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This fixture-gaging alternative is a fast, easy way to measure simple parts.
Bill Chambers Published: 05/11/2005
The aforementioned more sophisticated measuring methods require more lengthy, involved measuring procedures, a relatively high-level skill set and considerable expertise. Although necessary for many applications, complex measuring methods on manually operated systems are also more prone to human error.
Unlike more complex measuring methods, fixture gaging is less labor intensive and requires much less training. Gage operators don’t have to be highly trained. In fact, little or no on the job training is needed—which means short lead time to get operators up and running and the product out the door.
The basic procedure for fixture gaging is to load the part, bring the measuring probes into contact with the part and enter the data. Then remove the part, load the next part and repeat the procedure.
“Go/no-go” gaging may seem like old technology, but add the power of probing combined with a microprocessor and your capabilities will significantly increase. A typical, basic example might involve a probe such as a linear variable displacement transducer that contacts a part and measures the variance from a perfect part.
The simplest “go/no-go” gages have straight-forward digital readout displays or columns that provide a direct reading of the values from the probe. The more sophisticated systems for fixture gaging are computer-based, require skilled operators and are expensive to run and maintain. Some manufacturers offer a new middle ground via advanced gage amplifiers. For example, Gage Chek by Metronics Inc. features a microprocessor-based amplifier that’s simple to read and compact, and measures just 7.5 in. by 11.5 in.
Advanced gage amplifiers display the number value of the part being measured and provide visual and audio clues when parts fail. Their highly visible, intuitive and familiar interfaces with standard color cues instantly informs operators of pass/fail performance details. In some instances, relay connections can be automatically programmed to open and close if certain conditions are met, providing instant feedback when dimensions are out of tolerance.
Advanced Gage Amplifier Performance Details |
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| Numerical values are displayed, but there are also visual and audio clues. Measurements close to nominal values are green. Yellow appears at the warning level. Red shows an out-of-tolerance condition. These displays are familiar to an operator who’s accustomed to using column gages or dial indicators. The more sophisticated computations happen in the background, keeping the system user-friendly. |
Sophisticated gage amplifiers provide direct probe outputs that can be algebraically and mathematically combined for dimensions such as thickness, flatness, dwell angles and maximum tip heights. Results can be displayed numerically, graphically or archived for process studies such as simple statistical process control (i.e., X-bar and range charts). Trigonometric formulas can convert linear measurements into angular measurements. Other formulas can also be created for total indicator runout (TIR), volume, angles between camshaft lobes and more.
When using a display device, it’s important to have access to external interfaces. It should provide connectivity to PCs and other devices for data collection, printouts, reports and other documentation requirements. Also beneficial, SPC functions can be integrated right into the device so operators are able to ensure a process is corrected before out of tolerance parts are manufactured, as shown in the figure below.
| Example of Integrated SPC Functions |
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| Integrated SPC functions eliminate the need to send the data to an external SPC program. Data tables can be displayed with range, mean, maximum, minimum, standard deviation information. X-bar and R charts can also be viewed and display red when the process is out of control limits. Source: Gage Chek by Metronics Inc. |
Fixture gaging using an advanced multifunction gage amplifier can be the perfect solution to quickly ensure the quality of a new product. It’s easy to operate, yet its powerful and flexible microprocessor offers a range of gaging solutions for many manufacturing applications.
By answering the following questions during the planning stage, you can save money by specifying the correct measuring system from the start:
Before creating a fixture and a part program, try to thoroughly think of possible requirements of your application. Planning ahead will save you time and money in the long run. Although this applies to fixture gaging and coordinate measuring systems, asking the right questions will help you design and select the most effective system, regardless of the type of measuring equipment.
Think about what you need. Do you want to see all the data or just the end results? For example, a TIR is the maximum position value minus the minimum position value. Do you just want TIR, or do you need the maximum and minimum values included?
Think about what you need to accomplish. Do you want an angle? Use a trigonometry function. Do you need to trigger an external device? Use a formula that controls a relay or an I/O line.
Think about how your tolerances are written. Do you want a warning zone for parts that approach the out-of-spec condition? What’s the accuracy and resolution? In general, it’s wise to specify gaging that has five to 10 times the accuracy capability of your current application, so you can be prepared for future accuracy needs in other applications.
Think about your math. Inches or millimeters times each other will be squared or cubed. Divided, they become ratios, which are unit-less numbers.
Do you want the data to be simply displayed without being recorded? Do you want to create printed reports directly to a printer? Do you want data to go to a computer? Will you use the data for SPC purposes, (i.e., charting histograms, attributes, X-bar, etc.)?
Will the parts be contacted with conventional probes or is the application non contact? What are the types and how many are needed? How will they be held/fixed? Will the measuring take place during manufacturing or post process?
Bill Chambers is a product specialist at Metronics Inc. in Bedford, New Hampshire. He has been with Metronics for more than two years and has 16 years of experience in the scientific and industrial instrumentation.
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