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balden

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balden last won the day on September 24 2016

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  1. Hi all, I just had a case where I need to slow down the print speed at a given height for better bridging. In the past (maybe as early as Cura 15.04 but probably also with a previous 2.x version) I have successfully used Tweak-at-Z for such purpose. But for today's attempt with latest version 2.5.0, my Tweak-at-Z instructions don't seem to be really applied. I use Cura from the official AppImage under Linux OpenSuSE Leap 42.2, if that matters, and this is on an Ultimaker 2+ with default "fast print" settings. My exact settings: I tried to set print speed at 50% starting at layer number 379 and keep value for 4 layers. The post-processing icon (hammer and wrench) was present near the "save file" button. The resulting gcode actually has comments like follows: ;POSTPROCESSED;TweakAtZ instances: 1;Generated with Cura_SteamEngine 2.5.0 ...but when I look at layer number 379 and following, I don't see any change in print speed (assuming this would be reflected in instructions like "G1 Fxxx"). Am I missing something or doing something wrong? Can anybody confirm that confirm that it is still possible to tweak speed at select layers with Cura 2.5 (and explain how to set it up)? Thanks in advance.
  2. Thanks for the video Eraser. I feel like watching myself and my bearings mid-June. Be patient and you'll get rid of this jamming. It is worst when the rod is vertical because there is no load on the ball bearings so the balls start to skid easily when the least resistance is encountered along the ball races. At first I was able to jam the bushing even when the rod was horizontal, and then progressively the sole weight of the bushing would become sufficient to avoid the jamming in the horizontal and then increasingly oblique rod slopes (the bushing was able to roll back and forth freely and reverse direction without jamming just by rocking the rod up and down), and eventually up to the vertical. Also, don't forget to add weight on the platform (under the hood between the rods). In my case I sawed an iron bar in small chunks then piled them up and taped them on both sides of the screw. It's very simple and can be easily added almost at any time since it requires no (or very basic) disassembly.
  3. Unfortunately, from France I have not been able to order from Misumi without a company ID. I haven't tried to order from Misumi US but as you say the shipping costs are likely to be a rip off (assuming they ever accept to ship outside North America). Anyway, I'll remember to check that possibility: after all I already uselessly invested in a couple of costly Igus polymer bearings which did not fit well and only made the situation worse ;-). About exercising the bearings: in my case, I made several runs over several days (probably cumulated about the equivalent of one continuous hour exercise for each bearing). I also made several (2-3) cycles of spraying WD40 into the ball races, then exercising with WD-40 inside, then applying degreasing agent (regular bike degreaser fluid), then rinsing with hot water, drying with hair dryer, exercising again the dried bearing, and repeat... While exercising, I deliberately applied slight torque on the bearing (wrt to the rod) in order to increase friction between the balls and rods, between the balls and races and between the balls themselves. You'll notice that the jamming almost always happens when reversing travel direction (hence bed drops essentially happening at the bottom of the prints and much less frequent afterwards when the first jamming has been overcome and the bearings are rolling again) so I concentrated the exercising around the points of distinct jamming, sliding back and forth over a few millimeters: the intent was to apply many friction cycles to progressively wear off any roughness preventing smooth operation inside the ball races. At first you'll be desperate because it takes very long for the feeling to become noticeably better. But after a while the function will start to improve, to the point where there is almost no jamming any more (or very slight and easily overcome by the platform weight). I read somewhere on the forum (or maybe another forum) that such low-cost bearing are sometimes shipped with a layer of some sort of anti-corrosion agent that makes them slightly over-tolerance and prone to such jamming. It definitely feels like this exercising helps wearing off some friction-causing layer somewhere: I don't know if this is truly a protection layer or if those low cost bearings just need to be "run in" at the beginning...? In any case, I think that Ultimaker should be aware of this problem now, and check the operation of their bearings more cautiously (or use higher quality bearings): my UM2 (with "2+" extrusion upgrade) is 2 and 1/2 years old now, so in my case it may be a "youth problem" on the early models. I have had this problem on most prints from the very beginning until last June. I have no idea if this has been robustly fixed on the more recent UM2 models.
  4. Funny, there are definitely several ways to look at the same problem, kind of "chicken and egg" situation... I personally would say that a "perfect" nut does not exist (some amount of play is essential for the screw to run through the nut). So what you want is to lower the play in the nut to well below the layer resolution of the printer (for Ultimakers with 40 or 60 microns layers, I guess this translates to nut/screw tolerance below 10 microns or so... Clearly, the original Ultimaker parts do not reach this level of tolerance. I have no idea what the standard industrial tolerances are for such parts: maybe by sourcing screw AND nut from one same quality manufacturer, they will be adjusted to tighter tolerances...? So in my view, we should accept the fact that there is some play in the nut, and this should not be an issue as long as the weight of the platform brings "natural preloading" by pushing down on the nut and leaning its bottom-facing threads against the top-facing screw threads. When the regular weight of the platform is not sufficient for this, the problem can be greatly mitigated by adding weight (and possibly cleaning dirt in the screw threads), which in my opinion is the simplest of all suggested fixes and unbeatable efficiency / simplicity ratio. Unless I misunderstand something, the suggested "anti-backlash-nut" fix is also based on preloading the nut threads against the screw threads, which will work even for axes without the weight-load, but in our case we do have some weight and it seems to be a more natural way to obtain a similar effect. Moreover, I personally don't feel comfortable with the (lack of) stiffness and geometrical alignment of the plastic adapter, especially in case the bearings begin to severely jam (wouldn't the whole thing slightly twist?) which in my experience happens about once in 20 or 30 prints. I prefer the nut mounted directly against the platform (metal against metal, very stiff). Still in my view, the part of the mechanism that is really not sound (and not working as designed) is the "sticking / jamming" of the linear bearings (especially common 10-15 mm after direction reversal of the Z-movement at the beginning of prints). Bearings are supposed to roll, not jam... Many people noticed this and it is clearly due to the low quality of the standard Ultimaker bearings. Sure, a very tight screw/nut (less than 10 microns) will mitigate this by "tearing off" the jammed bearings without noticeable shift in the Z-layers, but to me this is not the proper (intended) functioning of the mechanism. In my case (UM2+), additional weight (1 kg) together with a lot (really a lot) of exercising of the linear bearings completely solved the problem (I haven't had any visible "bed drop layer" in months and tens of prints at various Z resolutions, including 3 challenging tests at 60 microns). Still, I'd be willing to replace my original bearings with Misumis if I get an opportunity to buy them, but unfortunately Misumi itself only sells to companies, so if any of you knows a reseller who accepts dealing with individuals (and ships to France), I would be very thankful for the hint.
  5. Looks like yet another case of sticking in the vertical linear bearings / rods. Short suggestions to remedy: add some weight (500-1000g) on the platform between the rods, wipe off any lubricant off the Z-rods (they should be dry and non slippery), remove the linear bearings and exercise them (a lot) by running them back and forth along the rods until the motion feels smooth and rolling (no skidding). If you find a good source of components, you could also try to replace the linear bearings with higher quality parts (Misumi parts have been recommended by some). See here (for example, but there are other similar threads): https://ultimaker.com/en/community/11123-z-axis-layer-error
  6. Hi gr5. I think this is the same symptom here: in my opinion this phenomenon always revolves about the same factors : - slight play in the Z-stage screw/nut (probably almost unavoidable at 60 micron scale) - friction in the linear bearings (especially upon direction reversal after ~ 10-15 mm) My understanding of the phenomenon is as follows: depending on the variable friction and sticking along the rods, the Z screw/nut is EITHER retaining the platform from falling OR pushing it downwards, the Z-difference between those two conditions being the screw/nut play. Goo in the Z-screw threads will probably increase the susceptibility to friction and lean towards the "pushing" state. Adding weight to the platform, cleaning the Z-screw threads and optimising the linear bearings leans towards the "retaining" state. Irregularity in the layers results from transitioning between those two states more or less randomly during the print. In my experience, once the balls get rolling inside the bearings, there is no more friction and the rest of the print goes all right (unless there is some serious goo in the screw threads). By the way, the weight addition definitely works great on the UM2 platform: I followed your original advice for the wooden UMO and it clearly made a huge difference also in my UM2. My initial guess was that the weight should be ideally added right between the pillars to avoid inducing significant bending moment on the mechanism, so in my printer I added it under the hood on both sides of the screw (there is not much space in front of the hood anyway). However, I must admit that I'm not entirely sure that it would not be even more favorable to also deliberately add some bending moment by putting the weight slightly forward of the pillars: indeed, when I manually manipulated the linear bearings, I noticed that the friction/binding phenomenon upon direction reversal was much less likely when manually exercising slight bending force between the linear bearing and the rod. Supposedly, a slight bending force puts a non-zero load on the bearing and may help prevent the balls skidding and force them rolling... but of course this is only the way I felt it when manipulating my own stock bearings (which were definitely not the best out there). Probably there are specialists out there who have more clues about how linear bearings operate when there is no load on them (ie when they are set up to travel vertically under negligible bending moment as in the Ultimakers). One could also try to tilt the printer (10 or 20 degrees backwards?) while printing.
  7. OK here's some feedback about this. After the previous exchange, I gave my stock bearings another serious run of manual exercising, WD40 cleaning and degreasing cycles. Indeed one can feel the situation slowly becoming better, but it's a pain because it really takes a long time and a lot of patience. Following other advice in this thread, I also decided to add some weight (about 1 kg) between the pillars, which brought a big improvement. After that, I have been able to print the visually highest quality parts ever with my printer. However, since the bearings are still slightly sticking around Z=15mm, and since I seemed to notice some faint residual irregular layers, I decided it would be worth to attempt to replace them with higher quality parts. Unfortunately it seems impossible to order Misumi bearings as an individual, so instead I chose to order a couple of (costly) Igus polymer bearings referenced in the other thread. In short: don't do this, don't go for Igus, it's a mistake. While the Igus bearings feel about fine when you slide them manually, they also generally have more friction than the ball bearings, and they have it all the time, not just upon direction reversal. The result (still with additional weight on the platform) is that they make the problem worse: slightly irregular layers all the way, which is especially noticeable on 60 micron prints. Also, be aware that the Igus bearings are not a perfect fit for the UM2: they have a much thicker base which would require longer screws for a good hold (with the stock screws they hold on only 2 screw turns which does not feel sufficiently stong), and they have a slightly larger outer diameter of the casing (+1 mm) which makes them not fit in the hollow inserts under the hood. Besides this, while the parts look very pretty with anodized aluminium dark grey finish, they seem rather grossly machined so their actual "quality" is not evident to me (considering the price). So after I realized my mistake, I disassembled the Igus bearings and mounted the stock bearings back, after yet another run of heavy exercising, cleaning and degreasing. This is where I am today. Honestly the quality of the prints with this setup is highly satisfactory, but I'm still wondering if you guys know any way to buy those Misumi replacements: do you know resellers who accept to sell those parts to individuals? Thanks in advance for any advice.
  8. I would like to mention FreeCAD. This is a very powerful set of tools under a single roof (possibly including the slicer engine although I personally prefer to use a standalone program for that). It is very actively developed and becoming increasingly powerful. For that kind of object (raised drawing), you can for example: import a bitmap image or picture of a model shape draft a B-spline curve on top of it convert this curve to a sketch (2D section for 3D operations) extrude or dig the sketch into a 3D solid object convert the solid object into a mesh and export it (STL...) for slicing
  9. First, if you haven't already done so, I would systematically go through checking all the items in this troubleshooter chapter: http://support.3dverkstan.se/article/23-a-visual-ultimaker-troubleshooting-guide#z-drop If the splitting always occurs at the same height (even not exactly the same layer but around the same height), my highest suspicion would still be with binding on the Z-axis and subsequent bed drop. There seems to be a significant fraction of printers out there with a tendency for the linear bearings to bind (albeit more frequently within the first 20mm at the bottom which doesn't seem to be your case): the binding is causing slight bed drop in combination with the little play between the Z-nut and Z-screw. Also, your prints on the picture seem to split more consistently on one side than the other: if this is the left or right side of the printer, this may indicate which of the two bearings could be responsible for the binding. I don't see why splitting from insufficient layer adhesion alone (due to suboptimal temperature setting, too high printing speed, too much fan or unforgiving material) would always occur around the same height on different printed objects, but it will definitely make the problem worse and more apparent on the final result. Although I don't really see the scale of your prints in the picture, it could be that you use rather thick layers: maybe there are some adjustments to the print settings that would optimize layer adhesion for thick layers, but I never experimented with that. Anyway, there must be something else triggering the phenomenon only around certain heights so you might want to closely monitor possible unexpected fluctuations of the nozzle temperature around these heights (the Tinkergnome firmware will display this information while printing)...
  10. Thanks a lot for the link neotko. I laughed when I read chrisw's post about being unable to stop the Misumi bearing from rolling, even holding the shaft horizontally: my current bearings are definitely very very very different, even when I hold the shaft vertically, the bearings will not slide all the way under their own weight without sticking somewhere halfway. I agree that everything must play together but I was just saying that the root cause seems to be the bearings (at least in my case and for this particular problem of banding aroud 10-15 mm from the bottom). I may well end up adding a little weight to the platform, too.
  11. Hello all and first of all thanks a lot for all your excellent contributions and sharing your experiences, this is a great community. I, too, am having the same problem: frequently (about 50% of prints) one or very few bad layers, always around the same height (10-15mm from the bottom). I have had this problem from the very beginning 2 years ago (Ultimaker 2 delivered in April 2014). Until recently, stupid me, I thought it was due to some "magical" underextrusion phenomenon that would only occur at a certain height. I even bought the extrusion upgrade partly in the hope it would solve it, but obviously it didn't. I have read quite a few topics about this and found JohnFox's input (not only in this thread) very interesting and relevant. I think the root of the problem is not with the nut or the lubrication, it is indeed a problem with the linear bearings and the way they roll on the rods: other suggestions I found (lubrication, nut, Z-travel speed, weight addition) are probably only secondary factors that just help mitigate the fundamental problem with the bearings. Here's my understanding of how it happens (at least in my case): when the print starts, the table lifts up and the bearings roll fine along the rods until they reverse direction: this is where the sticking occurs, about 10mm AFTER direction reversal, EXACTLY around the height where the bad layers happen. I disassembled rods and bearings from my printer and can reproduce this phenomenon by hand very consistently (there is a sticking for approx 6 reversals out of 10, and even a big sticking for approx 1 reversal out of 20). I have tried to degrease, clean, lubricate, everyhing: no matter how much effort, degreaser and lubricant I put, the sticking won't go away, it's just a little attenuated. This sticking certainly feels like it's due to the balls jamming inside the bearings when they reverse direction. I really think that JohnFox is right when he says that the balls slide and skid instead of rolling which makes them jam, but curiously this only seems to happen shortly after direction reversal (one also hear a faint clicking noise of balls piling up against each other when jamming, which some on this forum described as "like sand in the Z-screw mechanism"): after the sticking point is passed, I can distinctly feel (and hear) the balls rolling again. I have also noticed that the sticking point is clearly more frequent and more pronounced when the bearing slides vertically: probably the bearing's own weight is sufficient to better press the balls against the rod and prevent the skidding when sliding horizontally. So right now I am strongly suspecting a quality problem with the bearings design and looking for good quality replacements to see if it makes any difference. My current bearings are marked "LM12UU". I found JonnyBischof's advice about the Misumi brand and ended up with their reference "LHFSWF12G": can anybody please tell me if this is the right part or otherwise point me to the good one (or advise another trustworthy manufacturer)? Thanks in advance.
  12. Pardon me if this has already been brought up, but I am currently comparing the two branches of Cura and I am puzzled by some obvious differences with the new version : - the slicing seems much slower - the printing times are much higher (maybe related to the previous one) - the raft layers do not show in the layer view - the supporting structure seems sometimes questionably illogical - more oozing during travel (lots of "hair-like" filaments left on the way) Are these known features? Is this due to some configuration options? I have tried to set up both versions with equivalent settings, but I may have missed something.
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