M3-CRETE Preliminary Motion Checkout

These development notes cover limited current, direction, sensorless-homing, and Z-alignment observations for qualified technical teams. They are not the last step before printing and do not replace a risk assessment, engineered controls, guarding, professional electrical review, commissioning plan, or material-process validation.

Part

4 of 4

Time

Defined by test plan

Audience

Qualified team

Needs

Approved risk controls

Safety first

Software-controlled axes can move unexpectedly. Do not energize or test motion from this page alone. A qualified team must first define exclusion zones, energy isolation, guarding, stop/reset behavior, supervision, and an approved test plan. Keep all material-delivery equipment isolated during preliminary motion work.

What you need

A fully assembled frame (Part 1), wired (Part 2), with software installed and showing Klipper: Ready (Part 3).
A tape measure or calipers to check the corners are level.
A browser open to Mainsail (the printer's dashboard).
Notes from Part 3 on any motor that jogged the wrong direction.

Words to know

Run current: How much electrical current each motor gets. More current = more force, but more heat.
StallGuard: A feature inside the motor driver that senses when a motor pushes against a hard stop ("stalls"). We use it instead of limit switches.
Sensorless homing: Finding the "zero" position by driving an axis until it gently stalls against the frame, using StallGuard.
SGT: The StallGuard sensitivity setting. Higher = less sensitive; lower = more sensitive.
Coplanar / level: All four corners of the gantry sitting at the same height.
Dry run: Moving the printer through its motions with no concrete, to check everything works.

Validate the Z axis

Set the motor current

In Mainsail, open printer.cfg. For each Z driver section ([tmc5160 stepper_z], stepper_z1, z2, z3), find run_current. Start at 1.2 to confirm nothing is wrong, then raise toward 1.5–1.8 so the motors can lift the gantry. Never go above about 2.0 for these 2.8 A motors. Click Save & Restart after changes.

Watch the heat

After a few minutes of holding, a motor should be warm, not too hot to touch. If it is too hot, lower run_current.

Fix any wrong directions

Using your notes from Part 3: if a corner went down when you sent it up, that motor's direction is reversed. In printer.cfg, find that motor's dir_pin and add or remove a ! in front of the pin name. Save & Restart, then re-test with ZJOG MOTOR=n DIST=5 VEL=3. All four should now raise their corner with a positive number.

Tune the stall sensing (this is the careful part)

Each Z motor must reliably feel when it reaches the top of the frame. Tune one driver at a time. First make sure run_current is already at your final value (the sensing changes if you change current later). Then adjust driver_SGT in that driver's section:

If a motor stops too early (before reaching the top): raise driver_SGT by 1 (less sensitive).
If a motor crashes into the top without stopping: lower driver_SGT by 1 (more sensitive).

Change one number, run FIRMWARE_RESTART, and test again. The command ZSTATUS shows live load numbers to help. Repeat until each corner stops cleanly and repeatably at the top.

Home all four corners

In the console, type:

HOME_Z

All four corners drive up. You should see (and hear) four separate gentle stops as each corner meets the top, then a small back-off. Each corner sets its own zero at the point it stalled. This is how the printer levels itself without any probe.

Check the gantry is level

After homing, measure the height of the gantry at each of the four corners (from the build surface, or from the base). They should all match within a couple of millimeters. If one corner is off, re-check that corner's belt tension and re-run the stall tuning for it, then HOME_Z again.

Dry-run the Z motion

Jog the gantry up and down through its travel a few times (small moves first, then larger). Watch and listen for: smooth motion, no grinding, no slipping belts, and no corner lagging behind. The four corners should stay level as they move.

Professional safety-function verification (outside this guide)

Record qualified stop-function verification

Do not design or test an emergency-stop function from this public guide. A qualified controls/electrical professional must define the required stop behavior, energy removal, reset/restart controls, fault response, test method, and acceptance evidence for the actual machine and jurisdiction.

Route the system to a formal readiness review

The observations below can support a review, but they are not a readiness gate. Printing remains blocked until responsible qualified owners approve the complete mechanical, electrical, controls, guarding, pump/pressure, material, facility, operating, and emergency-response scope.

Preliminary motion-check evidence

Record these observations only within an approved test plan. Completion does not authorize material printing.

Motor current set to working value and motors stay only warm, not hot.
All four Z corners jog the correct direction.
Stall sensing tuned — each corner stops cleanly and repeatably at the top.
HOME_Z gives four clean stops and a back-off, every time.
Gantry measures level at all four corners after homing.
Z dry-run is smooth, no slipping or lagging.
Qualified professional's separate stop-function verification record is identified.
Equivalent axis-specific checks are defined for X, Y, and any extruder drive; no axis is inferred from Z results.

If you get stuck

See the per-stage commissioning notes in the firmware repo: M3-CRETE-FIRMWARE.
Ask on M3-CRETE Discussions.
Klipper sensorless-homing reference: klipper3d.org.

Completing these limited observations does not mechanically or electrically validate the machine and does not make it ready to print. Qualified engineering, electrical, controls, guarding, pump/pressure, material, facility, and commissioning reviews remain separate requirements.

M3-CRETE is an experimental open-hardware reference, not a finished certified appliance or construction machine. It is intended for qualified technical users, R&D labs, supervised institutional programs, and experienced builders. Any AC mains wiring, control-box integration, grounding, disconnects, or emergency-stop power work must be done by qualified personnel or a licensed electrician where required. Hardware is published under CERN-OHL-W-2.0; this guide is CC BY 4.0.