Comparative instruments, such as an adjustable bore gage, can feature an electronic readout or dial that displays the direction and amount of variation in the test bore, from the nominal size. If you are using adjustable bore gages this way, you need to set the gage to the required nominal size, to which the bore is to be compared. There are various ways to set the bore gage to the nominal size. The methods explained below can provide a balance of versatility and reliability, precision, and speed. Read on to find out which setup method will work best for you:
Setting Via Gage Block Assemblies
If you are looking for something that can serve as a highly accurate reference master, you can consider utilizing a gage block assembly. It is recommended that you get a clamp that has jaws at both ends. If you need to measure multiple sizes and flexibility is key, you will be pleased to know that this is the preferred method. It is important to note that gage blocks are the most basic reference standard. The blocks are readily available and provide exceptional accuracy. When it comes to assembling the gage block stack to the nominal size, it may take up some time but that’s normal. Next, only a single stack is used so there is no way to verify the presence of wringing errors. That’s a small issue but may affect the performance of the bore gage.
Setting Via Master Rings
Using master rings is currently the best way to set one’s adjustable bore gage. As master rings can be made very close to the part size, they can duplicate the actual measurement. Most bore gages feature a flat surface on the head and it is parallel to the sensitive contact and reference point. This method works by placing the ring on a granite surface plate. The gage is then set in the ring to be supported. Next, the sensitive contact will be adjusted until the indicator reads zero. Alternatively, you can incorporate a ring gage (as the offset) into the set of the dial indicator. It does not have to be exactly the nominal size. Are there other scenarios where ring gages come in handy? Certainly! A) When the gage is going to be dedicated to a particular size. B) When you need to set repetitive sizes.
Setting Via Outside Micrometers
If there is a need for speed, you can never go wrong with outside micrometers. However, micrometers can pass inherent errors to the bore gage. Another common issue that people face is not being able to accurately align and load the spherical measuring points of the gage on the micrometer contacts. To be exact, this setup method offers an accuracy of no better than 0.002 inch.
Proceed with Caution
Just like how you would set any gage, you need to set bore gages with an equal amount of care. When setting up with gage blocks or masters, you must ensure that these materials are free of dirt and clean at all times. Additionally, they must be temperature stable. Once you set the reference contact to the desired size and secure the locking screw (by snugging it down), you should test again for repeatability and zero. You may need to repeat the steps until the results give you the confidence that the gage is performing accurately.