Strange Ringing artifacts on coreXY

mrehorstdmd

I second the vote for extrusion problem. Try changing the extruder motor current up or down 20% and see if the pattern changes.

I've seen this in direct extruders with no gear reduction and relatively large filament drive gears.

What kind of extruder is on the machine?

makerdise

@whosrdaddy @mrehorstdmd @kuhnikuehnast did test a bowden setup as an alternative, while currently running a zesty nimble (which sounds like a hot candidate having a non concentric part or imprecise worm drive etc.)... This was also one of my first ideas (inconsistent extrusion). However, the pattern remains nearly the same on both setups. The distance between the "waves" is very consistent so this could only be caused by a part moving around in circles with a non-concentric bore or wrong clamping (in theory).

Damn.

@mrehorstdmd - are you the guy with the belt driven z-axis printer, do I remember right? If so, respect.

kuhnikuehnast

as @makerdise already told: at first, I was "hoping" to have an extrusion problem... But as I tried 2 different types of extruders and also with 2 different stepper motors, the problem persisted. And if you watch the video, you can also se the "sine wave like" spinning on the axis. These videos were made by just "printing" a g-code like:

G21
G91
M564 S0 H0
G0 X300 F6000
G0 X-300 F6000
G0 X300 F6000
G0 X-300 F6000
...

So all the possible interfering factors were eliminated.

Neoxio

Does it get worst when u print @ 0.1mm layer hight? (does the "ringing" changes, increase?)

T3P3Tony

@kuhnikuehnast, @makerdise It looks like you have carried out a detailed investigation so far. To try and isolate the problem to a subsytem (electronics/mechanical) can you try changing:

Movement axis interpolation this line in config.g "M350 X16 Y16 Z16 E16 I1 " change so that X and Y are not using interpolation:
M350 Z16 E16 I1
M350 X16 Y16 I0
As a seperate test, try different microstepping for movement axis:
"M350 X64 Y64 Z16 E16 I1 "
You may need to reduce the print speed. Also make sure you follow the documentation about how the microstepping and steps/mm interact. https://duet3d.dozuki.com/Wiki/Gcode#Section_M350_Set_microstepping_mode

whosrdaddy

I had a look at the videos, it seems that X axis has issues (20 micron range is a lot).
Could be something simple as binding or a bad bearing.

kuhnikuehnast

Would be great if it was that simple... As I only wanted to use high quality parts I installed Misumi long bearings... Bending isn't a probleme I think.

Steppings:
Already tried switching off interpolation and tried from full step to 1/32. But I will give a second try later (just out for dinner)

makerdise

@kuhnikuehnast - I am unsure if we did test the M350 X16 Y16 while setting the I flag to 0 explicit...

@T3P3Tony - for sure we did test a lot and discussed a bunch of common and uncommon things. It seems to be more complex in this case. I was focused on the mechanical subsystem since we did some tests today. As written in the OP, the belts, pulleys were changed, so they are out. We measured the rods, the movement was ~0.05mm. There's no measurable bending or movement of the frame. So we continued debugging within the XY frame, by measuring if the Y carriages does bend in x direction while moving x, and they didn't. The only measurable movement within a linear x move(as seen in the video) is into the y direction (+-0.2mm = 0.4mm). You can clearly see this sinus wave like pattern with a ball pen mounted on the x carriage painting on paper. In conclusion, we have to find all factors that can cause kind of a stuttering in the motors. As the motors were changed, it can be related to soft- or hardware issues.

I thought about an issue with M669 which was introduced in RRFW 1.1.9 - are there potential collisions with M667 or known issues related to CoreXY?

Maybe @dc42 can join the discussion to bring in some light into the darkness

mrehorstdmd

@makerdise

Yeah, I have the belt lifted Z axis. I recently put a Volcano and 0.8 mm nozzle back on it to print some structural parts and ran into some Z axis banding problems that I am starting to think are due to the gears in the worm drive that lifts the Z axis. I'll probably do a post on it to see what other think is going on.

Older prints made with a standard heater block and 0.4 mm nozzle in 0.2 mm layers don't seem to have the problem, or have it to a much lesser, more acceptable extent.

I have a CubexDuo with a relatively large diameter filament drive gear that produces little ridges in the walls of prints and seems to be related to the microstepping causing the motor to pulse enough to create the ridges. For some reason, changing the motor current changes the spacing/angle of the ridges.

makerdise

@mrehorstdmd - this is a real nice project. I like the worm drive, in my research I only found a very few ideas to stop the unwanted z movement and this is the best implementation.

OMG, another complex issue For sure, feel free to post it by pm or here. Did you thought about a PID related issue? Is it possible that the block itself is bending cause of this and the vertical alignment? Did you ever tune the PID's after changing the block? Are you using the volcano sock?

Do you have any detailed information on the motor pulsing, this seems to be interesting...

whosrdaddy

Question, what firmware are you currently using?

mrehorstdmd

@makerdise

The machine still has the smoothieboard in it, so I'll post here after I get it switched to the Duet if the problem persists. I was preparing to install the Duet and got side-tracked by the print quality problems that suddenly appeared when I switched to 1) volcano and 0.8 mm nozzle, 2) 0.4 mm layers, and 3) white ABS.

I'm hoping it isn't the worm drive...

kuhnikuehnast

Do not cap my thread

But back to topic:
Here a picture of my printer:
0_1526420009376_20180515_231101 (Large).jpg

And here the 2 tests:
on the left:
M350 Z16 E16 I1
M350 X16 Y16 I0

on the right:
M350 X64 Y64 Z16 E16 I1

Both look pretty identical...
0_1526420058702_20180515_232835 (Large).jpg

The 0.1 mm layer height is still printing.

makerdise

@kuhnikuehnast will arrange a test with unmounted motors and a flag on my recommendation...

hurzhurz

@kuhnikuehnast I had the same problem on my HEVO.
You may have a look at this thread:
https://forum.duet3d.com/topic/4246/vertical-banding

There is mentioned that the problem probably lies in a to small current and especially to few steps per mm.

I had 1.8° steppers with a maximum rated current of 1.2A from an aliexpress hevo kit.
Because of the thread, I then switched to these 0.9° 1.7A steppers:
https://www.think3dprint3d.com/motors?product_id=122

That helped a lot and practically solved the problem for me!

I drive them with 1.2A, 16x microstepping and 160steps/mm.

dc42

What is the pitch of the banding, and how many motor full steps and pulley teeth does it correspond to?

kuhnikuehnast

@dc42 The pitch seems to be 2 mm (full "sine wave") which corresponds to 1 tooth (GT2-Belts).
as I am using 1.8° motors :

80 steps per mm at 1/16 microstepping
so 5 steps per mm at fullstep
2 mm banding--> 10 full steps.

I yesterday did another test:
disconnetcted the stepper motors and connected the spools with jumper wire. (to produce a good holding torque). then I carefully tried to move the x-axis back and forward only using one finger and measured the maximum distance with a gauge-> this is +/- 0,1 mm, so 0,2 mm in total. And exactly the movement shown in the videos I posted...

cgcafer

Hi,
I guess you've checked it over and over again until now. but I want to ask you one more time. how are the spaces between the rod and the bearings(bushing) mechanically? and if you are using elastic coupling and the load is too much, you may have problems.

kuhnikuehnast

@cgcafer don't get what you exactly mean? The rods and the linear bearings? The linear bearings (Misumi) are directly placed on the rods. The linear bearings themselves are hold with a really thick printed part. You can't measure any flex while printing.

Or do you think of the Idler? There is a screw that holds them in place. As I first changed the Idlers (after ~ 1 month of test prints) you couldn't see any damage on the screw..

robm

@kuhnikuehnast,
As per comments and details in the vertical banding thread, I've had this problem for a while. I found some improvement increasing the steps per mm by using smaller pulleys and 0.9 degree stepper motors, and by vibration isolating the steppers, but I would not say that I have eliminated the problem.

You noted that you have changed the pulley and idler wheels, have you tried different tooth count pulley wheels?

This page under 'Stepper clipping' references this work on a similar pattern, but this is traced to different motor driver chips and stepper motors than either of us are probably using.

Mine is a DIY Prusa i3 design, some claim that these are more susceptible to motor vibration than other designs; possibly the Kossel I am building will be free of the problem?