing it completely from the machine and inserting some filament through it while one person holds it in the U shape. Preferably i nsert filament that has the pattern from the feeder. 15) Small nozzle. Rumor has it some of the .4mm nozzles are closer to .35mm. Not sure if this is actually true. I'm a bit skeptical but try a .6mm nozzle maybe. 16) CF filament. The knurled sleeve in the extruder can get ground down smooth - particularly from carbon fill. 4 spools of CF will destroy not just nozzles but the knurled sleeve also. Look at it visually where the filament touches the "pyramids". Make sure the pyramids are sharp. 17) Hot feeder driver. I've seen a more recent problem in the forums (>=2015) where people's stepper drivers get too hot - this is mostly a problem with the Z axis but also with the feeder. The high temps means the driver appears to shut down for a well under a second - maybe there is a temp sensor built into the driver chip? The solution from Ultimaker is that they lowered all the currents to their stepper drivers in the newer firmware. Another solution is to remove the cover and use desk fan to get a tiny bit of air movement under there. TinkerMarlin lets you set the currents from the menu system or you can send a gcode to lower the current. Ultimaker lowered the default currents in July of 2015 from 1300ma to 1200ma for X,Y,Z but left extruder at 1250. Other people (I think the support team of a major reseller but I forget) recommend X,Y,Z go down to 1000mA. M907 E1250 Above sets the extruder max current to the default - 1250mA. So try 900mA. This will only change until next power cycle so if you like your new value and want to save it use M500. You can just put these into an otherwise empty gcode file and "print" this and it will change. Or get tinkergnome marlin! You will wonder how you lived without it: https://github.com/TinkerGnome/Ultimaker2Marlin/releases M907 E900 M500 18) third fan broken. This tends to cause complete non-extrusion part way through a print. In the rear of the head for UM2 and the front of the head for UM3. Without this fan several things can go wrong. It can take a while as usually you also need several retractions to carry the heat upwards. There are a few failure mechanisms and I don't understand them all. One of them is probably that the molten PLA spreads out above the teflon and sticks to the metal in a core or fills the gap at the base of the bowden in UM2. Later it cools enough to keep the filament from moving up or down. 19) Spiralize/vase mode. This is a rarely used feature of Cura but you might have left it on by accident? In this mode the wall of your part is printed in a single pass. So if you have a .4mm nozzle and the wall is .8mm thick it will try to over extrude by 2X. This is difficult to do and may instead lead to underextrusion. 20) non-standard or bent fan shroud. Sometimes people print some fan shroud off of thingiverse or youmagine out of PLA or ABS. Some of these are great but most of them are crap. One needs to do good air flow modeling. Also if it's PLA it will slump and direct air differently. Air directed at the block or nozzle can cause severe underextrusion and also sometimes HEATER ERROR. Put the original shroud back on or just turn off the fan to prove that the fan is the problem. 21) Firmware settings - for example UM2+ firmware on UM2 or vice versa will cause 2X over extrusion or 2X underextrusion. Downgrading or changing firmware can mess up steps/mm and other settings - so if you updated firmware and then problems started then do a "reset to factory settigns" which corrects all the steps/mm values. 22) too many retractions (this causes complete failure) - if you have too many retractions on the same piece of filament you can grind it to dust. 10 is usually safe. 20 is in the danger zone. 50 should guarantee failure. You can tell cura to limit retractions to 10 per a given spot of filament. Do this by setting "maximum retration count" to 10 and "minimum extrusion distance" to your retraction distance (4.5mm for UM2 and 6.5 for UM3 and 8mm for S5). 23) Brittle filament. Espciallty with older PLA but even brand new pla can do this. If you unspool some (for example if it's in the bowden) for many hours (e.g. 10 hours) it can get extremely brittle and it can snap off into multiple pieces in the bowden. It's not obvious if you don't look for this. Then it starts printing just fine and at some point one of those pieces reaches the print head and gets hung up somewhere and the printer suddenly stops extruding for now apparent reason. This usually happens within the first meter of filament - once you get to printing the filament that was recently on the spool it should be fine from then on. 24) The "plus" feeder can have an issue where the filament doesn't sit properly for one print and it permanently damages the arm inside the feeder as shown by this photo - the hole is ground down asymetrically: http://gr5.org/plus_feeder_issue.jpg 25) Other feeder issues. You can test the feeder by putting the filament only part way down the bowden and with the feeder electrically turned on (or moving) pull very hard on the filament until it slips. You should be able to pull with about 5kg or 10 pounds of force before it slips. 4kg is acceptable. 2kg is a problem. If the stepper motor isn't engaged you can try going into the move menu. After a minute or so power is removed again from the feeder stepper.

That's very bad underextrusion. It can have many possible causes. Is your line width set to 0.6? I have to go now but I'll look at your 3mf file later.

There are 2 different S5 machines. R1 which has the Robot on the side panels and R2 which has the U on the side panels. R1 has deadly voltages underneath the printer. If you have an R1 then definitely talk to your reseller before opening the bottom panels. They have a pdf with detailed instructions on how not to die. It shouldn't void the warranty. There is no sticker or anything for them to tell if you opened the bottom. If you call them and tell them the issue and ask if it will void the warranty 99% chance they will tell you it's okay but you will feel better if you ask. Often they will be happy if you say you want to check the cables. Less work for them. They don't want to make you ship it to them and have them do all the work if it ends up being something you can take care of yourself.

But @CarloK do you happen to remember if this problem was only for the front fan? Or if it was for the front and also the side fans?

Yeah your gcode looks weird in cura:

Oh! It's very likely arcwelder. I don't know that the UM3 (nor the S3 - don't get them confused) supports arcs. Yeah - I see lots of G2 and G3 commands in your gcode. I doubt I had those in mine.

For PP, Ultimaker recommends adhesion sheets. More info here: https://support.makerbot.com/s/article/1667337602253 I have no idea if HDPE is similar but you asked. These are available at office supply stores but I don't know how to describe them. So buy them from ultimaker or a reseller so you know what they are and then you can get them from Avery or 3M. I've used the adhesion sheets for PP and it worked great but I tore the sheet every time. What a pain in the neck. But it works.

heated bed I've printed very difficult filaments, but not HDPE. It's a high temp filament. So the first thing is to try to get the bed above the softening temp. If you can do that then the bottom few layers will warp by the tiniest amount (possibly 0.01%) which is insignificant for dimensional accuracy but hugely helpful for distributing the forces in the corners (where parts lift off the bed). So I'd cut off a few cm and place it on the heated bed and start at 100C and put a little towel or something over it. After 1 minute at that temp, remove it and bend it and see if it's A) super flexible like a rubber band or B) takes a new position when bent (like clay) If B happens I would lower the temp. If A happens I would raise the temp and try to find what I call the "softening temp". If the softening temp is well over 100C then you can't take advantage of B. Hopefully instead it gets super flexible (like nylon gets more and more flexible as you heat it). For PLA this temp is 52C. For CPE I seem to remember around 60-70C. For ABS it's right at 99C. For nylon it never happens it just gets more and more flexible and eventually melts. Anyway this experiment will teach you a lot. Hopefully the temp where it gets soft isn't much above 100C because you want the bed about 10C hotter than this goal temp of where the material gets soft (like clay) or super flexible (like rubber). This will help a lot. surface prep Nothing beats magigoo as they work really hard to get good formulas that work for each material. I don't know if they have something for HDPE. I find PVA is a great surface prep for almost every material. Take some elmers glue or elmers wood glue, mix it with 10-30 parts water (1 part glue, 20 parts water). Paint it on the glass bed with a paint brush, heat up the bed to 60C or hotter and wait for it to dry clear. Print on that. rounded corners Brim is the best but if you really really don't want brim then at least try to round the corners. Or design in your own "brim" just on the areas that are a problem (the extremeties of your part). air temp If you don't have an air handler you can still cover the printer. Just find a cardboard box and flip it over and put it on top of the printer. Usually one can find a box of the right size without any changes. It's okay if there are huge air gaps. It will help a lot. Getting the air to around 35-40C is perfect. Don't let the air get above 40C as at some point the steppers can get too hot (40C is quite safe). This also allows the heated bed to get warmer

apparently some call it a "knurled head thumb nut". It's an M3 thread like this one but I think taller: https://www.mcmaster.com/90368A150/

Oh and keep in mind, any changes you make to either firmware will get overridden the next time you upgrade your UM3 with "latest firmware".

So there is the linux computer you ssh'ed into and then there is an arduino board with a flavor of Marlin on it. The firmware on the arduino board is derived from Marlin so UM is required to supply source code if you ask because Marlin is open source. I asked. I just put it here for you to look at: gr5.org/jedi_marlin.zip You can (hopefully) easily grep for "260" to see if it's implemented. Most likely it is. I suspect instead the code is blocked by linux from sending most gcodes onwards to the marlin board. If I'm right then you'll have to find the list of which gcodes are sent on to marlin, which gcodes are interpreted (like T0 and T1 are probably converted into many gcodes. Perhaps.) and which gcodes are discarded. Even though you do "sendgcode" it doesn't necessarily do what you tell it. Even if it claims it did. Also there are some codes that will work after you enable something. So to set the nozzle temp using gcodes you first have to enable power to the nozzle or something and I forget how to do that but it's somewhere on this forum. I doubt this has anything to do with I2C and M260. Anyway hopefully you find the code that triages gcodes and it's an easy fix.

I'd remove as much grease as possible in the top 3 inches (where you are doing most of your printing) and I'd try to get that z nut from mcmaster.com or some other seller. See if they have a higher quality version. LIke I said before - I know a guy who got great results ( @neotko ) who replaced his z nuts with a much more expensive (I think it was 80 cents at the time) z screw. The quality was just another 10X better in precision and smoothness. I'm not 100% convinced it's the Z movement but it seems like the simplest explanation. Again I'd look at the part with a magnifier and try to identify individual layers where the problem is the worst and see if it's pretty consistent all the way around. Although it's slightly possible the Z would continue moving another few 0.01mm (yes 1/100th mm) slowly enough that the problem gets slowly worse/better as you go around the print.

So I just looked at pictures of the bottom of a UM3 and I think it's that ribbon cable. That's unfortunate. It's not shielded. So keep it away from other cables if possible. Maybe re-route it on the other side of the Z stepper? And slide it in and out a few times on both ends to get a good connection. With all the vibration in a printer, those connections can slip a little and/or degrade (oxidize?). Route away from other cables as you can get something called "cross talk". Look it up. Happens when you have a long run of wire very close and parallel to another. You get both inductive and capacitive coupling. "long run" might be 2 inches. Maybe take pictures of where the red line goes on each end before disconnecting.

Okay, first of all, this is strange. But let's calrify things please. This must be the second layer, right? Because on the first layer, in the project file you sent me, it prints the black first, then the clear. But on the second layer it prints the clear first and then the black so it's possible on the second layer for black to be above the clear. Can you confirm that it is the second layer for the Q and the V? Also this is a very very cool clock. I love it. Okay well this is very bizarre. The movements are quit exacting and aren't related to non-printing moves. They appear to be on normal printing moves. So no retraction is occuring. The travel moves don't explain the pattern seen. On any layer. So I think it is truly moving to the wrong position. Which implies a bit is getting flipped. There are two computers in your UM3. The linux computer which is a powerful computer - similar to the ones in an old iphone. Running an advanced operating system with the ability to hook up an hdmi monitor and keyboard and mouse and has full blown operating system. The second computer is a wimpy arduino style computer. It doesn't have an operating system but has just a single app on it called Marlin. Marlin is open source (as is the linux stuff). It controls the servos. It has the motion controller software. These two computers communicate through I believe a USB cable under your printer. Basically in serial mode. The linux computer sends the gcode as ascii code (which is a strange way to do it but whatever). So the gcodes might look like this: G1 X100.731 Y70.555 E1.333 I've seen this issue on UM2 printers but not UM3. The ascii in say a 5 ends with bits "0101". Literally a binary 5. If you flip the first bit it is "1101" which is an illegal character and will interpret the remaining digits as zeros. If you flip the second you get 1, third bit you get 7, and last bit you get 4. So what happens is you tend to get errors of exactly 1,2 or 4 mm or 10,20,40mm or 0.1 0.2 0.4mm. Or 100,20,40,10mm. Those look like errors of around 2 or 4mm on the Q and V and about about 20 or 40mm on the N. You can probably measure them. The errors are only in one axis for the Q and N but the V is extra bizarre and I can only explain it if 2 of the numbers had a bad bit. There may be checksums which just means the errors are much more frequent then we thought and we are seeing the 1 in 100 to pass the checkum test however I don't think checksum testing is enabled. So what is the fix? I'd disconnect and reconnect any cables that conned the 2 computers together. I'm pretty sure it's a usb cable. You could take some pictures. I forget if the UM3 has the olimex board (the linux computer) mounted to the main board or if they are literally separate boards connected by a single cable. The cable should be cleaned if possible (the connector/connectors). Maybe replaced. Maybe rerouted away from other cables that might contribute noise although it's a shielded cable so that shouldn't be an issue. I have to tell you I've never seen this on a UM3. You are probably having other errors you don't notice. LIke the extruder. I bet the extruder occasionally retracts 10, 20,40, or 100mm and then reinserts the filament. It would be an obvious pause in printing for maybe 5 seconds while it does this if you are nearby and have a musical ear it will be obvious. I've heard it on my UM2 before I fixed it. On occasion the error is great enough for the print head to be asked to go out of bounds. Instead of moving X to say 100.243 it might get flipped to 400.243 which is out of bounds and is an error. Also many errors go unnoticed as they are in the tenths or hundredths of a mm. Or the extruder might extrude an extra 10mm and then retract 10mm and it will skip on the extrude and will then underextrude for a minute until things balance out. The Z axis is unlikely to ever have an issue as only about 1 in 5000 gcodes move the Z axis.

@CarloK - are you still at UM? I think you should be able to answer this regardless. I've seen people who have trouble with active leveling failing due to noise (fails the noise test) and they fix the printer often by changing a side fan!! Which is "off" during leveling. Now it could be acting as a passive antenna with it's coils and such but is it possible that the side fans are also slightly "on" when they are "off"?? If so, then this is extremely important - your simple fix to completely turn off the fans (all 3) should get implemented as soon as possible as it is causing a world of hurt for some people.

Please post your project file that corresponds to one of these photos - hopefully the simplest one where it's obvious in the photo what the problem is. In cura do menu "file" "save project as" and post that file here. It will contain your models and your machine settings, profile, and settings.

That noise in the video is fine but I'd add triple the weight amount - the idea is to have the weights on there while it prints - after it gets started - right where you put that weight. The idea is that if there is an issue with the screw - if there is some excess friction, the weights should overcome that such that you get more consistent level heights. So from other's experiences, the most important part to replace is the Z nut. Someone said you can get the 50 cent version or the 80 cent version and the more expensive one is like 10X better. Did you order one from UM, a reseller, or did you buy it directly from some store? I'm not sure but I think you want to get them directly, and you want to get the more expensive version (again - should only be a few dollars/euros). I mean don't get it from a store that sells Ultimaker printers/parts. Get it from a store that sells millions of different part types including these z nuts and where they sell at least 2 versions of these z nuts. After you replaced, how much grease did you put on the z screw? Every UM2 and UM2+ came with a tiny tube of grease. You need very little. Just a pea sized drop for the entire screw. Also during the replacement process, while the Z screw is removed it is good to check the friction of the z bearings and rods. They should very low friction.

Okay so short of fixing your "block" model I think your best bet is to just do it how you did it originally. At least you will be able to read the letters "test". Internal layers aren't visible anyway so maybe it's fine. But the "correct" answer is to have you model the "block" part properly where the letters are subtracted out of it.

Oh wait! That doesn't work either. It is printing BOTH in the same spot. Hold on...

Uncheck the cura feature: remove mesh intersection Basically when you model things like this, Cura expects you to subtract those letters from the block. But you didn't. So you asked cura to print both at the same time. So it has to make decisions. Note that you also had alternate mesh removal so that was why you saw the issue every other layer. So ideally you will create models that don't overlap but it's not a big deal in this case.

You have many issues - the two most prominent to me are (2) the ringing along the letters and (1) the horizontal lines. I'm only talking about the horizontal lines but we can talk about the other issues if you want. So do the lines continue all the way around the cube? I mean taking the 2 most prominent lines on the cube that I see - do those 2 continue onto all 4 sides? If so then it's most likely a Z screw issue. If you zoom in with a magnifier check to see if it's exactly one layer sticking out or if it's 2 consecutive layers. If 2 consecutive then it's probably *not* a Z issue. Or if a "sticking in" or "sticking out" layer doesn't go quite all the way around then it's also probably not a Z issue. Did it get worse or better when you replaced the Z parts? Did this start after changing the Z nut? Other possibilities include: temperature fluctuations If the PID is tuned badly or if the sensor has a loose connection then you will see the temperature vary quite a bit - like by at least 5C - then you can see the hotter layers stick out more and the cooleler layers don't. If you watch the temperature on the front of the printer for 10 minutes it should be pretty steady. It drops when the fan comes on - that's normal. But by the time you have done 20 layers the temp should be pretty steady within +/- 1C from goal. If the problem is with the temp sensor then it's even more obvious as the temp can jump around a lot. Maybe 10C or even 30C instant changes (which obviously don't reflect the actual temp). feeder In theory, it seems like the feeder could be on the edge of it's capability and on some layers the feeder slips more. You could lower the speed by 50% in the TUNE menu on the printer and if the problem goes away then there is your (partial) answer.

This horizontal banding is usually caused by Z axis issues. So the z screw moves the bed down a tiny amount between each layer so you are relying on the weight of the bed to make it go down the same amount. But if, for example, the z screw is dirty some layers it doesn't go quite all the way down (imagine some dirty grease that doesn't compress as much) and then on the next layer it might go extra far down because there's less grease a little farther around the screw. And if the bed goes down less than it should then it over extrudes and the layer sticks out a bit. And if the bed then on a later layer goes down *more* than it should then you get an underextruded layer. Am I making sense. One experiment is to add some heavy bricks to the rear of the test bed to see if that helps. Or you can clean the Z screw. Or you can replace some of the Z parts - particularly the Z nut followed by z bearings and the 2 z rods and finally the z screw. Personally I would clean the z screw - near the top - the part of the screw that is in the nut when printing benchy so like the top 3 inches maybe. Clean with some WD-40 and a toothbrush or just a paper napkin and your fingernail. Keep in mind that the z screw is a triple helix so if you get your fingernail in the groove and spin it around and around you only get one of the 3 grooves. You probably don't need to add any grease. Ultimaker says one pea sized drop of grease is enough for the entire z screw. If that doesn't help try my brick idea.