16.6 Fabrication and Assembly
Fabrication Process
A significant portion of our components are manufactured using laser cutting or 3D printing. These fabrication methods were selected based on the available equipment and resources at Texas InventionWorks, as well as their cost-effectiveness compared to alternative manufacturing processes.
Laser Cuts
The fabrication process involved the heavy use of a laser cutter. The entirety of our base structure, including the back plate, the front plate, and the bottom plate were laser cut from 1/4” wood. This allowed for ease of prototyping, while still providing a rigid structure. Similarly, for the 8-bar mechanism, 1/4” acrylic was used to fabricate each link. Acrylic was chosen to give a cleaner and more professional aesthetic. Additionally, to prevent interference between the links and the bolt heads during motion, 1/4” acrylic spacers were laser cut and added between the links.
During the prototyping process, we observed that the through holes for the bolts to act as joints were oversized, resulting in a loose fit and not a smooth gait profile. To address this issue, a tolerance test plate was laser cut to verify the fitting of the holes with the hardware being used. This was done in 0.1 mm increments for the joint holes, as well as, .25 mm increments for the bearing press fit. After testing the hardware, the link designs and base structure designs were updated on CAD to incorporate more accurate tolerances. Based on the results of the tolerance test, the joint hole diameters were modified and adjusted to 3.9 mm to ensure a proper fit with the M4 bolts.
3D Printing
A significant aspect of our fabrication process involved the use of 3D printing. While inherently more time-consuming than laser cutting, 3D printing allows for the creation of intricate three-dimensional geometries that cannot be achieved with traditional 2D cutting methods. This capability enabled us to design and produce a range of custom components tailored to the system's specific requirements, including electronic mounts, structural brackets, and the base for the paper assembly.
3D Printed Components:
Pulley Spacer
Paper Base
L Brackets
Marker Mount
Arduino Holder
Servo Mount
Paper Holder
Motor Controller Mount
The components were fabricated using both the Bambu Lab printers available at TIW and a personal Ender 3 Neo, chosen for its consistent availability. Larger components that exceeded the Ender 3's build volume—such as the Paper Base—were printed using the Bambu printers. To demonstrate the optimal manufacturing configurations for each part, STL files were prepared and arranged in Cura, taking into account the specific geometry and functional requirements of each component.
While a wide range of print settings were adjusted throughout the process, the key parameters consistently modified to optimize production time without compromising quality included setting the layer height to 0.2 mm and wall thickness to approximately 1.3 mm. An infill density of 15% was selected, as it provided sufficient structural integrity for the relatively simple application of the components. PLA was used as the printing material, with a print speed of 60 mm/s to prioritize rapid fabrication. These settings yielded fast prints with excellent quality, well-suited to the project's functional requirements.
Assembly
The assembly process for the final product required some alterations and took some time to fine tune for the demos. Throughout the assembly process we learned the most effective way to assemble the various systems of our final product, as well as redesign and re-fabricate some of our components.
The first step to assembly was to fully build the base structure. This was done by connecting the three different base panels with the L brackets and paper base using M5 hardware. One critical part of this process was using heat set inserts in the front and back of the paper base to allow for threading into the part directly. Another piece of this process was to press fit the bearings into the back and front plate as this step cannot be done later.
The next step was to assemble the linkage mechanism. This was initially done separately from the base structure. The acrylic links used for the 8-bar mechanism were assembled using M4 bolts and lock nuts in the planned order to eliminate interference.
The third stage of the assembly process was to mount much of the hardware. This included mounting both shafts for the paper-feeder system with the belts and pulleys loosely in place. For the driven side of the paper feeder system, we also assembled and mounted the DC motor to the shaft and the back plate with the shaft coupler and custom motor mount respectively. Once the custom motor mount was on, we used the slots to effectively tension and fasten the DC motor to allow the belts to be tensioned properly. Lastly, we mounted the DC motor for the crank and the Servo motor with its link link attached.
The next step was to attach the 8-bar linkage to the main assembly. This is done through two points, the DC motor via a shaft coupler, and through the slotted arc to the Servo Link
Lastly, we attached the remaining pieces needed to run the mechanism, including the paper flattener, placed at custom height using the slotted holes, the electronics in their respective mounts in the rear of the back plate, and the paper needed to write which will be taped to the belt.
Setbacks and Solutions
Several challenges were identified and addressed during the assembly process. One common issue involved the tolerances of the holes in the 3D-printed components. The through-holes were initially printed undersized, requiring post-processing with a drill to achieve the correct fit. Additionally, integrating the linkage assembly posed difficulties due to tight spacing and the need to accommodate all eight links with minimal play. It was discovered that bolt heads in contact with the back plate generated significant friction, hindering smooth motion. To resolve this, additional spacers were laser cut, and longer bolts with low-profile lock nuts were used to minimize play while maintaining free movement of the mechanism as the marker operated. Additionally, during the wiring process, it became apparent that the initial Arduino controller mount did not accommodate the protruding wires from the L298N Motor Drive Controller. To resolve this, a revised mount specifically designed for the motor drive controller was modeled and 3D printed. The updated design provided adequate clearance for wire routing and ensured a more secure and organized installation. During testing of the encoding process, it was also observed that the paper frequently folded and buckled due to inadequate attachment to the belt and a loose fit within the system. To address this issue, a custom paper holder with precision slots was 3D printed, ensuring a secure and consistent paper feed into the mechanism. Finally, the front and back plates had to be re-fabricated due to miscalculations in belt tension. Upon further inspection, it was noted that timing pulley belts can exhibit 1–3 mm of slack, prompting a redesign with an increased center-to-center shaft distance to maintain appropriate belt tension.
Final Assembly
After all components were fabricated and sourced, and several iterations were made to refine the product, the final system was successfully assembled. Special attention was given to precise alignment of mechanical elements, tidy wiring of electronics, and seamless integration of all motion systems to ensure smooth and reliable operation.