Mylar Overlays: A Staple of Traditional Optical Comparators
Optical inspection has allowed the manufacturing industry to accurately verify that its parts meet compliance standards. Today, this method relies on digital optical comparator technology to measure a part against its computer-aided design (CAD) file.
However, optical comparators have been around since the 1920s, and modern units have changed very little. They still use a light source to cast a magnified image of the part and rely on physical overlays for comparison, including mylar overlays.
However, as technology advances, the need for physical mylar overlays is diminishing. And for good reasons, too.
This guide will explain why mylar overlays are essential for traditional optical comparators and how digital optical comparators from VisionGauge® offer a faster, easier solution.
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The Role of Optical Comparator Mylar Overlays
Mylar overlays are transparent charts that serve as guides for manually comparing a part with its original design.
They help optical comparator operators measure a given part and determine whether its critical dimensions are within specifications or whether the part has sustained damage and should be replaced.
Although time-consuming, using traditional optical comparators is quite simple:
- An operator turns on the optical comparator and places the desired part in the staging area for observation.
- Once the image is displayed, the operator places the corresponding mylar inspection overlay on the screen and physically aligns it with the projected part’s image.
- Finally, the operator manually compares the design on the mylar overlay to the projected image of the part. If the part has any discrepancies, the operator then determines if it is still within tolerance to operate safely.
While this process gets the job done, it depends heavily on operator precision and can introduce variability from one inspection to the next.
How to Choose a Mylar Overlay
Using the right mylar inspection overlays is essential for accurate, reliable measurements. The wrong overlay can lead to a poor fit, misaligned comparisons, or inaccurate readings.
Choosing a proper mylar overlay comes down to a few key factors:
1. Style of Chart
Mylar overlays come in several styles, each suited to a different type of measurement:
- CAD charts: overlays with the part’s CAD drawing for direct comparison
- Grid charts: measure radius and angles, ranging from simple four-quadrant grids to complex screw thread form checks
- Protractor charts: use 360-degree lines for precise angle measurement
- Combination charts: combine grid and protractor features for more versatile measurements
2. Type of Optical Comparator
When ordering an overlay, you’ll want to specify what model and type of comparator you’ll be using it with. This matters because comparators vary in screen size, mounting method, and projection distance, so an overlay made for one model may not align correctly on another.
Some manufacturers also design overlays to fit specific materials, sizes, or thicknesses, so using the wrong overlay type for your comparator can lead to an improper fit or inaccurate inspections.
3. Lens Magnification
Mylar inspection overlays should be printed to match the lens magnification of your optical comparator. Magnification scale can vary depending on the machine, the overlay manufacturer, and the material used.
If the overlay is printed at the wrong magnification, the operator won’t be able to take accurate measurements or make a reliable assessment of the part.
4. Overlay Material
The material of an overlay plays a role in how well it performs. When choosing an overlay, consider:
- Material type: Optical comparator overlays are most commonly made of mylar, though plastic and vinyl are also used.
- Thickness: Thickness varies by material and can influence how the overlay performs on the comparator.
- Finish: Overlays can have a frosted or clear finish, affecting how visible the chart appears on the projector screen.
The Limitations of Traditional Mylar Overlays
Though traditional mylar inspection overlays are simple to use, they present many limitations for modern manufacturers.
Selecting the right overlay takes careful planning. Even a well-chosen overlay still depends on manual alignment and operator judgment to deliver accurate results.
Traditional mylar overlays are easily damaged, especially when handled frequently. Over time, physical overlays can stretch or distort, affecting accurate readings.
Many manufacturers need to store numerous overlays to inspect each piece of machinery, which requires significant storage space. If an overlay is misfiled, locating it can be time-consuming and delay the inspection process.
Optical comparator mylar overlays are also expensive to make. When product designs change, replacement costs quickly add up.
As manufacturing demands grow more precise, many teams are looking for a way to eliminate these limitations, which is where digital optical comparators come in.
Digital Optical Comparators
Digital optical comparators are becoming increasingly popular and necessary as machinery gets more advanced. Far more efficient and precise, digital optical comparators eliminate the need for mylar inspection overlays.
Instead of physical charts, a digital optical comparator uses digital CAD charts and an internal projector to display a part’s image, offering several advantages over traditional overlays:
- Automatic magnification adjustment: Virtual charts instantly adjust to magnification changes, without requiring a new physical overlay.
- Automatic alignment and comparison: Digital CAD charts align to the part and compare it to the chart automatically, and stay aligned even as the part moves.
- No new overlays needed: Since digital CAD charts are used directly, design changes don’t require printing a new mylar overlay.
- Faster, more accessible files: CAD files can be imported without limit and stored securely on a network, making part comparisons even faster.
These advantages are why more manufacturers are shifting toward digital inspection methods using advanced machines like the VisionGauge® Digital Optical Comparator. These systems allow producers to measure parts more accurately without relying on physical overlays.
Want to know how VisionGauge® can simplify your inspection? Reach out to our team today.
The Benefits of Digital Optical Comparators
As manufacturing tolerances tighten and production schedules accelerate, more industries are turning to digital optical comparators to keep pace.
Their versatility makes them fit for a wide range of manufacturing industries, including:
Here’s a closer look at what makes digital optical comparators such a valuable upgrade over traditional inspection methods.
1. Simplified Use
If you thought traditional comparators were easy to operate, digital optical comparators are even simpler.
The operator only has to complete one step: position the part on the staging area. The digital optical comparator’s advanced software takes care of the rest.
Because digital comparators work directly with CAD files, there’s no need for physical overlays or templates. That alone makes the entire process faster and more automated than traditional inspection methods.
2. Improved Accuracy
Digital comparators remove manual alignment and measurement from the process. This eliminates the risk of human error and provides exceedingly accurate results.
These systems are also equipped with software that automatically documents statistics, measurements, and pass/fail results, all safely stored on a secure network.
3. Fully Automated
Digital optical comparators require little to no operator input once a part is placed. Using automated software and cameras, the system analyzes and measures parts within seconds, freeing up operators to focus on other tasks.
This automation also increases throughput, since parts can be inspected and compared far faster than with manual methods.
4. Additional Benefits
Beyond simplified use, improved accuracy, and full automation, VisionGauge® Digital Optical Comparators offer several other advantages that make them a strong upgrade over traditional inspection methods:
- Electronic documentation and reports
- Smaller footprint than traditional comparators
- Advanced patented technology, including CAD Auto-Align™ and CAD Auto-Pass/Fail™ tools
- Easy installation
- Superior-quality images
- Eliminate the need for optical comparator overlay charts
- Highly reliable
- Support for automated rotation for multiple views of the same part
- Automatically analyze multiple parts
These benefits are why more manufacturers are moving away from traditional mylar overlays in favor of digital solutions like VisionGauge® Digital Optical Comparators.
Upgrade Your Inspection Process with VisionGauge®
At VISIONx, Inc., our goal is to help your company’s inspection process become accurate, fast, and effective. VisionGauge® Digital Optical Comparators can help you streamline measurement and verification processes.
This helps employees complete tasks more quickly with high accuracy and reliability. Our operator-independent technology enables a wide range of automated results.
In addition to our state-of-the-art optical comparators, we also develop, sell, and support software, hardware, and other systems for all your inspection, measurement, and imaging needs. No matter what industry you’re in, you can rely on VISIONx, Inc. for standard or custom solutions.
Browse our available products or contact us for more information today.
Mylar Overlay FAQs
What are mylar overlay charts used for?
Mylar overlay charts are physical transparent guides that operators use to manually compare a part’s projected image to its CAD drawing on a traditional optical comparator. They help confirm whether a part’s dimensions fall within tolerance limits.
How often do mylar inspection overlays need to be replaced?
Optical comparator mylar overlays are prone to stretching, distortion, and damage from frequent handling, so they often need replacing sooner than expected. Design changes can also require a brand-new overlay, adding to long-term costs.
Are plastic overlay charts better than Mylar?
Not necessarily. Plastic overlay charts are a common alternative to Mylar, but the best material depends on your comparator, the level of durability you need, and how the chart will be handled. Mylar remains the most widely used option due to its balance of clarity and durability.
How do I know which optical comparator overlays I need?
Choosing the right optical comparator overlays depends on four main factors:
- The style of chart (CAD, grid, protractor, or combination)
- Your comparator’s model and type
- Lens magnification
- The overlay’s material
Getting each of these right ensures accurate, reliable measurements.
Can overlay charts be used with any optical comparator?
No, overlay charts need to match the specific model and magnification of the comparator they’re used with. An overlay made for one comparator may not align correctly on another, which is why it’s important to specify your equipment when ordering.
Do digital optical comparators eliminate the need for overlay charts entirely?
Yes, digital optical comparators use digital CAD charts instead of physical overlays, so there’s no need to print, store, or replace mylar overlay charts, even when part designs change.
What’s the difference between a traditional optical comparator and a digital optical comparator?
Traditional optical comparators require an operator to manually align a physical overlay chart with a part’s projected image.
Digital optical comparators use digital CAD charts that align and compare automatically. This makes digital comparators faster, more consistent, and less dependent on operator skill.
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