Diameters explained
| Diameter | What it is | Used for |
|---|---|---|
| Datum Ø (dd) | The diameter at the groove's datum width (where the belt's datum line runs). | All speed, ratio and length calculations for SP and classical belts (ISO 4183). |
| Outside Ø (de) | Across the top of the flanges: the only one you can measure easily. | Field measurement. dd ≈ de − 2b. |
| Pitch Ø | For timing pulleys, the diameter of the belt's pitch line: p × z / π. | Timing drive calculations. |
| Effective Ø | RMA (3V/5V/8V) system: based on the outside of the belt. | Inch narrow belt tables. |
Groove profiles
Classical and narrow pulleys follow ISO 4183 / DIN 2211 (narrow) and DIN 2217 (classical). The groove angle depends on the pulley diameter: small pulleys use a smaller angle (about 32–34°) and large pulleys a larger one (about 36–38°), because a belt bending round a small pulley spreads at the bottom.
- SP-profile grooves suit both narrow (SP) belts and, generally, the classical belt of the same datum width. Classical-profile grooves are too shallow for SP belts: never fit SP belts in classical grooves without checking.
- The belt should sit with its top roughly level with, or slightly above, the top of the groove. A belt sunk well below the rim means a worn groove or the wrong belt.
- Belts must never touch the bottom of the groove.
Groove wear and gauging
Dust, slip and abrasive environments (cane, timber, coal, sand) wear the groove walls into a dish shape. A worn groove lets the belt sink, lose wedge grip and slip; the belt then burns and glazes. Fitting new belts in worn grooves is the most common cause of "these belts don't last".
- Use a groove gauge (template) for the section and pulley diameter.
- Hold it in the groove against a light: the gauge should sit flat on both walls. Light showing between gauge and wall, or a step or dish you can catch a fingernail on, means replace the pulley. Follow the gauge maker's limit if stated.
- A polished groove bottom means the belt has been bottoming: replace.
- Uneven wear between grooves (one deeper than others) also kills banded belts.
Rim speed and materials
| Material | Typical use | Typical rim-speed limit |
|---|---|---|
| Grey cast iron | Standard stock V-belt pulleys | ≈ 30 m/s |
| Ductile (SG) iron / steel | High speed, heavy duty, large diameters | Higher: as rated and balanced by the maker |
| Aluminium | Timing pulleys, light drives | As rated |
| Steel (fabricated) | Very large pulleys, special profiles | As designed |
Balancing
Stock pulleys are usually statically balanced. Pulleys for high speed, wide pulleys, and pulleys on vibration-sensitive machines (fans, centrifuges, decanters) should be dynamically balanced to a suitable grade under ISO 21940 (formerly ISO 1940-1). Unbalance shows up as vibration at 1× the pulley speed. Machining a bore off-centre also unbalances the pulley.
Pulley types
- Taper-bore pulleys take a taper-lock bush: one pulley fits many shaft sizes. The standard for most new drives.
- Pilot-bore pulleys are supplied with a small bore to be machined to the shaft, with keyway and set screw.
- QD / split-taper pulleys (common on American machines) use a flanged bush.
- Variable-pitch pulleys for variable-speed belts and fine speed adjustment.
- Flat and crowned pulleys for flat belts.
Custom machined pulleys
We supply pulleys machined to your drawing or sample: non-standard diameters, special bores and keyways, multiple sections on one hub, extended hubs, and replacement pulleys for old imported machines. Send a photo with the outside diameter, number and type of grooves, bore and keyway, and hub length.
Timing pulleys
- Specify profile (e.g. HTD 8M), number of teeth, belt width, flanged or plain, and bore (pilot or taper-lock).
- The smaller pulley is usually flanged on both sides; on vertical shafts flange the lower pulley as well.
- Check teeth in mesh: at least 6 on the small pulley.
- Worn timing pulley teeth (hooked or polished) wear new belts fast: replace them together.
Taper-lock bushes
A taper-lock bush is a split, tapered sleeve that locks a pulley (or sprocket or coupling) to a parallel shaft. Tightening the screws pulls the bush into the tapered pulley bore, squeezing it onto the shaft. One pulley can then fit many shaft sizes simply by changing the bush.
- Size code: the last two digits are the bush length in tenths of an inch (2517 → 1.7″ ≈ 44 mm); the first two indicate the size.
- Each size accepts a range of bores up to a maximum, metric or inch, with a keyway to the shaft standard.
- Fit the bush from either side: hub-side (H) or face-side (F) mounting depends on the pulley. Check before fitting so the screws stay accessible.
Find the bush for your shaft: taper bush finder.
Fitting a bush
- Clean all surfaces: bore, shaft and bush taper. No oil, grease or anti-seize on the tapers or screws: it lets the bush over-tighten and can crack the pulley.
- Place the bush in the pulley, line up the half-holes, and screw in the grub screws loosely (oil the screw threads lightly only if the maker says so).
- Slide the assembly onto the shaft (key in) and position it.
- Tighten the screws alternately and evenly to the specified torque.
- Tap the large end of the bush with a drift and soft hammer, then re-torque. Repeat until the torque no longer falls.
- Fill the empty holes with grease to keep dirt out.
- Re-check torque after a short run.
Removing a bush
- Remove all screws.
- Oil the threads and point of one screw and put it into the removal hole (the threaded half-hole in the bush).
- Tighten it: the bush is pushed out of the taper and the assembly comes loose.
Bush size table
Typical values for the common (Fenner-pattern) taper-lock series. Torques are typical published values: always use the value stamped on the bush or in the maker's data sheet if it differs.