Double Lobe Connecter

 


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CAD Modelling Challenge — Engineering Drawing Breakdown NX Modelling Challenge #18 | NXDATUM 04DTM23 This week's challenge is a universal joint yoke coupling — a symmetrical, multi-lobe rotational component used extensively in power transmission applications. The geometry looks organic and intimidating at first glance, but if you read all three views carefully and plan your feature sequence, it breaks down into a logical and satisfying model. Understanding the Overall Geometry The part consists of two perpendicular oblong lobes intersecting at a central cylindrical boss. Top View: Shows the overall envelope — 260.3mm × 98.8mm with a central Ø40 bore. Front View: Reveals the true depth of the assembly: a total length of 203mm, a central boss width of 70mm, and two flanking collars of 30mm each. Bottom View: This is the most dimensionally rich view. It defines the lobe geometry with an overall span of 260.3mm, inner spacing of 120.2mm and 194mm reference dimensions, lobe width of 50mm, and the critical radii of R27.5 and R17.5 that form the stadium-shaped profile of each lobe. The Lobe Profile — Where Most Students Get Stuck Each lobe is not a simple rectangle or an extruded oval. The profile is a slotted round-end shape — two parallel lines capped with semicircular ends, technically called a stadium or discorectangle profile. In Siemens NX, this is sketched using two tangent arcs and two straight lines, fully constrained with the R27.5 outer and R17.5 inner radii. The two lobes are oriented at 90° to each other — one runs along the X-axis, one along the Y-axis — and they intersect at the central boss. The Ø55 and Ø60 dimensions visible in the bottom view define the boss transition diameters at the lobe junction. Modelling Strategy in Siemens NX Start with the central cylindrical boss — extrude a Ø60 circle to the full 203mm length as your base body. Then sketch the first lobe profile on the top face datum plane and extrude it to a depth of 50mm. Mirror or separately sketch the second lobe perpendicular to the first and extrude identically. Use a Unite operation to merge all bodies into one solid. The Ø40 central through-bore goes in last as a simple hole operation through the boss axis. The 8.6mm groove visible in the bottom view is a narrow channel cut — use a revolved cut or a slot feature on the boss surface. Apply edge blends at all lobe-to-boss junctions to match the isometric view. What This Challenge Tests This task tests multi-body Boolean operations, stadium profile sketching, perpendicular feature orientation, and the ability to extract 3D geometry from three incomplete but complementary views. No single view tells the full story here — you must synthesise all three simultaneously. This is exactly the skill that separates a CAD operator from a CAD engineer. Complete the model in Siemens NX, calculate mass properties, and submit your answer on the NXDATUM validation tool. Created by NXDATUM | Siemens NX CAD Modelling Series | All dimensions in mm | Scale 1:1 | Sheet A3
This platform is curated by 04 DTM 23, a mechanical engineering professional with a background in Tool and Die Making from the Indo-German Tool Room. Driven by a strong passion for advanced 3D modeling, precision engineering, and computer-aided design—specifically utilizing Siemens NX—this blog serves as a dedicated repository for CAD drawings and design practice. The core objective of NXDATUM is to share high-quality, practical design exercises, document technical progression, and build a valuable resource for fellow designers and engineering enthusiasts aiming to refine their CAD proficiency and mechanical design skills.

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