To calibrate your extruder, it is necessary to mark the filament with a tick mark before it goes into the extruder, typically 100 mm away from the entry port of the extruder. Then one "extrudes a fixed length of filament (ie: 100 mm) and then measures how accurate the extruder performed. That is, did it extrude too little (less than 100 mm) or too much (more than 100 mm). With the "actually extruded" measurement in hand, one can perform a few simple calculations to determine the proper extruder calibration value.

THE PROBLEM - I always find that holding a ruler or micrometer up to the filament to place a 100mm tick-mark on the filament with a Sharpie is difficult at best. It always seems that I need three or more hands to keep ruler, filament, and sharpie stable and accurate. Furthermore, I have found it helpful to actually place three marks on the filament; one at 90 mm, one at 100 mm , and one 110 mm away from the entry to the extruder. With three marks I can easily take a measurement reading even if the extruder has gone too far and gobbled up the 100 mm mark. Seeing the 90mm mark just tells me I'm extruding way too little filament.

To address this problem, I have developed this calibration tool to help out. It is simply a special purpose ruler that you 'stand-up' right on top of your extruder filament entry port. By placing the filament into the filament 'guide slot", one can easily use a marker pen to make tick marks on the filament at each of the three "cross-slots" near the top of the tool. This will locate marks at 90, 100, and 110 mm away from the extruder entry point. Once the filament is marked, you can easily perform the 100 mm extrusion to check or recalibrate your extruder.

This guide prints quickly using PLA, PETG, or any other filament you have on hand.
After you finish the print, just measure the distance from the start of the ruler to each of the cross-slots to ensure things scaled properly. Then you're ready to give it a try.

This is definitely not a break-through design that is destine to save mankind, but just a handy gizmo that I thought I'd share. Take care and stay safe!