Sun Gear Tooth Count and Planetary Geometry
For a standard unshifted planetary stage, the sun, planet and ring tooth counts are linked by the center-distance relationship.
Basic relationship
For a standard system, the internal ring tooth count is related to the sun and planet counts by zc = za + 2zb. Profile-shifted designs require a more complete center-distance check.
Planet spacing
The number of planet gears and their equal spacing also impose assembly conditions; tooth counts cannot be chosen independently.
RFQ implication
Provide all three tooth counts and the number of planets when replacing a component from an existing stage.
Use the drawing as the controlled record
A technical guide can explain which variables matter, but the final sun gear must be approved from the actual drawing and operating requirement.
If a value is missing, identify it for confirmation instead of copying a dimension or material from a different supplier or gear family.
RFQ checklist
Send the sun gear drawing or measured tooth data, mating planet/ring information, interface dimensions, material/process requirements, duty, quantity and destination.
Deeper buyer guidance
Tooth counts determine pitch diameters and influence the center-distance and assembly relationships across the entire stage.
For new designs, use the complete planetary geometry and functional datums before deciding the process route. For replacement work, use photos and equipment references for context but let measured tooth and interface data control the new part.
What to control on the RFQ or drawing
| Punkt | What to define |
|---|---|
| Planetary mesh | Sun, planet and ring tooth data plus planet count when known. |
| Center interface | Bore, key, spline or shaft features with functional datums. |
| Operating duty | Rated/peak torque, speed, reversals/shock, life and environment. |
| Material/process | Controlled material, heat treatment, finish and coating requirements. |
| Acceptance | Gear/runout/dimensional checks and required documentation. |
Frequently asked questions
Can a visual match confirm interchangeability?
No. Similar outside dimensions can hide different pitch systems, pressure angles, profile shift or interface fits.
Should mating gear data be included?
Yes whenever available, because planetary geometry is easier to verify as a system.
What if a value is unknown?
Mark it as open and provide the available sample, mating component or application data rather than guessing.
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