Direct Drive E-Steps Calibration Tool for Calipers

Note that these parts were made for the VINCA 6" Digital Caliper, DCLA-0605, so they likely won't fit other brands or models without modification. Step versions are included to facilitate this.

These models are designed to allow calipers to be used to calibrate the e-steps of your direct drive 3D printer. I've never liked the sharpie and a ruler method and it leaves me feeling like I could've used a third hand.

No supports are required when printing and PLA works fine. 

Repeatability:

To check the repeatability, I used this tool five times to measure my printer's extrusion amount and here is the data I recorded:

The small sample size with a 95% confidence level yields an expected variation of +/- 0.09%.
 

Instructions:

1) After printing the parts, insert an M-3 nut and bolt into the clamp part of the upper piece, along with a washer as shown.

2) Attach them to your calipers as shown in this image. Side-to-side placement isn't critical, but do make sure they are snug and try to align the top and bottom parts.

3) Zero your calipers with the jaws as closed as they'll go, then open them to about 125 mm (no need to be exact) and lock them. Now feed the filament you'll be measuring with through the top v-notch and the bottom guide hole and then load it into your extruder, supporting the weight of the calipers. Place the bottom guide against the top of the extruder and lightly take slack out of the filament (no need to pull hard at this stage). Now tighten the filament clamp, being sure it grips securely. Zero the calipers again (not strictly required but I find it's easier), and unlock the calipers.



4) Push down on the bottom jaw part while pulling upwards on the filament above the calipers firmly to remove any slack. Note that you should not push on the top jaw as it will stress the calipers and the clamp's grip on the filament. Instead, pull the filament. Record the caliper reading.

It is tempting to try to zero the calipers while taking out the slack, but I found this a lot trickier to do (at least with only two hands) than recording a start and end value.

5) Now raise the lower jaw of the calipers and support the weight of the tool while you run the included gcode. The goal here is to not make the extruder have to pull the top jaw down, minimizing resistance. This is probably being overly cautious, but being easy to do I chose to anyway.

The gcode will extrude 100 mm of filament. The temperature is set hot (10 C above the usual extrusion temperature) and the speed is slow to minimize impact on the extruder feed rate. 

6) Once the gcode has finished extruding, lower the bottom caliper jaw again until it touches the top of the extruder. Now measure again, pushing down on the bottom jaw and pulling firmly up on the filament above the calipers as in step 4, again being sure not to push on the top caliper jaw directly. Record this measurement.

To get the distance extruded, subtract the second measurement from the first (the two minus signs will cancel out).

For example, if the calipers read 0.26 mm when first measured in step 4, and -100.94 mm in step 6, we'd get 0.26 mm - -100.94 mm = 101.2 mm. That is 1.2% higher than the 100 mm we would expect if the e-steps were calibrated properly.