Most people are familiar with the Z offset. It’s the distance, in the vertical plane, between our nozzle and the print bed. It’s responsible for achieving the correct filament compression(known as ‘squish’) and proper adhesion for the first layer. The X and Y offsets tend to be overlooked because their effect is not seen as dramatically. These offsets refer to the distance the probe tip is from the nozzle tip along the horizontal planes. Prints will still stick to the bed, and may still look good, even when the X and Y offsets aren’t entirely accurate. Eventually though these inaccuracies will affect your prints, and not in a positive way. Whether it’s a wider than normal print, a taller than normal print, or a print that spans the length of several days - like a helmet that can print for 48 hours plus - the effect of incorrect X and Y offsets will eventually become apparent, resulting in the loss of a print and precious filament. Even more insidious is that it can have you scratching your head at the cause of failure, and lead you to fix problems that don't exist.

Measuring The Offsets

  Even knowing how important these offsets are, actually measuring them can still be a bit tricky. We need to measure along two planes, the X and the Y. We can't simply measure a straight line from nozzle to probe, we need to measure straight out in one direction and then 90 degrees in the other. There's many different ways to do this. I've tried using a ruler, measuring with a set of calipers, drawing dots along my bed surface… the list goes on. The problem with those methods is they can be difficult to get accurate. The best and simplest way I've found to measure these offsets is to use the on board the screen coordinates that your printer provides, and a post it note.

• Home the printer and write down the coordinates

  On your printer screen there will be the current coordinates for all the axes (X, Y, and Z). After homing the printer, write down the current X and Y coordinates on a sheet of paper, we’ll call these STARTING.

• Get a post it note, make a dot, line it up with the bed probe, and stick it to the bed

  Grab a post it note (or similar sticky paper- painter’s tape, etc) and using a pen place a dot somewhere on the note. Then stick the post-it to the print bed making sure to line up the dot just underneath the probe tip. You’ll need to be examining the dot and the probe tip from all sides to make sure it is lined up. (also if you’re using a PEI bed you may want to remove it before this process so you don’t get your fingerprints all over it.)

• Move your nozzle over to the dot, just as the probe was and record the coordinates

  Now using your screen (or web page if using Octoprint of Fluidd) move your nozzle until it is directly over the dot on the post-it note. If you overshoot the dot don’t worry, all that matters is when you end this process the nozzle is lined up with the dot just as the probe tip was. When you’re satisfied you’ve gotten it right, look at the coordinates on your screen and record this new set of X and Y coordinates. We'll call these numbers ENDING

• Subtract the STARTING coordinates from the ENDING coordinates

  Take your ENDING coordinates and subtract your STARTING coordinates. If you get a negative number that’s fine as the offsets may be negative. For the X coordinate if the probe is to the left of the nozzle(based on the front of the printer) it will be a negative number. For the Y if the probe is in front of the nozzle (based on the front of the printer) it will be a negative number.

You now have accurate offsets for your ABL probe!