Screw Gear (Crossed Helical)
Screw Gears for Skew-Axis Drives
We manufacture custom screw (crossed helical) gear sets for the unique challenge of transmitting motion between non-intersecting, non-parallel shafts.
- Connects Non-Intersecting Shafts
- Ideal for Light-Duty Applications
- Dissimilar Material Pairs for Longevity
- Precision Helix Angle Control
Manufacturing Capabilities
We manufacture crossed helical gear sets to your drawings, advising on the best material combinations to ensure reliable performance and minimal wear for your specific skew-axis drive.
| Gear Type | Screw Gear / Crossed Helical Gear |
| Shaft Orientation | Non-Intersecting, Non-Parallel (Skew) |
| Shaft Angle | Typically 90°, other angles possible |
| Helix Angle | Sum of helix angles equals the shaft angle (e.g., 45° + 45° = 90°) |
| Hand (for 90° Drive) | Both gears must have the same hand (RH/RH or LH/LH) |
| Module Range | 0.5 to 6 Module |
| Materials | Steel/Bronze, Steel/Cast Iron, Steel/Engineering Plastics (Delrin, Nylon) |
| Heat Treatment | Hardening and tempering on steel gear, as required |
Common Industrial Applications
Screw gears provide a simple and effective solution for light-duty drives where shaft alignment is non-standard:
- Automotive Auxiliary Drives (e.g., oil pumps, distributors)
- Light-Duty Conveyor Systems
- Textile Machinery Feed Mechanisms
- Scientific and Medical Instruments
- Vending Machine Mechanisms
- Printing Press Ancillary Drives
- Machine Tool Indexing Mechanisms
Understanding Screw Gear Terminology
Screw gears operate on principles different from parallel or intersecting axis gears. These terms are key.
| Term | Definition for Screw Gears |
|---|---|
| Skew Axis | The fundamental geometry: the two gear shafts are non-parallel and do not intersect in space. |
| Point Contact | Unlike the line contact of parallel helical gears, screw gear teeth theoretically touch at a single point. This concentrates stress and limits load capacity. |
| Sliding Action | The motion between teeth is almost pure sliding, with very little rolling. This generates friction and heat, necessitating careful lubrication and material choice. |
| Same Hand Rule | For a 90° shaft angle, both gears in the pair must have the same hand (e.g., both Right-Handed). This is opposite to parallel helical gears. |
| Shaft Angle (Σ) | The sum of the individual helix angles of the two gears (Σ = β1 + β2). For a 90° drive, two 45° helix angle gears are common. |
The Importance of Dissimilar Materials
The high-sliding, point-contact nature of screw gears makes them prone to wear, especially if both gears are made of hard steel. A common engineering practice is to use a dissimilar material pair. By making one gear from a hard material (like hardened steel) and the mating gear from a softer, more compliant material (like bronze or a specialized polymer), a durable system is created. The softer gear "beds in" and can handle minor misalignments, while its self-lubricating properties reduce friction. This significantly increases the lifespan of the drive.
Frequently Asked Questions
Standard helical gears are used for parallel shafts and have line contact, giving them high load capacity. Screw gears (crossed helical) are used for non-parallel, non-intersecting shafts. They mesh with point contact, which results in high sliding and limits them to lighter loads. Also, for a 90° drive, screw gears must have the same hand (RH/RH), while parallel helical gears must have opposite hands (RH/LH).
Due to the high sliding friction between screw gear teeth, using two identical hard steel gears would cause rapid wear and potential galling. Pairing a hard material (like steel) with a softer, self-lubricating material (like bronze or a specialized polymer) creates a durable system where the softer gear can wear sacrificially at a slow, predictable rate, protecting the overall drive.
Both connect non-intersecting 90° shafts. Use a worm gear when you need a high gear ratio (e.g., 20:1 or more) and high load capacity. Use a screw gear for low-ratio, light-duty applications where a simple, cost-effective solution for a skew axis is the primary goal. Screw gears are generally not suitable for high torque transmission.
The Shreeji Gears Advantage in Screw Gears
Our expertise in specialized gearing delivers reliable solutions for your unique drive challenges.
Skew Axis Drive Expertise
We understand the complex geometry and contact mechanics of crossed helical gears. We can translate your skew-axis requirements into a functional and reliable gear set that meets your motion transfer goals.
Material Science for Wear Reduction
Our experience allows us to recommend the ideal dissimilar material pairing (steel/bronze, steel/polymer) for your specific load and speed, maximizing the service life of your drive by managing friction and wear.
Precision Helix Angle Control
The performance of a screw gear depends on the accuracy of its helix angle. Our precision CNC hobbing ensures that the helix angles are cut correctly, guaranteeing proper meshing at the desired shaft angle.
Screw Gear vs. Worm Gear: Choosing the Right Skew-Axis Drive
Both solve the 90° non-intersecting shaft problem, but for very different applications.
Understanding the Application's Goal
The choice between a screw gear and a worm gear comes down to two main factors: **Gear Ratio** and **Load Capacity**.
Choose a Screw Gear (Crossed Helical) When:
- The gear ratio is low (often close to 1:1).
- The load is light and torque transmission is not the primary goal.
- The main objective is simply to transfer motion between two skew shafts.
- Cost-effectiveness for a light-duty mechanism is important.
Choose a Worm Gear When:
- You need a **high gear ratio** (e.g., 20:1, 40:1, 60:1) in a compact space.
- The application involves high torque and significant load.
- Self-locking properties (where the output shaft cannot drive the input) are desirable.
- Smooth, quiet, high-load transmission is required (e.g., in elevators, heavy conveyors).
"We required a custom 90-degree crossed helical gear set for an instrument drive. Shreeji Gears manufactured a steel and Delrin pair that was perfect for our low-torque application. Great communication and quality."— R&D Engineer, Medical Device Manufacturer
Get a Quote for Your Screw Gear Set
Provide your skew-axis drive specifications for a custom quote.
For the fastest service, please email your technical drawing to support@shreejigears.com. If you don't have a drawing, include these parameters:
- Shaft Angle (e.g., 90°)
- Gear 1: Number of Teeth, Helix Angle & Hand (RH/LH)
- Gear 2: Number of Teeth, Helix Angle & Hand (RH/LH)
- Normal Module or Diametral Pitch (DP)
- Materials for each gear (e.g., EN24 Steel / PB2 Bronze)
- Bore Sizes & Keyway Details
- Required Quantity (Sets)