Massive X shift @ 30mm tall

After finally getting past my second MOAC (mother-of-all-clogs) and printing well, another issue has cropped up and I'm stumped (not a recent phenomenon). On this one particular piece, I get about a third of the way through a looong print and then the x axis does a massive shift. The first two times it was a Repetier slice and this last one was a complete reload and slice from design to Cura to printer. It was working so well I left it alone and came back later to find my third failure. It goes fine and then when it reaches around 25mm tall, it starts to shift to one side (x axis) and by 30mm it is almost completely separate from the piece when it should be flush. ROBO seems good, belts and cogs tight, so perhaps the design software is failing in its STL description. Especially since it happens in the same places each time. I"m open to suggestions.

 

Hey 1d1, try a different file that goes about the same height. Maybe just a hollow column or something that will run quickly. If it doesn't do it then it is something weird with the software. If it does do it then its probably something in the printer.

 

Ill give that a try...

 

Well, a 40mm hollow column just printed fine. Yay, ROBO. As it was 2 different slicers that made the same mistake, I'm going with: design software being wonky in the STL. What a waste of good plastic and an otherwise good mood.
Thanks, guys.

 

Here: The black lines show successive slipped layers until the Big Shift. Hmm, didn't work. I'll try again.

 

Fun, huh?

 

I would if I could afford the filament. I have to admit that I was impressed with the platform that arose off of the air printing.

 

I've had that happen and never been able to figure out why.

Does it happen often?

 

After an overnight of contemplation, I have to agree with Matt at least somewhat. Can't find any mechanical reason yet. I also ran the slices visually and the model is fine so there must be some mechanical conflict somewhere between the design and the printer - particularly since it happens in two different g-codes. At this point, I am just going to have to make the print in sections and mechanically bolt/glue it together. I may even be able to salvage that lower block and go from there. At least that way if it does it again it will be at the beginning instead of the middle.
No, Mike. It is only this particular piece that does this. I can print past that height without issues like that. For some reason I can't discern on this print, I'm thinking that the hot end bumps the print hard enough to offset the hot end/x axis. Why it doesn't clear the previous layer, at that particular place, I don't know. I have had a few x slips where belt tension was an issue, but nothing like this.

 

Wow, it is amazing like you said, that it actually managed to recover the print in thin air enough to practically finish it.
Sorry I guess I'm just saying the same thing you did, But its cool to me nonetheless.

 

I'm printing past the shift now and it looks good - so far. Of course, now that I am not watching it, failure, right?
Upon really closely examining where it fails, I think it may be an issue of thin filament edges curling up in both x and y planes just enough to harden and bump the print heat successively until it gets totally whacked. Printing with support would probably solve it along with a piece orientation change. I hate support.
Back to the print...

 

Wow. Moments later, theory confirmed. When bridging without support, the filament raises up after flowing from the hot end. This eventually (several layers) bumps the entire hot end off axis. I have had plenty of successful bridging without support but in this instance I suppose I am trying to go a bridge too far. Plan B: Orient to the vertical, and add support. I hate support.

 

Is you bridging fan setting set for 100%? I think the print fan is a bit weak and could benefit from a duct. I had a Klein ottle print get hit and knocked over about 10 hours into a print because of insufficient airflow and curling.

 

OK. The print is doing much better with support. It has still had a couple of areas that were potential problems that I caught before they bumped the head out of alignment. It is at its critical point right now and I'm up here typing so it is that much better but I remain tremulous.
If I could lift the head .5mm higher on travel moves, it would likely all work out. I know how to do that in Repetier, but not in Cura. Anyone?
Another thought is that I still get some "wavy" layers on the perimeters. The filament curls a bit on the thin edge of things. I wonder if step per mm on the z axis could minimize that. I am using 2269.4. I know someone worked them out to be something else and I will look around for that. I think Melody has that in her reference section.
Finally, using the RepRap XXL display, there are definitive motion options that could give me that vertical lift but I'm uncertain which ones would do that; VMax? Vmin? A-Retract? Does anyone here know what those refer to?
I appreciate your thoughts!
Dean

 

Done successfully. I pretty much sat through the whole print and made about 20 "curl corrections" (i.e., I snip 'em or flatten 'em on the fly) along the way. I may have been overly cautious, but I really needed this part for my project. Now I am going to try out calibrating everything over the next few days. I plan on using Leon's 80 steps per x and y axis and Melody's empirical testing to determine the exact needs of my z axis. The extruder seems pretty close to spot on for amount of filament it spews so I won't bother with that right away.
I do not use a part cooling fan. When I tried it today, it seriously affected my layer adhesion and nearly boinked the print. Since I print in my basement, it is a very dry (40%) and somewhat cool environment (about 18-19 C) so, YMMV.
Now that I have printed this part, I will be assembling a one person, ultralight electric vehicle that is joined throughout with printed pieces. It is pretty cool so far and I will share pics soon. As this is just a "test mule", it isn't all that pretty but it should yield a lot of valuable info regarding potential of the project. If it is viable, I will be making a prototype. I have already changed my designs repeatedly to be better suited for both my purposes and 3d printing realities but, so far, it looks as if it might actually work. It is so cool to be able to conceive, design, alter, print and create such a thing at home. Regardless of my success or failure, consumer level 3d printing is a genuine revolution in personal potential for all of us.
Sweet.