<p>I'm going to answer this myself, as I believe I have found the issue. It was purely a mechanical issue.</p>
<p>On this particular model, the extruder motor rides just on top of / above the crossbar that the linear rail is mounted under. The extruder motor was mounted very close to this crossbar, there was barely any clearance between the two. I figure that due to a slight deviation in height or non-squaredness in the ZY-axis, the motor started to heavily rub on the bar toward the left extent of the X-axis. I tested with a piece of paper, which I slid between the motor and the bar. This immediately caused the same &quot;resistance&quot; I was feeling before, but now everywhere along the X-axis.</p>
<p>After re-mounting the extruder motor about 1 mm higher, which the frame already allowed for, there is no longer any improper resistance noticable along any axis:</p>
<p><a href="https://i.sstatic.net/GRuxN.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/GRuxN.jpg" alt="Adequate clearance between motor and bar" /></a></p>

CC BY-SA 4.0
2023-05-01T12:05:05.630Z
2023-05-01T12:05:05.630Z
Floris
<p>I have recently acquired a 'CraftBot XL' 3D printer (sold by CraftUnique), which is a CoreXY 3D printer with linear rails. It is a second-hand purchase and the seller were a company that had several. This particular unit has an issue where sometimes during X-axis movement, the Y-axis would move as well. They replaced the stepper motors, but the problem persisted so they opted to sell the machine.</p>
<p>I have found a possible cause of this issue. When I tried to move the carriage around manually, I noticed a particular heavy resistance / &quot;drag&quot; on approx. 1/3rd to 1/2 of the X-axis motion, toward the left extent of the build space. The remainder of the X axis and the Y and Z-axes are completely free to move as they ought to.</p>
<p>The force required to move the carriage in the problematic part of the X-axis is (subjectively) quite large. Much much larger than any other movement. I believe that during some combined XY-manouevers (diagonal movement), this force is too large, causing the carriage to only move in the Y-axis, resulting in errant behavior (at best: layer shift, at worst: carriage getting stuck and the printer needing to be reset). The behavior arises during homing often, as the home position is in the problematic area. An additional reason that I think the X-axis force is too large is that, when this problem occurs and I ever so slightly help the carriage along the X-axis with my hand, the movement can complete without issue.</p>
<p>Steps I have undertaken to no avail yet:</p>
<ul>
<li>Re-tension belts, make sure they are of roughly equal tension all around</li>
<li>Lubricate all axes with PTFE dry lube spray</li>
<li>Disconnect belts to see if they are causing the issue (they aren't, with belts completely disconnected the problem is unchanged)</li>
</ul>
<p>This is a diagram of the setup:</p>
<p><a href="https://i.sstatic.net/9QiUF.jpg" rel="nofollow noreferrer"><img src="https://i.sstatic.net/9QiUF.jpg" alt="CraftBot XL layout" /></a></p>
<p>What else could be causing this? I don't hear any out of place noises like metal grinding.</p>
<p>The next thing I want to check is the squareness of the gantry. I think I know how to measure it, but I'm not sure how to adjust it if it's off. Any help there?</p>

CC BY-SA 4.0
2023-05-01T06:23:04.520Z
Please remove the tension from the belts or remove them completely; then see if the motion system still has a problematic issue with resistance. You can then exclude the belts from the equation.
0scar
CC BY-SA 4.0
2023-05-01T10:16:14.227Z
I have, and it persisted. Managed to accidentally pull one belt loose from the carriage so I will have to disassemble the whole extruder assembly now. As a bonus that will allow me to judge the linear rail and its carriage separately.
Floris
<linear-motion><belt><corexy><carriage>
CraftBot XL (CoreXY) part of x-axis movement resistance / high force required
Floris
# CraftBot XL (CoreXY) part of x-axis movement resistance / high force required

(Asked by: username_0 on 2023-04-30)

I have recently acquired a 'CraftBot XL' 3D printer (sold by CraftUnique), which is a CoreXY 3D printer with linear rails. It is a second-hand purchase and the seller were a company that had several. This particular unit has an issue where sometimes during X-axis movement, the Y-axis would move as well. They replaced the stepper motors, but the problem persisted so they opted to sell the machine.

I have found a possible cause of this issue. When I tried to move the carriage around manually, I noticed a particular heavy resistance / "drag" on approx. 1/3rd to 1/2 of the X-axis motion, toward the left extent of the build space. The remainder of the X axis and the Y and Z-axes are completely free to move as they ought to.

The force required to move the carriage in the problematic part of the X-axis is (subjectively) quite large. Much much larger than any other movement. I believe that during some combined XY-manouevers (diagonal movement), this force is too large, causing the carriage to only move in the Y-axis, resulting in errant behavior (at best: layer shift, at worst: carriage getting stuck and the printer needing to be reset). The behavior arises during homing often, as the home position is in the problematic area. An additional reason that I think the X-axis force is too large is that, when this problem occurs and I ever so slightly help the carriage along the X-axis with my hand, the movement can complete without issue.

Steps I have undertaken to no avail yet:

* Re-tension belts, make sure they are of roughly equal tension all around
* Lubricate all axes with PTFE dry lube spray
* Disconnect belts to see if they are causing the issue (they aren't, with belts completely disconnected the problem is unchanged)

This is a diagram of the setup:

[![CraftBot XL layout](https://i.sstatic.net/9QiUF.jpg)](https://i.sstatic.net/9QiUF.jpg)

What else could be causing this? I don't hear any out of place noises like metal grinding.

The next thing I want to check is the squareness of the gantry. I think I know how to measure it, but I'm not sure how to adjust it if it's off. Any help there?

**Tags:** linear-motion, belt, corexy, carriage
> **Comments:**
> **username_1**: Please remove the tension from the belts or remove them completely; then see if the motion system still has a problematic issue with resistance. You can then exclude the belts from the equation.  
> **username_0**: I have, and it persisted. Managed to accidentally pull one belt loose from the carriage so I will have to disassemble the whole extruder assembly now. As a bonus that will allow me to judge the linear rail and its carriage separately.  

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## 1 answers

### Answer by username_0 on 2023-05-01. Score: 2 | Accepted answer

I'm going to answer this myself, as I believe I have found the issue. It was purely a mechanical issue.

On this particular model, the extruder motor rides just on top of / above the crossbar that the linear rail is mounted under. The extruder motor was mounted very close to this crossbar, there was barely any clearance between the two. I figure that due to a slight deviation in height or non-squaredness in the ZY-axis, the motor started to heavily rub on the bar toward the left extent of the X-axis. I tested with a piece of paper, which I slid between the motor and the bar. This immediately caused the same "resistance" I was feeling before, but now everywhere along the X-axis.

After re-mounting the extruder motor about 1 mm higher, which the frame already allowed for, there is no longer any improper resistance noticable along any axis:

[![Adequate clearance between motor and bar](https://i.sstatic.net/GRuxN.jpg)](https://i.sstatic.net/GRuxN.jpg)


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