Sheaves and pulleys
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Frequently asked questions
What should I measure to order a replacement V-belt sheave?
You need the outside or datum diameter, groove profile (A, B, SPA, SPB and so on), number of grooves, bore diameter and keyway size. If the sheave uses a taper bush, note the bush code instead of the bore. Speed ratio depends on datum diameter, not outside diameter, so keep them apart when calculating speed.
What is the difference between pilot bore, finished bore and taper bush sheaves?
A pilot bore sheave has a small hole to be machined to suit the shaft. A taper lock sheave clamps onto the shaft via a taper bush that already has the bore and keyway, so it is easy to fit and shaft size changes only need a new bush. In a bush code such as 1610 or 2012, the first two digits are the bush outside diameter in tenths of an inch and the last two are its length.
How do I know sheave grooves are worn and need replacing?
Place a groove gauge in the groove: a gap at the sidewalls, or a shiny groove bottom where the belt has bottomed out, means wear. Worn grooves let the belt sink, slip and wear fast, even when new. Replace the belts at the same time.
What is the maximum speed for a cast iron sheave?
Standard grey cast iron sheaves are normally limited to around 30 m/s rim speed; above that, steel or ductile iron sheaves with dynamic balancing are needed. Rim speed equals pi times diameter times revolutions per second. Large, fast sheaves should be balanced to avoid vibration loads on the bearings.
How do I fit a taper bush sheave so it runs true?
Clean oil and grease from the taper and bore first, because the taper must grip dry to transmit torque. Tighten the bush screws alternately and evenly to the maker's torque, then tap the bush lightly and retighten. Check axial and radial runout with a dial indicator after fitting.
Does a sheave need dynamic balancing?
Standard cast iron sheaves are usually statically balanced, which suits normal rim speeds. For high speeds, large diameters or vibration sensitive machines, ask for dynamic balancing to a suitable ISO 1940 grade. Reboring or remachining a sheave can upset its original balance.
Can a SPA groove sheave run an A section belt?
SPA grooves and classical A belts have similar top widths, so an A belt usually fits a SPA groove, but it sits at a different height and the effective diameter changes. That alters the speed ratio and machine speed. Check the groove tables of the relevant standards before mixing them.
Why do sheaves crack or burst?
Cast iron sheaves can crack when the taper bush is overtorqued, when the bore has excessive interference, or when run above the permitted rim speed. Hammer blows during fitting and removal also leave hard to see cracks at the spoke roots. A cracked sheave must be replaced, not welded, because centrifugal force can make it burst.
