<p>All the Prusa-based designs I've seen have only one end stop.  While you are correct that it's theoretically possible for the two Z-drives to get out of sync, it's very unlikely in practice (barring serious friction, binding, etc.).  </p>

<p>But even if it happens, remember that the endstop microswitch is only used to keep the extruder assembly from crashing into the print bed.  The stepper motors do not have shaft encoders, or any other position sensing mech, so if they were to get out of sync, there'd be no way to know this.  </p>

<p>The reason there's provision for a stop mount, on both sides, is simply to make the physical parts of the frame the same.  </p>

<p>That said, it is important to check the extruder support assembly to verify it's level as you build the printer - "level" meaning both supports are the same distance from the screw-drive shaft couplers.</p>

CC BY-SA 3.0
2016-11-18T15:36:27.520Z
2017-06-10T04:15:39.373Z
2017-06-10T04:15:39.373Z
Carl Witthoft
<p>My newly built ANET A8 has dual Z-axis steppers (and two threaded rods), but only an end-stop on one side. Am I missing some detail for ensuring proper alignment of Z as the extruder moves along the Z-axis? I notice there are mountings for a 2nd end-stop, but nowhere to attach this on the MCU board.</p>

<p>It seems that even after I check the leveling, there is scope for the two steppers to get out-of sync once the servos are turned off - is this something to worry about? I realise that during a print run, if I start with good alignment this should stay good.</p>

<p>I've only managed about 10 minutes of printing so far, and everything seems to work, but this is my first printer, so obviously I might have missed a vital step in the instructions quite easily.</p>

<prusa-i3><z-axis>
Alignment of dual Z-axis steppers
Sean Houlihane
# Alignment of dual Z-axis steppers

(Asked by: username_0 on 2016-11-18)

My newly built ANET A8 has dual Z-axis steppers (and two threaded rods), but only an end-stop on one side. Am I missing some detail for ensuring proper alignment of Z as the extruder moves along the Z-axis? I notice there are mountings for a 2nd end-stop, but nowhere to attach this on the MCU board.

It seems that even after I check the leveling, there is scope for the two steppers to get out-of sync once the servos are turned off - is this something to worry about? I realise that during a print run, if I start with good alignment this should stay good.

I've only managed about 10 minutes of printing so far, and everything seems to work, but this is my first printer, so obviously I might have missed a vital step in the instructions quite easily.

**Tags:** prusa-i3, z-axis

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## 1 answers

### Answer by username_1 on 2016-11-18. Score: 6 | Accepted answer

All the Prusa-based designs I've seen have only one end stop. While you are correct that it's theoretically possible for the two Z-drives to get out of sync, it's very unlikely in practice (barring serious friction, binding, etc.).

But even if it happens, remember that the endstop microswitch is only used to keep the extruder assembly from crashing into the print bed. The stepper motors do not have shaft encoders, or any other position sensing mech, so if they were to get out of sync, there'd be no way to know this.

The reason there's provision for a stop mount, on both sides, is simply to make the physical parts of the frame the same.

That said, it is important to check the extruder support assembly to verify it's level as you build the printer - "level" meaning both supports are the same distance from the screw-drive shaft couplers.


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