When a leading engine manufacturer looked to reduce machine down-time and reduce scrap, it decided to invest in a Zenith fully automated boring-tool compensation system supplied by Cornwall-based Rigibore (www.rigibore.com).

This was selected for its ability to make cutting-edge compensations automatically — from measurement data to an accuracy of 1µm on diameter.

Maintaining much closer machining tolerances on crankshaft bearing journals not only enhances the quality of the finished component but also has a direct impact on engine efficiency and emissions.

Rigibore’s solution was to produce line boring bars with five semi-finish cartridges set 0.1mm below nominal to allow five ActiveEdge finish cartridges to machine all journals in a single pass.

The ActiveEdge line bars were automatically compensated to nominal from data provided by off-line gauging that was transferred to the machine control as part of Rigibore’s closed-loop system, Zenith.

Before installing the ActiveEdge tools on its production line, the customer carried out verification checks to confirm Rigibore’s confidence that each cartridge could be independently adjusted in increments of 0.001mm on diameter.

With this confirmed, an extended live cutting trial was started on a twin-spindle machining centre, with each spindle machining 946 crankshaft bores over a 24hr period — 1,892 in total.

The trial was very successful, with not a single bore out of tolerance, thanks to ActiveEdge. The finished bores had a mean diameter of 52.965mm with a tolerance of ± 0.015mm; in the test period, bore sizes were maintained within a variance of just 2µm.

Before installing the Rigibore tooling, the engine manufacturer had two line bars running on a multi-spindle CNC, and adjustments were made by the operator using a dial indicator and adjusting each cutting edge manually.

Once the adjustments were completed on all 10 cutting edges, the parts were machined, measured with a bore gauge and checked for size. Often, several cartridges needed further tweaking to reach the desired tolerance.