Vision Quest: Drilling Performance

Courtesy of Pointe Precision

Pointe Precision’s machine operators have access to a 10× stereo microscope mounted on a swivel arm at every bench.

How microscopes and vision systems are used in machine shops for noncontact inspection and measurement.

When inspecting and measuring parts and part features on the shop floor, operators can choose among capabilities to see them, see them really well, and to document what they see. The equipment required to perform these functions varies in capability and price, and a machine shop must determine exactly what it wants to accomplish when choosing microscopes and vision measurement systems.

3-D Look

Stereo microscopes provide a 3-D view of the part and generally are used for visual inspection, not measurement. “A stereo microscope works like the human eye, which means it has good depth of field,” said Darrell Sanderson, national sales manager for Nikon Metrology Inc., Brighton, Mich. “You can see a 3-D image magnified maybe 20× or 30× on a stereo microscope.”

It is most common to look through the eyepiece when using stereo microscopes, but they also are available with a digital camera to view the part on a computer screen. Shops that want to document a defect can do so by adding the camera and software.

A common misconception with stereo microscopes is the part has to fit on the microscope stage. Instead, these microscopes can be removed from their stand and mounted on a boom stand or articulating arm. “You can bring the microscope to the part,” Sanderson said. “You can scan over an engine block or large turbine blade looking for very small defects.”

Stereo microscopes are appropriate for the shop floor as well as the QC lab to inspect a part after it has been machined. “It is popular for users to look for strange artifacts, defects or burrs,” Sanderson said. “Also, they might want to see the surface condition of the part.”

An example of a larger shop using stereo microscopes is Pointe Precision Inc., Plover, Wis. Founded in 1995, Pointe is a contract machine shop specializing in milling, turning, grinding and heat treating. About 75 percent of Pointe’s work is in the aerospace industry, 8 percent is in medical, and the rest is recreational, industrial and commercial.

The company has 2,000 part numbers. The smallest parts measure less than 0.100 ” in diameter and the biggest are 28 “×24 “×16 “. A simple part might have three or four features that need inspection but some have 200 or more features.

Pointe’s machine operators are responsible for inspecting their parts. They have access to a variety of inspection equipment, including a Unitron 10× stereo microscope mounted on a swivel arm at every bench. “We have additional microscopes that can go up to 30× for visual inspection located throughout the shop,” said Sam Crueger, Pointe’s director of engineering services.

Courtesy of Nikon

The iNEXIV VMA 2520 vision measurement system from Nikon has a black-and-white camera, 250mm × 200mm stage travel and up to 300× magnification.

Operators must document frequency of inspection as well. “We inspect every part feature using various methods with a dimensional tolerance accuracy from 0.020″ to 0.000040″,” Crueger said.

Pointe’s final inspection department visually inspects the parts, looking for scratches and burrs. “Controlling burrs is a major part of what we do,” said Tom Dickman, quality manager for Pointe. “We are accountable for the removal of all of the burrs on a part. The inspection department inspects all part features that have a tolerance of 0.003 ” or tighter. Pointe is dedicated to quality at the source, so our shop floor operators are just as skilled as our final inspectors.”

Another application for stereo microscopes is cutting tool inspection. Contract manufacturer Stark Industrial LLC’s operators use them on the shop floor. “We use a Mitutoyo stereo microscope on parts with small, intricate geometries, but also on cutting tools to get an idea of developing cutting tool wear patterns,” said Jonathan Wilkof, manufacturing engineer for Stark Industrial, North Canton, Ohio. “For instance, after drilling 250 holes, we might check the drill on a stereo microscope to determine what is happening on the edge or how the coating looks.”

Back to 2-D

While rough measurements can be performed on stereo microscopes, measuring microscopes, or toolmakers’ microscopes, produce a 2-D image for more critical measurements.

“Optical measuring systems have specific characteristics, notably a relatively small depth of field,” said Tim Sladden, director of marketing communications for Quality Vision International, Rochester, N.Y., a vision metrology company with divisions that include Optical Gaging Products and RAM Optical. “For precision measurements, it’s important that the feature of interest be in very good focus. Typically, the higher the magnification, the smaller the DOF and the greater the resolution. In other words, the ability to measure something small gets better because we see things in more detail at a higher magnification.”

There are tradeoffs, Sladden continued. “At a higher magnification, the imaging area is smaller, so you may be limited in the number of features you can image in a single field of view.”

While an eyepiece is typically used with stereo microscopes, with measuring microscopes the image is usually shown on a computer screen using a video camera. The measurement is made in the software using the image from the camera, not using the part itself.

Courtesy of Gradient Lens

The Luxxor video microscope from Gradient Lens being used to measure a surgical needle.

“It is easier for the operator because they don’t have to strain their eyes,” Stark Industrial’s Wilkof said. “They can move the microscope stage in the X and Y direction and see the part moving around while looking comfortably at the computer screen. The operator takes a series of data points, say around a circle, and the software takes those points and calculates the circle that those points make up. He can take a number of points and measure diameters, lengths, arcs and angles.” If documented inspection is required, the data can be output in a spreadsheet or statistical process control program.

In addition to making parts for the medical, oil and gas and aerospace industries, Stark Industrial is a distributor of Mitutoyo and ST Industries measuring equipment.

The company specializes in small-hole drilling. “We produce holes from 0.008″ to 0.250″ in diameter. Depending on the hole size and depth, we can hit tolerances of less than 0.001″,” Wilkof said. “Placing a measuring microscope on a table with a vision setup is an excellent way to measure those features.”

These types of measuring microscopes are considered semi-automated. The operator is responsible for taking the data points and feeding them to the computer.

In a clean, well-maintained machine shop environment, these microscopes are suitable for the shop floor.

Manual Matters

The Luxxor video microscope from Gradient Lens Corp., Rochester, N.Y., is a manual video microscope. “It has great image quality and good capabilities, but it doesn’t have a lot of complex features,” said Doug Kindred, president and chief scientist. “The Luxxor provides the ease of video and the image capture and measurement capability of more expensive vision systems. The idea is very much like the traditional toolmaker’s microscope. You use it for measurements that are difficult to do with a caliper or micrometer.”

The lens and zoom are manually focused. “Higher priced systems have automated edge detection,” Kindred said. “With the Luxxor, the crosshairs are aligned on the part with the mouse, producing measurements accurate to ±0.001″.” The magnification of the Luxxor is from 15× to 83×; adapters are available that allow 200× magnification.

Courtesy of Optical Gaging Products