= Gear contact pattern
A <gear contact pattern> is the observed region of tooth-flank contact during a stated mesh test. Its position and extent reveal how the installed tooth surfaces meet. A <gear contact marking test> uses a thin marking layer and controlled rotation to make that region visible; the mounting position, transmission direction and applied <torque> belong in the test description. Manufacturer guidance treats surface-contact checks as evidence about the assembled mesh, including shaft alignment.<Elements of Metric Gear Technology by SDP-SI>[Section19, “Features of Tooth Surface Contact”, and §19.1, “Surface Contact Of Spur And Helical Meshes”, printed T-221]{ref}
A useful bench comparison holds the gear pair and test conditions fixed, records the initial mark, then changes one alignment setting and repeats the test. A mark moving toward one face edge indicates a change in where the flanks meet. This is an observation of contact location, rather than an automatic measurement of operating pressure or a universal diagnosis of the alignment error.
For example, a mark occupying the full20mm <gear effective face width> is compatible with a hypothetical uniform line load $w=50\,\mathrm{N/mm}$, but also with the tilted positive distribution
$$
w(z)=50\left[1+0.6\left(\frac{2z}{20\,\mathrm{mm}}-1\right)\right]\,\mathrm{N/mm},\qquad0\le z\le20\,\mathrm{mm}.
$$
Both integrate to1000N, yet their peak line loads are50 and80N/mm. Merely observing full-width contact cannot choose between those <gear face load distributions>. The <gear face load factor> or local stress needs additional load/deformation information.
Loaded and lightly loaded patterns can also differ because shaft, housing and tooth deformation change the gap. A quantitative loaded assessment may use strain measurements or a validated contact model alongside the pattern; the2006 gear-rating standard explicitly distinguishes comprehensive load assessment from the limited information in a bearing pattern.<ISO 6336-1:2006>[§7.3.1, Method A, assessment using tooth-root strain and limited interpretation of bearing patterns]{ref}
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