Imagine having to machine a bucket wheel excavator so big it needed to have the surrounding shed walls torn down to move it for servicing.

But that sort of task is all in a day’s work for Victoria-based rotary welding and line boring specialist Metro Machining, a small engineering company that has earned a big reputation.

Bucket wheels combine robustness with outstanding speed and high throughputs and are used worldwide in the handling of bulk materials such as coal, iron ore, petroleum coke, limestone, bauxite, lignite, phosphate, and other kinds of ore.

These excavators are the largest machines found on mine sites, and it’s no surprise that one of them is the largest land vehicle built in human history, measuring 96m in height.

As such, they need to be maintained and serviced regularly to ensure worn out parts are repaired or replaced, or if they are new, to ensure that specifications are accurately adhered to.

Metro Machining co-director Patrick O’Hara said the bucket wheel that the company worked on was shipped in from Germany in three sections.


“It was a massive wheel the size of building with lugs on the outside,” he said.

“We machined where the joints were, and also line-bored hole circles where drive couplings were mounted.

“This was a very precise operation, where we only had 0.03mm clearance across each of 20 holes.”

Working on the holes also provided some practical challenges, such as technicians trying to keep a footing on the well-oiled bucket wheel at a 30o angle to reach the drive coupling mounts.

“If the workmen slid on the wheel, they’d slide for up to 5m,” he said. “There’s an art to standing on the equipment which we quickly mastered.”

Patrick O’Hara boring out an excavator quick hitch with two line borers.

Tools of the Trade

That Metro Machining was given the bucket wheel job speaks volumes for the quality of service and level of workmanship that the company has become renowned for.

The business boasts clients throughout Australia and also overseas.

Recent jobs have included work done for power plants in Nauru and the Marshall Islands.

The latter assignment involved reclaiming the foundations of a waterbox for the Majuro power station, which had not been used for 15 years and had been strongly corroded.

Metro Machining co-director Karl Hansen, who carried out the machining, said he worked on one of four diesel engines in the box and brought it up to spec.

“We machined the bore head and pull sleeves, from the mouth to the top of the block,” he said.

“We got the contract because of word of mouth of our capabilities.”

Karl also worked on the Nauru assignment, where he machined the crank journals for the country’s power generation plant.

Closer to home, as well as specialising in in line boring and associated machining, Metro provides on-site and workshop services to the industrial repair and maintenance industry.

Patrick said Metro team members had specialised skills which enabled them to complete complex refurbishment and maintenance projects.

“We have the ability to work on heavy equipment in the workshop or while it is still in the field, delivering significant savings to plant operators by greatly reducing the equipment downtime,” he said.

“We strive to provide a professional, cost-effective service, regardless of the size of the job, and whether or not it is part of ongoing preventative maintenance, or emergency breakdown repairs.”

The company machined a MASTIS antenna for an amphibious assault ship for the Australian Navy, which involved bore work on 800mm holes.

Metro also regularly undertakes repair and maintenance work on a wide range of plant and equipment, specialising in earthmoving plant.

“Our expertise includes line boring, rotary welding, pin and bush replacement, face welding and machining, crack repairs and attachment modifications. We can provide a total refurbishment service, including everything from disassembly to reassembly,” Patrick said.

“With our line boring, we do the whole process: strip, line bore, insert the bushes, pin it back together, and commission it.”

Metro Machining has four mobile line boring trucks capable of refurbishing bores from 40mm to 1200mm and ripping out cuts of 16mm per pass.

They consist of a Mitsubishi Canter, two Isuzu 200s with 400A welders capable of boring from 35mm to 800mm, and one Isuzu 400 with two 400A welders, 25kVA genset and 25CFM compressor capable of boring from 35mm to 800mm, all with oxy sets and liquid nitrogen for bush changes.

“Boasting 25kVA 450A Denyo generator welders, 100t on-site pressing gear and the liquid nitrogen tank, we can take on any project anywhere,” Patrick said.

Metro Machining’s in-house workshop capabilities include:

  • Line boring
  • Turning (up to 5m)
  • Milling (6m type bed)
  • Horizontal and vertical boring machines
  • 200t press
  • Slotting
  • Boiler making, fabrication and repair

On-site machining services include:

  • Line boring
  • Inside diameter rotary welding
  • Milling
  • Flange facing
  • Key way cutting
  • Outside diameter turning
  • On-site hole drilling and tapping
  • Stud removal
A 680mm bore being machined for a Swing Stock jaw rock crusher.

Metro Machining’s mobile line boring service is supported by the permanently staffed factory in Campbellfield.

The company manufactures its own line-boring equipment, such as ID welders, boring bars, bearing mounts, wireless controlled power packs and specialised equipment for out of the ordinary works.

The on-site milling machine was initially custom-built to refurbish train bogies.

“There are also two 400A welders and 800A welders, a 100t hollow cylinder pressing gear, a thermic lance kit, plasma cutting, oxy cutting and gouging, air arc gouging and Flexi  cylinder hones,” Patrick said.

“We also stock precision ground and hardened 4140 bar stock for making custom pins.

“Because of COVID, custom pins are in short supply, so we are making a lot of pins to cater to demand.

“We perform a large variety of general engineering works from manufacturing hydraulic cylinder components to making excavator H-Links and loader bell cranks, and we also manufacture custom designed tooling.”

Other services Metro handles includes crack repair work using Non-Destructive Testing (NDT), and outside diameter (OD) turning. “The onsite lathe is mounted on the end of a shaft and rotates around it, which allows us to build up the shaft with weld or shrink fit a sleeve on it for repair in situ,” Patrick said.

An impressive tool in Metro Machining’s arsenal is its own 250l cryotank, which allows the company to provide liquid nitrogen services and store the compound in-house, making it available at any time.

“Using nitro has proven to be the most cost-effective method to fit multiple bushes, big bushes and interference fit pins,” Patrick said.

More information:
Metro Machining

Unit 3/32 Onslow Avenue
Campbellfield, Victoria
Phone: 0408 638 549 or 0402 256 874