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strange shift in print

PostPosted: Sat Feb 28, 2015 7:55 pm
by Hassi
Hi, I'm about to use my Hadron for larger prints and run in shifts during the Print and don't know how to fix them. They occur in the X- and Y-plane.
when they occur, i don't hear strange noises, or something, I checkt the screw on the sprocket wheel, the fixture of the belt on extruder wagon and bed wagon,
taped the mirror down on the heatbed, so it really can't shift. I don't know what else could be wrong.
I read in "Mike's ORDish Bot build" about reducing the current of the stepper driver.
But if i go down with the reverence voltage, the motors won't move, just wiggle and grind. (rev V about 0.15V on printrboard)
Foto 28.02.15 20 20 42.jpg

I printed this part two times and every time it shifted nearly at the same layer (+-2) but one time only in y and the other time in x and y in one layer (and for the same length => 45 degree o.O strange)

hope someone can help, everything works just fine, but it shifts and ruins every print...

Re: strange shift in print

PostPosted: Sun Mar 01, 2015 12:46 pm
by Hassi
Ok, i set the acceleration from 0 (default in repetier host) to 500mm/s^2 and got one good print.
Currently I'm trying it with 750mm/s^2.

Re: strange shift in print

PostPosted: Sun Mar 01, 2015 1:28 pm
by Zebethyal
Hi There,

A couple of suggestions based on some similar experiences on my printer (Prusa i3), and also other reading I have done trying to troubleshoot my problems.

One issue I was having was as a result of too high a "jerk" value which resulted in the print skipping due to trying to accelerate the head from stationary too fast, however this tended to be a little more random as to where it skipped.

The other related to not using a fan on tall prints with overhang - the print curls up at the edge and then the print head catches on the curled up part and either drags the print off the bed, or drags the print head to a new location to continue the print.

The third, which I did not personally experience, relates to the stepper drivers temporarily switching off to "cool down" due to over heating.

Based on your picture and the fact that the issue seems to occur part way through printing an overhang, I would personally be betting on the second item I have mentioned.

I was also having other issues with back EMF from my heated bed relay causing random skips, but only about 0.2mm in X or Y direction at any one time.

Hope this helps.



Re: strange shift in print

PostPosted: Sun Mar 01, 2015 5:58 pm
by Hassi
@Zebethyal, thank you :)
Firstly I dont't think that the overhang could have coused it.
Secondly if it was the jerk-value, wouldnt it be more random and more often?

I guess it could be your third suggestion, as i found out that the Fan on the printrboard sucked the air ofer the heatsink instead of blowing it.
since i changed this every print went fine. Now I'm going to increase the acceleration to speed up my prints a little bit :D

Re: strange shift in print

PostPosted: Mon Mar 02, 2015 10:03 am
by Zebethyal

Glad that you have sorted your issue.

I don't have any fans on my controller board (sanguinololu), however it is not enclosed, and to my knowledge I have never had any overheating issues.

The fan I use on my printer is a tiny 40mm one and does not move that much air - I can barely feel the airflow even after the funnel. However, it moves enough air to prevent the hot end reaching start temperature when it is on and also makes the difference between the edge of an overhang curling up and staying flat so as not to catch the hot end when it is moving rapidly across the print.

I agree entirely regarding the jerk setting - it would be much more random.