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Surface plates and tables were one of the first types of metrology equipment. In British Inventor Henry Maudslay recognised the importance of a high precision surface plate. Named the father of the machine tool industry, Maudslay developed machinery that could produce identical tool parts. With his student Joseph Whitworth, they manufactured standardised and interchangeable parts. To ensure the parts they produced were standardised, a surface plate was required for precision tool production. The history of surface plates started with the development of mass production and continues to be important today.



It Started with Metal

As Henry Maudslay and Joseph Whitworth worked together, there is some dispute over who was the inventor of the surface plate. In Whitworth wrote a paper &#;On producing True Planes or Surfaces on Metals&#; and presented this to the British Institute of Mechanical Engineers in . In developing metal surface plates Maudslay and Whitworth created the system to scrape a cast iron plate to a flat plane.

Crown Windley

In a British Company called Crown Windley started to produce metal surface plates for sale. Due to the demand for machined tools created in the industrial revolution, it was important for engineers to have access to precise metal surface plates. Crown Windley created their own standard of close-grained cast iron. The surface plates were &#;state of the art&#; and were purchased by precision engineering workshops all over the world.

The product range developed by Crown Windley included box angle plates, squares and master straight edges. Crown products were a fundamental need during the first and second world wars as precision engineering became a necessary part of the war effort.

The Introduction of Granite

In the s, the demand for metal increased due to the second world war, but it&#;s availability limited. The introduction of granite for surface plates is credited to an American monument and metal shop owner called Wallace Herman. Along with his colleague Donald V Porter, they started using granite instead of metal for surface plates. It was soon established that black granite made a great alternative to metal due to its strength and vibration damping.

In Britain, Crown Windley also investigated granite as an alternative to metal and discovered it to be superior. Engineers working with iron had to spend a great amount of time to &#;stress relieve&#; an iron casting. As a natural substance granite has been weathering in the ground since time began so it is already stress free!

The benefits of granite as a hard-wearing surface plate that is non-magnetic and resistant to corrosion meant that iron was no longer the preferred material.

As the engineering industry developed granite remained the preferred material for surface plates. In , Crown Windley joined Eley Metrology. Eley had been manufacturing granite plates since and had started producing coordinate measuring machines with all granite guides. These are hand lapped to tolerances of 2 microns. Air bearings run superbly well on the high precision flatness and straightness that can be achieved with granite.

Eley&#;s coordinate measuring machines, as well as the ground-breaking Long Bore Machine (LBM), have the main bed and the X & Y Axis produced in granite. These plates are produced to limits which would be impossible in any other material other than granite.

Surface Plate Calibration

Like all items employed during the engineering manufacturing processes, wear does take place. Even granite may need re-conditioning before certifying the flatness in accordance with BS817.

It is a great advantage to carry out the res-surfacing work on-site. There is no need to employ a large surface grinding machine. A skilled engineer can perform this work by hand even on the largest table within a matter of days.

Although granite is a hard-wearing material, damage can still occur. It is important to follow guidance on surface plate maintenance to ensure they stay in good working order.

Eley Metrology, along with Crown Windley personnel, continue with both the sale of new granite plates and the service support and resurfacing of those that require re-certification.

The History of Surface Plates

The surface plate could be considered an important but underrated tool in the history of engineering. Having a standard to work from to ensure parts could be machined consistently is of great importance to modern engineering. The skill and expertise in standardising equipment and tools over the decades has had the surface plate at the base of everything.

It has been 80 years since granite began as an alternative to cast iron and it is now completely established as the foundation to many standards in the metrology field. The coordinate measuring machine (CMM) and the Long Bore Machine (LBM) represent the ultimate acknowledgement of granite as the only material used in this vital area of metrology.

The post The History of Surface Plates appeared first on Eley Metrology.

The Origin of Machine Precision and its Powerful Implications For Your Life

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You&#;re very likely looking at these words on a screen that is almost perfectly flat &#; on a device that required incredible precision to produce. If you find yourself in a modern building, the walls stand as straight as the milled lumber or steel behind them. The vast majority of technologies you and I enjoy were made possible, affordable, accessible &#; because of flatness, straightness &#; or as an engineer might say: trueness. We take physical accuracy for granted. For instance, think of the times you&#;ve borrowed a friend&#;s charger, it fit&#;s your device perfectly. But what makes that possible? The answer and it&#;s implications are startling.

I like tools, my garage is full of them. I&#;m not sure what prompted the question, but I thought to myself recently, &#;How did we get accurate tools?&#; It&#;s an extremely interesting question. How did we go from stone tools to iron axes to Mars rovers? A quick search honed my question: &#;How did we get precision tools?&#; The question was then distilled further: &#;What is the origin of precision?&#; The answer to this question is utterly mind blowing.

Precision &#; that is, the closest man has come to physical perfection is the product of imperfection correcting imperfection. Did that go over your head?Parts which are imperfect &#; lacking trueness in themselves, have the ability to bring other untrue objects into true. But there&#;s a big catch.

The Surface Plate

To unlock this knowledge, we must focus our attention on one of the cornerstones of the machine-tool world: the surface plate. A surface plate is a nearly perfectly flat plate, accurate to millionths of an inch, often made of granite or iron. The purpose of the surface plate is to serve as a reference to ultimate flatness. To know if a tool or part is flat, it is measured against the surface plate. Machine tools are calibrated by this plate, its flatness is thereby transferred to a myriad of machine-crafted products that make modern life possible.

A surface plate starts it&#;s life as a cast hunk of iron whose surface is roughly flat. To bring its surface into a true plane requires a process involving three imperfect plates. It must be stressed: at this stage, not a single plate is flat &#; assume we&#;re talking about the first three surface plates ever produced. At this point, the fundamental reference of physical flatness doesn&#;t exist, all the tools used up to this point are flawed.

The process which gives birth to a perfect plane is called the Whitworth three-plate method. In a nutshell, three iron plates &#; call them A, B and C &#; which are only kind of flat on their own, are rubbed (lapped) against each other in a process which will bring all three into near perfect planes. The powerful requirement for precision is three plates working together. My intention here is not to give a detailed technical explanation of the process, but to humbly open the door to all of its implications. If you are interested in reading more about the Whitworth method, check out this great article.

One cannot achieve a perfect plane with only two slabs of iron, it takes three.

What is the result of lapping only two plates together? Agreement and conformity &#; both technical terms. The plate&#;s surfaces will come into closer contact as they&#;re abraded; they will get flatter, but neither will become true. In fact, they will pick up a portion of one another&#;s errors even as they correct one another. The key to attaining a perfect plane is the introduction of plate C to the process &#; there is a wonderful lesson and mental model in this needed third plate.

Practical Applications

How accurate are any one of us in our view of the world? In our ideas and ideologies? In the opinions we hold about ourselves and others? In the last few years we&#;ve put up a lot of fences, we&#;ve spent a lot of time and effort lapping only two plates together &#; us and our pet ideas.

Like iron plates, it is vital that we interact with one another and with ideas we might find uncomfortable to gain greater accuracy in our personal models of reality. It is naive to think that accurate thinking is even possible without introducing plate C to the picture &#; that person or idea with whom we disagree, dismiss, dislike, whatever the case. We will correct and introduce error into one another, therefore, we must persist in the process of seeking out interactions with those who are different from ourselves, with ideas we&#;ve not taken the time to understand.

When we wall off and dismiss plate C, we create echo chambers where the outcome is mere conformity and progress is traded away for comfort.

If diversity in iron plates is a requirement for precision, how much more is this true for you and I?

Are you interested in learning more about Precision Surface Plate? Contact us today to secure an expert consultation!