The Challenge
AMJ Electrical has been engineering, repairing, and refurbishing industrial switchgear and power equipment since 1996. Their work spans low, medium and high-voltage systems, where component availability directly affects repair and maintenance schedules.
A plastic cover on one of their indicator switches had broken. They contacted Printer Under The Stairs without a CAD file, a drawing, or a technical specification, just the broken part and a requirement to get it replaced.
The original component, shattered and no longer available as a direct replacement.
Our Approach
We took the physical component and worked backwards from it. We measured the part manually and translated those measurements into a precise 3D CAD model in Fusion 360, with no existing file required.
From that model, we could assess the component's fitment requirements, wall thicknesses, and functional geometry before committing to any material or production run.
A practical constraint came up early: we didn't have transparent PETG, the specified final material, in stock. Rather than put the job on hold and wait, we made a deliberate decision to begin prototyping immediately in orange PLA. Within two days, AMJ Electrical had a physical prototype to test against the original mounting. Dimensions were verified, fitment was confirmed, and any refinements were resolved, all before the correct material had even arrived.
When the transparent PETG was delivered, the design was already proven and the final component was completed within a day of the material arriving.
Prototype printed in orange PLA. Fitment and dimensions were verified against the original mounting before the transparent PETG arrived.
Design & Prototyping
During the CAD process, we identified that the original component's circular top geometry wasn't well suited to additive manufacturing. Replicating it exactly would have introduced unnecessary print complexity and potential structural weak points in the finished part.
We discussed the design change with AMJ Electrical and proposed a rectangular top profile as an alternative. Their requirement was straightforward: the internal volume needed to match the original to ensure the indicator switch had the same clearance. We designed the rectangular geometry to meet that specification, verified it in CAD, and confirmed with the customer before proceeding.
The prototype measured 141 × 117 × 32 mm, with a volume of 68,211.6 mm³. It was produced in orange PLA, fitted, and verified before the final material was committed.
The original circular dome profile is highlighted. It was not well suited to additive manufacturing, so this was the feature we redesigned.
The redesigned CAD model in Fusion 360. The rectangular top profile was verified against the original internal volume requirement before prototyping began.
Final Solution
Before committing to the final material, we advised AMJ Electrical that a transparent PETG cover produced by additive manufacturing would not achieve the same optical clarity as the original injection-moulded part. The indicator switch would remain visible through the cover, but the finish would differ. AMJ Electrical confirmed that was acceptable for their application.
With the design verified and expectations aligned, the final component was produced in transparent PETG as specified. Fitment and function were confirmed, and the indicator switch was clearly visible through the cover. AMJ Electrical were satisfied with the result, and no issues have been reported since installation.
The finished component, produced in transparent PETG from a verified design and ready for installation.
Key Outcome
- No CAD file needed: Reverse engineered directly from the physical component using Fusion 360.
- Prototype delivered within two days: Printed in orange PLA while transparent PETG was sourced.
- Final part completed within one day of material arriving: No delays and no rework.
- Design modified in consultation with the customer: The rectangular top profile matched the original internal volume while improving manufacturability.
- Material limitations communicated upfront: The customer made an informed decision before final production.
- Complete process, single point of contact: Physical sample, reverse engineering, CAD, prototype and verified replacement.
Need a Replacement Component Designed and Manufactured?
If you have a plastic component that's broken or no longer available through normal supply channels, contact Printer Under The Stairs to discuss your requirements.
We work with engineers, maintenance managers, and businesses across South Africa on reverse engineering, custom replacement parts, rapid prototyping, and low-volume manufacturing, working directly from a physical sample where no drawings or files exist.
