First layer bad in one corner? Bed levelling vs Z-offset explained

Your first layer sticks perfectly in one corner, and peels up in another. Today: bed levelling and Z-offset. Two different fixes, and how to tell which one you need.

Same printer, same file. In one corner the lines look perfect. In another, there are gaps and it peels. In a third, the nozzle scrapes. So you turn every knob, and it gets worse.

In Start Here number one, we learned to read a first layer. Now let's fix a bad one. The secret: there are two jobs under that nozzle, and they're easy to mix up.

Job one: levelling. The bed has to run parallel to the path of the nozzle. Tilt it, and the gap changes as the nozzle moves. Squashed on one side, gaps on the other. Level it, and the gap evens out.

Job two: the Z-offset. A level bed can still have the wrong gap, everywhere. The Z-offset is one number that moves the nozzle up or down over the whole bed at once.

Pause and guess. Your first layer is perfect in the middle, with gaps in one corner. What do you fix? A: the Z-offset. B: the bed levelling. Or C: the print speed?

It's B, the levelling. One bad corner means the gap isn't even. Change the Z-offset, and you fix that corner but squash the rest.

Why so fussy? The first layer is usually 0.2 millimeters thick. A sheet of printer paper is about 0.1. So one sheet of paper is half your first layer.

You saw these three in Start Here number one. Here's the math behind them. The slicer pushes out the same plastic per line, whatever the gap. Nozzle 0.05 too high? That plastic fills a taller space, so the line shrinks to roughly 0.34 millimeters wide. Gaps. 0.05 too low? It wants to be 0.56 wide, a third too much. Ridges.

So test the whole bed. This episode's free model: five pads, one layer thick. Four in the corners, one in the middle. The dots tell you which corner is which. It's 160 millimeters across, so it fits most beds, and it's about a gram of plastic. Bigger bed? Scale it in X and Y, never Z, so the pads sit near your corners.

Print it, and watch the lines go down. Then peel off the pads and lay them side by side. All five the same? Your bed is level. One different? That corner is off.

First: many newer printers probe the bed and correct small tilts on their own. Some set the Z-offset too. If yours does, run that calibration first.

Knobs under your bed? Heat the bed first, because a hot bed can change shape a little. Slide a sheet of paper under the nozzle at each corner, and turn the knob until the paper just drags. Go round twice: one corner can shift the others. Still one bad spot? The plate itself may not be flat. Auto bed mesh can make up for that; knobs can't.

Is the first layer off everywhere, the same way? Then it's the Z-offset. Many printers let you change it on the screen while the first layer prints. Go in tiny steps: 0.05 millimeters is already a quarter of a layer.

Gaps between the lines? Bring the nozzle closer. Ridges, or plastic barely coming out? Move it up. Some slicers have a Z offset field too. Negative usually means closer, but check your manual.

In short: one corner off? Level the bed. Off everywhere? Change the Z-offset. Go in small steps, and print the test again.

The levelling test is free to download. Print it, and tell me in the comments: which corner of your bed was off? Next time in Start Here: reading the slicer preview, so you catch problems before you print. Subscribe so you don't miss it. I'm Spoolbert, see you in the next one.