V-Core: the bed mesh looks tilted or twisted and the first layer is uneven
Guide based on the manufacturer's official documentation; usi3d has not yet verified it on a machine.
Technology: FDM · Brand: RatRig · Symptoms: Unlevel or warped bed, Uneven first layer (thin and thick areas), Does not stick to the bed · Updated on 9 October 2026
Symptom
On a Rat Rig V-Core, the bed mesh shown in Mainsail looks tilted or twisted instead of flat, and the first layer is squished more in some areas than in others or does not stick well.
Likely causes, from most to least likely
- The frame is out of square: according to Rat Rig, a twisted mesh is a symptom of a non-squared frame.
- On the V-Core 4, the X gantry is twisted: the two XY joiners do not rest against their front Y-axis bumpers at the same time.
- The Z offset was set cold: the nozzle and bed expand when heated and the offset changes with temperature.
- The first layer is too thin for a large machine: Rat Rig recommends at least 0.25 mm.
- The PEI surface is dirty, and the adhesion problem gets mistaken for a wrong Z offset.
Checks to tell which one it is
- View the mesh in Mainsail with the scale gradient enabled and the Z max scale slider all the way up: if it is flat, the problem is the Z offset or the surface; if it is tilted or twisted, check the frame.
- On the V-Core 4, with the X gantry at the front, check that both XY joiners touch their Y-axis bumpers at the same time, with no gap on either side.
- Check at what temperature you calibrated the Z offset.
- Check the first layer height in your slicer profile.
Before you start
Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.
Step-by-step fix
Z-Tilt and a new mesh
First run the Z-Tilt calibration from the RatOS dashboard, then home, and create a new mesh from the calibration section.
Check: The mesh comes out flat.
If that does not fix it: If it is twisted, fix the frame squareness (next step).
Square the frame
With the machine off, follow the figure in the V-Core 3.1 commissioning guide: adjust only points A and B, because C and D are very hard to adjust (peak at C, fix it at B; peak at D, at A). Loosen the screws of that extrusion, tap it gently on top for a peak (or push it upwards for a dip), tighten and mesh again. Make very small adjustments each time.
Check: Each new mesh is closer to flat.
If that does not fix it: Take your time and check the frame carefully before moving on to the first layer.
Align the X gantry (V-Core 4)
On the 4.0, loosen the M4x6 set screw and slowly adjust the M4x20 tensioning screw on each side (tightening pulls the joiner towards the front bumper) until the gantry sits flush on both front plates with no play; then move the toolhead so the belts do not touch the pulley flanges and tighten the pulley set screws. On the 4.1, its build guide loosens the M5 screws under each joiner, rests both joiners on the Y-axis bumpers and tightens them again in order.
Check: Squeezing each XY joiner against its front plate shows no play on either side.
If that does not fix it: Mesh again; if it is still twisted, check the frame again.
Set the Z offset hot
Heat the nozzle to 230 °C and the bed to 80 °C and wait 10 to 15 minutes (values from the V-Core 3.1 guide). Run Z-Tilt, home, put a sheet of paper under the nozzle and send PROBE_CALIBRATE; lower the nozzle in small steps until the paper moves with resistance, neither loose nor stuck, press ACCEPT and then SAVE_CONFIG. Careful: the nozzle and bed are hot.
Check: The paper drags evenly and Klipper restarts with the new value.
If that does not fix it: Fine-tune the offset during the first layer (next step).
Fine-tune with the first layer test
Print Rat Rig's first layer test with a first layer of at least 0.25 mm and a first layer line width of 130 %, as the guide recommends. While it prints, adjust the Z offset in small steps until the squish is right, press SAVE and, when it finishes, SAVE_CONFIG.
Check: The first layer is even across the whole bed.
If that does not fix it: Clean the print surface (next step).
Clean the PEI surface
Wash the sheet with warm water and soap and dry it with a microfibre cloth (Rat Rig advises against kitchen cloths and paper towels). Day to day, wipe it with 70 to 91 % isopropyl alcohol.
Check: Parts stick evenly across the surface.
If that does not fix it: If the mesh is flat, the offset is right and it still fails, ask Rat Rig support for help with photos of the mesh and the first layer.
Prevention
- On the V-Core 3.1, check that the mesh is flat before sticking on the heater pad, which cannot be removed or repositioned afterwards.
- Always calibrate the Z offset with the machine at printing temperature.
- Keep the PEI clean with isopropyl alcohol.
Still not fixed?
Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.
Printers it applies to
The RatRig V-Core family: V-Core 3.1 and V-Core 4.1.
Official sources
This guide summarises the official documentation linked here:
- V-Core 3.1 Commissioning Guide · Rat Rig
- V-Core 4.0 - Gantry Alignment · Rat Rig
- V-Core 4.1 - X-Axis and Belt Installation · Rat Rig
This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.