Troubleshooting bed adhesion and first-layer problems¶
Bed adhesion and first-layer calibration are the first great mysteries new users encounter with the any 3D printer. They are two different topics, but both must work well together for consistent good printing results. Problems with bed adhesion or first-layer adjustment will likely cause a variety of problems.
Prints pop off mid-print, resulting in a tangled mess of filament spaghetti.
Walls and vertical surfaces are uneven as the print wobbles on upper layers.
The print warps away from the print surface in corners, resulting in wobbly bottom surfaces and uneven vertical surfaces.
Lower surfaces are compressed, resulting in the “elephant’s foot” effect.
Bottom surfaces appear uneven or stringy.
Simply put, if your print doesn’t adhere well to the bed on the first layer, your print is very likely to fail. They first layer is key to good bed adhesion.
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.
Causes of poor bed adhesion and first-layer problems¶
Assuming you have no fundamentsl hardware problems, there are two challenges you must master to get consistently good prints:
A dirty print surface. The Prusa PEI print surfaces work amazingly well, but must be kept clean. Very clean. Once your printer is initially calibrated, most print shifting and adhesion issues can be resolved with regular cleaning. It doesn’t take more than an errant fingerprint or a spot of hand lotion on the filament to foul the PEI print surface.
Poor “Live-Z” initial nozzle height adjustment. If you’ve never been able to get a good first layer, have changed nozzles or done hardware adjustments, your “Live-Z” (the initial gap between the nozzle and print bed) needs to be calibrated.
Too high and molten filament won’t “squish” sufficiently to get a good grip on the surface, resulting in stringy, loose 1st layers. This leads to shifts and the resulting “spaghetti” results when a part pops loose and gets dragged around by the nozzle.
Too low and the nozzle digs into the freshly-laid down filament, causing distorted surfaces and nozzle snags. In additoin to a stringy mess, this can result in the dreaded “Blob of Doom” that encases the nozzle, hotend, fan and other parts in a moltend mass of melted filament.
Let’s take a look at these two topics in more detail.
Understanding the PEI sheet and adhesion¶
The first thing to understand is that PEI is very different than most other print surfaces. Do some searching on the internet and you’ll find hundreds of articles on using glue stick, hair spray, glass sheets, blue painter’s tape, sugar syrup, and a host of other “solutions” for improving bed adhesion. Ignore these. They are written for printers that require manual bed leveling, ship with warped parts, lack removable print surfaces, use rudimentary print surfaces, or suffer other shortcomings.
The one and only trick to PEI is to keep it clean. How do to this depends on just how contaminated the surface is. The biggest enemy is grease, and the biggest source of that grease is your fingers as you handle the sheet. No matter how you clean your sheet, try to avoid touching the PEI surface as much as possible. The PEI sheet used on the Mk3 is a wonder. When properly cleaned and cared for, printed parts will stick firmly enough to get a solid print, yet pop off easily when cooled.
There’s no magic to getting good 1st layer results and excellent bed adhesion with this surface. The only requirement is proper maintainenance of the PEI surface and first layer (Live-Z) calibration to get the best results.
Refer to the print bed cleaning procedure for details on properly cleaning and maintaining the PEI print surface.
When you adjust Live-Z, you’re increasing or decreasing small amounts of distance of the initial gap between the nozzle and the print surface at the start of a print. Live-Z adjusts the 0 (zero) nozzle position. All nozzle heights are calculated based on this 0 level. Getting your Live-Z set properly is essential to get a good 1st layer.
Too low and the filament has to be squeezed out between the nozzle and print surface. Extrusions may be distorted and jagged. Adjacent lines will be crooked. Filament may be pushed so deeply into the print surface that it’s difficult if not impossible to remove.
Too high and the filament is not squished onto the print surface. The extruded filament has a circular cross section with minimal contact with the print surface, leading to parts warping or coming loose mid-print. This can result in the frustrating “spaghetti monster” of filament extruded in air, or the potentially damaging “blog of doom” formed when loose heated filament latches onto and begins buiding up on the nozzle and hotend.
The goal of Live-Z is to find that “just right” Goldilocks height where filament will adhere solidly but not distort, providing an optimal foundation for our prints.
Unfortunatley, the on-board 1st layer calibration routine is difficult to use and understand. It works and can be helpful for the practiced eye to make quick adjustments, but for anybody starting out, it’s difficult to identify good results.
It is important to complete the on-board Live-Z calibration at least once to set a flag in non-volatile storage indicating Live-Z is set. Failure to do so can result in a floating Live-Z height between prints.
To understand the importance of the Live-Z adjustment, consider what happens at the start of every print:
Startup g-code homes the printer to establish the X=0, Y=0 & Z=0 position of the extruder.
G-code that your slicer generated moves the extruder up to the layer height you specify for your 1st layer and starts extruding.
The Z=0 position may be sub-optimal for a number of reasons:
We want a bit more or less squish with some filaments for adhesion purposes.
Your print surface may not be perfectly flat.
We may have mis-calibrated thanks to the simplistic on-board Live-Z adjustment routine.
Live-Z lets us add or subtract a small increment from that 0 position to correct for these problems
Understanding Mesh Bed leveling¶
In theory, once you’ve got your print surface clean and Live-Z adjustment calibrated, printing should be straightforward. Unfortunately, physics come into play on the relatively large surface of our print bed. The surface is large enough that physical warping can occur due to repeated heat and cooling cycles. Removal and replacement of the spring steel sheet may result in surface variations between prints. “Bed warping” is the bane of 3D printing, causing 1st layer variations that can result in inconsistencies and adhesion problems on larger prints. Fortunately, the Prusa Mk3 provides an automated mesh bed leveling feature that can measure small variations over the entire print surface and compensate for these at print time. This is another of the top “quality of life” features that distinguishes Prusa printers from low-cost competitors.
To do this, the printer moves to the Z=0 position, then successively moves over the entire print surface probing the actual distance to the bed at each position using the PINDA probe attached to the extruder mechanism. You can select between 3x3 and 7x7 (recommended) mesh bed leveling and the number of times to probe at each position in your printer settings menu. This procedure has been optimized to the point that there’s very little difference in the time it takes for a basic 3x3 level with 3 probes and 7x7 level with 5 probes (roughly 45 seconds), so using the maximum resolution is recommended.
Once mesh bed leveling is completed at the start of a print, the Mk3 will vary the nozzle height during the print to compensate for small print surface variations. Unless your bed is severely warped, this should provide a consistent first layer over the entire surface.
A few notes:
On other printers, 1st layer calibration is a manual process that involves adjusting screws and using a sheet of paper to gauge the distance between the nozzle and bed. Disregard bed leveling or 1st layer calibration measures for other printers. The Prusa i3 Mk3 handles this work for us.
It’s very common to see heavy sheets of glass used on other printers. These are usually used to correct for severely warped print beds. A large slab of glass adds tremendous weight to the Y carriage, often contributing to ringing print defects. Such measures are unnecessary on Prusa printers.
Mesh bed leveling techniques are also referred to as Auto Bed Leveling (ABL) on many other printers, and may require adding hardware and making firmware modifications to add this capability to other printers. Again, these capabilities are included as standard on the Prusa printers.
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. We may wind up squishing the 1st layer for better adhesion or backing off a bit to avoid dragging the nozzle.
Refer to the Live Z calibration procedure for details on adjusting your Live-Z 1st layer nozzle settings.
Testing bed adhesion¶
If you’ve not seen the Prusa PEI surface in action, here’s a quick test showing just how good the Prusa PEI flex surface is. Let’s start with matteeee’s bed adhesion test.
This is an ideal model for testing the limits of adhesion.
The print is attached to the bed with only a small surface area. No brim, raft, or other adhesion aids should be used.
The severe, unsupported, tall print angle applies downward force to pull poorly-attached surfaces away from the print surface.
The tall print will come under maximum pressure and bumping from the nozzle as it moves throughout the print.
Here’s the same model ready for slicing in PrusaSlicer.
Here are the results of slicing, verifying the lack of bridge, raft, supports or infill.
Here’s the model printed on a 9 month old, heavily used but cleaned PEI surface using PLA with 0.20mm layer heights with a 0.40mm nozzle.
Finally, here’s the process involved in removing the print without damaging the PEI surface or operator injury.
The same prints that are used for Live-Z calibration can be useful for testing bed adhesion. Here are the STLs for the 75x75, 210x205mm, 3x3 grid, and 20mm cube prints:
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Last updated on 20200130