Print came loose mid-print: why parts pop off the bed

This guide is for anyone who has come back to a nest of filament where a print used to be, or found a part lying loose on the plate. It covers how to tell detachment from layer shifting, the five usual causes, what each slicer offers to anchor a part, how plate cleaning fits in, and what Bambu Lab's spaghetti detection can and can't do. If the first layer never sticks at all, start with our first layer adhesion guide.

Came loose, or shifted?

Look at the bottom of the failed print before changing anything.

Bambu Lab describes a bed adhesion failure as the entire model shifting, sliding, or popping "fully off the bed partway through the print." Prusa describes layer shifting as layers moving "from their intended positions," usually because of abnormal X or Y axis movement, and says it's most often caused by wrong belt tension or pulleys that aren't secure. In that case the part stays put and the toolhead loses its place. See our layer shifting guide for that.

The two can overlap. Bambu says that if a model warps, the nozzle "may strike the warped section, leading to step loss or displacement of the model." Its collapse category also includes a tall, thin model knocked over by the nozzle, which can look like shifted layers on top of a sound base. If the base is still firmly attached, treat it as a shift. If it lifted or moved, treat it as detachment.

When it fails, Bambu says, "the nozzle keeps extruding filament into the air," leaving a tangle it calls spaghetti that wastes filament, can clog the nozzle and makes the printer hard to clean.

Cause 1: The first layer never gripped properly

A weak first layer can hold for a while and then let go once forces build up. Polymaker says that if the nozzle is too far from the plate, "your part won't stick and will be knocked off mid print," whatever other adhesion methods you use.

Bambu's quick fixes for a model that "pops off mid-print" are to rerun automatic bed leveling, check Z offset ("first layer must be squished"), and confirm the right plate type is selected in Bambu Studio. Its common causes for this failure are:

• Fingerprints or grease on the plate. Bambu calls skin oils "the #1 cause."
• The wrong plate type in the slicer. Bambu's example is slicing for the Cool Plate (35 °C for PLA) but printing on the Textured PEI Plate, which needs 55 to 65 °C for PLA. It adds that the Textured PEI Plate lowers the nozzle by 0.04 mm automatically during leveling, so choosing the wrong plate type also leaves the first layer too high.
• Z offset too high, so the nozzle is too far from the bed on the first layer.

Speed and cooling matter too. Bambu recommends an initial layer speed of 30 mm/s or less and an initial layer infill speed of 60 mm/s or less. Polymaker suggests a first layer no faster than 30 to 45 mm/s with the part cooling fan off. Simplify3D says that if a layer "seems to stick initially, but later separates from the print bed as it cools," temperature and cooling settings may be to blame, and suggests disabling the cooling fan for the first few layers.

For checking the nozzle height and bed across the plate, see our bed leveling guide.

Cause 2: Warping lifted the corners

Bambu describes corners that "slowly lift during printing." When the lift gets higher than the nozzle gap, "the nozzle knocks the model loose or pushes it off the heatbed." It says this is common with high-shrinkage filaments such as ABS, ASA, PC, PA and PA-CF, and ranks shrinkage risk from highest to lowest as PC, PA-CF, PA, ABS, ASA, PETG, then PLA.

Prusa says warping is mostly seen with high-temperature materials such as PC Blend, ASA or ABS, and is "usually a result of a sudden temperature difference" between the nozzle and the surrounding air. Its fixes include a draft shield, a brim, slower printing, and keeping the printer away from open windows and air conditioning. Polymaker says you will need a brim on any material with high shrinkage and internal stress, such as ABS.

Our warping guide goes through these checks one at a time.

Cause 3: The nozzle hit the print

Bambu lists "nozzle scraping" as its own failure: "You hear a 'clunk' sound during printing. After that, the whole model is knocked loose." It gives two causes:

• Not enough Z hop, so the nozzle scrapes the part while traveling. In Bambu Studio, it suggests changing the Z hop type to Normal in the printer's extruder settings.
• An unstable part, with a small contact area or a high center of gravity, which even normal nozzle contact can tip over.

Infill can build its own obstacles. Bambu says Grid and Triangle infill patterns cross within a single layer, "building a small bump that the nozzle clips on the next pass." It suggests slowing infill or switching to Line, Rectilinear, Gyroid or Concentric.

Curling edges give the nozzle something to hit too. Polymaker separates curling of individual layers from warping off the plate, and says it most often happens when printing PLA without enough part cooling. It recommends 100% fan for PLA after the first layer and warns against printing PLA in a fully enclosed chamber. Bambu adds that a model with steep overhangs can collapse without supports, and "the nozzle then hits the collapsed area and causes a chain failure." It suggests enabling supports in Bambu Studio when a model has overhangs at an angle greater than 45°. Our overhangs and bridging guide covers this.

Cause 4: Tall parts with small footprints

A tall, narrow part has little to hold onto and a lot of leverage. Bambu's brim guide says "a taller part with a smaller footprint usually needs a wider brim to prevent itself from being toppled by the printer's nozzle," and is also "easily detached from the heat bed as the part is cooling down."

What makers suggest:

• Slow down. For tall, thin models that collapse, Bambu suggests cutting print speed and acceleration by 20 to 30%, enabling supports, and considering laying the model flat.
• Add a brim. Prusa recommends a brim for "tall objects with a small base" and for "multiple small objects at once."
• Stabilize it with supports. Bambu suggests paint-on supports to add stabilizing structures to branching or long, thin shapes. PrusaSlicer's "Enforce support for the first" setting generates support for a set number of layers from the bottom, which Prusa says is useful for objects "having a very thin or poor footprint on the build plate."

Supports can come loose too. Polymaker says tree supports are "more prone to being knocked off the build plate during printing, especially if the base is narrow or the print is tall and wobbly," while normal supports "are less likely to detach from the build plate mid-print."

Cause 5: A dirty or worn plate

Adhesion fades as a plate picks up oils and wear.

• Bambu Lab: clean the plate with warm water, dish soap and a new, grease-free sponge, then hold it by the edges. Bambu says dust, grease or fingerprints on the plate are the most common cause of first-layer spaghetti.
• Prusa: wipe with 90%+ isopropyl alcohol. Prusa says smooth PEI "can lose its adhesive powers after a couple of hundred hours." When models come loose regularly, it suggests wiping the smooth PEI sheet with acetone, no more than about once a month, and never on its textured or satin sheets.
• Polymaker: says PEI "really loses adhesion fast if it isn't cleaned" and suggests cleaning with isopropyl alcohol about every 5 prints. Don't use acetone on PEI, Polymaker says, because it can destroy the plate.

Cleaning advice is plate-specific, and makers disagree on acetone. Follow the maker of the plate you own. Our guide to a print stuck to the bed has a full cleaning comparison.

Which brims, mouse ears and rafts does each slicer offer?

All the main slicers can enlarge or anchor the footprint. Settings and defaults differ, so check your own slicer.

A few notes from the makers:

• Mouse ears without a slicer feature. Prusa suggests that if a brim isn't enough, add "a small geometry (like a tiny cylinder)" to the problem area, only a few layers tall so it's easy to remove.
• Rafts. Bambu suggests a raft for warp-prone materials such as ABS. Polymaker says it isn't a big fan of rafts unless you're printing a lot of small parts, where a raft keeps them from being knocked over.
• Not every print needs a brim. Polymaker doesn't recommend one for PLA or other non-warping materials, because brims "can be a nuisance to remove." It suggests 10 to 30 brim lines when one is needed.

Spaghetti detection (Bambu Lab X1 series)

Bambu Lab documents Spaghetti Detection for its X1 series, which uses the chamber camera and the printer's on-board processor to spot failures and pause the print. Bambu's article says:

• Turn it on and set sensitivity. Enable it in Print Options and pick low, medium or high. Bambu suggests low if you'll be away for a long time, so small defects pause the print less often.
• Keep the chamber light on. The detector needs good lighting. If you switch the light off manually, it won't come back on by itself.
• It works in LAN Only mode. Processing is done locally. Bambu recommends updating firmware regularly, because a printer that isn't connected to the cloud, and isn't in its user improvement program, relies only on the detection information in its latest installed firmware.
• It isn't foolproof. Bambu warns of false positives and cases where it may not work as expected, "especially when using black/dark filament."

Alongside detection, Bambu recommends always washing the plate with warm water and detergent and making sure slicer settings are correct. If only some parts on a full plate fail, Bambu suggests its Skip Objects feature to cancel the failed parts and finish the rest. Check your own printer's documentation before assuming it has detection, because the article we reviewed covers the X1 series.

What should you do after a failure?

Before the next attempt:

1. Check under the plate. Bambu and Prusa both say to make sure no filament or debris is between the plate and the bed, and that the plate sits flat.
2. Wash or wipe the plate the way its maker recommends.
3. Rerun bed leveling or calibration, especially after moving the printer, maintenance or a firmware update, as Bambu suggests.
4. Confirm the plate type in your slicer matches the plate on the printer.
5. Add a brim, mouse ears or a raft if the part is tall, small, or in a warp-prone material.
6. Watch the first few layers of the next print. Prusa notes a skirt lets you check the first layer before the model starts.

A sensible order

1. Look at the failed part: lifted and loose, or still stuck with shifted layers?
2. Clean the plate and check the slicer's plate type.
3. Rerun bed leveling and check the first layer is squished, not floating.
4. Slow the first layer and keep the part fan off for it.
5. For warping materials, add a brim and control drafts and room temperature.
6. For tall, thin parts, add a brim or mouse ears, slow down, and consider stabilizing supports or reorienting.
7. If you hear a clunk before failures, look at Z hop and infill pattern.

Build plates: what to check before you buy ↗