This multipurpose calibration cube checks dimensions, accuracy and fit. I use it all the time.

According to the creator of this test model: “ The base is a 20 mm x 20 mm x 10 mm solid block. In the middle of the block is a 10 mm diameter cylindrical hole that goes straight through. That’s where the two pegs come in. The cylinder with the number 3 on top is 9.7 mm in diameter. And the cylinder with the number 2 on top is 9.8 mm in diameter. Ideally, both should fit into that 10 mm diameter hole.

On top of the block, there is a 4.5 mm thin wall frame. This thin wall continues up for 10 mm. The entire height of the block is 20 mm high.”

This multipurpose calibration cube prints quickly (a few minutes) and lets me test dimensions of the cube and cylinders with my digital calipers. The Marlin firmware configuration file for my printer has a very important line:

#define DEFAULT_AXIS_STEPS_PER_UNIT {AXIS_STEPS_PER_UNIT_X, AXIS_STEPS_PER_UNIT_Y, AXIS_STEPS_PER_UNIT_Z, AXIS_STEPS_PER_UNIT_E}

With this line, you tell your firmware how many steps the stepper motor needs to turn for the print head to travel one millimeter, or for the extruder to push out one millimeter of filament. This needs to be set for your particular printer. Without it, the firmware does not know how to command the stepper motors for the X, Y and Z axis or the extruder. A detailed explanation of how this work is given here. Once you know the dimensions and gear ratio of your printer’s parts, there is also an online calculator you can use to come up with the correct values.

Generally, these are “set and forget” configurations. For the extruder, you can also make small adjustments in your printing software using the “extrusion multiplier”. You can modify this above or below 100% if you are getting too much or too little filament out the nozzle.

Multipurpose Calibration Cube – Fitting Parts into Holes

Even after you calibrate the stepper motors to your mechanics, you might still have problems getting parts or hardware to fit into holes. This can be addressed in several ways.

• If you are modeling your own parts in a CAD program, make a decision about how much clearance you want to leave between the inner diameter of the plastic hole, and the outer diameter of the part or hardware that you want to insert in the hole. I generally leave a clearance of 0.5 to 1.0 millimeter, although I experimented successfully with clearances down to 0.6 millimeter.
• Consider your slicer settings (such as layer height and extrusion width) and the characteristics of your filament. These can effect how well your outer and inner diameters provide the right dimensions.

Obviously, if you can snugly fit both the 9.7 and 9.8 millimeter diameter cylinders into the 10 millimeter hole provided by this multipurpose calibration cube, you can be confident that you are doing something right.