Deep Hole Borer

In early 2006 HMG Hardchrome identified a shortfall in the steel market as certain large sizes of hollow bar was not available in all of Australia. Australia uses less than 3% of the world wide steel usage for carbon steel hollow bars. To overcome insufficient steel sizes and quantities that are carried in Australia by all steel suppliers, a commercial decision to purchase a deep hole borer was made. A borer with a long bed was available out of NSW that was previously used to machine gun barrels for Australian naval vessels.

The machine frame, bed and head was purchased and shipped to HMG Hardchrome in Brisbane. After engineering, modification and implementation of a state-of-the-art cutting head, the borer was installed.

The first project to utilize the deep hole borer was a solid billet of K1045 carbon steel that was 550mm in diameter and 4.1 metres in length. The solid billet had a weight of over 7.5 tonnes. No hollow bar material was available at the time to enable a hydraulic cylinder barrel to be manufactured. The finish size of the hole to be placed up the full length of the barrel bore was 420mm internal diameter. The billet of steel required steady tracks to be machined on the outside diameter to ensure concentricity when being bored in the deep hole borer. Once the steady tracks had been machined it was then loaded into the deep hole borer. The first process cut was made using a drill bit that is approximately140mm in diameter.

Finally, the drill bit passed through the steel billet, a drilling head was then fitted and passed thru the steel billet. The drilling head comes in a variety of sizes but for this barrel, HMG Hardchrome was required to finish at a bore size of 420mm. A total amount of 4.5 tonnes of steel was required to be machined out of the centre of the billet, which gave a total weight of the billet after machining at three tonnes. The solid billet was now a piece of hollow bar.

The hollow was produced over a three to four day period once the solid billet of steel had arrived. The only other options at the time was a three month wait for a forging to be produced locally or 14 months to await the hollow bar to arrive from the mills in Europe.

The hollow bar was honed to a correct tolerance finish size and the barrel eye was then welded to the piece of hollow bar. Holes were drilled and tapped in the end face to complete the process of manufacturing the hydraulic cylinder barrel.