Strange Ringing artifacts on coreXY

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?

dc42

@kuhnikuehnast said in Strange Ringing artifacts on coreXY:

@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...

In that case I think the problem is definitely related to belt teeth and not to the motors or the firmware.

Phaedrux

If possible, try what I did to solve this for my DBot. Replace the rear toothed idlers with smooth ones and give the belt a flip.

kuhnikuehnast

Did some further tests now:
I flipped the belts, so all Idlers are run on the smooth side of the belt (and are changed to smooth Idlers with no teeth) except the Pulleys of the Stepper motor. Therefore I had to flip the belt. This reduced the ringing a lot. It is still there but almost gone. Here a photo of the new belt-lineup (only for one motor otherwise my painting skills would be to confusing )
0_1526899461325_20180521_123135 (Large).jpg
I also had to loose the belt tension a lot to reduce the ringing even more. So it is still visible but you can't feel it any more...
0_1526905575813_20180521_131937 (Large).jpg

Also performed a second test:

changed to 0.9° stepper motors to increase the steps/mm. (and also tested 16 teeth Pulleys instead of 20. So I could compare the print quality from 200 steps/mm with 80 steps/mm… But there was no difference.

Next, I will try to replace the belt by a fishing line. So there won't be any toothed pulleys in the hole system any more. (the line just wrapped around the motor shaft 5 times to ensure enough friction). I know, that this isn't a solution, but it may help to find out whether the ringing is really caused by the belts...?

It is really strange!I think I just masked the problem with this conversion, but I did not fix the cause…
Almost everybody else uses the Hypercube evolution with a regular belt line-up...?

kuhnikuehnast

So, next test finished:
The problem seems really to be due to the toothed belt... Using fishing line (the line wrapped around the motor shaft 5 times) the ringing was completely gone! (Despite by a damn poor accuracy )

Now that the culprit has been located, the question remains: Why do I have a ringing problem while others don't? And what else can I try to solve the problem?

Phaedrux

It's not just you having ringing though. I'm going to be testing some supposedly genuine gates belts soon to see if that helps, but I wonder if this isn't more of a common problem than you'd think.

kuhnikuehnast

Sorry, didn't get it right what you meant...? So do you think more people than me suffer from this problem or do you think it is a specific common problem on my printer?

kuhnikuehnast

for example: a friend of mine also owns a Hypercube evolution- and he can't reproduce the problem at all???

Phaedrux

I meant that I wonder how many other people have the problem but just don't notice it or ignore it or get frustrated and give up trying to fix it.

I'm also trying to chase down the exact cause of it. Is it the belt? Is it the tooth profile? Is it an eccentric pulley?

What is different between the people who have the problem and the people who don't?

robm

@phaedrux
I suspect most 3d printers have the problem, the users just don't notice it or consider it normal. When I started recognising it, I realised I had it on some of my oldest prints, with completely different frame, extruder, hotend, motors. I see the problem in most images of printed parts online now.

Probably more massive printers like Deckingman's avoid it.

Mine seems to be stepper motor vibration, Here's some things I have found can affect it:

PETG vs ABS : I think PETG solidifies faster and locks in the waves, while ABS stays soft and they even out. Also PETG tends to be more shiny so the pattern is more noticeable. I don't use PLA (don't have a fan), but my previous experience was it is very soft and slow to harden so should not show the problem.
lower belt tension - causes other problems of course, but my theory is that the vibrations are not transferred as well with lower tension. Created this tensioner so I could vary the belt tension in a controlled fashion to test this. @kuhnikuehnast interesting idea to replace with fishing line, but again this might be just reducing the tension and hence the linkage between the vibration and the extruding filament at the nozzle.
more steps per mm as noted elsewhere (so 16t pulleys, created this GT2 belt clip to help with that, and 0.9 degree stepper motors).
in my case it seems to be a constant frequency around 25 Hz (with 1.8 degree steppers), so the pattern is most pronounced printing at 30mm/sec. Slower speeds run the peaks together so the surface is rougher but without the pattern, higher speeds spread the peaks out so they are less noticeable. If yours is belt teeth or a wheel issue I would expect the pattern to be consistent regardless of print speed.