The pattern blocks are an inspection tool that, with a very high precision (and delicacy) allow us to know exact measurements; by using it in negative with measuring machines or tools, we can calibrate them .
What are pattern blocks?
The pattern blocks are solid rectangular tools, capable of materializing a finished length with a very high precision. These pieces are polished to ensure excellent parallelism and fullness.
The instruments are also called Johansson blocks , since their inventor was Carl Edward Johansson, who in 1888 worked as an inspector. The need for a new design of inspection tools, had the idea of building rectangular blocks with fixed measurements. Over time these blocks were called pattern blocks.
Important: They are not used to measure directly (a space, an opening, a light between pieces), but are used in a controlled, clean environment and to measure tools, which will then measure spaces, openings or light between pieces.
What are pattern blocks used for?
As we mentioned in the previous paragraph, the pattern blocks are used to materialize a length and use it as its name indicates as a pattern. This allows:
Know and allow to correct errors of machines or measurement tools .
Calibrate the measuring machines based on the pattern blocks.
Game and scales of pattern blocks
Although a set of pattern blocks has scales and different pieces for all uses, when a measurement is not possible to obtain, then the solution is to join pattern blocks to add their dimensions and thus be able to measure.
Note : Some heavy machinery industries make their own gauge blocks, due to the size of their parts and the need for a larger scale.
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Zoom Image – Appreciation of scale and variety of individual pieces in a pattern block set .
Requirements that the pattern blocks must meet
From its creation until today, the pattern blocks have evolved, meeting different quality requirements. Today the characteristics of these tools comply with ISO 3650 standards. The requirements to comply with this standard are:
Dimensional and geometric accuracy . It must meet length, parallelism, and flatness requirements.
Adhesion capacity with other pattern blocks. This quality is provided by the surface finish.
Dimensional stability over time.
Wear resistance.
Have a coefficient of thermal expansion similar to that of metals .
Be resistant to corrosion.
Types of gauge blocks
There are different types of pattern blocks depending on the material with which they are made.
Steel gauge blocks : They have high precision and dimensional stability. As for its coefficient of thermal expansion, it is low. They must be protected from moisture and corrosion and must be properly cleaned after use.
Carbide gauge blocks: These are generally made of tungsten or lead carbide . They offer a very good adhesion and are very resistant to wear.
Ceramic pattern blocks: They are the ones with the highest wear resistance and adhesion and stability properties. They are made of zirconium oxide. It has the advantage that magnetic impurities do not adhere as if it could happen in the other pieces, which causes them to be damaged.
How to use a pattern block
The pattern blocks come in a set of many pieces in boxes where said blocks grow by 1 mm or 0.5 microns depending on the number of pieces it contains.
It happens that many times we want to make a measurement and it does not exactly coincide with the length of an individual block, so a pattern block coupling process must be carried out to achieve the exact measurement.
The pattern blocks have the ability to adhere to each other through their faces. In this way they are joined to each other until reaching the measure that you want to materialize.
The indicated way to join pattern blocks is as the image above shows it; join them perpendicularly, rotate them until their sides to be joined are parallel, then raise/lower to center them, and finally we have image IV , a larger pattern block.
Care of the pattern blocks
As we mentioned in previous paragraphs, when we talk about pattern blocks we are talking about very high precision parts . This means that special care must be taken whenever a gauge block is used. For this, the following points must be taken into account:
TEMPERATURE
Work in a work environment with temperatures close to 20 °C ; no sudden changes in temperature, nor intense cold or heat because they can expand/contract.
WORK TABLE
Work on soft surfaces, always using gloves or tweezers , avoiding handling them with bare hands. This is due to grease from the hands and possible minor blows.
GENERAL CLEANING
Gauge blocks after use should be cleaned and lubricated before storage; this is because of the oil on your hands which can change the measurement.
What tools can we calibrate with gauge blocks?
Any space measurement instrument that is mobile (this is not the case of a tape measure or instruments that do not measure it directly but digitally or with light), can be calibrated with a set of standard blocks.
