Sprocket installation is governed by four measurable interfaces: chain pitch (e.g. 04B at 6 mm through 32B at 2 in), bore tolerance (H7 up to 180 mm), keyway fit (JS9 rectangular parallel up to 25 mm), and shaft-to-shaft angular alignment, which most field failures trace back to [S3].
This procedure covers pilot-bore and taper-bore variants, BS and ASA standard pitches, and the tensioner/guard options a maintenance engineer should select on a retrofit or new drive build. Read it as a field checklist, not a marketing summary, and cross-check any sprocket dimension against the chain manufacturer's current catalogue [S3].
Pitch, tooth count, and chain family selection
British Standard (BS) and ASA chains cover two parallel size systems; both are in active use, and mis-pairing is the single most common procurement error on mixed-fleet sites. BS chain pitch runs 04B (6 mm) through 32B (2 in), with intermediate sizes 05B (8 mm), 06B (3/8 in), 081 (1/2 x 1/8 in), 083 (1/2 x 3/16 in), 08B (1/2 in), 10B (5/8 in), 12B (3/4 in), 16B (1 in), 20B (1 1/4 in), 24B (1 1/2 in), and 28B (1 3/4 in) [S3]. ASA equivalent pitches run ASA35 (3/8 in) through ASA100 (1 1/4 in), with ASA40 at 1/2 in, ASA50 at 5/8 in, ASA60 at 3/4 in, and ASA80 at 1 in [S3].
Tooth count is chosen from the speed reduction ratio and the desired wrap angle on the smaller sprocket; small sprockets below ~17 teeth reduce chain life and accelerate articulation wear, so designers target Z ≥ 19 for power drives and Z ≥ 23 for high-speed or shock-loaded service. Material choice between steel (ST), stainless steel (SS), cast iron (CI), acetal (AC), and nylon (NY) is a corrosion-versus-load trade, and the same part number must be quoted with the material code from the supplier's ordering system [S3]. For the geometry behind tooth-count selection and sprocket meshing, see the sprocket reference page.
Bore, keyway, and hub machining tolerances
Standard rebore capacity is up to 180 mm diameter to H7 tolerance; bores beyond 180 mm require an enquiry, and field reworking to a tighter fit than H7 risks hub fracture under press loads [S3]. Keywaying is offered as JS9 rectangular parallel up to 25 mm width, with larger or special profiles also moved to the enquiry queue [S3]. Tapped holes for fixing screws or puller threads are stocked to M16; above M16, the lead-time and pricing model changes, and the part must be re-quoted [S3].
For ordering, a typical pilot-bore part code reads PW A80 DR 57 ST D = 25 mm, decomposing as product type (PW = platewheel), pitch (A80 = ASA80, 1 in), style (DR = duplex), tooth count (57), material (ST = steel), and bore (25 mm) [S3]. A taper-bore example, CS 10B SR 28 SS 2012 To Drg, breaks down as chain-sprocket, 10B pitch (5/8 in), simplex, 28 teeth, stainless steel, 2012 taper-bush series, machined to customer drawing [S3]. Plain-bore parts with grub-screws (G/S) or keyway (K) are the field-replaceable format; finished-bore (D) parts are usually reserved for volume OEM fitments.
Direction of rotation, hub fixation, and chain wrap
Drive sprockets are stamped with a direction arrow on the hub or web, and the rotation arrow on the driven sprocket must match the conveyor or machine rotation before any bolt is torqued [S4]. For drop-forged conveyor chain, link assembly follows the sequence Bolt (3) → Fender (5) → Flat Washer (4) → Hollow Pin (8) → Flat Washer (4) → Fender (5) → Lock Nut (7), and after tightening, the connected link must articulate freely by hand [S4]. Flight engagement is set by the slot on the flight seating into the lug on the link, which prevents the flight from rotating under load [S4].
Shaft fixation uses either a parallel key (JS9 keyway, grub-screw back-up), a taper bush (2012/2517/3020 series are common), or a shrink-fit disc for high-cyclic loads. The sprocket body acts like a crossed-roller guide for torque transmission: any clearance at the bore is amplified at the chain wrap, and a loose hub will shear the key within hours, not weeks.
Alignment, tensioning, and chain protection
Shaft-to-shaft angular misalignment should be held below 1°, and parallel offset below 0.5 mm per 100 mm of centre distance; a laser-alignment pass after mounting is cheap insurance, and most premature sprocket-tooth wear on otherwise correct parts traces back to alignment drift, not material. Tensioning options are not adjustable, manual (occasionally), drip-feed, oil-bath, or pressure-circulation, and the decision is fixed by the ambient conditions and duty cycle: dust, fibres, sand, humidity, temperatures up to the chain maker's stated maximum, and corrosion risk all feed the choice [S3].
Chain protection boxes are specified as dust-proof, not dust-proof, or protected by the machine housing; unprotected chains in dusty or sandy environments are a known failure mode and should be escalated to an enclosure, not left in service. For drives where tension is critical, an automatic chain tensioner is preferred over a fixed jockey sprocket because it tracks chain elongation as the pitch grows under wear [S3]. A related timing belt installation walkthrough follows the same alignment-first logic and is a useful cross-check when a drive is being converted between chain and belt.
Lubrication regime and ambient limits
Lubrication must be specified as one of: not permitted, manual (occasional), drip feed, oil bath, or pressure circulation; manual lubrication is acceptable only on low-speed, intermittent-duty drives, and any continuous-duty drive above roughly 1 m/s chain speed should be on drip, oil-bath, or forced circulation [S3]. Operating temperature ceiling is set by the chain and the lubricant together, with humidity and corrosive atmospheres pushing the spec toward stainless-steel sprockets (SS) and food-grade lubricants.
Acceptance test after install: rotate the drive by hand through two full wraps and confirm (a) chain engages tooth roots centrally on both sprockets, (b) no tight spots caused by a high-fidelity key seat, (c) tensioner travel sits in the middle third of its stroke at cold-start, and (d) no side-to-side chain slop beyond the maker's limit. Where a drive must coexist with belt drives on the same shaft, follow the timing belt total cost of ownership guidance for shared-shaft load and bearing-life budgeting.
Common failure modes and when to replace, not repair
Replace the sprocket, do not re-machine, when tooth profile shows hook wear, when the tip-to-tip chord across three teeth measures below the minimum on the manufacturer's gauge, or when the bore has ovalised beyond H7; a worn tooth profile accelerates chain pitch elongation and destroys a new chain within a single shift. Replace also when keyway walls show fretting or when grub-screw holes have stripped more than one thread — these are hub-fatigue precursors. Repair (rebore, new keyway) is acceptable when the hub is sound, the wear is on the bore or keyway only, and the new bore keeps the part within published rework limits, namely bore to H7 up to 180 mm, keyway to JS9 up to 25 mm, tapped holes to M16 [S3].
Trackable signals to log on each install: date, chain pitch, sprocket part code (e.g. CS 10B SR 28 SS 2012), tooth count before and after one duty cycle, alignment report values, and lubricant grade. A 5% rise in chain elongation at 1,000 hours is the threshold to plan a tensioner adjustment or a chain-and-sprocket replacement, not a bolt-tightening visit.
Spec-level background on the components involved: linear guide.