belt pitch causes ribs on surface

Hi,

After calibrating a lot my printer really prints very very well.
But on large flat surfaces in X and also Y direction I do get this fine ribs every 2mm - and guess what: my belt has a 2mm pitch.

- the idler gear is also toothed (not a simple ball bearing)
- belt is perfectly tightened in both directions
- acceleration set to 200mm/s2 (but I gues it has nothing to do with it)
- print speed on outside perimeter 30mm/s at 0,15mm layer hight

As it is every 2mm it's definitely not axis vibration I guess...

Anybody had the same problem!?

#######
- standard X Y Z printer with 2mm belts
- dual extruder with 2 0,4mm nozzles

(parts shown are for a > 300 mm tall Lego figure )

Edited 2 time(s). Last edit at 02/22/2015 10:15AM by RepRapper_Austria.

You mentioned 200 mm/sec . with dual extruder, and I'm guessing both extruders are in the x carriage right? If so, there is your problem. Can't go that fast with so much weight in the axis.

If you don't have the extruders in the carriage, the you might need to adjust the power to the steppers.

that's not from belt teeth, it's from overpowered drivers and acceleration settings.

Quote
ggherbaz
You mentioned 200 mm/sec .

I travel 80mm/s (G0) and print at maximum 60mm/s (30mm/s for outer perimeter) and and acceleration of 200mm/s²

Quote
Dirty Steve
that's not from belt teeth, it's from overpowered drivers and acceleration settings.

But every rib is exactly above the other: and I printed over 100 layers high (0,15mm * 100 layers)
Acceleration is at 200mm/s²

Thanks for your replies, but I still think it's caused by the belt itself

It is not the belt teeth, but the degrees of the stepper motors. I had this in my prints and chased it down to motors, went from T5 to GT2 belts, no change, tried belt flip trick, no change, tried toothed idler pulleys, no change, swapped 1.8 degree for 0.9 degree steppers----exactly doubled the pattern! Dropped stepper driver current a low as I could without dropping steps and practically completely eliminated the pattern.

Regardless of micro-stepping, the stepper motors 'click' (higher torque) into the 200 steps per rotation, 1.8 degrees for most steppers. It's not that the belt is in the same position but the motors are in the same position of rotation.

If you move an axis by hand while the motors are powered, that point it clicks to is 1.8 degrees of the motor rotation.

Run a test cube at 10mm/s, you will see a smoother surface. High acceleration and over-current driver settings increase the ribbing.

Edited 5 time(s). Last edit at 02/22/2015 04:22PM by Dirty Steve.

Quote
Dirty Steve
It is not the belt teeth, but the degrees of the stepper motors.
..
If you move an axis by hand while the motors are powered, that point it clicks to is 1.8 degrees of the motor.

Hmm - sounds reasonable.
The only thing I don't understand is that one rotation of the gear is as following (just an example):
14mm pitch circle diameter * Pi = 37,67mm for one full rotation on the stepper
37,67/360*1,8= 0,1884mm for a single step (without microstepping)

Why is the "pitch" on the marks of the printed surface constant 2mm and not 0,188mm?

I can't justify it thru math, i just know it's the degree of the steppers. Been printing for over 2 years, took a year for me to solve.

If you move the x axis by hand one 'click', it should match the pattern spacing.

Edited 2 time(s). Last edit at 02/22/2015 04:33PM by Dirty Steve.

Quote
Dirty Steve
If you move the x axis by hand one 'click', it should match the pattern spacing.

But one "click" is about 0,188mm (see above)!
Hmm - that will give me another sleepless night till it's solved for me too

physically move the axis.

Was this problem ever solved? I have had a similar problem here- [forums.reprap.org] although it doesn't always appear so pronounced. Played with acceleration and tweaked the driver POT's but no change. I did notice an effect on this issue during a recent print, I typically print slow (20-40mm/sec) but decided to crank up the speed to 400% and although things started to get a little sloppy, somewhere between 100 and 400%, the ribbing went away. Why did this happen?

Quote
Bill Clark
Was this problem ever solved? ... I did notice an effect on this issue during a recent print, I typically print slow (20-40mm/sec) but decided to crank up the speed to 400% and although things started to get a little sloppy, somewhere between 100 and 400%, the ribbing went away. Why did this happen?

I guess it's because your X and Y carriages have some significant weight too and the faster you go (intertia!), the faster you're running over those bumps caused by the belt which leads in a better surfase.

On my side it is not solved so far: contacted the manufacturer and they will switch to another supplier for the gears. To be honest the ribs are VERY small and the overall quality is far better than other printers that's why it's not my first priority to solve this at the moment.

Edited 1 time(s). Last edit at 03/11/2015 11:45AM by RepRapper_Austria.

mine isn't too bad either. Looks far worse in the photo I posted than actual. Parts I make are usually very small so its more obvious. My rib spacing didn't jive with belt pitch rather seemed to match the cogging of the stepper. I plan to eventually put x, y or both through a reduction to see the effect