<p><em>This is mere supposition on my part, and not a definitive answer. This was posted prior to Alvaro's answer.</em></p>
<hr />
<p>In response, or - rather - with respect to, to the comments under the question by <a href="https://3dprinting.stackexchange.com/questions/3015/z-axis-top-brackets-of-p3steel-differ-between-v1-x-2-x-and-v4#comment3919_3015">tjb1</a> and <a href="https://3dprinting.stackexchange.com/questions/3015/z-axis-top-brackets-of-p3steel-differ-between-v1-x-2-x-and-v4#comment3916_3015">Tom</a>, I have been reading around the topic, and found some interesting articles.</p>
<p>The excerpt below from &quot;<a href="http://www.soliforum.com/topic/2342/backlash-hysterisis-and-wobble-an-exploration-of-the-topic/" rel="nofollow noreferrer">An exploration of the topic</a>&quot;, backs up Tom's argument about constraining the rods at both ends being bad practice, and explains why it is so. Whilst acknowledging that a loose, or floating end, is still an issue that needs to be dealt with, the article also states that constraining the end is not really a solution, as it can create more problems elsewhere (I have added the bold highlighting to the relevant text):</p>
<blockquote>
<p>Wobble is pretty simple. Because the lead screw is mounted rigidly to
the motor, it needs to be perfectly straight and square to the axis
its trying to move. If it's not, as the motor rotates, that offset will
be converted into an elliptical motion instead of turning in a perfect
circle.  In big CNC world, as the axis is normally bolted to a
huge/heavy table which refuses to yield to this movement, it results
in breaking your motor or motor coupling (weakest point in the
connection). This is what flex couplings are designed to fix – if you
can’t guarantee a perfectly square mating between motor and axis, you
use a coupler with flex so that any movement can be soaked up in
flexing the coupler and the lead screw/rod moves in a nice circle
without busting your motor or mounts.  This is true when you have a
good solid supported connection on the lead screw like you’d see on a
‘proper’ CNC.  <strong>However on the Solidoodle, as the top end of the Z-Axis
is ‘unsupported’ and its only connection to <em>anything</em> is to the table
via a tiny little nut, its free to ‘flop about in the breeze’ so to
speak.</strong> Even a small 0.1mm offset from center can result in a much much
greater ‘wiggle’ at the top of the screw clearly visible to the eye.
Throw in even a 0.05mm bend in the rod, and it gets further amplified.</p>
<p>Adding better support to the axis, through a taller nut, multiple
nuts, or <strong>supporting the end, would reduce the influence of this
wobble. You do however, risk moving it to something else entirely</strong> –
for example, making the lead screw rigid would mean that the forces
would end up moving the motor itself, potentially causing fatigue
issues with how its bolted to the sheet metal case (mine already moves
a fair bit and its ‘stock’... making the screw rigid would see the
motor having to absorb all that movement instead of half of it
disappearing in movement of the screw...). Solving the motor movement
by securing it ‘better’ to the case would mean that the movement now
gets soaked up in the motor shaft and bearing, leading to premature
stepper motor death.</p>
</blockquote>
<p>Thus, when first posting this question, I had originally presumed that the earlier versions of the model would be superior: Due to the fact that the earlier versions secured the top of the z-axis screw mechanism, then that would reduce the amount of &quot;flapping about&quot; of the loose end, which in turn would result in <em>less wobble</em>. However, I had not bargained for the negative consequences (such as the increased motor wear, mentioned above).</p>
<p>So, is the reason that the top brackets of the z-axis, in the version 4 of the frame, lost their threaded rod/leadscrew top-end constraint, therefore to prevent premature motor wear, at the expense of exhibited wobble?</p>

CC BY-SA 3.0
2017-05-29T01:12:25.167Z
Nice research and learning.  I have run into this sort of design problem many times where what seems to make sense in concept doesn't work in reality because of imperfections like warp alignment or tolerance.  At the last company I worked at we used a LOT of flexible couplers.  We also used gears that had a floating center to deal with multi-gear couplings where gear alignment could not be assured.
markshancock
CC BY-SA 4.0
2017-05-28T05:50:36.183Z
2022-06-12T18:12:43.647Z
2022-06-12T18:12:43.647Z
Greenonline
<p>I've just seen this right now, I'm Alvaro Rey, the designer of the p3steel v4 mod. The change was made, because with previous versions with the extruder homed, if you go up in the Z axis, the extruder motor could hit the Z axis top plate. So, in order to avoid that, I just changed the design.</p>

<p>The bearing in the z axis is not necessary but some people prefer to use it, in order to avoid wobble in the threaded rod. </p>

<p>Anyways, I designed a printer part to fix the bearing in the Z top plate.</p>

CC BY-SA 4.0
2019-02-16T16:06:43.650Z
Excellent! Many many thanks for getting back to me, Alvaro and answering this question. And welcome to SE.3DP by the way... it is a real pleasure to have a designer onboard! :-)  BTW, do you have a link to the new printer part, which will fix the bearing?
Greenonline
CC BY-SA 4.0
2019-02-16T14:56:39.560Z
2019-02-16T16:09:56.347Z
2019-02-16T16:09:56.347Z
Álvaro Rey Rodríguez
<p>I have been studying the differences between version 2.x and version 4 of the <a href="https://reprap.org/wiki/P3Steel" rel="nofollow noreferrer">P3Steel frames</a> - in particular the AC08 bracket at the top of the frame which secures the top of the smooth bars and threaded rods of the Z axis on both the left and right sides. Here is the laser cut parts, for version 1.x, showing the part labelled as AC08:</p>

<p><a href="https://i.sstatic.net/2AN9z.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/2AN9z.jpg" alt="Laser cut parts for P3Steel v1"></a></p>

<p>Version 1.x/2.x has the AC08 bracket with two holes, one for the threaded rod and one for the top of the smooth bar (from the <a href="http://reprap.org/wiki/P3Steel_Vitamins#Lasercut_parts" rel="nofollow noreferrer">lasercut image</a>):</p>

<p><a href="https://i.sstatic.net/6yZMo.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/6yZMo.jpg" alt="P3Steel v2 Z axis top bracket"></a></p>

<p>However, in version 4, the corresponding top Z axis bracket only has one hole for the smooth bar and just an indentation for the bearing which holds the top of the threaded rod (from <a href="https://twitter.com/AlvaroReyRdz/status/738406531943763968" rel="nofollow noreferrer">Twitter</a>):</p>

<p><a href="https://i.sstatic.net/MZe2i.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/MZe2i.jpg" alt="P3Steel v4 Z axis top bracket"></a></p>

<p>Here is a close up of the <a href="https://drive.google.com/open?id=0BxUhvFbuwEAZNjA0dUhwNmFMd2c" rel="nofollow noreferrer">diagram</a> from the <a href="https://drive.google.com/open?id=0BxUhvFbuwEAZfkJDUUE0bm1pTXNfMFRKemdUUzJNZ2xIT0xybFJLdmdyQV9MZGFpcG42UlE&amp;authuser=0" rel="nofollow noreferrer">google docs repository</a>, listed in the <a href="http://reprap.org/wiki/P3Steel#Frame_versions" rel="nofollow noreferrer">v4 section</a> on the RepRap Wiki page for the P3Steel, which shows the bearing assembly just apparently "resting" against the indentation:</p>

<p><a href="https://i.sstatic.net/dAVUM.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/dAVUM.png" alt="Close up of P3Steel Z axis top bracket"></a></p>

<p>Here is the bracket shown with the bar and threaded rod (again, from <a href="https://drive.google.com/file/d/0BxUhvFbuwEAZQjkyTDM3SndMSTA/view" rel="nofollow noreferrer">google docs</a>):</p>

<p><a href="https://i.sstatic.net/X0fcG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/X0fcG.png" alt="P3Steel v4 z axis top bracket"></a></p>

<p>Does anyone know why the top of the threaded rod is not secured by a hole, as it was in version 1.x/2.x? It just does not look particularly well secured.</p>

<p>Under the list of version 4 changes, see <a href="https://reprap.org/wiki/P3Steel#Frame_versions" rel="nofollow noreferrer">2. Frame versions</a>, it is mentioned:</p>

<blockquote>
  <p>The extruder no longer hits the Z axis top bracket</p>
</blockquote>

<p>Is this the reason why the change has been made?</p>

CC BY-SA 3.0
2016-11-03T22:10:04.360Z
I don't know about the specific design of this printer, but constraining the rods at both ends is considered bad practice. If the leadscrew is somewhat non-straight, then with both ends constrained the wobble is transferred to the carriage, whereas with the top end free the top end wobbles, transferring less force to the carriage. But that doesn't explain an apparently floating bearing.
Tom van der Zanden
CC BY-SA 3.0
2016-11-04T08:10:13.307Z
@TomvanderZanden - I understand why that would be true for designs that employ, the less precise, threaded rod  Would that also be true for designs which use lead screws, instead, as they are meant to be of a higher quality?
Greenonline
CC BY-SA 3.0
2016-11-04T11:34:40.953Z
What do you gain by constraining the end even if it was perfectly straight?
tjb1
CC BY-SA 3.0
2016-11-04T11:56:55.293Z
@tjb1 - I am not sure, probably nothing... But it seems to me (as a complete novice) that having a "loose" bar/rod end seems a bit insecure, and, for want of a better word, somewhat "untidy". I had hoped that by constraining the end, that wobble would have been reduced - which could be the case, although other issues would thereby arise (such as increased motor wear)...
Greenonline
CC BY-SA 3.0
2017-01-20T13:27:18.087Z
@Greenonline, when you constrain both ends you take most of the movement you seen at the top and force that movement to the center (where the Z axis is riding).  When you leave the top open, the rod is only constrained by the motor connection and the nut on the Z axis which allows it to move at the top assuming your motor connection is flexible.  I really fail to see what you hope to gain by fixing the top?
tjb1
<prusa-i3><p3steel>
Z axis top brackets, of P3Steel, differ between v1.x/2.x and v4
Greenonline
# Z axis top brackets, of P3Steel, differ between v1.x/2.x and v4

(Asked by: username_0 on 2016-11-03)

I have been studying the differences between version 2.x and version 4 of the [P3Steel frames](https://reprap.org/wiki/P3Steel) - in particular the AC08 bracket at the top of the frame which secures the top of the smooth bars and threaded rods of the Z axis on both the left and right sides. Here is the laser cut parts, for version 1.x, showing the part labelled as AC08:

[![Laser cut parts for P3Steel v1](https://i.sstatic.net/2AN9z.jpg)](https://i.sstatic.net/2AN9z.jpg)

Version 1.x/2.x has the AC08 bracket with two holes, one for the threaded rod and one for the top of the smooth bar (from the [lasercut image](http://reprap.org/wiki/P3Steel_Vitamins#Lasercut_parts)):

[![P3Steel v2 Z axis top bracket](https://i.sstatic.net/6yZMo.jpg)](https://i.sstatic.net/6yZMo.jpg)

However, in version 4, the corresponding top Z axis bracket only has one hole for the smooth bar and just an indentation for the bearing which holds the top of the threaded rod (from [Twitter](https://twitter.com/AlvaroReyRdz/status/738406531943763968)):

[![P3Steel v4 Z axis top bracket](https://i.sstatic.net/MZe2i.jpg)](https://i.sstatic.net/MZe2i.jpg)

Here is a close up of the [diagram](https://drive.google.com/open?id=0BxUhvFbuwEAZNjA0dUhwNmFMd2c) from the [google docs repository](https://drive.google.com/open?id=0BxUhvFbuwEAZfkJDUUE0bm1pTXNfMFRKemdUUzJNZ2xIT0xybFJLdmdyQV9MZGFpcG42UlE&authuser=0), listed in the [v4 section](http://reprap.org/wiki/P3Steel#Frame_versions) on the RepRap Wiki page for the P3Steel, which shows the bearing assembly just apparently "resting" against the indentation:

[![Close up of P3Steel Z axis top bracket](https://i.sstatic.net/dAVUM.png)](https://i.sstatic.net/dAVUM.png)

Here is the bracket shown with the bar and threaded rod (again, from [google docs](https://drive.google.com/file/d/0BxUhvFbuwEAZQjkyTDM3SndMSTA/view)):

[![P3Steel v4 z axis top bracket](https://i.sstatic.net/X0fcG.png)](https://i.sstatic.net/X0fcG.png)

Does anyone know why the top of the threaded rod is not secured by a hole, as it was in version 1.x/2.x? It just does not look particularly well secured.

Under the list of version 4 changes, see [2. Frame versions](https://reprap.org/wiki/P3Steel#Frame_versions), it is mentioned:

> The extruder no longer hits the Z axis top bracket

Is this the reason why the change has been made?

**Tags:** prusa-i3, p3steel

> **Comments:**
> **username_1**: I don't know about the specific design of this printer, but constraining the rods at both ends is considered bad practice. If the leadscrew is somewhat non-straight, then with both ends constrained the wobble is transferred to the carriage, whereas with the top end free the top end wobbles, transferring less force to the carriage. But that doesn't explain an apparently floating bearing.  
> **username_0**: @username_1 - I understand why that would be true for designs that employ, the less precise, threaded rod  Would that also be true for designs which use lead screws, instead, as they are meant to be of a higher quality?  
> **username_2**: What do you gain by constraining the end even if it was perfectly straight?  
> **username_0**: @username_2 - I am not sure, probably nothing... But it seems to me (as a complete novice) that having a "loose" bar/rod end seems a bit insecure, and, for want of a better word, somewhat "untidy". I had hoped that by constraining the end, that wobble would have been reduced - which could be the case, although other issues would thereby arise (such as increased motor wear)...  
> **username_2**: @username_0, when you constrain both ends you take most of the movement you seen at the top and force that movement to the center (where the Z axis is riding).  When you leave the top open, the rod is only constrained by the motor connection and the nut on the Z axis which allows it to move at the top assuming your motor connection is flexible.  I really fail to see what you hope to gain by fixing the top?  

---

## 2 answers

### Answer by username_4 on 2019-02-16. Score: 5 | Accepted answer

I've just seen this right now, I'm Alvaro Rey, the designer of the p3steel v4 mod. The change was made, because with previous versions with the extruder homed, if you go up in the Z axis, the extruder motor could hit the Z axis top plate. So, in order to avoid that, I just changed the design.

The bearing in the z axis is not necessary but some people prefer to use it, in order to avoid wobble in the threaded rod.

Anyways, I designed a printer part to fix the bearing in the Z top plate.

> **Comments:**
> **username_0**: Excellent! Many many thanks for getting back to me, Alvaro and answering this question. And welcome to SE.3DP by the way... it is a real pleasure to have a designer onboard! :-)  BTW, do you have a link to the new printer part, which will fix the bearing?  

---

### Answer by username_0 on 2017-05-28. Score: 3

*This is mere supposition on my part, and not a definitive answer. This was posted prior to Alvaro's answer.*

---

In response, or - rather - with respect to, to the comments under the question by [username_2](https://3dprinting.stackexchange.com/questions/3015/z-axis-top-brackets-of-p3steel-differ-between-v1-x-2-x-and-v4#comment3919_3015) and [Tom](https://3dprinting.stackexchange.com/questions/3015/z-axis-top-brackets-of-p3steel-differ-between-v1-x-2-x-and-v4#comment3916_3015), I have been reading around the topic, and found some interesting articles.

The excerpt below from "[An exploration of the topic](http://www.soliforum.com/topic/2342/backlash-hysterisis-and-wobble-an-exploration-of-the-topic/)", backs up Tom's argument about constraining the rods at both ends being bad practice, and explains why it is so. Whilst acknowledging that a loose, or floating end, is still an issue that needs to be dealt with, the article also states that constraining the end is not really a solution, as it can create more problems elsewhere (I have added the bold highlighting to the relevant text):

> Wobble is pretty simple. Because the lead screw is mounted rigidly to
> the motor, it needs to be perfectly straight and square to the axis
> its trying to move. If it's not, as the motor rotates, that offset will
> be converted into an elliptical motion instead of turning in a perfect
> circle. In big CNC world, as the axis is normally bolted to a
> huge/heavy table which refuses to yield to this movement, it results
> in breaking your motor or motor coupling (weakest point in the
> connection). This is what flex couplings are designed to fix – if you
> can’t guarantee a perfectly square mating between motor and axis, you
> use a coupler with flex so that any movement can be soaked up in
> flexing the coupler and the lead screw/rod moves in a nice circle
> without busting your motor or mounts. This is true when you have a
> good solid supported connection on the lead screw like you’d see on a
> ‘proper’ CNC. **However on the Solidoodle, as the top end of the Z-Axis
> is ‘unsupported’ and its only connection to *anything* is to the table
> via a tiny little nut, its free to ‘flop about in the breeze’ so to
> speak.** Even a small 0.1mm offset from center can result in a much much
> greater ‘wiggle’ at the top of the screw clearly visible to the eye.
> Throw in even a 0.05mm bend in the rod, and it gets further amplified.
>
> Adding better support to the axis, through a taller nut, multiple
> nuts, or **supporting the end, would reduce the influence of this
> wobble. You do however, risk moving it to something else entirely** –
> for example, making the lead screw rigid would mean that the forces
> would end up moving the motor itself, potentially causing fatigue
> issues with how its bolted to the sheet metal case (mine already moves
> a fair bit and its ‘stock’... making the screw rigid would see the
> motor having to absorb all that movement instead of half of it
> disappearing in movement of the screw...). Solving the motor movement
> by securing it ‘better’ to the case would mean that the movement now
> gets soaked up in the motor shaft and bearing, leading to premature
> stepper motor death.

Thus, when first posting this question, I had originally presumed that the earlier versions of the model would be superior: Due to the fact that the earlier versions secured the top of the z-axis screw mechanism, then that would reduce the amount of "flapping about" of the loose end, which in turn would result in *less wobble*. However, I had not bargained for the negative consequences (such as the increased motor wear, mentioned above).

So, is the reason that the top brackets of the z-axis, in the version 4 of the frame, lost their threaded rod/leadscrew top-end constraint, therefore to prevent premature motor wear, at the expense of exhibited wobble?

> **Comments:**
> **username_3**: Nice research and learning.  I have run into this sort of design problem many times where what seems to make sense in concept doesn't work in reality because of imperfections like warp alignment or tolerance.  At the last company I worked at we used a LOT of flexible couplers.  We also used gears that had a floating center to deal with multi-gear couplings where gear alignment could not be assured.  

---

