Sketchup Joint Push Pull !exclusive! Crack

Report: Analysis of "Joint Push Pull" Cracking Issues in SketchUp Date: October 26, 2023 Subject: Technical Analysis of Geometry Fracturing via the Joint Push Pull Plugin 1. Executive Summary This report addresses a common technical issue encountered by SketchUp users known as "Joint Push Pull Cracking." This phenomenon occurs when using the popular extension Joint Push Pull (by Fredo6) to extrude curved or complex surfaces. Instead of a smooth, continuous surface, the resulting geometry displays visible fissures, gaps, or "cracks" along the edges or faces. This report outlines the causes of this issue, distinguishes between visual artifacts and geometry failures, and provides actionable solutions for mitigation. 2. Background: The Joint Push Pull Tool The native "Push/Pull" tool in SketchUp is limited to extruding flat faces along a single axis. The Joint Push Pull plugin expands this functionality, allowing users to extrude faces along their normal vectors (Vector Push Pull), thicken surfaces (Joint Push Pull), or project them. The "crack" issue typically arises when these tools are applied to curved surfaces or UV-mapped geometry . 3. Phenomenon Description Users report two distinct types of "cracks" when using the tool:

Visual Cracking (Texture/UV Mapping Errors): The geometry remains solid, but the applied textures or materials separate at the seams, creating white lines or disjointed patterns. Geometric Cracking (Topology Failure): The actual 3D geometry splits apart. Triangulated faces do not meet at the edges, leaving physical holes in the model.

4. Root Causes A. Segmentation of Curves SketchUp represents curves using a series of straight line segments (facets). When a curved surface is thickened using Joint Push Pull, the plugin calculates the offset for each segment.

The Issue: If the original curve has a low segment count, the offset geometry may not align perfectly with the original surface topology, creating gaps at the corners or "starbursts" at vertices. sketchup joint push pull crack

B. The "Thickening" Logic and Normal Vectors When using the "Joint Push Pull" mode to thicken a surface (creating a shell), the plugin extrudes faces along their normals.

The Issue: On a tightly curved surface, the normals of adjacent faces point in slightly different directions. When extruded, these faces can diverge, leaving a gap (crack) on the sides of the extrusion where the faces fail to meet and weld.

C. Texture Mapping (UV) Limitations This is the most common cause of "visual" cracks. This report outlines the causes of this issue,

The Issue: The plugin must recalculate UV coordinates (texture position) for the new geometry. The algorithm sometimes stretches textures across new triangles or fails to align textures across the seams of the extrusion, resulting in a "cracked" visual appearance even if the model is watertight.

D. Small Scale / Precision Errors If the model is very small or located far from the global origin, SketchUp's internal precision limitations can result in vertices snapping to incorrect coordinates, causing micro-cracks. 5. Solutions and Mitigation Strategies Strategy 1: Adjust Tool Settings Before completing an operation in Joint Push Pull, check the dialog box settings:

Weld Edges: Ensure the option to weld edges is checked where possible, though this can sometimes interfere with textures. Smoothing: Adjust the angle threshold for smoothing edges. Sometimes "cracks" are merely unsmoothed edges that appear harsh. Keep Original Faces: Sometimes keeping the original face helps bridge gaps, though it may require manual cleanup later. The Joint Push Pull plugin expands this functionality,

Strategy 2: Workflow Adjustments (The "Curved Surface" Fix) To avoid geometric cracking on curves:

Increase Segments: Before extruding, increase the number of segments in the arc or circle. Smoother input curves tend to extrude with fewer gaps. Use "Vector Push Pull" instead of "Joint Push Pull": If thickening a curve, try using the Vector Push Pull mode to extrude all faces in a single uniform direction (e.g., straight up) rather than along individual normals. This prevents faces from diverging.