Keyhole E-steps Calibration Tool

This tool allows you to calibrate your 3D printer's e-steps. It keeps the filament straight and also guides the depth gauge of a set of calipers, allowing consistent measurements. I've never liked the sharpie and a ruler method as it leaves me feeling like I could've used a third hand. “Keyhole” refers to the cross-section of the guide channel. Two gcode files are included to perform the extrusions required.

No supports are required when printing and PLA works fine. 

Depending on the dimensions of your caliper's depth gauge, you may need to remodel the tool, so a step version is included to facilitate this.

Repeatability:

To check the repeatability, I used this tool five times to measure my printer's extrusion amount and the small sample size with a 95% confidence level yields an expected variation of +/- 0.05%.
 

Instructions:

Note I've only tested this with a direct drive printer, but a bowden setup should be very similar, except with the filament being pushed through the tool rather than pulled.

1) Insert the filament you'll use to calibrate your e-steps into the round section of the guide channel. This is the side of the tool that is chamfered. Pull it all the way through and leave a few inches of excess.

2) Load the filament into your 3D printer.

3) Press the tool against the extruder and hold the filament at the top straight, but do not pull on it. Then snip the filament off at the top of the tool a square as you can.

4) Print the “esteps 1 - 20 mm.gcode” file. This will extrude 20 mm of filament. The temperature is set hot (10 C above usual PLA temperature, so adjust it in the file if your filament differs) and the speed is slow to minimize impact on the extruder feed rate.

Once the gcode has finished extruding, insert the depth gauge of your calipers into the top slot of the keyhole tool and lower it until it contact the filament. Be sure to have the depth gauge inserted so it contacts the filament properly, as they often have a cutout on one side). The filament is on the side of the channel that is rounded, which is the side that is also chamfered (see step 1). Do not press with force. Zero the calipers and then remove them.

5) Now print the “esteps 2 - 100 mm.gcode” file. This will extrude 100 mm of filament, again slowly and at high temperature.

Once the printer has finished extruding, insert the depth gauge again as in step 4 until it touches the filament at its new location and record the value. This is how much the printer actually extruded.
 

What this design retains is the concept of a channel guiding the filament to keep it straight, while having a slot in it. I remodeled it from scratch, but felt I should attribute the original creator as it inspired my design, when I noticed my caliper's depth gauge could fit in the slot easily. Thank you!