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Guide · Buyer essentials

Precision Shaft Design Checklist for Pump, Motor and Gearbox Shafts

What to specify on a shaft drawing: material, fits, runout, keyways, threads, finish and heat treatment.

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On this page10 sections

What a shaft drawing has to state

A pump, motor or gearbox shaft is cheap to quote and expensive to get wrong. Everything below is routinely missing from first-issue drawings.

Specify these

  • Grade and condition together, for example SS 316 annealed, or EN24 hardened and tempered
  • An EN 10204 3.1 material certificate where traceability matters, requested at RFQ stage not after dispatch
  • ISO 286 fits on bearing seats and seal diameters: k6 or j6 on journals, h6 where a sliding fit is wanted
  • ISO 2768-m as the general tolerance so non-functional lengths and diameters are priced sensibly
  • Runout or concentricity referenced to the bearing journals as the datum; 0.02 mm TIR is typical for pump shafts
  • Keyways dimensioned to DIN 6885 or the ANSI equivalent, with the width tolerance class stated
  • Thread class, normally 6g for external metric threads, with an undercut or relief at the root
  • Circlip grooves to DIN 471, and DIN 332 centre holes where the shaft may be reground later
  • Ra values on bearing and seal surfaces only, around Ra 0.8 µm on journals
  • Export protection: VCI wrapping and individual tubes or cradles so long shafts cannot bend in transit

These drive cost or cause rejections

  • A tight fit on every diameter instead of on the two or three that locate a bearing or a seal
  • Runout called out with no datum, so it cannot be measured or disputed
  • A keyway width with no tolerance class, leaving the key fit to chance
  • A seal diameter with axial machining marks or a sharp lead-in edge that cuts the lip on assembly
  • Hardening specified after final machining, with no allowance for distortion or for a finishing operation
  • Expecting a certified hardness or metallurgical test in house; heat treatment is done by qualified partners and the parts are re-inspected dimensionally on return
  • Requesting CMM or optical measurement of a profile; inspection is by hand metrology on a granite surface plate
  • Shipping long shafts loose in a crate with no cradle, tube or VCI film

Start here

Material and condition

State the grade (for example SS 316, SS 410, EN8, EN24) and condition (annealed, hardened and tempered). Ask for an EN 10204 3.1 certificate if traceability matters.

  1. 01 / 04

    Fits and tolerances

    Specify ISO fits on bearing seats (k6, j6, h6) and seal diameters, and keep general tolerances to ISO 2768-m to control cost.

  2. 02 / 04

    Geometric tolerances

    Add runout or concentricity relative to the bearing journals. 0.02 mm TIR is typical for pump shafts.

    Dial indicator checking shaft runout — illustrative machining image
    Illustrative machining and inspection imagery.
  3. 03 / 04

    Features

    Dimension keyways to DIN 6885 or ANSI, specify thread class (6g), circlip grooves to DIN 471 and centre holes if the shaft will be reground.

    Micrometer inspection of a shaft shoulder — illustrative machining image
    Illustrative machining and inspection imagery.
  4. 04 / 04

    Finish and protection

    Give Ra values on bearing and seal surfaces (Ra 0.8 µm typical). For export, request VCI wrapping and individual tubes or crates to prevent bending in transit.

Typical callouts, feature by feature

Usual practice for shafts of this type. Replace any line with the figure your bearing, seal or coupling supplier specifies, and mark that dimension as functional.

Bearing journal

Inner ring seat

Fit
k6 for a rotating load, j6 where the ring must still be pressed by hand
Geometry
Runout to the journal datum, typically 0.02 mm TIR
Finish
Around Ra 0.8 µm, ground or finish-turned
Shoulder
Square face with a fillet smaller than the ring corner radius
Measured with
Outside micrometer, plus a dial test indicator between centres

Seal diameter

Radial lip seal counterface

Fit
h6, or the diameter band the seal maker specifies
Finish
About Ra 0.2–0.8 µm, free of axial machining marks
Edges
Lead-in chamfer or radius so the lip is not cut on assembly
Condition
No nicks, no burrs, no spiral turning lay under the lip
Measured with
Outside micrometer; finish by comparison against a roughness sample

Keyway

Parallel key seat

Standard
DIN 6885-1, or the ANSI equivalent, stated on the drawing
Width class
N9 for a normal fit, P9 for a tight fit, H9 for a free fit
Depth
Dimensioned from the opposite surface, not from the keyway floor
Corners
Radius or run-out specified so the cutter can finish the slot
Measured with
Vernier caliper and depth measurement; indicator for symmetry

Circlip groove

External retaining ring

Standard
DIN 471 groove diameter and width for the nominal shaft size
Edges
Sharp-edged groove walls, deburred bore mouth
Position
Dimensioned to the located face, with its own tolerance
Measured with
Vernier caliper and a groove gauge or the ring itself

Threads

Lock nuts and couplings

Class
6g for external metric threads unless the mating part needs otherwise
Relief
Undercut or runout groove at the root of the thread
Alignment
Runout of the thread relative to the journals where a nut preloads a bearing
In house
CNC turning and auto tapping from M3 to M32

Centres and protection

Regrinding and transit

Centre holes
DIN 332 protected centres, retained if the shaft will be reground
Straightness
Called out over the free length where the shaft is slender
Packing
VCI anti-rust film, then an individual tube or V-block cradle
Crate
ISPM-15 heat-treated and stamped, marked with part number and weights

General tolerance against a named ISO 286 fit

Both appear on the same shaft drawing, and confusing them is the single most common cost error. The figures below are for a nominal Ø25 mm diameter.

CriterionISO 2768-m general tolerance

Everything not functional

ISO 286 fit, for example h6

Journals, seals, coupling seats

Tolerance band at Ø25±0.2 mm, a 0.4 mm wide bandØ25 h6 is 0 to −0.013 mm, a 13 µm band
Where it belongsFree lengths, step diameters, chamfers, non-mating facesBearing journals, seal diameters, pulley and coupling seats
How it is checkedVernier caliper, one readingOutside micrometer, temperature-settled part, logged reading
Finishing operations neededAs-turned finish is normally acceptableFinish pass with a dedicated tool, often a separate operation
Surface finish impliedNo requirement unless statedRa 0.8 µm or better so the fit means something
Effect on piece priceBaselineAdds setup, finishing and inspection time per feature
Applied to every diameterCorrect and intendedThe most expensive mistake on a shaft drawing

IT6 widens with diameter: about 13 µm at Ø25 and about 16 µm at Ø80. A mating H7 bore at Ø25 is +0.021 to 0 mm. Quote the nominal size with the fit, never the fit alone.

Shaft figures worth memorising

0.02 mm
Typical runout, TIR, on a pump shaft

Referenced to the bearing journals as datum, measured with a dial test indicator.

13 µm
Width of an IT6 band at Ø25

Ø25 h6 is 0 to −0.013 mm; the mating H7 bore is +0.021 to 0 mm.

Ra 0.8 µm
Usual bearing journal finish

Seal counterfaces are finer, roughly Ra 0.2–0.8 µm with no axial lay.

Ø400 × 1200 mm
Conventional turning envelope

Longer shafts and second operations are run alongside the CNC turning centres.

The short answer

What to put on a precision shaft drawing

Name the grade and its condition, apply ISO 286 fits only to the journals, seal diameters and coupling seats, and leave the rest to ISO 2768-m. Add runout referenced to the journals as datum, around 0.02 mm TIR for pump shafts. Dimension keyways to DIN 6885 with a width class, circlip grooves to DIN 471 and threads to class 6g. Give Ra values on bearing and seal surfaces only, and specify VCI wrapping with tubes or cradles for export.

  • Common grades: SS 316, SS 410, EN8, EN24, with condition stated
  • EN 10204 3.1 material certificate on request, asked for at RFQ stage
  • Plating and heat treatment by qualified partners, re-inspected dimensionally in house
  • Inspection by micrometer, bore gauge, height gauge and dial test indicator; no CMM on site
  • Auto tapping M3 to M32; conventional turning to Ø400 × 1200 mm

Keep exploring

Related capabilities, materials and markets

Everything below is machined in the same Pune plant to the same ISO 9001:2015 system. Follow whichever is closest to the part you are sourcing.

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