printing shifts on X-Axis

Hallo friends,

I use:
- Prusa mendel
- Power: ATX 250W
- 1.4 Ramps
- Marlin Firmware

and while printing the extruder carriage shifts along the x-axis at some points of the print.(it can print some small models without problems)
I already tried to change the X and Y motor-drivers (the y-axis is working fine) but the problem wasn't solved.
Then i changed the X and Y motors on the Ramps board which resulted in a shifting problem on the Y axsis.

So it looks like it is not a hardware problem or at least not a motor/-driver problem.

i could really use some help with this, so if u know what could be the problem or know a way to work around this, please reply.

Ps. i don't post often here, and my english might be bad, so please ask if something is not clear.

Thanks!

Hi Friend!


-Did you well-calibrated your extruder from embedded software?

-Did you try manually bad carriage movement? any sound or something?

-Did you measure the stepper motor driver amps? yes you might have changed the drivers but amps of the driivers? if your drivers using very much amps, motor going to skip step.

-Is the bad carriage working well before the problem occur?

-

---

Custom 3D Printer,

Mechanical Engineer

try tightening all the gear drivers on your motor shaft. they might be loose enough to slip

Hi there,

- it should be calibrated right(it already worked with this calibration fine some time ago).
Could it be that the motor moves in one direction further than in the other because of bad calibration?

- when the power is off and i move the carriage, there is a little resistance frome the motors but no strange sound or anything. If it is on i can't move it.

- i tried measure the ampere of the output between 2B and 2A it was about 0.02 and 0.05 mA (i think it was a little less at the X-driver). After that the x and y motor became to weak to move the bed/carriage(i might did something wrong while measuring), so i turned it off and back on and it worked again like before.
In my opinion the amps might most likely be the problem, if they are what could i do about it?

- the problem occured since i bought a new Ramps board.


- the gear drivers are tight. This couldn't explain how the problem occures only on one motor and after switching the motors on the ramps only on the other one.

Did you replace the stepper motor controller when you got the new RAMPS board? Do your stepper motor controller boards have heatsinks?

It probably needs a little bit more voltage. It's not scientific but I'll turn the pot on them with my finger on the chip and turn it clockwise slowly (increasing voltage). When I can feel it start to heat up rapidly I'll turn it back down until the temperature is no longer increasing uncontrollably.

You just want enough voltage and current to not slip but not to much as to fry the stepper motors.

I bought new ones with the new ramps so i have now 8 motor drivers(A4988) with heasinks and exept for one they seem to work fine.

I tried to increase the voltage on der driver board and it worked a little better but then it shifted again after about 30 layers, still only on the x axis.

How much did u turn the pot on the driver board?

Hi Gnarrr,

I also have a Prusa i3 with exactly the same Print Shifts on the X-Axis problem.
When I exchange the plugs for the X-Axis and Y-Axis stepper motors on the RAMPS board the print shifting problem moves to the Y-Axis.
It seems to be in the electronics (not mechanical).
Have you had any luck finding a solution to this Shifting Problem?

Regards,
Paul

Hi,
I also am a new user (2 weeks & counting) having this problem. My printer is a Vellman k8200 kit that I built which is basically like the "3drag" on [reprap.org].

The electronics is not a "Ramps" but is similar (uses similar stepper modules).

I have not tried increasing voltage on modules yet, but will try that later this week... For anyone else following tthis issue who might have helpful suggestions... I have noticed that the issue seems to occur more often when the printer is trying to "zig-zag" very small distances in X and Y; like when filling a very narrow wall.

For example: I was trying to print the I2-x-end-idler (http://reprap.org/wiki/File:I2-x-end-idler.png). As it printed one of the short ends (which prints out on the right side of my printer), the printer laid down the two edges of the wall along Y (about 2 -> 3 mm apart) and then did a zig-zag fill between the two edges on the short dimension first( ie moves in X then Y). The x/y belts barely move and shakes the whole machine instead of filling by moving in the long dimension first( ie Y then X). Other objects I have printed seem to fill walls in long dimension first and don't seem to have bad prints. As a side note, if left to print to completion I only see a single shift, that is, layers 1-13 print correctly and layers 14-n print correctly but all offset by same amount in x. I have not looked at the g-code yet to see if there is something unique at the layer of discontinuity.

Even though this sharp motion occurs almost from the start (when printing idler), the issue always seemed to occur starting somewhere arround layers 12->14 and always seemed to shift to the right and not to the left. I would have assumed it would have equal chance to shift to the left during this violent motion, but all the attempts have shifted to the right. Could this be due to fractional stepping and where the detents on the stepper are (think I read somewhere motor is moved fractional steps)???

Richard

Hi,

I too am experiencing a shift in my Y axes. It started out of the blue, my printer was running without any problems for months.

@Richard: I think you're right with the zig-zag motion. In one of my prints it starts on the same point every time (See the attached image), like it couldn't cope with the tiny rapid movements.

Can it be that when the movements are smaller than the degrees of what the motor can turn it loses track of itself?
Maybe there is a way to limit/prevent tiny movements.

edit: I've got a Prusa i3 ramps 1.4 With Marlin. Using Repetier and slicer.

Peter

Edited 3 time(s). Last edit at 10/03/2014 07:28AM by peterv3210.

I think i figured it out...

Turned out that DEFAULT_XYJERK was to high.

#define DEFAULT_XYJERK 20.0 // (mm/sec)

I changed it to 10 and now although the printer shakes vigorously when doing the zig-zag movements it does not lose track of itself.

I hope this works for you to.

Peter

if you are using a prusa i3

-the x-axis belt is 6mm and the bearing on the rework version is 4mm wide, so the belt catches for a milisecond and shunts the work. does it every layer

-it is helped by your acceleration from one side to the other of the x-axis.

-try printing at a slower speed, and print an 6mm idler for the 4mm wide bearing,

-you can also print a bearing idler for the y-axis, so the belt doesn't slip

Hi,
Finally got a chance to play, and seem to have fixed my problem with shifting x-axis....

The K8200 Vellman kit that I purchased recommends setting the (initial) stepper driver voltage to 0.425V ( for their drivers which are not pololu, but similar, so your millage may vary). The instructions also state that in case of a motor skipping steps, the voltage can be set to 0.55V. So I tried increasing the voltage on my X and Y motors to 0.5V, and the issue seems to have disappeared for me.

Now the only issue I seem to have is rough sides, most likely due to backlash. The kit came with the old standard T5 belts. Even with good belt tension, I can see these belts flex on rapid X/Y direction change. I have ordered some of the new standard GT2.5 belt (and pulleys) which are meant for linear motion to see if that problem can be eliminated as well.

Richard