Bed Leveling, First Layer Thickness, and Z-Offset
Three of the most popular topics in 3D printing are bed leveling, first layer thickness, and Z-offset—and for good reason. These areas are the foundation for a successful print and without any one of them, your print will be set up for failure. We will go through each of the three topics to help you avoid common misconceptions we often hear from beginners and even advanced users.
-Read our article on "The Perfect First Layer"
-Basic Understanding of Bed Leveling
The most important concept to understand with bed leveling using the “Four Corner Paper Method” is that it is doing more than just leveling your bed; it is also setting your Z0 (commonly referred to as Z offset). The goal is to not only level your bed with respect to your nozzle, but also tell your machine where the top of your build surface is. This is important because your first layer height should be measured from the top of your build surface. Most users understand the idea of leveling but many struggle to understand setting Z0.
A question we see on nearly every forum is something along the lines of this:
“What is the ideal distance between the nozzle and the bed when leveling”
“I own feeler gauges, which thickness should I use”
The answer to the first question is 0, and the answer to the second question is 0. Of course, there is no such thing as a 0mm feeler gauge so a better answer would be: level your bed with the thinnest paper (or feeler gauge) you have. The closer to zero, the better.
It is important to understand that if you level your bed with a sheet of paper that has a thickness of 0.1mm and then tell your slicer to make your first layer height 0.24mm, you will actually end up with a first-layer thickness of around 0.34mm. Why? Because you lied to your machine and told it the build plate was 0.1mm higher than it actually is.
So why do we use paper to level at all? If you have good eyesight, you don’t have to. We normally place a flashlight behind our machine and adjust our leveling knobs until the nozzle just makes contact with the build plate. This is a true Z0 and the machine now knows where the build surface really is. If you don’t have perfect vision and can’t use this method, try to use whatever the thinnest material you have available (receipt paper works well). While 0.1mm paper might not seem like a big discrepancy, when you are talking about such a small layer height, you could cause your machine to be off by as much as 50% by using standard copier paper.
First Layer Thickness and Z-Offset
Certain filament types need a different first layer height AKA “squish.” Please note this should not be done using your Z-offset. You also should not try to achieve this by using different thicknesses of paper to level. We hear time and time again people suggest that for PETG, you should use an index card to level because this will give you the thicker first layer PETG requires--this is incorrect. After you level using the backlight method or paper method (using the thinnest you have available), this should never change. All you did was tell the machine where the top of the build surface is. If you print PETG, simply increase your first layer height to something like 0.28mm in your slicer settings and this will give you the desired thicker first layer. When you go back to something like PLA, change your first layer back and you're good to go; no machine adjustment required. So to summarize: Your Z-offset should never change after you get it set unless something on your machine changes.
Leveling your bed with a sheet of paper is actually telling your machine that the top of your bed is higher than it really is. This will cause your first layer height to be different than what you set in your slicer. To prevent this, use the backlight method to level or use the thinnest paper you have available. If you need different amounts of “squish” for different filament types, control this using your first layer height setting in your slicer and not by leveling with different thicknesses of paper.
Bonus: Peel the skirt off your build plate, which should be one layer thick, and measure it with digital calipers. This should match the first layer height set in your slicer. If it doesn’t, you should adjust your Z-offset in your slicer or on your machine (this should be a one time task). Repeat this process until your slicer settings and what you measure match.