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Ripples on edges...

Posted by o_lampe 
Ripples on edges...
May 15, 2015 09:45AM
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.


Edited 1 time(s). Last edit at 05/15/2015 09:45AM by o_lampe.
open | download - ripples.jpg (187.2 KB)
Re: Ripples on edges...
May 16, 2015 08:12PM
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?
Re: Ripples on edges...
May 17, 2015 03:06PM
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
open | download - speed-test-cube.jpg (250.5 KB)
Re: Ripples on edges...
May 20, 2015 04:34AM
looks fine to me except the layers looks quite thick
Re: Ripples on edges...
May 21, 2015 02:36AM
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
Re: Ripples on edges...
May 23, 2015 11:00PM
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.
Re: Ripples on edges...
May 24, 2015 05:13AM
I thought so, especially my LM8UU are rattling sometimes, making the whole printer hop from the table winking smiley

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
Re: Ripples on edges...
May 24, 2015 10:00AM
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.
Re: Ripples on edges...
May 24, 2015 11:15AM
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
Re: Ripples on edges...
May 29, 2015 10:54AM
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.
Re: Ripples on edges...
May 31, 2015 12:28AM
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):
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