OctagonTestThe current state of the art in consumer home 2D laser printer is that I can expect perfect prints immediately. Take it out of the box, load paper, load toner cartridge, hit print, and out pops a crisp printout.

The current state of the art in consumer home 3D printing is not anywhere near that level of maturity. It took several days of experimentation and many failed prints before I had something that was charitably described as passable.

Example #1: With a laser printer toner cartridge, the user doesn't need to care about the chemical composition of the toner or the physical attributes of the powder within. The 3D printer counterpart is the plastic filament, and today the user has to know a lot. The user can choose the category of plastic (ABS? PLA? etc.) but the precise chemical composition varies from brand to brand. The user has to adjust the printing temperature to match the plastic. The user also has to keep an eye on the filament diameter because it may vary from the nominal quoted dimension, which impacts the volume of filament being fed into the extruder and thus print quality.

Example #2: With a laser printer paper tray, the user doesn't need to care about the texture or the thickness of the paper. The 3D printer counterpart is the print bed, and today the user has to know a lot. The bed has to be level relative to the print head movement plane and also spaced appropriately for that important first layer. If it is a heated bed, the user has to specify the proper temperature for the plastic filament. The surface of the print bed has to strike a balance of adhesion. If the extruded plastic can't adhere well enough, the part would detach mid-print and ruin everything. If it adheres too tightly, the resulting print would be hard to remove from the printer, possibly damaging the printer if you force it.

Because of those and many other variables, it is wise to start with something simple. Something small and fast to print so I can quickly iterate between test prints. Yet complex enough to show if the printer is doing a good job or not hitting the desired dimensions and holding tolerances.

For this, I created a small octagonal solid in Onshape(*). It has straight edges - both aligned with printer axis and not. Two round surfaces, and several horizontal surfaces. One or more features would go bad when the print settings aren't ideal.

Print, fail, adjust, repeat.

(*) available as a public Onshape document. Log in to Onshape and search under public documents for the name "Octagon test piece"