Wavy prints on Rostock

Hi !
Please have o look at the attached picture.
My setup:
Rostock delta printer, about 400mm printable height with magnetic joints and 200mm springs for extra tension between the pushrods.
PLA 1.75mm, 0.5mm nozzle, 0.1mm layer height, 30mm/s print speed. printing at 180 degrees celcius
I have insulated the heat block and have two small fans blowing on the printed part.

The bulging looks like it comes every 7 or 8th layer or so and is even on all sides.
After some googling i found someone having the same problem on a Printrbot, the Z-motor was a little loose and had to be mounted differently, but since this is delta, all motors move upwards on Z, right?
[www.youtube.com]
At about 5:33

Anybody know what can be causing this ?

Edited 1 time(s). Last edit at 05/09/2015 04:41PM by mrg78.

On a Cartesian printer this is called Z-wobble, and is due to an oscillation of the Z-axis.

On a linear delta such as the Rostock I would think it could be due to frame flexing, lack of tension in the belts or some other cause for oscillation. Could you post a few pictures of your printer?

It can be caused by fluctuating temperature of bed/hotend too. Height of bed/hotend changes a bit with changing temperature and this is the result.

Ah a fellow large delta builder I have gotten into a bit of trouble with similar looking artefacts as well.

Yours look very regular though. Do you also have little wave along the layers?

As far as I traced the problem its stems from the frame resonating. [groups.google.com] here you can read my special situation
but its basically moving all vibration frequencies out of the range of resonance for the frame and especially the arms. btw how long and thick are yours?

My first inclination was to order DVR8825 drivers, the doubled resolution hopefully solves everything. It would be much easier than building thicker arm and strengthening the frame.

Hi mrg78,

I had the same horizontal banding problem when I built a 1 metre tall Mini Kossel derivative with Onyx heated bed.

The problem was indeed caused by temperature oscillation of the heated bed while under bang-bang control.

Enabling and tuning PID for the heated bed solved the problem completely in my case.

wouldnt that mean that the issues becomes less and less pronounced as it print moves more and more away from then bed?

No. The print, along with the bed, will be flexing up and down with the temperature fluctuations for the duration of the print (unless the temperature stabilises.)

That makes sense as well. one more argument for a heated chamber

Hi !

Sorry for delay, been to France over the weekend, really nice place
Sungod3k: I have some waves due to vibration if I print fast, but now I have put a metalbracket and bolted the whole thing to the wall, solid as a rock so I think that's not a problem anymore.
Will post some pictures later.

Tris: That is very interesting, have not tuned PID at all, will try it on both the hotend and bed I think. Bed first.
Be back with results.


///M

Yeah my frame is everything else but solid, but I just got some plexiglass that changes that hopefully.

Tris!! I actually didn't believe that the temperature of the glass could do so much to the quality.
Take a look at the attached picture, left owl is before PID-tuning, and the right is after, with same gcode-file = same settings

Will do some tuning on the hot end as well, maybe it won't help but i guess it can't hurt.


Thanks a lot for your tip!!


///M

Glad to help, thanks for sharing your result.

Happy printing!