Keychains Exposed: A Look Into our Sample Parts

Sample Part Background

Markforged parts often have to be seen to be believed. As much as we would like prospective customers to believe that our parts are as strong as aluminum immediately, most people need to get their hands on a fiber reinforced sample part to actually trust us. Luckily, we've created an easy-to-use sample part request system where any user can request parts that demonstrate the strength of our materials. Our most popular sample part is a two keychain set: the first keychain contains Nylon with no fiber, and the second keychain contains Onyx with Continuous Carbon Fiber reinforcement.

Fulfilling sample part orders is easier said than done. We produce all parts in house with significant production goals: during a satisfactory month, we create and send 3000 sets of two sample keychains. Producing 6000 parts a month isn't impossible; however, it creates some unique design considerations:

1. The parts must be materially efficient: In order to achieve this throughput without diverting too much material from being shipped to customers, the parts must be small and not wasteful of fiber.
2. Prints must never fail: In order to meet demand for these sample parts, we print in builds of 24. This increases our printer uptime while minimizing human labor in our sample part process. However, this means that if any one of the 24 parts fails, it's liable to sabotage the entire build. This is unacceptable, so these parts must be incredibly reliable to print.
3. No post processing: At this volume, parts need to be nearly ready to mail right off the build plate.

Even parts as simple as keychains require some design consideration. In this post, we'll walk you through how we went about designing each of these parts.

Nylon Keychain

The Nylon Only keychains serves as a control. Though Nylon is no longer our base plastic material, this keychain represents the mechanical properties of our most ductile material printed in our base configuration while also being translucent enough for observers to see the internal structure of the part. The resultant part is tough but malleable; anyone can easily bend the part. In base configuration, we print with 50% triangular infill and 100 um layer heights. This infill is clearly visible in this composite image, which shows a backlit Nylon print (left) cut together with a screenshot from our slicing software Eiger. The internal triangular membrane gives the sample part strength while limiting weight and reducing warping.

Even the lettering has to be tested and verified on these parts. Since Nylon is slightly less dimensionally stable than Onyx, we manually altered the font to ensure that each of the letters printed properly.

Onyx-CCF Keychain

In contrast to the Nylon parts, the Onyx and Continuous Carbon Fiber parts are made from our strongest thermoplastic reinforced with our highest quality fiber. However, high quality materials alone do not make a strong part. This introduced our major design tradeoff: how strong could we make the part while still insuring that it was cheap and reliable to produce? In the past, our stronger keychain used as much Continuous Carbon Fiber as possible with Nylon to show the clear difference between the control part and the fiber reinforced part. While this made the parts virtually unbreakable and simpler to understand, it also decreased print reliability enough that build success rate was unacceptable. A redesign was necessary to increase reliability and decrease cost.

A three part cutaway of the Onyx and Carbon Fiber sample part. The exterior of the part (left), the interior cutaway of the part (center), and the eiger slice of the part (right) comprise the image.

To meet our objectives, we made two key changes to our sample parts. First, we changed our thermoplastic from Nylon to Onyx, which prints more reliably with fiber. Second, we changed the fiber fill regime from fully filled to shelled. Shelled parts significantly reduce fiber in parts by removing most of the fiber from the center of the part. By doing this, we significantly reduced fiber while minimizing strength loss. In execution, the part has three fiber regions; full concentric fill on the top and bottom layers of the part and single-ring concentric fill in the middle layers. The composite image above shows an external/internal view of the printed part aligned with the corresponding Eiger part layout.

Our sample parts are critical to the success of our outreach program. By designing them tactically, we can get the most bang for our buck.

Interested in learning more about our software? Get a free trial of Eiger!