Splined Shafts specifications: what the numbers mean
Splined Shafts is a shaft with a series of ridges that transmit torque to a mating hub. It is used for drive applications where a keyway would be too weak or would need an accurate fit. This entry explains what it is, what the numbers on a data sheet mean, and what to put on a drawing.
It is written from the point of view of the buyer and the drawing office: the values that are realistic in production, the ones that cost money, and the way the result is verified. Where an industry sets the requirement, rail is used as the example: documented welds, coatings and fire smoke toxicity compliance.
What the numbers mean
A data sheet for Splined Shafts is only useful if the numbers are read against the job. The usual entries, and what they tell you, are these.
- Common forms – involute, straight sided, serration.
- Fit classes – sliding to permanent.
- Typical tolerance – ±0.01 mm on the major and minor diameter.
- Surface finish – Ra 1.6 µm on the flanks.
- Measurement – over pins or with a spline gauge.
- Manufacture – hobbing, shaping, rolling or wire EDM.
Comparing offers
Two suppliers can quote the same common forms and mean different things, because the figures are often quoted under the most favourable conditions. Ask what the value is measured over, what the material was, and whether it is a typical or a guaranteed figure.
| Specification | Typical value |
|---|---|
| Common forms | involute, straight sided, serration |
| Fit classes | sliding to permanent |
| Typical tolerance | ±0.01 mm on the major and minor diameter |
| Surface finish | Ra 1.6 µm on the flanks |
| Measurement | over pins or with a spline gauge |
| Manufacture | hobbing, shaping, rolling or wire EDM |
What to check before specifying
Make sure the value you need is the value you have called up. Call up the standard and the fit class, not just the number of teeth, and the difference between a typical and a worst case figure is where most disputes start.
Applications
Splined Shafts is used for drive applications where a keyway would be too weak or would need an accurate fit, and in practice it appears most often in gearbox input shafts, pump drives, steering columns, aerospace actuators.
How it fits into a machining route
Splined Shafts is produced by whichever route reaches it most reliably, and it is usually the reason the rest of the part is dimensioned the way it is. Datums are chosen so that this feature is measured from what it actually has to be square or concentric with.The route is fixed before the first part is cut, and it is the route rather than the individual setting that holds the result: the cutting method, because hobbing needs a special tool. Where a drawing calls for something the route cannot hold economically, that is raised at quotation rather than after the parts are made.
Standards, documentation and what is issued
The documentation requirement is dimensional report with a spline measurement over pins. Material is supplied against a certificate where the application calls for it, inspection results are recorded with the job, and the records are kept so that a repeat order can be compared with the first instead of being measured from scratch.
Spline gauge and a measurement over pins is the verification step. Where a customer format or a standard report is required, it is agreed before the batch starts, because a report written after the event is a report nobody can use.
Frequently asked questions
What tolerance should be specified for Splined Shafts?
±0.01 mm is realistic in production. Tightening it beyond the functional requirement increases cost without improving the part.
Which material is usually used?
4140 alloy steel is the usual choice, supplied against dimensional report with a spline measurement over pins.
How is the result verified?
Spline gauge and a measurement over pins, with the results recorded so a repeat order can be compared with the first.
What is the most common mistake?
A sharp corner at the root, which starts a fatigue crack.
How long does it take and what does it cost?
A realistic cycle is 30 to 90 minutes depending on the size, and the cost driver is the cutting method, because hobbing needs a special tool.
Related capability
If you are specifying Splined Shafts on a drawing and want a second opinion on the route, send the model and the quantity. The first response is a manufacturability review with the likely risk points and a quotation, so the decision can be made on facts rather than on a price alone.
Machining, inspection and documentation are handled in one place, which is why the dimensional report and the material certificate arrive with the parts rather than after them.
Related entries
These entries sit next to Splined Shafts in the encyclopedia: Heat Sinks, Mould Inserts, First Article Inspection. Reading them together gives a fuller picture of how the process, the material and the measurement affect each other.
