<p>Your assessment is correct, after probing before printing it deploys several times, after that it is stowed till the end of the print unless you call for deployment.</p>

<hr>

<p>The probe is used by G-code command <code>G29</code>; <a href="https://reprap.org/wiki/G-code#G29:_Detailed_Z-Probe" rel="nofollow noreferrer">this command</a> is used by a few printer firmwares to perform a bed probing sequence where, depending on the options set in the firmware, the surface of the bed is scanned by deploying the sensor at various locations. From these measurements, the firmware will determine the shape or tilt of the bed to compensate for deviations in Z height during the first couple of layers or millimeters of the print. Basically, it will keep your nozzle (approximately, as it is based on calculations) at the same distance all over the bed area.</p>

<p>Once the print starts after the <code>G29</code> command, the sensor is stowed until the next print calls the <code>G29</code> command (or <code>M280</code> with arguments to deploy on Marlin/Duet/Smoothieware, or <code>M340</code> on Repetier firmware).</p>

CC BY-SA 4.0
2019-07-31T22:04:32.093Z
2019-08-31T06:25:36.273Z
2019-08-31T06:25:36.273Z
0scar
<p>I was looking at a BLTouch probe, and saw the recent question about one with intermittent failure. That was kind of scary, where I might spend a bunch of money for something that would make my printer harder to use, rather than easier.</p>

<p>But I was curious. I don't have any personal experience using these, but it seems like the probe would only be used during an initial level and when homing the Z axis. Thus, as long as the probe works most of the time, and failure to home properly doesn't damage your nozzle or print bed, maybe this kind of thing isn't too bad.</p>

<p>Is this assessment of how the probe functions (that it's not really used after the start of a print) accurate?</p>

<p>In the spirit of stack exchange, I'm not interested in the subjective issue of nozzle or print bed damage; I'm only asking about the objective assessment of how a probe is used by the printer.</p>

CC BY-SA 4.0
2019-08-01T15:18:30.927Z
If by failing you meant this question: https://3dprinting.stackexchange.com/q/10345/16827, I believe that was due to user error and I am having no issues with the probe currently and it works as intended.
Blubberguy22
<z-probe><bltouch>
Is a BLTouch probe used during a print after the first layer?
Joel Coehoorn
# Is a BLTouch probe used during a print after the first layer?

(Asked by: username_0 on 2019-07-31)

I was looking at a BLTouch probe, and saw the recent question about one with intermittent failure. That was kind of scary, where I might spend a bunch of money for something that would make my printer harder to use, rather than easier.

But I was curious. I don't have any personal experience using these, but it seems like the probe would only be used during an initial level and when homing the Z axis. Thus, as long as the probe works most of the time, and failure to home properly doesn't damage your nozzle or print bed, maybe this kind of thing isn't too bad.

Is this assessment of how the probe functions (that it's not really used after the start of a print) accurate?

In the spirit of stack exchange, I'm not interested in the subjective issue of nozzle or print bed damage; I'm only asking about the objective assessment of how a probe is used by the printer.

**Tags:** z-probe, bltouch

> **Comments:**
> **username_1**: If by failing you meant this question: https://3dprinting.stackexchange.com/q/10345/16827, I believe that was due to user error and I am having no issues with the probe currently and it works as intended.  

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## 1 answers

### Answer by username_2 on 2019-07-31. Score: 1 | Accepted answer

Your assessment is correct, after probing before printing it deploys several times, after that it is stowed till the end of the print unless you call for deployment.

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The probe is used by G-code command `G29`; [this command](https://reprap.org/wiki/G-code#G29:_Detailed_Z-Probe) is used by a few printer firmwares to perform a bed probing sequence where, depending on the options set in the firmware, the surface of the bed is scanned by deploying the sensor at various locations. From these measurements, the firmware will determine the shape or tilt of the bed to compensate for deviations in Z height during the first couple of layers or millimeters of the print. Basically, it will keep your nozzle (approximately, as it is based on calculations) at the same distance all over the bed area.

Once the print starts after the `G29` command, the sensor is stowed until the next print calls the `G29` command (or `M280` with arguments to deploy on Marlin/Duet/Smoothieware, or `M340` on Repetier firmware).


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