Gauge blocks come with a purpose to serve as a reference standard for length. We use them whether in lab or workshop.
Dimensional measuring instruments such as micrometers (outside, inside, and depth micrometers), calipers (both the vernier, dial, and digital caliper models), indicators (both dial and dial test indicator), and height gauge benefit from these blocks for inspection and calibration.
Even, it can be used as a shop floor tool, for example, it’s used together with a sine bar to measure an angle.
If you are the person that frequently uses the above measuring tools, you should keep a set of gauge blocks so that you can use it to regularly check the accuracy of your measuring tools such as caliper.
And if this is your first time buying gauge block, there are several important things you have to put attention in terms of gauge block buying. Imagine if you need a gauge block for calibration in your company lab, but you waste money because you buy the workshop grade. Vice versa, if you buy the calibration grade gauge blocks for workshop use, it’s overkill.
Here are 7 factors to consider when buying gauge block.
- The gauge block grade
- Physical characteristics
- Unit measurement system (mm or inch)
- Amount of gauge block units in a set
- Manufacturer’s certificate of inspection
1. What Grade to Choose?
The first thing you need to pay attention is the grade. When talking about grade, it means talking about accuracy.
Grade = Accuracy
Gauge blocks are not made equal in terms of accuracy. Some of them fall between a certain accuracy, thus it has a certain grade. They are also classified into several grades to indicate their best application. The grading criterion depends according to the size or length’s tolerance of gauge blocks. The higher the grade, the lower the tolerance, the higher the accuracy.
Aside from that, gauge block grading standard varies in details depending on location such as the US, British, and Japanese Standard.
a. Workshop level gauge blocks
Any gauge blocks that are used in the workshop are workshop level gauge blocks. Whether for working standard, calibration, inspection, machine tools setup, sine bar setup, gap gauge checking, etc, as long as it runs in the workshop, it is worksop level gauge blocks.
That said, the Grade 0, Grade AS1, and Grade AS2 of ASME grading are considered workshop level gauge blocks. However, Grade AS1 and Grade AS2 are more common to use on the shop floor, while Grade 0 requires extra care.
b. Inspection level gauge blocks
This gauge block is mostly used in the inspection area to verify the accuracy of gauges and measuring instruments. Before the process of measurement or gauging operates, an inspection over the gauges and measuring instruments will require these inspection gauge blocks.
Inspection level gauge blocks include Grade 0, Grade AS1, and Grade AS2 of ASME grading standards. It depends on the accuracy requirement for the inspection.
If you are working with common measuring instruments for your manufactured goods, these gauge blocks are required to conduct daily tool verification on your inspection area. It is also used for sampling inspection of mechanical parts, tools, and other manufactured goods with strict dimensional requirements.
c. Calibration grade gauge blocks
Keep in mind that calibration is different from inspection. Calibration requires documentation and even the uncertainty is recorded.
Calibration level gauge blocks are used for calibration. Calibrating the gauge blocks (the other lower grade ones) and measuring instruments require these blocks. That said, the ASME grading system of Grade K, Grade 00, and Grade 0 are categorized as calibration level gauge blocks.
The grade 00 will be compared to Grade 0 in order to check the accuracy of Grade 0. While the grade 0 can be used to calibrate the micrometer.
These calibration gauge blocks are used only by certified calibration experts which are stored and monitored in a controlled environment where thermal expansion is strictly observed. Manufacturers of high precision tools and companies which offer calibration services use Grade 0 gauge blocks.
Other manufacturing companies with certified internal calibration staff also purchase this gauge block.
d. Reference grade gauge blocks
The reference level gauge block is the master gauge block that serves as the length laboratory reference. That said, it’s unusual to put these blocks on the shop floor. This grade is designed to calibrate gauge blocks only, not instruments.
Grade K (ASME) and Grade 00 (ASME) gauge blocks refer to reference-grade gauge blocks.
2. Gauge Block Physical Characteristics
Another factor to consider when buying gauge blocks is material. The material composition characteristics give advantages as well as disadvantages to the users. As long as the disadvantage is manageable, that should be the choice. Durability, thermal expansion, rusting, and maintenance are some points to consider derived from the gauge block material.
There are 4 known materials to make gauge blocks: Steel, Tungsten Carbide, Chromium Carbide, and (Zirconia-based) Ceramic.
a. Steel gauge blocks
- Gauge blocks made of steel has a physical property that is high resistance to wear
- Steel gauge blocks are the most affordable choice
- The hardness score is 800 HV
- Steel, tungsten carbide, and chromium carbide are very stable in terms of material stability.
- The thermal expansion coefficient of steel is pretty large which is 11.5 × 10−6 K−1. And this number can vary 10% according to ISO 3650. However, it is manageable. As long as you control the temperature at 20°C, this disadvantage can be eliminated. Another way is by figuring out the temperature itself in calibration. Another case is when you work at 25°C, you have to cut oversize the tools that are being made by the machine tools. So, when the machined tools are measured at 20°C, the tools shrink and the measuring instrument shows the correct size.
- Corrosion. Needs proper care to maintain it. Use gloves.
Steel gauge blocks were the most common kind of gauge block from the beginning. Since most industrial products that need gauge blocks are mostly metal parts, the most efficient use of gauge blocks also requires hardened steel or a metal material since it is more likely to be durable.
This gauge block is also the cheapest material type of gauge block that is very convenient if you want to have a more extensive set of gauge blocks in your workshop. However, steel gauge blocks have the highest thermal expansion coefficient making it to be the least kind. Its precision will decline faster than the other kinds of block gauges over a period of time.
Steel material can rust if we do not use gloves while using it. Frequent maintenance and application of necessary oil are necessary to prevent it from corrosion.
b. Ceramic gauge blocks
- No corrosion
- highly resistant to scratches and wear
- Hardness is 1400 HV
- Ceramic’s thermal expansion coefficient is (9,7 ± 0,8) × 10−6 K−1. This model even comes with a nearly zero thermal expansion coefficient. This advanced ceramic allows you to perform calibration although the environment is impossible/difficult to reach 20°C.
Ceramic gauge blocks have a lower thermal expansion coefficient compared to steel alloy. Since it has a low thermal expansion coefficient and non-magnetic properties, it should be the best choice for calibration.
It will also not rust and corrode compared to other metal alloy gauge blocks.
In measuring soft material products with a strict dimensional requirement, ceramic gauge block is best used.
c. Carbide gauge blocks
Carbide gauge blocks can be tungsten carbide or chrome carbide.
– Tungsten Carbide
- Like steel, tungsten carbide is very stable
- Tungsten’s coefficient of thermal expansion is interestingly about 3 times lower than steel (4,23 ± 0,1) × 10−6 K−1.
- Hardness is 1400 HV
- Tungsten carbide’s wear resistance is as 10 times as steel gauges
- For frequent use
- Incredible wringing ability; this quality leads to a reliable result
– Chrome Carbide
- Very stable; its high stability lets you assure that there is no material growth after years of use.
- Chromium carbide’s coefficient of thermal expansion is lower than steel which is 8.4 × 10−6 K−1 (Source)
Carbide consists of a combination of the elements of carbon and tungsten. These two elements form an alloy that is more heat resistant compared to steel. In other words, its length will not easily change. Aside from that, carbide gauge blocks are also harder than steel alloy. It does not rust easily compared to other metals.
Gauge blocks made of carbide mainly were used as reference masters due to their characteristics.
3. Imperial or Metric?
The gauge block is available in the metric (mm) and imperial (inch) systems. However, the length is marked in one system only (inch or mm). So, you have to pick one. If you live in the USA, you’ll be likely to pick the inch markings unless you have another need. If you pick the mm system, but you actually need the inch ones, you will end up doing math a lot. It’s not convenient for you.
4. Gauge Block Classification based on Shape
There are 3 typical gauge block shapes available in the market: rectangular, square, and custom-size gauge blocks.
A rectangular gauge block is the most efficient gauge block in measuring smaller spaces. It was the original shape of the gauge block that was first developed. It is also the most common gauge block that you can see in the inspection area.
In terms of rectangular shape gauge block, the dimensions of measuring face length and width are defined depending on the central lengths of the gauge block. From 0.5 mm to 10 mm length of gauge block, measuring face dimension length and width is 30 mm × 9 mm. On the other hand, the measuring face length and width are 35 mm × 9 mm for a more extended gauge block.
These are the definition of the terms of the cross-sectional dimension of gauge blocks:
- Measuring face. It can be any of the two parallel planes that can be wrung to an auxiliary plane.
- Length. It is the perpendicular distance from any point of the measuring face to the other end of the block wrung to the auxiliary plane.
- Central length. It is the length of a gauge block taken at the center point of the free measuring face.
Square gauge blocks have holes in the center making it the easiest type to make a stack connected by rod and screws. It is the most efficient type to use to make limit gauge and Go No-Go Gauge.
For square gauge blocks, the cross-sectional dimension is 24 mm × 24 mm.
– Customized Shape
Custom-size gauge blocks are those gauge blocks that may or may not be available in the market. It is manufactured based on the request and needs of the customer.
Selecting the length of the gauge block that you need depends on your needs. Make sure that you know first the Grade of the gauge block that you need to purchase. Upon deciding the grade, you must check the lengths that you need. Gauge block manufacturers sell sets of gauge blocks in different lengths.
5. Individual or Gauge Block Sets
Several manufacturers of gauge blocks offer different sets of lengths of gauge blocks. You may purchase it by sets of different lengths or individual sets for a certain nominal length.
For industrial processes, the most commonly used length of gauge block set ranges from 1.0005 mm to 1000 mm for a rectangular gauge block.
A smaller workshop requires a smaller range of length. For example, Mitutoyo 516-404-26 which contains 81 blocks starting from .1001″ to 4″ is good for the workshop. Further, the gauge block set for micrometer inspection only may have a smaller range of length and fewer blocks, especially the micrometer that has a 1-inch range.
There is also an individual length option that the manufacturers offer. In case you need a particular set of gauge blocks for only a certain length you need to measure repeatedly, buying an individual gauge block is highly recommended.
Most suppliers do not have sets of gauge blocks for a certain length that you desired. You may contact them if you really need to purchase, however it will be custom-sized. Again, custom-sized gauge blocks are more expensive than the sets that are sold in the market.
6. Gauge Block Manufacturer’s Certificate of Inspection
When buying gauge blocks, make sure to check the manufacturer’s inspection certificate. Some manufacturers provide inspection certificates to ensure that their gauge block meets the standards and was produced in good condition during the time of inspection.
When purchasing a set of gauge blocks, don’t forget to consider the accessories that come with it. An optical flat for flatness inspection (of micrometer calibration), gauge block holder, etc may include in the box. These accessories can be a nice consideration when buying gauge blocks.
That’s all the 7 factors of the gauge block buying guide that we compile to let you consider yourself. Perhaps, it covers the entire questions that pop up in your mind. As gauge block (whether a set or individual) is expensive, investing some time to research will be worth it spending.