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Removing damaged studs and threads with just one machine


Regular readers of the Portable Performance Blog will know about the tools available to remove studs as part of a decommissioning project. But what can be done if the stud needs to be replaced and the thread needs refurbished?

This happens regularly in the power generation sector on critical items such as turbine casings, flange coupling studs, nuclear reactor studs & bonnets, recirculation pumps and heat exchangers.

Mirage is pleased to introduce the addition of the new fully portable geniSYS IV CNC 3-axis milling machine to the product line-up – a great new machine tool that’s purpose designed to solve these difficult machining challenges.

Before looking at the benefits of the geniSYS IV machine, it’s worth considering the alternative methods to remove studs and refurbish threads.

Metal Disintegration 

Using this process, an electrical spark is created between the electrode and the stud to be removed. The electric spark produces an incredibly intense heat, with temperatures of up to 12000 degrees Centigrade.

Fresh water is pumped through the electrode - causing the molten metal to break down and be
flushed out it out in small particles. Following this operation, the remnants of the stud need to be removed and the thread chased/cleaned up with a tap.

Disadvantages of this method are;

  • A hot work permit is required
  • Coolant is needed to flush out the material.

Drilling and Tapping

A drilling machine (such as the Mirage HT50) can be fixed to the work piece, often using an electromagnetic base. The drill is then fed into the bolt to remove the material. As with the metal disintegration process, remaining material needs to be removed from the hole and the thread cleaned up with a tap.

Disadvantages of this drilling method are;

1.Its a manual operation, and  2. As with the above process, potentially the thread needs cleaning up with a tap.

The geniSYS IV machine

The Mirage geniSYS™ IV is a highly portable 3-axis CNC milling machine. The motion control command centre provides the ultimate in performance monitoring and technician safety.

Unlike the metal disintegration method, the geniSYS machine operates as a cold cutting machine. There is also the advantage that metal chips are evacuated automatically during the cutting stages.

When using the geniSYS machine, the potential for errors caused by manual operation are eliminated because the machine is CNC controlled. The process is therefore repeatable and precise – particularly useful when several of studs need to be removed and their hole threads refurbished. The unique feature of the geniSYS machine is that studs can be removed and threads refurbished and using the same machine – therefore eliminating the need to finish the thread with a manual tap.

What is the geniSYS machine capable of doing?

The geniSYS is capable of machining up to 11” diameter (279.4mm) and hole depths of up to 15.12” (384mm). The spindle motor produces an impressive 5kw (6.7hp) and can rotate up to 3000 revs per minute.


Using a turbine casing refurbishment as an example, installing the machine is done by creating and fixing an application specific mounting plate to the work piece and attaching the geniSYS machine to this mounting plate. Squaring up is carried out using the levelling screws, hold down clamps and a dial indicator.

How is the machine controlled?

The diagram below shows what else is used to control and drive the machine.



Operating the geniSYS IV CNC 3-axis milling machine

Once the tool has been inserted, the X, Y and Z origin points can be set for the application. The machining program is then created. The first pass cores out the centre of the bolt. Removal of the remaining stud material can be done in two ways:

1. Milling out the remaining material, leaving just the crest of the thread - which can be pulled from the hole, (however the coiled material can get wrapped around the tool, potentially damaging the thread).
2. Removing the remaining stud material using the ‘radial plunge’ method. This is the preferred method as it avoids the coiled material problem mentioned above.



Tooling is used with carbide inserts. When removing stud material, an indexable shell mill with carbide inserts is used with an extension to suit the axial depth required. When refurbishing threads carbide inserts are used to match the desired thread root depth.




The end results speak for themselves. The geniSYS CNC 3-axis milling machine carries out accurate and repeatable machining operations, giving turbine casings, reactors, flanges and heat exchangers a whole new lease of life. The unique ability of a single machine to remove studs and to also refurbish damaged threads makes it an invaluable addition to a plant operator’s or machining contractor’s maintenance equipment list.

To find out more get in touch with Mirage here.

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