Curved Gear Rack for Greenhouse Vent Systems

An arc-form toothed steel segment used where a greenhouse vent sash travels through a curved path rather than a straight line. Produced from galvanized steel to the radius, chord length and hole position required by the vent geometry. Standard and OEM parts both accepted.

Where a Curved Rack Is Required

Not every vent mechanism moves a rack in a straight line. Where the sash pivots about a fixed hinge and the rack is fixed to the sash itself, the rack travels along an arc centred on that hinge. A linear rack forced into that path binds within a few degrees of rotation; the geometry simply does not allow it.

The curved rack solves this by being manufactured to the arc the sash actually follows. The pinion stays in a fixed housing and the curved segment sweeps past it, so tooth contact is maintained throughout the swing without any part of the mechanism having to flex.

This is why the radius is the defining dimension of the part. It is not a styling choice — it is set by the distance from the sash hinge to the rack mounting line on your specific structure. Two greenhouses with identical span can require different radii if the hinge positions differ.

If you are not sure whether your vent needs a curved or a linear rack, our comparison of curved and straight rack geometry works through how to tell from the mechanism.

Manufacturing Capability

We are a source factory for transmission components, producing gears, gear racks, sprockets, roller chain, timing pulleys and timing belts, alongside linear guides and ball screws. Curved racks for horticultural facilities are produced within the same gear-cutting operation as our linear rack work.

What this means in practice for a curved rack order:

• The radius is cut, not bent. Forming a straight toothed bar into an arc distorts the tooth profile — pitch opens up on the outside of the curve and closes on the inside. Teeth produced on the finished arc keep a consistent involute profile along the whole segment.
• Tooth form follows the pinion you specify. Module, pressure angle and tooth count per segment are set against the mating pinion rather than a fixed house standard.
• Segment length is a production variable, not a catalogue constraint. Chord length and the number of segments per vent are worked out from your opening angle.
• Hole positions are drilled to your fixing pattern. Retrofit work rarely allows new holes in the sash, so the rack is made to suit the existing fixings.

Material and Surface Protection

Curved racks are supplied in galvanized steel. The zinc layer is doing a specific job in a horticultural facility: interior air stays near saturation for much of the growing season, and steel surfaces pass through a condensation and drying cycle every night. Bare or painted steel fails first at the tooth flanks, where contact strips any film during each opening cycle.

Zinc behaves differently because it protects sacrificially — a scratch does not become an undercut corrosion site the way a breached paint film does.

If the installation is coastal, or the facility runs fogging or chemical spray that reaches the mechanism, state it at enquiry. Surface protection is specified against the environment rather than applied uniformly.

Dimensions We Manufacture To

A curved rack is defined by four figures. We produce to whichever of them you can supply, and work out the rest with you:

We do not publish a fixed size table for this part, because a curved rack that is not made to the actual vent geometry has no value — a segment with the wrong radius cannot be shimmed or adjusted into service.

How to Order Without a Drawing

Most enquiries for curved racks come from replacement work where no drawing survives. That is workable. Send us:

1. The worn segment itself, or a photograph of it laid flat on a marked surface
2. Chord length — straight-line distance between the two end holes
3. Rise — the perpendicular height from that straight line to the middle of the arc
4. A photograph of the teeth against a steel rule, close enough to count teeth over a measured distance
5. Hole diameter and distance from each end

Chord and rise together give us the radius by calculation, which is more reliable than trying to measure a radius directly on a part that may already be deformed.

Applications

• Commercial glasshouse roof vents with pivoting sashes
• Multi-span horticultural facility ventilation
• Polycarbonate-clad growing structures
• Vegetable production facilities
• Replacement of deformed or corroded arc segments on existing mechanisms

Supplied Alongside

Curved racks are rarely ordered alone. Because we manufacture the mating components in the same facility, a single order can cover the rack, its pinion and the rest of the drive line — see our matched rack and pinion set.

We also produce sprockets, roller chain, timing pulleys and timing belts, so where a ventilation project also needs shading or screen drive components, these can be consolidated into the same shipment rather than sourced separately.

Quality Control

• Tooth profile checked against the mating pinion specification before dispatch
• Radius and chord verified against the approved drawing
• Hole position and diameter checked to drawing
• Coating coverage inspected across tooth flanks and cut edges
• First-article sample available for approval on OEM orders before batch production

On a first order for a new radius, we recommend taking the first-article sample. Fitting one segment to the actual sash is the only check that catches a geometry misunderstanding before it becomes a full batch.

FAQ

Q: Can you make a curved rack from a sample?
Yes. A physical sample is the most reliable input, particularly where the original drawing no longer exists. Send the worn part and we will work from it.

Q: What radius range can you produce?
Radius is produced to the requirement rather than selected from a range. Send your chord length and rise and we will confirm feasibility for that geometry.

Q: Why not just bend a straight rack to the radius?
Bending distorts the tooth pitch — it opens on the outer side of the curve and closes on the inner. The pinion then meshes correctly at only one point along the segment. Teeth cut on the finished arc avoid this entirely.

Q: Do you supply the pinion as well?
Yes. Supplying both from one factory means the tooth form is verified as a pair rather than assumed compatible across two suppliers.

Q: What is the minimum order quantity?
Depends on whether tooling for your radius already exists. Send the geometry and we will confirm MOQ with the quotation.

Q: Can you match a rack from another manufacturer?
Usually yes, working from the physical part. What we need is the tooth geometry and the arc dimensions — brand markings on the original are not required.

Why Source From Our Factory

• We cut the teeth ourselves. Gear and rack production is our own operation, not subcontracted, which is what allows the radius and tooth form to be varied per order.
• Twenty years in transmission components. Gears, racks, sprockets, chain, pulleys and belts, plus linear guides and ball screws.
• OEM parts accepted. We work from customer drawings and samples as standard practice, not as an exception.
• Rack and pinion verified as a pair. Both come from the same facility, so tooth compatibility is confirmed before shipment.
• We say when a figure is not yet fixed. Dimensions on this page are marked as per-order because they genuinely are — a published table would be misleading for a made-to-geometry part.

Request a Quotation

Need arc segments matched to your vent geometry?

Send us the chord length, rise, tooth pitch or module, hole positions and quantity per vent. A drawing is ideal, but photographs of the existing segment against a steel rule are enough for us to work from.

Developing a new vent mechanism? Send the sash hinge geometry and required opening angle and our engineering team will work the rack arc through with you before anything is cut.

Send Drawing or Sample Details →