Live-Z Calibration

Getting the proper initial spacing between the nozzle and print bed is critical for a successful first layer. A successful first layer is critical for a successful print. Unfortunately, the process can be a bit difficult to master when starting out. These notes contain some images that help illustrate the process.

Note

These notes are based on my experiences with the Prusa i3 Mk3 printer. If you are using a different printer, please verify the hardware details are same. These pages may be a bit rough as I revise them and add new material. Please check back regularly for updates.

When you adjust Live-Z, you’re adding or subtracting a small amount of height from the 0 position of your Z axis to get a good 1st layer. A quick description of the process used for positioning the nozzle during a print is helpful:

  • Startup gcode contains the command to home the printer to establish the X=0, Y=0 & Z=0 position of the extruder.
  • A slicer generated command moves the extruder up to the layer height you specify for your 1st layer [1] and starts extruding.

Unfortunately, the Z=0 position may be sub-optimal for a number of reasons, including:

  • We want a bit more or less squish for some filaments for adhesion purposes.
  • We have a hard time gauging the thickness (but thanks to Jeff Jordan’s amazing “Life Adjust” procedure, this is much easier.)
  • Your print surface may not be perfectly flat.

Live-Z lets us add or subtract a small increment from that 0 position to make these adjustments. On your other printers, you may be doing a manual 1st layer adjustment that does something similar, only more manually.

Slicers do use the 1st height setting and will try to generate gcode to produce layers of that height. Live-Z adjusts the 0 position up or down slightly and independently of your slicer. Ideally, setting a 0.2mm 1st layer height in your slicer will result in a 0.2mm layer height being printed, but it can vary.

Mesh bed leveling further complicates all this (for our benefit) by making yet further adjustments at various spots on the bed to compensate for an uneven print surface.

Preparation

Before you begin, be sure you have properly and thoroughly cleaned the PEI print surface. A poorly cleaned surface will throw your results off, resulting in much wasted time and frustration.

Live-Z calibration using the on-board Prusa routine

Prusa provides a Live-Z calibration option as an on-board menu selection. This procedure prints a series of parallel lines with a small square at the end to allow adjustment of the Live-Z adjustment mid-print.

Note

The Live-Z menu option is only available on the top-level menu during actual printing. If you want to adjust it between prints, scroll down to the Settings menu and you’ll find it there.

First, here’s an overview of the completed print. Note that the thin lines are square and adhere to the bed well.

Successful on-board Live-Z adjustment print

Fig. 47 Successful on-board Live-Z adjustment print

If adjusted correctly, adhesion should be sufficient to allow gentle poking at the extrusions without them coming lose.

Testing adhesion during on-board Live-Z adjustment print

Fig. 48 Testing adhesion during on-board Live-Z adjustment print

Finally, the small square printed at the end of the run should be solid and adhere completely.

Close-up of final on-board Live-Z test

Fig. 49 Close-up of final on-board Live-Z test

While this procedure works, it can be a bit difficult to interpret the results, particularly for newcomers.

Jeff Jordan’s “Life Adjust” alternate Live-Z calibration procedure

Jeff Jordan’s “life-adjust” procedure has reached legendary status over on the Prusa support forums, with well over 50 pages of comments. The brilliance of Jeff’s approach is in it’s simplicity. Rather than printing thin lines and trying to extrapolate what they mean for an entire print, he uses an actual print with lines printed adjacent to each other. A simple 75x75x0.20mm single-layer print is large enough to see how lines interact, yet simple enough to print and adjust quickly.

Here’s a quick look at Jeff’s procedure mid-print.

Jeff Jordan's "Life Adjust" print

Fig. 50 Jeff Jordan’s “Life Adjust” print

Notice the gaps between lines at the lower-right, indicating the nozzle is too high (not negative enough). I’ve made gradual adjustments to lower (make more negative) the nozzle as the print progresses to the left. Notice the gaps between lines and holes at the edges closing up as the interior lines move to the upper left.

Here’s a result showing both extremes, printed from lower-right to top-left.

  • The gaps between lines and holes between the interior and perimeter lines at the bottom-right indicate the nozzle is too high (not negative enough).
  • I lowered the nozzle in large-ish increments (-0.02mm) until results start to even out just before the center of the print.
  • I continued lowering (making more negative) the nozzle until lines began to appear ragged and distort adjacent lines past the center mark, eventually getting so low that the filament is scraped away. Note that while this might appear as gaps between lines, the extrusions are ragged and inconsistent. Compare this to the uniform lines created with the nozzle too high and you’ll quickly be able to judge which way to move the nozzle.
  • Finally, I returned the nozzle to the “good” height with most consistent results at the top-left corner before the print completed.
Extreme "Life Adjust" results

Fig. 51 Extreme “Life Adjust” results

As you get familiar with this procedure, you’ll be able to make adjustments in a few minutes. Mastering Live-Z adjustment will provide the best foundation for the rest of your print.

When to calibrate the Live-Z setting

I suggest re-calibration any time the distance between the nozzle and bed may have changed.

  • When swapping between spring steel print sheets (unless you’ve verified sheets are the same thickness).
  • When replacing the nozzle.

It may also be necessary under other circumstances.

  • When updating firmware. I’ve noticed distances seem to vary between firmware versions.
  • When switching to PETG or other materials that don’t need as much “squish” as PLA for good adhesion. Backing off (making less negative) Live-Z between 0.2 and 0.02mm may help with filament that sticks to the nozzle. Otherwise, I don’t find it necessary to re-calibrate when swapping filament.

Variations on the Live-Z calibration print

As you move on, particularly when you start experimenting with new materials and nozzle sizes, you may need to re-calibrate your Live-Z setting. Here are the prints that I’ve created to calibrate my Live-Z setting.

  1. A basic 75x75x0.20mm single layer square with rectilinear infill. This basically replicates Jeff Jordan’s “life-adjust” print for different filaments and nozzle sizes.

  2. A full-bed grid of small test squares to test leveling across the entire print surface.

    3x3 bed level test print

    Fig. 52 3x3 bed level test print

  3. A large 210x205x0.20mm single layer rectangle that fills the bed with concentric infill. Joan.t on the Prusa forums suggested this method to quickly verify that the layer is consistent over the entire print surface. There’s no need to print the entire thing, just a few loops around the edge of the print surface to verify everything is even and adhereing well.

Models for Live-Z calibration

Here are the STLS for the 75x75, 210x205mm, 3x3 grid, and 20mm cube prints:

Here are my first layer calibration prints as pre-generated gcode for a variety of common nozzle sizes:

I also recommend other prints for additional testing.

  1. Stoempie’s complex 1st layer test also at 0.20mm single layer. If I can print this without problems, I know I’ve got my Live-Z and 1st layer down.
  2. Dezign’s Cali Cat as an overall test that prints much more quickly than the ubiquitous Benchy.

It’s worth spending some time to get familiar with this process and mastering the adjustments. You won’t need to re-calibrate frequently, but it is recommended when switching nozzles or making other hardware adjustments.

Other tips

Over on the Prusa forums, user jbinfl had a great suggestion to mark each sheet with a bit of blue tape designating the current Live-Z offset to facilitate quick changes between prints.

Marking removable print surfaces with current Live-Z setting

Fig. 53 Marking removable print surfaces with current Live-Z setting

Footnotes

[1]The actual height of your first layer is subject to a 0.15mm minimum based on settings in the Prusa firmware. This setting is intended to prevent inadvertently driving the nozzle into the PEI print surface and to provide some distance betwen the nozzle and PEI surface during heating.

Contact and feedback

You can find me on the Prusa support forums or Reddit where I lurk in many of the 3D printing-related subreddits.