Weird physical vertical bands on 2 opposite spots - symetrical to center. Not VFA.  

Weird physical vertical bands on 2 opposite spots - symetrical to center. Not VFA.

Dear all. 

My first post. I'm quite impressed... I played for 6 months tinkering an anycubic mega i3 to some real success (deep modding). But not reliable enough. My nerves... lost the game.

I ended up with the mk3s i just built one week ago. I carefully followed the instructions, except on 3 points (attached the Y engine to the frame with a tie - i was feeling screws were not enought ; twisting belts which helped on the anycubic limiting vertical banding ; igus bearings... until i can go to misumi. I disliked the stock LMU that i did not even tried. I attached the igus with holders from https://www.thingiverse.com/thing:2969556 which add some compression as well). 

I spent a lot of time investigating on anycubic on the famous VFA (vertical fine artifacts) to few success. Another debate. I deeply and humbly salute Guy for and related mates for the deep investigation made on these (0.9 motors, etc...). I deeply read the 6+36 pages of forum and will play with this later on (misumi rods & bearings, trinamics, pulleys...), because while i'm happy with the mk3s features and 1 week reliability... i'm somehow disappointed by the quality. I expected better. Mainly because of the VFA... well another story. But i mention this because the issue i reflect here is not about VFA.

All was fine in the early MK3s printing, and i took the STL is used from Anycubic/Cura - using Prusa profiles and altering to my needs (mainly z-scar management, combing, temperatures, low acc/jerk...). But only on the i3 MK3s did i endured the vertical "relief" bands. They are on the side of my print, a round side where X & Y move together. It's not existing on pure square ( 100% X or 100% Y) shapes. I can feel them with the tip of my finger while i cannot feel the VFAs for instance. They are rather depressed (vertical hole i would say)

On the picture they are exactly where the light falls on the top print. sorry 

Vertical physical bands on the round sides

There are 2 bands. One on the front left, the other on the rear right, fully symmetrical to the object center. I thought it was skew compensation because i was not fully perpendicular. I spent a (too) long time figuring how to achieve pure orthogonal XY shape. I finally achieved today ... Yay ! But alas the two bands are still there. 

I finally draw a simple cylinder on sketchup to check their presence. They are still there. If I rotate my STL, they are still there.

I still use Cura; but these bands were not on the anycubic prints.

I tried obviously the standard profiles (unaltered).

This is not the zscar either (i placed it on a specific angle using user coordinates + wipe + coasting)... but i also tried using random placement. Same. The picture one is using random z-scar place.

I use now the 0.25 nozzle, but that was also on the 0.4

I played with E linear calibration (you can see the print). Nothing changed

Voila... I tried to be accurate as required to beg for your help. I guess there is something mechanical to do with my built... but i can't see anything after checking.

Merci beaucoup ! Sincere & deep thanks for your kind help...

Wilfried