Using a plug gauge involves checking the internal dimensions and accuracy of a hole or threaded feature in a workpiece. Here's a breakdown of how to use a plug gauge, incorporating information about thread plug gauges:
Understanding Plug Gauges
A plug gauge is a precision tool used to determine if a hole's size is within specified tolerances. For threaded holes, thread plug gauges are used.
Steps for Using a Thread Plug Gauge
Here’s how to properly use a thread plug gauge:
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Clean the Workpiece: Ensure the threaded hole in the workpiece is clean and free from debris. According to the reference, the chip groove on the gauge is not to be relied upon for cleaning. It is much better to clean the workpiece first.
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Select the Correct Gauge: Choose the appropriate thread plug gauge that matches the thread size and pitch of the hole you are inspecting.
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Inspection: Carefully insert the gauge into the threaded hole.
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"Go" and "No-Go" Gauges: Thread plug gauges often come in "go" and "no-go" pairs.
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Go Gauge: The "go" gauge should screw into the threaded hole with minimal resistance. It checks the lower limit of the thread size.
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No-Go Gauge: The "no-go" gauge should not screw in more than a few turns. It checks the upper limit of the thread size. If the "no-go" gauge enters too far, the thread is oversized.
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Best Practices
- Avoid Force: Never force a plug gauge. Forcing can damage the gauge or the workpiece.
- Cleanliness: Always keep the gauges clean to maintain their accuracy.
- Calibration: Regularly calibrate plug gauges to ensure they provide accurate measurements.
Example
Let's say you are inspecting a 1/4-20 UNC threaded hole.
- You would select a 1/4-20 UNC thread plug gauge set (go/no-go).
- First, try the "go" gauge. It should screw in easily by hand.
- Next, try the "no-go" gauge. It should not screw in more than a couple of turns. If it does, the threads are likely out of tolerance (oversized).
