Who turns precision, hits the target faster and finishes first

Most hardened parts may be hard turned with regard to their properties and condition, unless they are not sufficiently stable due to their length/diameter ratio. As rule of thumb, a length/diameter ratio of 4:1 with tailstock and of 6:1 without is assumed. In case if ID machining, the tool is the decisive factor. Not qualified for hard turning processes are parts which cannot withstand the cutting forces due to deficient inherent stability.

The wide design of the guideways of Hardinge machines typically offer a 40% to 60% higher performance and capacity compared to similar machines. The wide distance of the linear guideways forms a solid basis to absorb the generated cutting forces.  The linear guideways are lapped and therefore grant absolutely minimal motion resistance. As a rule, the true running of the spindle exceeds the values specified in our documentation by 30% to 40%.

• Spindle run-out: Specified with 0.000375 mm, actual values lie around 0.00015 to 0.00025 mm.
• Positioning accuracy: Specified with 0.00125 mm, actual values lie around 0.0005 to 0.00075 mm.

Further measurements reveal similar results. Again, the accuracy clearly surpasses the requirements. Among others, this is due to:

Digital glass scales in the X & Z & Y axis

• Chuck and collet seats are ground in their own bearings
• Thermal shielding prevents "thermal growth"
• Spindle motor and collet closing mechanism are dynamically balanced
• Spindle pitch error compensation improves positioning accuracy with a resolution of 0.0001mm in the axes

All Hardinge T machines dispose of a highly rigid gray cast iron bed. In addition, this bed is filled with Harcrete polymer concrete in the critical areas - below the guideways and above the leveling feet. Harcrete is a synthetic granite and perfectly suited for absorbing vibrations. Thus, the basic structure of the machine alone guarantees successful hard turning and high-precision turning. The effects:

• 60% less vibrations
• Achievement of optimum grinding accuracies
• Improved part tolerances
• 30 % longer tool life - and more
• Lower tooling costs
• Less scrap and refinishing work

The in-house developed BMT45/55 tooling plate by Hardinge permits the use of live tools in all 12/16 turret stations. It comes equipped with a pin drive and special tool holders which allow for accommodating modular driven and static tools. The turret head may also be locked halfway at the station increasing the number of tool pockets to 24/32 which offers maximum flexibility and prevents restrictions in case of complex requirements through combined operational processes in one cycle. For the BMT 45 / 55 turret head plate, a great number of live tools is available; radial, axial and adjustable tool holders (+/- 90°), loadable in main and sub spindle, grant perfect machining results for all drilling and milling applications.

Concentricity is one of the main requirements! The Hardinge collet spindle ensures that the part is located as close as possible to the spindle bearings - the point of the highest stability and precision. In particular, this has a positive effect on the hard turning process and distinguishes Hardinge from other competitors. The farther away the part if from the spindle bearings, the worse becomes the spindle run-out, i.e. the concentricity at the turned part grows more and more.

Hardinge convinces customers as one of the world's largest manufacturer of workholding equipment for lathes.  The clamping means are especially designed for the Hardinge collet spindles - without any compromise - and ensure optimum workholding solutions for all machining tasks thanks to their high versatility.

A decisive factor for the hard turning result and the process optimization is the use of the correct cutting tool materials. CBN (cubic boron nitride) is the material most frequently used for hard turning processes. CBN is available in various grades and quality classes. Selection is made depending on insert, material, hardness, interrupted cut, etc. However, despite its hardness, CBN often tends to be brittle. Tools with negative rake angle offer the strongest support for the cutting edge and should be selected whenever possible.

Experience shows, that tools with larger cutting radii score better surface finishes than those with small radii.