Guides go full circle

Edited by the Engineeringtalk editorial team Jul 30, 2003

When Mirage Machines launched its portable milling machine, the level of accuracy and reliability provided by THK's integral circular guide was no illusion.

When Mirage Machines launched its portable milling machine, the level of accuracy and reliability provided by THK's integral circular guide was no illusion.

George Silk, Chairman of Mirage Machines, believes the enormous blades that his company's new portable blade-orbital milling machine helps to create are awe inspiring.

The blades, which are approximately 40m in length and two metres at the base, are used in wind-powered electricity turbines and require accurate machining to create flat paths around their bases, or roots, in order to secure efficient and effective power generation.

"From an engineering point of view, they're breathtaking", says Silk.

"The amount of work involved in building them is fantastic".

Unfortunately, all that hard work can go to waste if the milling machine's path, which creates a smooth interface between the blade and the turbine's central hub, is uneven.

"If it's not flat, the blade won't sit right, it won't perform, and the bearings underneath it will deform.

All this will build up and the turbine won't work correctly".

A fundamental component used to ensure that the WP2500 milling machine creates a perfect path is THK's HCR guide.

The circular-shaped linear motion guide, the first of its kind, features an innovative design that permits four-way, equal-load movements with no clearance, thereby enabling the WP2500 to achieve a maximum tolerance of just 0.1mm over a 2-2.5 machining measurement.

This is half the level prescribed by the American Petroleum Institute (API); a trade association responsible for publishing field equipment standards for the oil industry and also the major bearing manufacturer's recommendations at this size.

The HCR blocks and linear motion rail act as a transport mechanism that rotates the WP2500's milling head over the blade interface surface, creating a precise path that is crucial for aligning the blade with the hub.

Any misalignment caused by an uneven milled surface could cause vibration and, ultimately, turbine failure.

The level of accuracy and reliability provided by THK's HCR guides is therefore crucial if the WP2500 is to deliver accurate milling and the turbine blades are to operate correctly.

Silk explains how THK is able to meet the exact specifications laid down by the Derby-based manufacturer, which specialises in portable machine tools for the power, petrochemical and now wind-power industries.

"THK preloads the guides so they have zero clearance.

This means, at its heart, the machine is running dead true with absolutely no clearance.

Since any lapses are multiplied outwards, we can achieve the highest possible levels of accuracy at the edge of the machine.

As far as we're concerned, they're absolutely faultless".

Mirage Machines has been using THK's linear motion guides for over 10 years and is yet to experience a bearing failure.

Silk says that even in the harshest-possible conditions, THK's guides continue to secure accurate movements and precise milling in all of Mirage Machines's externally mounted equipment.

"Our relationship with THK has been developed over the last 10 years.

During that time we've fitted THK guides to hundreds of machines that have been used in some of the harshest environments in the world".

He concludes: "We know that THK's guides are good when they are first fitted, but now we also know they last for 10 years - and that's really something.

The HCR is a light, strong, accurate bearing".