The groove is the only part of a sheave the rope ever touches. Get the profile right and the machine grips the rope with the least possible pressure; get it wrong and you either lose traction or chew through ropes. When you order a sheave — new or replacement — the groove profile is the first thing worth deciding deliberately, not copying blindly.
Here’s how the four profiles behave, and how we’d help you choose.
Why the profile matters
A traction lift drives the car by friction alone: the grooves press on the ropes, and that pressure times the friction coefficient is all the grip the machine has. Every groove profile is a different trade in the same tug-of-war:
- More grip means the groove pinches the rope harder — higher contact pressure, faster wear on both rope and groove.
- Less pressure means longer rope life — but if grip drops too far, the ropes slip under load, which is a safety issue, not just a maintenance one.
The profile you specify sets where on that line the sheave sits for its whole service life.
The four profiles
U groove (round seat)
A semicircular seat that cradles the rope over a wide arc. Contact area is the largest of any profile, so specific pressure on the rope is the lowest — and rope life the longest. The price is grip: a plain U generates the least traction, which is why it belongs on wheels that don’t have to drive anything.
Where it belongs: diverter and deflector sheaves, idlers, and double-wrap gearless machines where the second wrap supplies the missing traction.
V groove
The rope wedges into a vee — commonly cut at a 35° or 40° included angle — and the wedging action multiplies grip. It’s the highest-traction profile, and the hardest on ropes: contact is concentrated on two narrow lines of the rope’s flanks. As the groove wears, the sharp vee gradually beds in toward a U shape, and the traction it was chosen for fades with it.
Where it belongs: geared machines and lower-speed duties where maximum grip matters and rope pressure can be tolerated.
Undercut grooves (U or V with undercut)
Take a U or V seat and machine a relief slot out of the bottom. The rope can no longer bear on the base of the groove, so its weight rides on the two flanks — pressure goes up, grip goes up, but far less brutally than a full V. The width of the undercut sets the balance: a wider undercut means more traction and shorter rope life. That balance isn’t a matter of taste — it comes out of the traction calculation for the machine (the EN 81-style check your designer runs).
One behaviour worth knowing: as an undercut groove wears, the rope sinks deeper until it starts to bottom out in the undercut slot. When that happens the extra grip disappears — it’s the classic sign the sheave is due for re-grooving or replacement.
Where it belongs: single-wrap traction (drive) sheaves — this is the default profile on most geared and gearless passenger lifts.
Round seat (pulleys)
Governor, compensating and deflector pulleys carry no traction duty at all, so they get a deep round seat sized to guide the rope and nothing more. Minimum pressure, maximum rope life, quiet running.
The four profiles side by side
| Profile | Traction | Rope pressure | Rope life | Typical use |
|---|---|---|---|---|
| U (round seat) | Lowest | Lowest | Longest | Diverters, deflectors, double-wrap drives |
| V (35°/40°) | Highest | Highest | Shortest | Geared machines, low-speed high-grip duties |
| Undercut U/V | Medium–high | Medium | Medium | Single-wrap traction sheaves — the usual choice |
| Round pulley seat | None needed | Lowest | Longest | Governor, compensating, deflector pulleys |
Matching the groove to your rope
Profile is only half the specification. The groove still has to fit the rope that runs in it:
- Seat radius. The seat is cut slightly larger than the nominal rope radius — a window of roughly 0.53–0.55 × rope diameter is common practice. Too tight and the groove pinches the rope; too slack and the rope rides on a point contact, which raises pressure instead of lowering it.
- Groove pitch. On a multi-groove sheave the centre-to-centre spacing must match the machine’s rope centres, or the ropes run misaligned and wear on one flank.
- Equal groove diameters. All grooves must finish at the same diameter. If one groove sits deeper, its rope travels slower than the others — the ropes fight each other, tension goes uneven, and both ropes and grooves wear fast. This is why a tired sheave gets all its grooves re-cut together, never just the bad one.
- Rope size. 8, 10 and 13 mm are the usual lift rope diameters; the groove is cut to the specific rope you run, not a generic size.
Choosing in practice
- Ordering a diverter or pulley? Plain U or round seat. Don’t let anyone sell you an undercut on an idler — it only eats ropes.
- Ordering a traction sheave? The profile and undercut come from the machine’s traction calculation. If you have the original drawing or machine model, we machine to that. No documents? Send the worn sheave — the original geometry can be measured off it.
- Replacing a worn sheave? Match the original profile unless you have a reason not to. If the old sheave slipped or wore out unusually fast, say so in the enquiry — that’s usually a profile or hardness conversation, and better had before the new part is cut.
What we need to machine yours
We machine main and traction sheaves and diverter sheaves to drawing or sample in our Mayapuri workshop — grooves turned to your rope pitch, seat radius and undercut, and checked before dispatch. To quote a groove spec we need:
- Rope diameter and number of ropes
- Groove profile (or the machine model / original drawing / the worn sheave itself)
- Outer diameter and groove pitch
- Bore and keyway details
Have those — or even just some of them? Send your requirement with whatever you have, and we’ll come back with a quote and the questions that remain.
Common questions
Which groove profile does a diverter sheave need?
Almost always a plain U (round seat). A diverter only redirects the rope — it doesn't drive it — so there is no reason to pay the rope-wear penalty of a V or an undercut. Cutting an aggressive profile into an idler wheel shortens rope life for nothing.
Can you match the groove of a worn or obsolete sheave?
Yes. Send us the old sheave or a sample and we measure the seat radius, groove pitch, undercut and bore, then machine a replacement to the original geometry. If the original profile was causing rope slip or fast wear, we'll flag it before we cut.
What rope sizes do you cut grooves for?
8, 10 and 13 mm are the common lift rope sizes we groove for. The seat is cut to your specific rope diameter and pitch, so send the rope spec (or the rope itself) with your enquiry and we'll match it.