Ripples on edges...

Hi,
I´m getting quite some good results so far. Everything is scale and rectangular etc...
But there are these annoying dimples behind the edges.

How can I get rid of them? I installed an y-belt tensioner, because it happens always after y-direction turns towards y-Zero. But it didn´t help.
I also have a few smaller waves in the surface. Thats related to the crappy LM8UU.

Thx
-Olaf

Edited 1 time(s). Last edit at 05/15/2015 09:45AM by o_lampe.

This may be a printer stability issue, you could try slowing down the printer a bit, or bracing it.

Which axis is showing the problem?

It seems, the belt tension was too low. I installed adjustable belt tensioners and it got better.

I made a speed test with the infamous 20mm cube. I started with 40mm/s.
Every 2mm I increased speed about 20% and ended at 280%. ( 112mm/s )The edges looked all the same from bottom to top, but the ripples changed.

Still unsure, what it is
-Olaf

looks fine to me except the layers looks quite thick

Quote
sarf2k4
looks fine to me except the layers looks quite thick

Do you refer to the first picture I uploaded? Those ripples / echoes are normal?

Layer was 0.3mm with a 0.4 nozzle
-Olaf

Second pix (speed cube) appears to be resonance ripples. Belts aren't impervious to stretch and the parts aren't resistant to vibrating. As long as something can shake, they will be there. The key is not to set them off or make it as minimal as possible.

I thought so, especially my LM8UU are rattling sometimes, making the whole printer hop from the table

It would be nice to have an algorhythm, that prevents harmonic resonance.
Just alter the printspeed by a small random number up or down ( say 10% +/- )

We´d have to look for all "g1"-commands in a g-code file and change the "Fxxxx" numbers randomly.

Note to myself
Write this postprocessing code finally
-Olaf

My printer is an acrylic I3 from China. The Y bed is cut from Acrylic and only has one linear bearing on the right side instead of two like the left side. I can literally watch the bed oscillate on the edge when it rapidly changes direction. I made some reinforcments for the bed to make it stiffer and while that helped it didn't stop it. I can still see some oscillation so I need figure out some way to stop that. It prints good but I know it can get better and my next mod is to add another bearing where there is only one now. Next, I may try to make a new and stiffer bed with better linear bearings. The quality ones are expensive though.

Yes, you´re right.
The table always tries to go the way of lowest resistance. It looks like a "figure 8". Although I´m happy with the forgiving softness of the acrylic table.
Z-min endstop and the nozzle have an ongoing fight and the table acts as a bumper sometimes.

Another point on my todo-list
-Olaf

Hi
For the first picture I will first tight the belts, than reduce the jerk . You are changing more fast than your machine can support and create ripples.
Reduce jerk by 3 and try again.

For the second pic, I will reduce flow rate a lot. The corners are higher than the walls.
After this you will better where is your problem.

Edited 1 time(s). Last edit at 05/29/2015 10:57AM by Laopa.

I don't know if this is the same issue, but there's an exchange here about reducing or eliminating vertical ripples by slowing down speed on perimeters (about halfway down the page):