Time lapse video of my fail

[Aflac]

https://youtu.be/WfZyY7tRNko

[youtube]http://www.youtube.com/watch?v=WfZyY7tRNko[/youtube]

This has happened on three of my last 5 prints, any ideas what would cause this?

[nebbian]

Plastic curling up or causing a blob, then solidifying, closely followed by the head coming around for another pass, hitting the blob, and skipping a step. This throws your whole print off.

To remedy, ensure that your layer fan is on high enough, and bump up your X/Y/Z motor stepper currents.

[Aflac]

https://youtu.be/QMY7xxCYMtc

[youtube]http://www.youtube.com/watch?v=QMY7xxCYMtc[/youtube]

Here is another attempt at it, it seems to be the same kind of fail, but in a different direction. This time it jumped perfectly up in z height, but all the other directions where still perfectly lined up. If it was missed steps I would expect it to be off in all dimensions, not just one like that. I am suspecting something in the GCODE, or rather the transmission of the gcode to the printer.

I am using octoprint and was using the upload to SD function built into it. I noticed that it sent the gcode file one gcode line at a time. So if there was a problem in the transmission whichever line it was on when it messed up would be off. So i pulled the SD card out and copied the files onto it directly from the computer...lets see if this one works better.

[Polygonhell]

I doubt transmission of the GCode is at fault, most hosts send a line number and a checksum, and every line is ACK'd by the firmware. Usually the failure case is just the printer stops as the retry fails.

I guess it's possible octoprint is just ignoring the ACK's and assuming the transmission is successful, I have never used it.

Assumming it's not bad gcode, which is rare, I'd have to go with missed steps. The question then becomes why, I'd always assume mechanical first especially on a printer that has been working, belts, pulleys, binding UJoints, uneven motion of the trucks is where I'd start. Also worth just running the print at half speed to see if it goes away.

[bubbasnow]

agree with everyone here about miss steps caused by collision of the head with something. getting the nozzle over some humps of plastic some times is a bitch.

what are your motor currents set to? what speeds are you printing at? are you using any z lift on travels? are your belts right?

[Aflac]

I have my currents at 1.5 amps, belts are very tight, printing at 30mm/s, no z lift during travels, that could be the culprit if you guys are correct about it hitting something, how much z lift do you recommend?

[bot]

Are you using Simplify3D as a slicer? It has a tendency to skip layers sometimes.

[bubbasnow]

I have my currents at 1.5 amps, belts are very tight, printing at 30mm/s, no z lift during travels, that could be the culprit if you guys are correct about it hitting something, how much z lift do you recommend?

try 0.5mm

[Aflac]

Are you using Simplify3D as a slicer? It has a tendency to skip layers sometimes.

no, im using Cura, I also have slic3r but haven't used it in a while.

[bradjshannon]

[slicer name] is great until it's not.

I'll use Cura until I get to a print it can't handle. Then I switch to slic3r until I get to a print it can't handle. Then I switch to Cura...

[Polygonhell]

I have my currents at 1.5 amps, belts are very tight, printing at 30mm/s, no z lift during travels, that could be the culprit if you guys are correct about it hitting something, how much z lift do you recommend?

FWIW belts can be too tight, they put excessive side load on the bearings in the stepper, which can increase friction significantly.
What's your travel speed set to?
One issue with Cura is it tries to keep motions inside an island and as a result it tends to produce paths that result in a lot of motion over previously printed areas, which could be the culprit if your hitting the print.

I personally run 2mm of lift, it doesn't really matter on a delta, since you can move in Z as quickly as any other axis, if I were setting it for a cartesian printer I'd probably just lift 1 layer height or so.

[Aflac]

[youtube]http://www.youtube.com/watch?v=cAqe0xJhNkk[/youtube]

I am not sure if its coincidence or if I was right about the problem but the attempt with it copied onto the sd card worked. I will try putting more z lift in next time i do a print. I did however have one more failed print before the successful one and i noticed that it at one point the extruder was making a strange noise, like the gear was slipping on the filament, and nothing was extruding, i adjusted the tension on roller that presses the filament onto the gear...i can not remember what thats called, tighter didnt help so i loosened it and suddenly it started printing again. so I am suspicious that might have been part of my problem, at least with the one that was off in z height, if it printed a layer with no filimant it would look the exact same as what happened.

as for the other one that was off sideways and vertically a little I am going to guess you guys were right about it hitting something, we will see if the adjusted tension and the z hop help or if i just got lucky today.