A properly sized rotary index table is one of the most important parts of your automation system. Without the correct fit, equipment wears down more quickly, and machining and inspection become inaccurate. Engineers must optimize key sizing factors to protect operational costs and efficiency. Let us break down how to size a rotary index table so your teams can seamlessly integrate it into production.
Correctly sizing a rotary index table is critical in precision machining, automation, and manufacturing applications. The rotary index table is used to position workpieces at precise angles for operations like drilling, milling, or inspection. The right size ensures:
When sizing a rotary index table, many customers begin with a 3D model of their tooling created in design software. Computer-aided design (CAD) software can generate the inertia of the mass properties, but errors can occur if there are setup issues. Designers still have to double-check the results and may lack the experience to properly validate these values, which can lead to discrepancies. Common mistakes include:
It’s crucial that the software is set to select only the rotating components of the index drive and that the components have the correct material properties and densities applied. Engineers can avoid expensive errors by:
At Motion Index Drives, we use the mass properties provided by the customer’s design software as a starting point for sizing the application. We do not rely solely on these values. As a trusted partner, we meticulously review each application and cross-check the software’s inertia calculations with the mathematical formulas for inertia to ensure accurate loading. This extra step ensures that the index drive is neither undersized, which could lead to premature failure, nor oversized, which would result in unnecessary costs for both the index drive and the control system.
Rotary index table sizing will directly impact your inspection and manufacturing results. While engineers often focus on a single variable, sizing requires balancing load inertia, swing diameter, indexing time, and total load weight. Each of these elements impacts how the table handles torque and its accuracy. The wrong sizing will cause the table to wear out faster, increasing maintenance and expenses. Evaluate each of these four items for the best results.
The swing diameter should generally maintain a relationship with the cam follower pitch diameter of 8:1 or less, and never exceed 10:1. For example:
The maximum recommended swing diameter for each model can be found in the catalog for each product.
Determining load inertia can be complex. To estimate worst-case inertia, multiply the total load by the square of the radius. For example:
Using this estimate, you can calculate the required index time for a specific model. For example, an RT400-4 stop with this inertia would require an index time of 3.82s. If possible, use the center of gravity radius for more accurate calculations. Additionally, Motion’s internal TCC calculator can help estimate inertia.
The longer the indexing time available, the greater the inertia the index table can handle. If the application allows for a slower indexing time, this can help reduce the required size of the indexer and make the system more cost-effective. Slower indexing also reduces the stress on the table.
If index time is not a critical factor, the total load weight must be checked to ensure it does not exceed the bearing capacity. Bearing capabilities for each model are listed in the catalog.
The relationship between index time and dwell time also influences rotary index table sizing. These factors define the cycle profile and influence performance:
The formula is:
When acceleration and deceleration periods are defined, the velocity curve typically follows a triangular or trapezoidal profile. The area under the curve equals the total move distance. Adjusting these parameters allows engineers to balance throughput and indexer longevity.
When sizing trunnions, it is important to consider the factors mentioned earlier, but an additional consideration is the out-of-balance (static) torque. Static torque often becomes the deciding factor when sizing a trunnion. This type of torque arises from any imbalance in the system and must be accounted for to ensure proper performance.
Engineers can choose between flexible and fixed index drives for their operations. Each design will handle load, torque, and long-term performance differently. Find the option that meets your performance and durability requirements.
These drives are stronger than their fixed counterparts because they always have a minimum of two cam followers engaged in preload. In the case of TMF indexers, up to five cam followers can be in contact with the cam at any given time, which contributes to their increased strength and reliability.
For preliminary estimates, assume the same size for flexible and fixed rotary index tables until the final loading can be calculated by engineering. This initial sizing provides a starting point for further refinement.
For parallel and right-angle (globoidal) rotary indexers, output torque is typically the most critical factor when sizing the unit. To size these types of indexers, it is important to gather the following key information from the customer:
By following these guidelines, you can ensure that the rotary index table or trunnion is properly sized for its intended application, optimizing both performance and efficiency.
Rotary index table sizing goes beyond a single use. They are sized for the machine’s entire operating life. A system that runs one cycle every few minutes places different demands on the indexer than a multi-shift, high-throughput production line. The duty cycle refers to the number of cycles per minute, hours per shift, and days per year that the system operates. The longer and more demanding the duty cycle, the more wear on components.
The environment also plays a role in sizing. Systems exposed to heat, coolant, debris, or heavy dust require protective measures. Equipment needs seals, lubrication, and housing designs that protect delicate components. The right indexer will perform consistently under real-world conditions.
Finding the right rotary index table depends on more than a quick estimate. You need validated calculations, motion profiles, and real-world data. Simplify this process by partnering with engineers and companies with specialized tools. These strategies make sizing even more accurate:
In the example below, the customer’s fixtures and the center weldment frame have a combined weight of approximately 3000kg, representing the total moving mass. The customer estimates that the distance from the center of rotation to the center of the rotating tooling mass is 0.927 meters. To calculate the mass moment of inertia for the tooling fixtures and rotating structural frame, we used the following formula:
I=(0.927)²×3000kg=2577kg⋅m²
Motion Index Drives incorporates a safety factor into the calculated mass moment of inertia to account for any potential miscalculations in weight distribution or inaccuracies in the application of mass properties during the design process. In this instance, we used a conservative value of 3000kg·m² to determine the appropriate RT series fixed indexer and to properly size the motor power.
Here are some answers to common rotary index sizing questions to help you find the right fit:
Inertia is a more critical factor, although weight is important for bearing capacity. The distance of that weight from the rotational axis largely determines torque demand and index time. A lighter load placed far from the axis can create more inertia than a heavier load close to the center.
Yes, allowing more time for each index lowers the peak torque demand, making it possible to use a smaller indexer. This approach can reduce stress on the cam and followers, improving longevity and even lowering system costs.
Keep the center of gravity as close as possible to the trunnion axis. Reducing offset minimizes static torque, reduces cam loading, and decreases the motor’s current draw.
Incorrect material densities or misaligned coordinate systems in CAD can significantly inflate inertia values. Verifying results with checks prevents mis-sizing.
No, index increments are indexable, and engineers can customize them to match specific process stations or cycle requirements.
Yes, multiple cam followers engaged in preload create higher torsional stiffness and increased reliability under demanding loads.
Selecting and sizing a rotary index table is easier with the right partner. At Motion Index Drives, we ensure your equipment is engineered with precision and validated for accuracy. We have over 50 years of manufacturing and designing experience, so you can count on us for long-term reliability. We deliver rotary index tables with zero backlash, minimal maintenance, and proven uptime. Skilled engineers with decades of field knowledge review all our solutions.
Trust Motion Index Drives to go above and beyond for your application. We back all our work with a five-year warranty and hold an ISO 9001:2015 certification. Additionally, we offer 24/7 customer support. You can be confident your investment is protected and your production goals are met. Contact us online for your next project and receive an engineering-grade sizing recommendation tailored to your needs.
