Print-in-Place: The Additive Holy Grail

Print-in-place models are the height of design for 3D printing. These objects incorporate various types of joints, moving parts, and hinges that sometimes unfurl into designs much larger than the printer’s build area. Sharing platforms like Thingiverse and Youmagine now showcase a wide variety of design strategies that embrace and push filament-based desktop 3D printers to their limit.

In the last few years, desktop 3D printers have become increasingly more sophisticated, but not all 3D printers can reproduce the same results. While printer manufacturers put a lot of emphasis on layer resolution in their sales materials, layer height has little to do with successful PIP prints. The overall stability of a printer can have an effect — printers that experience issues with backlash, lack a rigid frame, or require frequent belt tensioning will certainly struggle. But the diversity of the results can be mostly attributed to the software layer. Slicing software does more than merely create the digital instructions for the 3D printer — slicers interpret the design — and each program uses different algorithms.

Slicers have eccentricities. Some are finely tuned to print bridges or easily removable support material. Others have a tendency to produce zitty surfaces, unsightly zippers, or have thin top surfaces. Individual profiles have an even greater effect, multiplying these innate issues.

Many of these aberrations can be attributed to the fact that there is no design standard. Designers individually create PIP designs to work with their printer. Through trial and error, they discover the right tolerances for their own preferred make and model. A designer optimizing for a MakerBot Replicator slicing with MakerWare might develop a different set of personal guidelines than a designer slicing with Cura for an Ultimaker, or a LulzBot TAZ using Slic3r.

Samuel N. Bernier’s articulated robot (used in our testing) is a smart but extreme example of a print-in-place design. The individual parts that make up the limbs have a gap of just over 0.3mm — if a printer can’t accurately print that gap, the joints will be fused together. The arms have overhangs of 65°, which, while in the range of possibility, are a challenge for many machines. Another tough spot are the hinged limbs, which are created with short bridges. It’s not a coincidence that many of these qualities were tested in our review process with individual test probes. If a printer isn’t set up to create flawless bridges, smooth overhangs, or accurate-sized parts, it won’t have a chance on a PIP design like the LeFabShop robot. In our testing, there were few printers that could print this design flawlessly with stock settings.

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If we want a future where 3D-printed products are ubiquitous in our homes, we need great designs. Not just useful replacement parts, but products that have just as much thought and development as the ones we buy off the shelves. The most unique will utilize challenging features, like overhangs and bridges, to push our printers to their limits. Additionally, consumers will expect accurate prints with the push of a button. The current culture of tweaking and calibrating won’t extend past the maker audience.

The growing diversity of both hardware and slicing software runs counter to a goal of universal printability. The solution might be found in design software. Programs like OpenSCAD, Autodesk Inventor, and SolidWorks can create adaptable, parametric designs. By changing values for elements like gap tolerances, designers can create variations to work with multiple printers. Web interfaces like Thingiverse’s Customizer let the consumer easily adapt a design on their own. Unfortunately, not all software or design workflows include parametric features.

Print-in-place designs like the LeFabShop robot test our assumptions. For our test team, the results of the print-in-place test provoked more questions than it answered. What do we expect from a 3D printer? And is there a future where we can expect all 3D printers to perform to the same threshold?

Having Trouble With a Print-in-Place Design?

Here are some things to try:

• Adjust the Z-offset. If the nozzle is too close to the platform on the first layer, the joints will fuse.
• Adjust filament diameter. If your filament is thicker than average, your nozzle could be extruding too much plastic. Measure your filament in several places with calipers and enter the average into your slicer. Or, just bump up the value by a few tenths of a millimeter.
• Create test prints and tune a profile. Design test prints that re-create the bridges or gap tolerances that are causing trouble, and adjust your profile before you tackle a time-consuming print.
• Adjust your extrusion width. If the design has been created with a specific wall thickness, try adjusting your extrusion width to match. Most printers have nozzle sizes between 0.35-0.5mm, and their default extrusion widths are different. On prints with thin walls, this makes an impact.
• Is it parametric? If the designer made the gap tolerances in their design adjustable, adjust to suit.