Summary

This is a printable pattern I've been using to check if my print bed and first layer settings are properly set. I find it more useful for filaments that don't like sticking to the bed.

Note: Certain versions of Repetier Host miss some of the little pieces of the circle. To fix this, select "Fix Normals" before slicing. (Checked on v1.0 beta.)

Instructions

The large pattern is used right after you have finished leveling your print bed (or if you think there is something wrong with your print bed). The small pattern is useful if you think a certain part of your print bed is not level. See the instructions for the part that inspired this one, as it is used the same way: http://www.thingiverse.com/thing:111720
Recommended tools:

Tweezers to keep junk from building up on your bed if something isn't set correctly
Something to cancel the print or turn off your printer quickly before things get ugly
Essentially, you do the following:
1. Set your print bed such that it is NOT TOO CLOSE to your hot end. (You don't want your print head crashing in to the table - by experience!)
2. Set your printer to print one of the patterns with NO bed adhesion aids (e.g. no raft, no brim, no supports, no skirt).
3. Be ready to cancel the print, and start printing the pattern.
4. If the pattern does not look like circles or the filament drags when your printer is turning the corner, re-adjust and try printing the pattern again.
  Tweaks:
You can set the diameter with objDiam if you have a bigger or smaller bed
Height should be your first layer height
ringthickness should be big enough that your printer has to do more than one pass for each segment

Circular Printbed Calibration Pattern