• Overview
  • Brief Spec
  • Main Options
  • Features
  • Optics
  • Technical Details

Planetary Grinding Machines for Single Crystal Diamond

Coborn make a range of machines for grinding single crystal diamond, the PG2, PG3+ and PG3B. The choice of machine depends on the application and the level of accuracy required.

The planetary motion allows the grinding direction to be changed so that the ‘soft’ directions of the diamond can be found. The planetary motion can be continuous or moved step-wise (jogged) in either direction.

To protect the wheel and tool, feed is achieved by a dead weight system.

A rotary fixture is available with indexing and continuous rotation for facets and cones.


The PG3B has air bearings for both the pivot and the water cooled wheel spindle. The machine is designed for making:

• Low or controlled waviness, radius tools
• Multiple facet tools, conical tools

The pivot motion is automatic and controlled via a touchscreen. Pivot angle limits, dwell time at end of stroke and pivot speed can all be pre-set.

If ‘hard’ spots exist on the diamond then temporary pivot limits can be selected whilst running.

Tools are inspected via a VS5G vision system.


The PG3+ has high precision angular contact bearings in both the pivot and HF Wheel spindle.

The machine is designed for making Radius and multi-facet tools.

Like the PG3B it uses the same Synthetic Granite base.

It can be fitted with optional Automatic pivot.

Brief Specification - PG3B

Main motions
Wheel spindle Air bearing
Speed 0 – 12,000 rpm
Spindle direction Clockwise and Anti-clockwise
Spindle tilt 0 - 20 degrees
Stroke length 0 - 28mm
Pivot spindle Air bearing
Pivot range 182 degrees (+/-91 deg)
Planetary motion Continuous/jog
Planetary direction Clockwise and Anti-clockwise

Work range
Maximum radius 75 mm
Conical clearance 0-20 degrees
Cylindrical clearance 0-20 degrees

Main Options

  • Rotary fixture - CF13
  • Metal bond or cast iron laps


  • Main controls sited off the machine to minimize transmitted vibrations
  • Automatic pivot motion
  • Variable lapping load 0.5 – 3 kg
  • Precision ‘place’ and ‘lift’ mechanism
  • Tool inspection by vision system
  • In-feed precision 0.1 μm
  • Digital pivot angle display
  • Synthetic granite base
  • Metric or imperial versions
  • Remote diagnosis over internet


The machines are supplied without optics. It is recommended that the VS5-G vision system and a x60 – x400 zoom lens is used with these machines (up to x600 as an optional extra). A fixed magnification lens may also be used if preferred.

See "Optics Series"

Technical Details

Characteristic PG3+ PG3B
- Dimensions (w x d x h) 900mm x 800mm x 1,800mm 900mm x 800mm x 1,800mm
- Total machine weight 800kg 830kg
- Machine control via Separate control box Separate control box and touch screen
- Memories None Last stored position
- Storage None Industrial PC
- Control box dimensions 600mm x 600mm x 1200mm 600mm x 600mm x 1,200mm
- Wheel spindle type High frequency High frequency
- Wheel bearings High precision Air-cartridge type
- Wheel spped range (via inverter) 0 - 12,000 rpm 0 - 12,000 rpm
- Wheel spindle tilt (conical clearance) 0 to +20° 0 to +20°
- Oscillation of wheel spindle Yes Yes
- Maximum stroke length 28mm 28mm
- Wheel position adjustment range 0 - 100mm 0 - 100mm
- Oscillation frequency (via inverter drive) 0 - 32 strokes/min 0 - 32 strokes/min
- HF spindle cooling system Not applicable Recirculating treated water
- Spindle nose taper 12 degrees 12 degrees
- Pump capacity Not applicable 100 litres
- Motor power Not applicable 0.14kW
- Coolant unit dimensions (w x d x h) Not applicable 700mm x 620mm x 450mm
- Coolant unit weight Not applicable 20kg - dry weight
- Wheel planetary motion Yes Yes
- Jog (clockwise and counter-clockwise) Yes Yes
- Continuous (clockwise and counter-clockwise) Yes Yes
- Lock in position Yes Yes
- Load application via dead weight via dead weight
- Weights provided 0.5kg - 3kg (0.5kg steps) 0.5kg - 3kg (0.5kg steps)
- In-feed table travel length 25mm 25mm
- In-feed table resolution 0.1 microns with optical scale 0.1 microns
- Travel length 12mm 12mm
- Tool height adjustment ('K' axis) 85mm 85mm
Movement ('C' axis) 182 degrees (+/- 91 deg) 182 degrees (+/- 91 deg)
Resolution (using vernier scales) 0.003 degrees  
- Digital readout via AD2 (optional extra) view on touch screen
- High resolution digital readout (optional extra) Not available 0.001 degrees
Pivot bearings High precision Air-cartridge type
Pivot motion Manual/Automatic option available Automatic
Radius maximum 75mm 75mm
Larger radii with special arrangement with special arrangement
- Hard spot arc focus facility No Yes
- Cylindrical (via tool holder tilt) Yes (+/-20°) Yes (+/-20°)
- Conical (via wheel spindle tilt) Yes (0-20°) Yes (0-20°)
- Options available (not included) Microscope OR projector OR VS5-G vision system VS5-G camera vision system recommended
- Projection light source Yes Yes
- Optics mount movement (X - Y) 12/12mm 12/12mm
Magnification (microscope & projection) x30 or x50 x30 or x50
Magnification (VS5-G vision system) Zoom x60 - x400 Zoom x60 - x400
- Grinding wheel recommended "SAM" metal bond "SAM" metal bond
- Roughing grade 1000# (typical) 1000# (typical)
- Finishing grade 2000# (typical) 2000# (typical)
- Super-finishing grade Cast iron lap or 5000# Cast iron lap or 5000#
- Grinding wheel adaptor/hub Required Required
- Adaptor bore taper 12 degrees 12 degrees
ELECTRICAL REQUIREMENTS Single phase 220v; 5.6 amp Single phase 220v; 5.6 amp

Optional extras Applicable
1. CF13    
- Coning and indexing fixture Yes Yes
- Capacity via collets (to be specified) up to 12 mm up to 12 mm
- Continuous rotation possible Yes Yes
- Indexing plate (to be specified) 12 or 16 position 12 or 16 position
Coborn PG Series Single Crystal Diamond Grinder