Machine Tool Spindles, Design and Principles
Cranfield Precision have been designing and manufacturing custom designed, bespoke spindles for machine tools and measuring machines for nearly 40 years. These spindles have been supplied into many industries, including aerospace, automotive, semiconductor, medical etc. We have designed and built spindles in volumes of between one-off and hundreds.
Our particular strength lies in the breadth of experience, built up over the years, that allows us to apply different technologies so suit a particular application. The fundamental bearing types can be broken down into three basic types, rolling element, fluid film, and magnetic levitation, and while we have experience with all three over the years, our main focus of expertise is in fluid film bearing and rolling element spindles. They can be further sub-divided into units that rotate at controlled speed, or require positioning capability – and often both.
The term fluid film bearing refers to a spindle where the rotor is supported within its housing by a pressurised film of fluid, either liquid or gas. The fluid can be pressurised externally, by a pump, or by features within the fluid gap within the bearing, or a combination of the two. Cranfield Precision fluid film spindles fall into the categories of hydrostatic (externally pressurised liquid), aerostatic (externally pressurised gas) and hydrodynamic hybrid (externally pressurised with enhanced internal pressure generation at speed).
Fluid film bearings can be capable of supporting extremely high loads, can exhibit extremely high levels of rotational accuracy, and can often be shown to be one of the stiffest elements in a machine system. Their smooth running and ability to damp out externally generated vibrations can also be a significant advantage when applied to a cutting or measuring process.
We do not offer a specific range of pre-designed spindles, but prefer to design a spindle that specifically meets the requirements of an application, however some examples of the products designed and built by Cranfield Precision are given below for illustration;
These, generally rolling element devices, are supplied into the position guidance systems manufacturing industry as a reference standard to calibrate motions. Speeds vary down to earth rate (1 revolution in 24 hours) to hundreds of RPM. Rate control is held within NOT MUCH and we have supplied them in single, two and 3 axis combinations.
Our market has primarily been the automotive market, with our designs incorporated into the cam and crank grinding products of our parent company; Fives Landis Ltd, but have also been applied to other products as diverse as gyroscope spindle grinding for aerospace and defence, and silicon wafer grinding for the semiconductor industry. Aerostatic and hydrostatic bearings have been built into spindles for wheel sizes up to 2 metres, powers of 100 KW and speeds to 24,000 RPM.
Ultra-precision hydrostatic spindles, combining synchronous and asynchronous error motions below 50 nm have been supplied, built into turning machines of the highest accuracy, while maintaining load capacity of 1000KG ???. These spindles also provide dynamic positioning capability of NUMBERS. We also supply spindles for our DeltaTurn machines, for hard turning up to 12,000 RPM. A water, porous ceramic spindle is also being applied to an ultra-precision lathe for optics manufacture.
Measuring Spindles and Rotary Tables.
Air bearing spindles have been incorporated into various Cranfield Precicion machines where extreme accuracy is required for measuring accuracy down to below 25 nanometres CHECK. Our rotary tables also contain air bearings, with axial load capacities of up to 3,000 KG.
Porous graphite air bearing spindles have been built for various high accuracy machines, such as turning in specific defence applications, grinding applications such as silicon wafer grinding, and measuring machines for the aerospace industry.
Our spindles are designed using state of the art CFD (computational fluid) and FEA (finite element) and thermal analysis. This is vital to ensure the design will meet the specification required.