Peter Kaltenbach
When we purchased our first 3D printer over a decade ago, it changed our approach to prototyping. The real time feedback the printer gave allowed us to evaluate things we wouldn’t have otherwise tested until much later in the design process. Over the years, our printer farm has grown, and the quality of the prints, materials, slicers, and print volume has only gotten better.
As awesome a tool as the printers are, every so often I see someone printing a part that could have been made faster, better, cheaper, or all of the above, using another approach. It’s always a good reminder that there are lots of other ways to prototype, and as critical as we need to be of our designs, it’s equally important to think critically about how we mock-up and test them.
There are endless ways to simulate and test a design without loading up the printers, but we are going to categorize our non-printed prototypes into three general categories: off the shelf, two dimensional, and virtual.
Off the Shelf
The other day we needed to drill a pattern of holes, in line, on eight and sixteen inch centers. There are those among us who would have jumped into CAD, modeled a rectangular block with hole guides, and thrown it on a printer. Some of the less patient in our office would have held a tape measure up, and aimed vaguely with a hand drill. In the end, taking a quick glance around the shop yielded a sheet of pegboard, with, surprise, holes on one inch centers. A scrap of pegboard allowed us to mark, and drill patterns of holes at 4, 8, 16 inch centers on both the horizontal and vertical axis.
There are times when a product is simply so large that 3D printing would take prohibitively long or the requirements do not align with the materials and processes available. When we designed the Lettuce Grow Farmstand, we needed to test our water delivery through live grow tests. The Farmstand has a 20 gallon water tank, which presented both challenges. We needed a stand-in that was properly sized, watertight, and could support our grow modules. Since the specific geometry of the tank wouldn’t impact our test, we purchased a standard, 20 gallon tank from US Plastic, printed an adapter which was affixed to the top, and were able to focus our printing time and budget on the parts that mattered.
(Early Lettuce Grow Farmstand tank prototypes. In addition to an off the shelf tank, we used potted plant liners to evaluate the overall size before printing the upper sections.)
Two Dimensional
Our Glowforge laser cutter opened our world to fast two-dimensional prototyping, but even before we owned a laser cutter, prototyping in flat form has been one of our go to ways to test an idea. In the most basic form, a full scale paper print cut out can serve to provide a sense of size, act as a template, or form a paper-doll mockup of a linkage. Purchasing a craft cutter like the Cricket saved our fingers from hours with the x-acto, and expanded our material options and precision greatly. A standard paper printer, craft cutter, and laser cutter, along with plenty of x-acto blades and jigsaw are key prototyping tools in our shop. Where we used to wait days if not weeks for foam and rubber gasket prototypes, we can fabricate our own on either the laser or Cricket, test a range of materials and sizes and dial in the fit the same day.
Sometimes getting a sense of scale is the main reason for building a prototype. When this is the case, a 2D cutout can often do the trick, and if some sense of the third dimension is needed, two or more of these cutouts can be combined together. After validating the function for the Lettuce Grow Farmstand using off-the-shelf tanks, we needed to check the proportions, and let the designer and client get a sense of the look and feel of a full system. A set of foamcore cutouts, assembled together allowed us to get a full scale view assembly, see the relative proportion, human interaction, and make some design tweaks before ordering an expensive machined mockup.
Virtual
Sometimes a design is so physically large, there is no practical way to get a sense of scale with anything less than a full size prototype. In other cases, the goal of a prototype is to understand how it interacts with its environment, but the feedback is needed before a physical mockup is feasible. Virtual prototypes can be a great bridge between CAD and physical parts. While considered more of a designer’s domain, we engineers often make use of rendering software. In Keyshot we can illustrate how a product will appear in realistic materials, the effects of lighting, and present an assembly in a convincing way, where the viewer can get a better sense of how it looks, works, or how to interact with it. When more dynamic experience is needed, augmented reality can be a great option. Keyshot and other programs can export 3D renderings in formats that the average iPad can open and place into the environment. Walking around a prototype, or simply visualizing it from various angles in your space is now relatively straight forward.
We spend a lot of time thinking, and talking about prototyping. That’s because it’s integral to our work and process. Once a tool becomes ubiquitous and comfortable (like 3D printers have become), it’s easy to fall into the trap of using that tool exclusively. Take a step back, look around and think about all the other methods available to make a prototype, your project schedule and budget may thank you, your coworkers will appreciate the free cycles on the printers, and you will add to your engineering toolbox.
