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kingcatwell

Second layer prints offset/skewed

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So been having a problem lately with some of my models, but weirdly not all.

With certain models when the printer reaches the second layer (after printing the first fine) it will move to a different co ordinate and print the second layer offset.

So that the second layers about 10mm off to one side.

Time and time again it does this, its not hitting anything. I've examined and fixed the geometry, re exported, re-sliced on two different versions of Cura on two different computers, yet it still skews. I have my ultimaker set quite slow, so i can watch the printhead purposefully move to that wrong coordinate when it all goes wrong.

But the chassis i printed today worked fine, no skewing. Then when i printed some legs, boom skewings back. Always on the second layer. So I'm not sure if it's the geometry, software or printer.

Kinda running out of logical steps to diagnose this, any help would be appreciated thanks.

 

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It's looking like my experiences may not be unique!

http://umforum.ultimaker.com/index.php?/topic/2047-resetting-firmware/

I did not have to rebuild the firmware in each of my three recoveries. I simply re-flashed with the same firmware. I'm sorry that I did not record which versions have been loaded when my three failures occurred. I'm currently running Illuminarti's "Marlin-Menu_fixes" with only a few personal code tweaks to suit my preferences, and it has not exhibited this problem, but I've only been running it for 2 or 3 weeks so it's early days yet!

Even if one finds a version of firmware that does not fail in this manner, I suspect the firmware is not the root cause of the problem, but rather there is a signal integrity problem or some type of data corruption occurring in the Arduino and, by chance, may not manifest itself or be as likely to manifest itself with certain firmware code.

In short, I'll wager that, at its root, this is not a software/firmware issue. It's a hardware issue.

 

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Well... here's what I found looking at the gcode... KC is printing the object with 'duplicate outlines' enabled. This setting is a horrible hack that prints the identical outline twice for each layer. I'm not convinced that it helps much, and it definitely can cause problems - for instance, someone had some oddities a few weeks back that ended up being due to trying to combine Joris and duplicate outlines.

As a result of this setting, what is happening on this print is that right before starting the second layer, the printer does a long X/Y travel move during which time it is also raising the head by 0.1mm. Marlin isn't terribly happy about combining x,y and z moves, and I'm aware of at least one as-yet-unpatched bug related to how that works (but I don't think the bug should cause the behaviour that KC sees). But during my speed testing, I've definitely seen some problems with moving all three axes at the same time - speeds and accelerations that individually work fine can reduce the printer to a howling mess of skipped steps when combined.

When I tried to print the gcode file, it basically worked fine for me, but the printer sounded absolutely awful on those long moves. I can imagine that on a less-well-bedded-in printer, or with different speed and acceleration settings, problems might happen.

My recommendation to KC is to try reslicing it with duplicate outlines turned off, and indeed just to forswear the setting totally in future. :smile:

Meanwhile, I'll dig into the firmware a bit more, and see if I can figure out what is causing the problem.

PS... is it related to Calin's problem - I'm not sure. I agree with his assessment that it's probably not the firmware per se, but some sort of reduced tolerance for hardware problems. Maybe reloading the firmware is resetting some parameter that creates enough headroom for the problems to not become critical. I just don't know. I'll keep digging...

 

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For me the limiting speed is the amount of plastic flowing through the nozzle which means I can print .1 layer parts just as fast (2x mm/sec) as .2 layer parts. In theory. In practice the acceleration and jerk parameters make it so that twice the speed isn't quite twice as fast. But still - I'm not sure the double outlines feature is worthwhile.

 

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MrcDesign - I don't think it's turned on, no - but I could be wrong. One way to check is to load the gcode back into cura using the 'Load settings from gcode' option, and then go see if that got set. But I don't think it does.

Is the layer offset too by a small amount, so that it wanders around a bit as the layers build up, or is it a pretty large offset - 5-10 cm or more? If its the former, it's almost certainly that one of your pulleys is loose, and slipping slightly - or maybe one of the short belts is catching on the frame?

If it's the latter, then I think it's because some part of the fast travel moves are failing when changing layers. If you have an UltiController, you might check what your acceleration speed is (Control -> Motion -> Acc) and try lowering it to say, 3000, if it is higher than that.

Also, try moving the head by hand when it's powered off, using fingertip pressure on the sliding blocks. It should slide equally easily in both directions. If there is any stickiness in one or other axis, check that everything is square, the end caps aren't too tight on the rods, and then add a little light (sewing machine) oil to all the rods.

 

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Oh i didnt recieve mail for this post, but i read it now.

It's kind of weird, for example 1 time it draws the outline to prepare the nozzle, and inside it should start printing the model, but then the model wont start in the middle.

Or that part is done well but layers 2 and higher are slightly off, i just did a checkup to make sure everything is fasten.

It used to print perfectly, but since 3 days it has this.

I dont have an Ulticontroller

Ill check up the rods, and everything should be square, because it used to work before.

Thanks for your reply

 

 

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I checked on the rods,

The X axis is all fine, smooth all the way.

The Y axis has the problem it seems. Its smooth, then its tight, smooth tight smooth tight.

Its not really a pattern, the more i move the head to the back of the machine, the faster the tight parts come.

 

So that would rule out a few problems i guess? Like sturdyness of the belt, because then the pattern would be the same. Same goes for a rod that has a slight bend?

Do you have any other ideas?

Edit---

I just loosen the Y Axis motor, and the problem is slightly less, could the problem be in the motor?, Or maybe the belt was too tight, although people advised me to tighten it because i had issues with the alignment before.

Edit---

I have loosen the Y axis motor, and put grease on the rods and the problem seem solved.

 

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Glad you sorted out the problem. Lubricating the rods helps a lot. Make sure you use light machine oil though, not the green grease that comes with the kit - that is just for the z-screw. If you put it on the horizontal rods then they will gunk up pretty quickly (I speak from experience).

 

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Thanks.

At the moment im looking through the troubleshooting topic to see what other problems there are and how they are fixed.

I guess i have to fine tune my UM more for better results.

Also had problem with my support structure not sticking on the blue tape when using the default high settings, now i have to go expert and use a raft and see what that does.

---Edit---

I also looked up the default high settings, i copied those to the expert settings so i could add the raft, but the print time is 3 hours instead of 6 with default high settings, so im missing something, but what?

 

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I don't use the default settings. In fact I go through every setting before I make a print because I change so many, so often, depending on the print.

>Also had problem with my support structure not sticking on the blue tape

This is usually fixed in two ways:

1) Wipe the blue tape with isopropyl alcohol. This cleans off the "oil" from the blue tape and makes PLA stick to it much better. Much much much better.

2) bed leveling: If the nozzle isn't squishing the PLA into the bed on the first pass then you need to raise the bed a little to get it closer to the nozzle. Before printing level with a piece of paper at each corner. Make sure you can feel the paper when it slides in and out of the gap between nozzle and print bed.

 

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Hi Gr5,

I have read some of your other posts with putting a paper between the nozzle and the bed, and i did that because i had probably room for 3 papers. So i allready adjusted that. I don't have that alcohol available at the moment. So ill have to see what else i can do.

Also when i have the nozzle that close to the bed, i can actually hear the plastic tick when its making the 2nd layer of the raft, isn't that bad?

 

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isopropyl alcohol is also called "rubbing alcohol". It can be found at any store that sells bandages such as a convenience store, a supermarket, or a pharmacy. Look for it next to "band-aids".

Sometimes my nozzle hits the layer below which is already dry and hard plastic. This makes a surprisingly loud noise and sometimes it breaks something or nocks the print off the bed but usually it's fine. Each layer should get better as you move up but possibly not - there are all kinds of problems that cause a layer to be too thick - warping being the worst and most common problem which has nothing to do with bed leveling and has many of it's own tricks to handle.

 

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Thanks, well the bed levelling should be fine.

I get the intention that while printing the movement from the front to the back, causes more problems then a movement in any other direction, i dont know why, but is that true?

I shall see if i can get my hands on isopropyl alcohol and see what that does.

 

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