ABOUT PORTABLE LINE BORING

Portable Line Boring was established in November 1988 with the purchase of a new Mark 1 Hofmann machine. It came with the optional small bore kit which enabled bores down to 1.5 inch to be machined. The whole kit was carried from job to job in a box trailer along with an ancient CIG stick welder to tack on support brackets and also to pad weld worn out holes with stick electrodes. After several months Hofmann manufactured a prototype automatic welder that allowed the line boring machine to weld the bores as well as to machine them.

It did not take long to manouver this attachment into the trailer for “field trial’s.” After some initial hiccups with unsuitable power sources this attachment has become the back bone of PLB’s business. This attachment allows bores to be machined pre machined then pad welded and line bored in the one operation without dismantling any equipment. Change over from welding to boring is a two minute operation. Since these early days there have been several more Hofmann machines added to the fleet including some prototype machines from which new models have been developed. Some of the new equipment includes facing heads capable of machining out to around a thirty-six inch face, large bore attachments for machining bores to around thirty-six inches diameter and also an alignment kit which enables us to line bore series of holes to within .001 of alignment over a distance of twenty feet.

Over the years a large inventory of tooling and brackets has accumulated allowing us to take on most jobs without having to "tool up" Currently we have two rigs that are fully equipped for on site line boring. One is a self contained 1998 Mitsubishi three tonne truck and is operated by Gary Goodman. The other is set up in a van bodied tandem axle trailer and is towed by a 1997 Ford F350 diesel and is operated by Ray Freeman.

All administrative work is handled by Erica Freeman. The bulk of our work is done on large mining equipment such as Liebherr , Hitachi and Komatsu hydraulic excavators. We also do a lot of work on Caterpiller front-end loaders of all sizes. It is not uncommon to be one day working on a 600 tonne digger and the next on a skid steer loader. Anything that pivots on machinery such as bucket , loader frames and articulation joints has need of our service eventually.

Another service provided by PLB is the fitting of bearings with liquid nitrogen on completion of a line boring job. Bores are normally machined to provide an “interference” fit of between .004” and .015” on the installed bearing. The bearing is immersed in liquid nitrogen which has a temperature of –196C. The bearing is thus shrunk and is able to be fitted into the bore. As the bearing returns to ambient temperature it swells to become a tight fit in the bore. The alternative to this method is to fit the bearing using a press which is labour intensive and also risks damage to both the bore and the bearing.

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