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What is a bore gage?

What exactly is a bore gage? Well, we are here to tell you! Most simply, a bore gage is as described by its name, a tool to gauge bores. 
“Bore” is the term used for any sort of hole. A “gage” is a tool used to measure an object. As a result, a bore gauge is a tool used to measure the size of a particular hole. 
Simple enough, right? 

Different Types of Bore Gages 

Although bore gages are straightforward in concept, there are many different types of bore gages used for a range of applications. 
Here are a few different types and what each bore gage is typically used for: 

Telescopic Bore Gage 

The telescopic bore gage is very similar to the inside caliper and used to measure the size of a bore. 
  • First, the user must insert the telescopic bore gage into the bore at a small angle. 
  • Then, the gage is locked by twisting the knurled end of the handles. The user will want to set the size of the bore gage just above the size of the bore itself. 
  • The telescopic bore gage must then be slowly rocked until the device reaches the other side of the bore. 
  • This results in determining both the diameter of the bore in addition to the bore axis at its center. 
  • Completing the full motion from one side of the bore to the other, the two anvils on the telescopic gage remain locked when removed. 
  • Lastly, use either a micrometer or a caliper to determine the actual measurement from the locked bore gage.
The signature feature of the telescopic bore gage is that it measures the size of a bore by transferring the diameter to a remote measuring tool. 
Remember to use either a micrometer or a caliper to determine the actual measurement from the locked bore gage.

Small Hole Gages 

Small hole gages are like telescopic bore gages but used a bit differently. They’re especially preferable when needing to measure a bore that is smaller in size. 
When using a small hole bore gage, the user will insert the gage into the hole, again at a slight angle. However, when using this particular type of bore gage, remember to set it at a size smaller than the bore measured. 
  • Insert the gage into the bore. The knurled knob adjusts until there is small pressure against the side. 
  • When the small hole bore gage is removed, the measurement is transferred and read on a micrometer or caliper.
There are two types of small hole bore gages: full-ball and half-ball. Generally, full-ball gages are easier to set and maintain. This compares to half-ball gages, which have more spring.

Beam Bore Gages 

Beam bore gages utilize the bore needing to be measured large in diameter. 
  • To use a beam bore gage, the beam must be placed at one end of the bore while the other end of the gage is slid along the diameter. 
  • While completing this movement, the user should watch the dial indicator. 
  • The measurement is complete once the dial indicator output begins to decrease.
  • For optimal precision, this should be completed three separate times to take an average for the final measurement.

Dial Bore Gage

The dial bore gage is a more direct tool to measure the size of a particular bore. 
To take a measurement of a bore, a knob on the dial bore gage is rotated. 
  • This rotation of the knob results in the inward and outward movement of three anvils. These anvils protrue symmetrically from the body of the gage. 
  • As the anvils adjust to match the size of the bore, the information is sent to the dial or micrometer mechanism. This produces a final measurement for the bore gage. 
Additionally, bore gages are available electronically to speed up this dial bore gage process.

Understanding Bore Gages with Higher Precision

Bore gages are simple, yet intricate tools important for any precision measurement shop. Understanding the different types of bore gages and how they work will help you find the right tool!

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