<p>This is the issue of your z-axis rather than x- or y-axis because printing speed doesn't have any influence on the results.</p>

<p>I bet:</p>

<ul>
<li>your threded rods are bent or</li>
<li>nuts on these rods have too high clearance or</li>
<li>nuts on these rods have eccentricity or</li>
<li>couplings (between motor and threded rods) are bent or</li>
<li>these couplings are badly fitted</li>
</ul>

<p>All above suggestions concern z-axis.</p>

<p><strong>[edit]</strong> because it's PrintBot its z-axis has the following disadvantage</p>

<p><a href="https://i.sstatic.net/a6QGr.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/a6QGr.png" alt="enter image description here"></a></p>

CC BY-SA 3.0
2016-05-18T12:53:11.923Z
None of these apply.. The way the printer was built makes it almost impossible for any eccentricity in the threaded rod (it's only one) to pass through to the printhead (you can see what I mean in if you look at the 'Printrbot simple). Also the movement is only on the X-Axis. I know this is not really clear from the picture but actually the front and back of the cube are quite smooth.
Cees Meijer
CC BY-SA 3.0
2016-05-18T17:13:30.997Z
@CeesMeijer I've looked at PB simple. Now I'm almost absolutely sure that one of my suggestions plays a role. PB simple is stiff enough in y-axis as it has 2 rods (so printer cannot swing in front-back direction) but left-right it really can. You can check it without actually printing - If I were you I'd check with the right angle (angle gauge) while moving in z-axis layer by layer. According to your picture the deviation is about +-1mm so you will be able to check it by eye.
darth pixel
CC BY-SA 3.0
2016-05-18T17:32:25.480Z
@CeesMeijer see edit
darth pixel
CC BY-SA 3.0
2016-05-21T10:07:33.937Z
You're absolutely right, and I was horribly wrong... After multiple attempts to solve the problem in by tuning the motor drive, this is exactly what I found. The motor of the Z-Axis is not correctly aligned and therefore the threaded rod makes the the movement as you illustrated. thank you very much for your help.
Cees Meijer
CC BY-SA 3.0
2016-05-21T12:17:18.407Z
@CeesMeijer you are welcome! Good to hear you've solved your problem
darth pixel
CC BY-SA 3.0
2016-05-18T09:44:07.230Z
2016-05-18T17:31:48.210Z
2016-05-18T17:31:48.210Z
darth pixel
<p>I've built a a PrintrBot inspired printer with a moving printbed for the X-Axis movement. It's controlled by a RAMPS board running Marlin firmware. And there is a problem with the X-Axis positioning.
<a href="https://i.sstatic.net/cIoZV.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/cIoZV.png" alt="Four S-Shaped blocks"></a></p>

<p>As can be seen in the image the X-Axis is not really stable. The blocks should be 10x10x10 mm, and the top and bottom are perfect. The waving does not appear in the Y-direction, it's only in the direction of the bed movement.<br>
Each block was printed at different speed, from medium to dead-slow. I limited the acceleration and in the last block I also limited the non-printing speed so the bed would never experience a higher acceleration than with the printing itself. But the wave effect remains. And it's also remarkably repeatable so it looks more like a synchronisation error somewhere. Does anyone has a clue, or experienced a similar effect ?</p>

CC BY-SA 3.0
2016-05-18T10:37:14.597Z
Welcome, @CeesMeijer! If you try to move the bed manually along the x-axis, does it have any slack or "deadzone"? (Deadzone would be the distance the motor has to move before the bed starts moving too.)
Tormod Haugene
CC BY-SA 3.0
2016-05-18T10:46:44.507Z
@TormodHaugene slack you've mentioned would rather cause irregularity or pseudo-regular changes but layer by layer. He mentioned that entities on the picture comes from different printouts, this suggests that these are not irregularities and also not pseudo-regularities, these are regular repeatable changes so they have to be caused by repeatable cause. What do you think?
darth pixel
CC BY-SA 3.0
2016-05-18T12:46:17.047Z
flag
 
@TormodHaugene : There is absolutely no 'deadzone' in the bed movement. I've checked this thoroughly, because that was my first idea as well.
Cees Meijer
CC BY-SA 3.0
2016-05-18T18:57:35.257Z
@CeesMeijer - it is not the bed that is moving to erroneous positions, it is the printhead being angularly offset to the left or right.  It looks like you probably have one of those 2mm spacing x 4 start screws that advances 8mm per rotation, which matches the vertical period of the error it introduces as an apparent eccentricity or bend in it puts a torque on the Z assembly that introduces this cyclic left-right error in the location of the printhead relative to the rest of the machine.  If you print something very long in Y you may find the error greater at one end than the other.
Chris Stratton
<print-quality><marlin>
'Sine wave' deviation in X-Axis on moving bed printer.
Cees Meijer
# 'Sine wave' deviation in X-Axis on moving bed printer.

(Asked by: username_0 on 2016-05-18)

I've built a a PrintrBot inspired printer with a moving printbed for the X-Axis movement. It's controlled by a RAMPS board running Marlin firmware. And there is a problem with the X-Axis positioning.
[![Four S-Shaped blocks](https://i.sstatic.net/cIoZV.png)](https://i.sstatic.net/cIoZV.png)

As can be seen in the image the X-Axis is not really stable. The blocks should be 10x10x10 mm, and the top and bottom are perfect. The waving does not appear in the Y-direction, it's only in the direction of the bed movement.  
Each block was printed at different speed, from medium to dead-slow. I limited the acceleration and in the last block I also limited the non-printing speed so the bed would never experience a higher acceleration than with the printing itself. But the wave effect remains. And it's also remarkably repeatable so it looks more like a synchronisation error somewhere. Does anyone has a clue, or experienced a similar effect ?

**Tags:** print-quality, marlin

> **Comments:**
> **username_1**: Welcome, @username_0! If you try to move the bed manually along the x-axis, does it have any slack or "deadzone"? (Deadzone would be the distance the motor has to move before the bed starts moving too.)  
> **username_2**: @username_1 slack you've mentioned would rather cause irregularity or pseudo-regular changes but layer by layer. He mentioned that entities on the picture comes from different printouts, this suggests that these are not irregularities and also not pseudo-regularities, these are regular repeatable changes so they have to be caused by repeatable cause. What do you think?  
> **username_0**: flag   @username_1 : There is absolutely no 'deadzone' in the bed movement. I've checked this thoroughly, because that was my first idea as well.  
> **username_3**: @username_0 - it is not the bed that is moving to erroneous positions, it is the printhead being angularly offset to the left or right.  It looks like you probably have one of those 2mm spacing x 4 start screws that advances 8mm per rotation, which matches the vertical period of the error it introduces as an apparent eccentricity or bend in it puts a torque on the Z assembly that introduces this cyclic left-right error in the location of the printhead relative to the rest of the machine.  If you print something very long in Y you may find the error greater at one end than the other.  

---

## 1 answers

### Answer by username_2 on 2016-05-18. Score: 3 | Accepted answer

This is the issue of your z-axis rather than x- or y-axis because printing speed doesn't have any influence on the results.

I bet:

* your threded rods are bent or
* nuts on these rods have too high clearance or
* nuts on these rods have eccentricity or
* couplings (between motor and threded rods) are bent or
* these couplings are badly fitted

All above suggestions concern z-axis.

**[edit]** because it's PrintBot its z-axis has the following disadvantage

[![enter image description here](https://i.sstatic.net/a6QGr.png)](https://i.sstatic.net/a6QGr.png)

> **Comments:**
> **username_0**: None of these apply.. The way the printer was built makes it almost impossible for any eccentricity in the threaded rod (it's only one) to pass through to the printhead (you can see what I mean in if you look at the 'Printrbot simple). Also the movement is only on the X-Axis. I know this is not really clear from the picture but actually the front and back of the cube are quite smooth.  
> **username_2**: @username_0 I've looked at PB simple. Now I'm almost absolutely sure that one of my suggestions plays a role. PB simple is stiff enough in y-axis as it has 2 rods (so printer cannot swing in front-back direction) but left-right it really can. You can check it without actually printing - If I were you I'd check with the right angle (angle gauge) while moving in z-axis layer by layer. According to your picture the deviation is about +-1mm so you will be able to check it by eye.  
> **username_2**: @username_0 see edit  
> **username_0**: You're absolutely right, and I was horribly wrong... After multiple attempts to solve the problem in by tuning the motor drive, this is exactly what I found. The motor of the Z-Axis is not correctly aligned and therefore the threaded rod makes the the movement as you illustrated. thank you very much for your help.  
> **username_2**: @username_0 you are welcome! Good to hear you've solved your problem  

---

