Creating a functional and reliable G scale locomotive model is no small feat, especially when it comes to designing complex linkages. This blog post outlines my journey in bringing a model to life using SOLIDWORKS, and the steps I took to ensure precision in every detail.
Building the Core
With the locomotive’s core structure complete, my next task was to develop the intricate network of linkages. Each linkage, while seemingly simple in design, required meticulous attention to ensure they aligned perfectly with the real locomotive, affectionately known as the “Big Boy.” I made sure to consistently reference my sketch picture and other images to maintain authenticity and accuracy.
Aligning the Connecting Rod
Crucial to the locomotive’s movement, the connecting rod required precise engineering. I used M3 washers placed between the connecting rod and three of the four driving wheels, facilitating smoother rotation. To achieve this, I first identified the appropriate hole diameters for the M3 screws, allowing them to secure the plastic and the driving wheels effectively.
Using unit tests, I conducted several small test prints to capture vital features quickly. These tests helped me define the exact hole sizes needed for both M2 and M3 screws on two different printers—the Markforged X7 FDM and the Formlabs Form 4 SLA. After two or three reprints, adjusting dimensions each time, I pinpointed the perfect fit.
Ensuring Proper Assembly
Having modified the hole dimensions in accordance with my tests, I proceeded to attach the connecting rod by adding three concentric mates to the remaining driving wheels. This allowed me to assess the motion for any irregularities, and as the connecting rod settled into place, my model began to more closely resemble its real-world counterpart.
Fine-tuning Clearances
Clearance was critical to avoid interference between mating linkages. I established 0.4 and 0.2 millimeter gaps on either side, ensuring parts could pivot smoothly. Applying this clearance to the crosshead and its guide allowed for seamless operation once the piston was installed. By measuring the stroke using the crank’s distance to the wheel’s center, I could ensure the cylinder was well-aligned with the stroke length.
Reassembly and Adjustments
Throughout this webinar, I reexamine past design decisions to highlight improvements. Aligning the cylinder with the chassis was aided by newly added screw holes, calculated to ensure precision at 191.56 millimeters from the drive wheel’s origin.
The process of adding the rest of the linkages followed a repetitive pattern—establishing concentric and coincident mates. Occasionally, complex scenarios required additional measures, like using a pathmate to guide the radius rod’s die block within a bean-shaped expansion slot, facilitating system testing at various extension positions.
Simplifying the Design
In any assembly, simplicity is key to maintaining stability. For instance, I managed the union link by centering it with the combination lever using a widthmate, avoiding unnecessary mate complexity. This streamlined approach not only prevented SOLIDWORKS from crashing due to excess calculations but expedited the opening and manipulation of assembly components.
Final Steps and Verification
The utilization of the measure tool was invaluable. It prevented external references from causing issues and ensured that everything fit cohesively. By the end of this phase, I had verified the functionality of the major motion systems of the model, confirming that they operated as intended.
More in this Locomotive Webinar Recap
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- Designing a 3D-Printed Steam Engine You Can Power With Compressed Air (Big Boy Inspiration)
- Designing Working Walschaerts Valve Gear in SOLIDWORKS: Validating Link Lengths, Lap & Lead
- Choosing FDM vs SLA for a 3D Printed Model: Stand Design, Part Planning, and Hardware Prep
- Crafting a G-Scale Replica: Designing the Iconic Big Boy Locomotive
- Designing and Testing Linkages in SOLIDWORKS: Clearances, Mates, and 3D-Printed Fit Checks
- Assembling a 3D-Printed Steam Engine Valve Gear: Fits, Clearances, and Iteration
- Why My 3D-Printed Steam Locomotive Kept Stalling (And How Quartering Fixed It)
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