TL;DR: 35mm diameter circle with text inside similar to a Benchy

This model provides is a simple but fast and effective first layer calibration method. The model is 0.2mm tall so at layer height of 0.2mm it will print just 1 layer.

Features

• Circles (generally better than squares for calibration since they engage both X and Y axes simultaneously)
• Diameter of 35mm (each circle prints in just ~2 minutes)
• 2 circle options without and with text (Similar to a Benchy's first layer text but much faster to print)

Instructions

Each circle takes about 2 minutes to print, so you can place several circles around the build plate when you are slicing the model.

For Z-offset calibration

Start with a low number of circles. During the print, change the z-offset for each circle and make note the z-offset value that was used for each circle.
After the circles are printed remove from the bed and compare the first layer to find the ideal z-offset.

• The lines that make up the circle should be fused
• No gaps in between lines
• If you try to pull it apart it should hold together like it's a sheet of paper.

I aim for keeping the nozzle the highest possible while still getting the a proper fusing of the layers. You will be getting closer to the right value when you are making z-offset adjustment as small as 0.02mm between circles.

The text is also an indication, it should be clearly readable and well defined.

1st Layer Adhesion

For a more general first layer adhesion test spread circles across a wide range of locations (corners, middle, etc) on the bed and let it print.