Engineer's blue
Encyclopedia
Engineer's blue is a highly pigmented paste used to assist in the mating of two or more components.
Joseph Whitworth
popularized the first practical method of making accurate flat surfaces, during the 1830s, by using engineer's blue and scraping
techniques on three trial surfaces. Prior to his scraping technique, the same three plate method was employed using polishing techniques, giving less accurate results. This improvement led to an explosion of development of precision instruments using these flat surface
generation techniques as a basis for further construction of precise shapes.
Engineer's blue is prepared by mixing Prussian blue
with a non-drying oily material (for example, grease). The coloured oil is rubbed onto a reference surface, and the workpiece is then rubbed against the coloured reference; the transfer (by contact) of the pigment indicates the position of high spots on the workpiece. This method has been used to test the flatness
of surfaces and the trueness of a bearing assembly.
When Prussian blue is mixed with methylated spirit
s it forms a quick drying stain which is known as marking blue
or layout dye. This stain is used in the marking out
operation in metalworking. Both the "marking out" blue, and the "scraping blue" may be referred to as engineer's blue, which can lead to substantial confusion.
The engineer may be told to "Blue it up" when using this piece of equipment.
Prussian blue is widely used by tool makers when the core
and cavity of a mould is matched during final assembly. It is also used in other tooling applications—especially during assembly—such as stamping tools and pressure die casting tools. A thin coating of Prussian blue is applied (usually with a paint brush) on the 'insert'—regardless of the shape or contour—of the mould or tool before the matching is done with the mating part. If the Prussian blue (generally called as just "blue") appears evenly on the mating area, it is considered—by the tool makers—as "good matching" and thus expecting a good final product from the tool. Usually no tool would be transferred to testing or production without "blue matching", a term generally used by the tool makers in Asia. In other words, Prussian blue is considered as an integral part of precision tool making.
Note: in the US, the terms machinist's blue, scraping blue, or simply bluing are used instead of engineer's blue.
Joseph Whitworth
Joseph Whitworth
Sir Joseph Whitworth, 1st Baronet was an English engineer, entrepreneur, inventor and philanthropist. In 1841, he devised the British Standard Whitworth system, which created an accepted standard for screw threads...
popularized the first practical method of making accurate flat surfaces, during the 1830s, by using engineer's blue and scraping
Hand scraper
A hand scraper is a single-edged tool used to scrape metal from a surface. This may be required where a surface needs to be trued, corrected for fit to a mating part, needs to retain oil , or even to give a decorative finish.Surface plates were traditionally made by scraping...
techniques on three trial surfaces. Prior to his scraping technique, the same three plate method was employed using polishing techniques, giving less accurate results. This improvement led to an explosion of development of precision instruments using these flat surface
Surface plate
A surface plate is a solid, flat plate used as the main horizontal reference plane for precision inspection, marking out , and tooling setup. The surface plate is often used as the baseline for all measurements to the workpiece, therefore one primary surface is finished extremely flat with...
generation techniques as a basis for further construction of precise shapes.
Engineer's blue is prepared by mixing Prussian blue
Prussian blue
Prussian blue is a dark blue pigment with the idealized formula Fe718. Another name for the color Prussian blue is Berlin blue or, in painting, Parisian blue. Turnbull's blue is the same substance but is made from different reagents....
with a non-drying oily material (for example, grease). The coloured oil is rubbed onto a reference surface, and the workpiece is then rubbed against the coloured reference; the transfer (by contact) of the pigment indicates the position of high spots on the workpiece. This method has been used to test the flatness
Flatness
Flatness may refer to:*Flatness *Flatness *Flatness *Flatness *Flatness , a geometrical tolerance required in certain manufacturing situations*Flatness...
of surfaces and the trueness of a bearing assembly.
When Prussian blue is mixed with methylated spirit
Methylated spirit
Denatured alcohol or methylated spirits is ethanol that has additives to make it more poisonous or unpalatable, and thus, undrinkable. In some cases it is also dyed....
s it forms a quick drying stain which is known as marking blue
Marking blue
Marking blue, layout stain or Prussian blue is a dye used in metalworking to aid in marking out rough parts for further machining. It is sometimes called Dykem...
or layout dye. This stain is used in the marking out
Marking out
Marking out or layout is the process of transferring a design or pattern to a workpiece, as the first step in the manufacturing process...
operation in metalworking. Both the "marking out" blue, and the "scraping blue" may be referred to as engineer's blue, which can lead to substantial confusion.
The engineer may be told to "Blue it up" when using this piece of equipment.
Prussian blue is widely used by tool makers when the core
Core (manufacturing)
A core is a device used in casting and molding processes to produce internal cavities and reentrant angles. The core is normally a disposable item that is destroyed to get it out of the piece. They are most commonly used in sand casting, but are also used in injection molding.An intriguing example...
and cavity of a mould is matched during final assembly. It is also used in other tooling applications—especially during assembly—such as stamping tools and pressure die casting tools. A thin coating of Prussian blue is applied (usually with a paint brush) on the 'insert'—regardless of the shape or contour—of the mould or tool before the matching is done with the mating part. If the Prussian blue (generally called as just "blue") appears evenly on the mating area, it is considered—by the tool makers—as "good matching" and thus expecting a good final product from the tool. Usually no tool would be transferred to testing or production without "blue matching", a term generally used by the tool makers in Asia. In other words, Prussian blue is considered as an integral part of precision tool making.
Note: in the US, the terms machinist's blue, scraping blue, or simply bluing are used instead of engineer's blue.