Advanced 3D Printer Calibration System

thingiverse

Updated with a new version of the expansion calibrator (optimized to use less filament and print faster) and spreadsheet (scroll to end to see the new validity factor calculation). This is a set of calibration objects for advanced 3D printer calibration of extruder flow, extruder and axis step values, and axis scaling to compensate for shrinkage of the print when it cools. This process assumes you already have your best nozzle temperature and print speed figured out. There are already numerous options for doing that out there, and I didn't see much value in reinventing the wheel. If you have multiple printers, save a separate copy of the spreadsheet for each printer, so that the proper step values will be calculated for each printer. Doing so will make it more likely a single profile will work with multiple printers. Tab 1: Start by printing the flow calibrator with a skirt or brim, and measure the skirt or brim every 3-5 millimeters. Enter the measurements in tab 1, along with your current printer Z offset, to calculate the correct Z offset. Hint: the spreadsheet will generate the proper M851 and M500 gcode commands to update and save the new Z offset value. Tab 2: Measure the thickness of the vertical wall at 2-3mm intervals all the way arount the calibrator. Enter the measurements and your current slicer flow rate and expansion adjustment values to calculate the correct flow rate. With the correct flow rate and Z offset set, you will not need to have a separate flow setting for your first layer. If your bed is prepared properly and at the correct temperature, you will have good bed adhesion and layer bonding using the calculated settings for all layers. Tab 3: The key component is the expansion calibrator cube. Instead of being the standard 20mm XYZ cube, it is 50mm, with a number of 5mm cubes attached to it. It also has a 30mm vertical hole, and four 6mm vertical holes. After printing the cube, take measurements as shown in the photos, and enter them in the Excel spreadsheet. For the X and Y large measurements, take 6 measurements along the edge of each face of the main cube as shown, for a total of 24 measurements for each axis. For the X and Y small measurements, measure each of the 5mm cubes twice along the axis, once parallel to the layers and once perpendicular to the layers as shown. Measure the Z large as shown, from the top of the top sub-cubes to the top of each bottom sub-cube as shown. Do this twice, for a total of 32 measurements. Measure the Z small as shown, taking two measurements between each gap between sub-cubes, for a total of 24 measurements. Take 12 measurements of each end of the 30mm hole at 15 degree intervals, for a total of 24 measurements. Take 4 measurements of each end of the 6mm holes at 45 degree intervals, for a total of 32 measurements. Hint: The recommended number of measurements is highlighted green in each column. DO NOT use the bottom surface of the expansion calibrator cube for any measurement! Use the reset buttons to clear measurements between iterations of the process. Once you change parameters and re-print, old measurements are invalid. By comparing measurements of the large cube and the smaller cubes on the XYZ axes, and the size difference between the large and small holes, dimensional errors due to print shrinkage when cooling and incorrect axis step values can be separated from the line width error, and the correct scale and expansion factors can be calculated to ensure dimensional accuracy on both large and small print features and holes. Tab 4: The flow and scaling factors can be used to adjust the extruder and axis step/mm values, so that axis scale and extruder flow factors are normalized to 100%. The printer can be optimized to a single filament if desired, or to a set of filaments (with separate scaling and flow factors for each filament averaging 100%). Enter the type of filament you're calibrating in tab 4, then Copy/Paste Value the flow rate from tab 2 and scale factors from tab 3 to their respective green columns in tab 4. Use a separate row for each filament you want included in the normalization. The spreadsheet will calculate the best overall step values for your extruder and each axis, along with the adjusted flow and scaling parameters you'll need for each filament after you change steps to the recommended values. Flow Rate Lookup: If using Octoprint, the spreadsheet also has a lookup table to convert measured filament diameter to a flow rate adjustment, which is useful for compensating for variations in filament diameter. Print that tab,and when printing a critical part, measure the filament diameter going into the printer periodically. Use the lookup table to find the appropriate flow rate modifier for the current diameter, and update as needed. Validity Explained: The validity factor calculated in tabs 1, 2, and 3 estimates the probability that changing the associated setting will improve the print by comparing the size of the proposed change to the standard deviation of the measurements and the number of measurements. Validity is scored 0-100%, and the higher the score, the greater the likelihood that the calculated change will improve the accuracy of your prints. The amount of calculated adjustment is multiplied by the validity factor, so if a calculated adjustment is essentially statistical noise, validity will be close to zero, and the adjustment amount will be zeroed as well. But if the adjustment is statistically valid, validity will be close to 100% and the full adjustment will be made. There are several reasons the validity factor can be below 50%. You may have a data entry error, too few measurements to be confident in the accuracy of the calculations, or the adjustment may be too small to be meaningful. If validity is below 50%, you should recheck your data, and avoid make any setting changes until you get a validity score >50%. If validity is less than 50% because the adjustment is small, then you have optimized that setting, and further iterations of the test are probably not useful.