Learn & Design
The oil film on a loaded tooth is usually thinner than the scratch marks. Grade, class, and which pail to buy all come from that.
Where the limits sit depends on who you read: Dudley puts them at λ 0.4 and 1.0, ISO/TR 18792 at 0.7 and 2, NASA at 1 and 4. The picture is the same in every source.
AGMA 925-B22 Annex H; ISO/TR 18792 §3.8; NASA SP-237.
The slow set's film sits inside its own roughness band. That is a λ under 1, and it is why that gearbox micropits. The additive layer, a tenth of a micrometre, is what is actually keeping the steel apart.
Films: AGMA 925-B22 Annex D (0.14–0.30 µm, 309 rpm, ISO VG 460), Gear Solutions 2013-03 (3.0 µm). Roughness: AGMA 925-B22 Table 3. Additive layer: NASA SP-237. Hair and blood cell are general figures, not from a standard.
Design
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Find my oil
Four questions: what it is, how fast, how hot, how cold it starts. ANSI/AGMA 9005-F16 gives the grade and class. The oils that fit are listed, buy button first.
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EHL analysis of a shortlist
Describe the gear pair once. AGMA 925-B22 runs along the whole tooth for every oil you shortlisted: film thickness, lambda, wear, scuffing.
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Pitch line velocity
Faster gears need thinner oils. The AGMA tables are indexed on the pitch line velocity of the slowest stage.
Learn
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How to choose an oil
Four questions. Temperature, speed, load, cold start. Then you have a grade.
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What each search box means
ISO grade, pour point, flash point, AGMA class, base oil, FZG stage. Every box on Find & Buy, in plain English.
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Lubrication system checklist
What to check so the oil, the pump, and the filter keep running.
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Copper corrosion
Sulfur in a lubricant eats copper and bronze. How to spot it and stay away from it.
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Viscosity index
How much an oil thins as it warms. A large part of the price, and of the temperature range it will run.
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Oil terms glossary
The words on a data sheet, each in a sentence or two.
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Viscosities of common fluids
From apple purée to whale oil, with sources.
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Synthetic or conventional for CNC
Synthetics are good. A CNC machine is not a car. Here is why the case is weaker.
Calculate
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Convert ISO, AGMA and SAE
Three systems, one thickness. Convert between them before you pick a pail.
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Viscosity index
From the viscosities at 40 °C and 100 °C. ASTM D2270.
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Pitch line velocity
From rpm and pitch diameter. The number the AGMA viscosity tables are indexed on.
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