PS2BS - Coborn Engineering

Planetary Scaife Bench - Steel

Coborn’s Planetary Scaife benches are generally used to polish facets on single crystal diamond tools.


Coborn’s Planetary Scaife benches are generally used to polish facets on single crystal diamond tools. They may also be used in gem diamond polishing. The bench combines the high speed rotation of a scaife plate with a relatively slow, smooth, horizontal planetary motion. The planetary motion speed is variable between 0-50 cycles/minute.

This motion gives a number of advantages over a standard scaife:

• The plate does not become tracked as polishing takes place over an annular band. The scaife surface remains smooth and flat.
• The motion results in a constantly changing angle of attack: this gives a ‘self-zooting’ action producing line free facets without manual work.
• In many situations the tang can be set on the machine and the diamond or tool left to polish
• ‘Knarted’ stones become easier to polish as the angle of attack constantly changes.


PS2BS bench in factory
centralises scaife plate so rotational axis of plate and Rotational axis of motorised shaft are exactly concentric Allowing best possible balancing conditions, extended motor life, and less vibration.
The rolled ground Steel table top is 23mm thick, and ‘floats’ on anti-vibration lattice rubber, so is independent to the motor and the bench Table Top is ‘Formica’ covered to protect the top surface of plate, and Aesthetic wooden surround is added.
The rotating parts are balanced to G0.1 (4x better than Gyroscopic limits) the faces are turned or ground to within 0.00001”. The bench can be run on 220V or380V 3 Phase power.


Machine type – Adjustable stroke |
Dimensions (w x d x h) – 934 x 610 x 815 ± 50mm |
Total machine weight – 380kg approx
Bench construction – Square Tubular Hand-Welded steel frame |
Bench top – 23mm laminate covered ground steel plate

Planetary Motion

Stroke amplitude adjustment facility – Yes – Adjustable |
Planetary motion adjustment method – mechanical adjustment – 24 steps
Planetary motion range – 4 – 32mm |
Planetary motion speed – Adjustable 0 – 50 cycles/min
Planetary motion direction (viewed from above) – Clockwise


Spindle type – Coborn precision spindle |
Spindle power – 2.2kW (2.9 H.P.) |
Height adjustable – Yes |
Height adjustment range – 19mm
Speed range (without inverter fitted) – 2.850 rpm at 50Hz

Electrical Requirements – 3 phase

  • Scaife Plates
    Coborn can supply Diamond Impregnated plates which come in three grades.
  • • FF – Fine grain final polishing
    • MM – Medium grain polishing, for larger stones
    • BB – Coarse grain for facet creation or stock removal

    The impregnations are 2.5mm deep and each grain type contains a different size of diamond particles, thus giving the types different polishing properties (softer or harder etc.)
    Particles in FF plate are all smaller than 20 Microns in size
    MM Plate are all smaller than 40 Microns
    BB Plate are all smaller than 60 Microns
    The impregnation area is usually about 2-5 millimetres from the edge of the plate and extends inward by the desired amount. Obviously, the larger the ‘band of diamond’ the greater the cost. Band widths are available in several steps from 20mm – 80mm.
    All plates from Coborn are balanced to perfection; there may be a slight vibration when used due to mis-location but with EN nose this should not be apparent.
  • Coborn also supply three types of cast iron scaife plates
  • Extra Fine (Turbo): Very small ‘pores’ (holes in metal), can only be used with small grain powders, for final polishing.
    Brinell Hardness Scale - 450 HB
    Vickers Hardness Scale - 485 HV
    Rockwell ‘B’ Hardness Scale - 117 HRB
  • Fine: Small pores, to be used for final polishing on stones less than one carat. Can be used with larger grain powder.
    Brinell Hardness Scale - 250 HB Fine
    Vickers Hardness Scale - 250 HV Fine
    Rockwell ‘B’ Hardness Scale - 101 HRB
  • Medium: Larger pores can be used with larger powder sizes, can be used for final polishing of stones greater than 1 carat or for quicker stock removal/blocking/facet creation.
    Brinell Hardness Scale - 220 HB Medium
    Vickers Hardness Scale - 220 HV Medium
    Rockwell ‘B’ Hardness Scale - 96 HRB

    These come in sizes either 330mm diameter or 310mm diameter, the 330mm size is perfect for our standard bench.
    All plates from Coborn are balanced to perfection; there may be a slight vibration when used due to Mis-location but with EN nose this should not be apparent.
  • Coborn can supply varying grades of Diamond powder and Specialised Cutting Fluid for Cast Iron Plate Preparation
    Bore of plates will be true to 1/10 thousandths of an inch and correct for spindle nose size.
    All plates impregnated or prepared plates must be worked-in/opened, prior to use, this is especially important for plates with a larger particle size, otherwise the stone will rip through the diamond paste/layer rather than running over it, thus cutting the diamond.

    Coborn have developed a Portable Balancing System , that can be used in conjunction with the Balance Cap Supplied on all PS2B Benches to FINE TUNE the balance of the Scaife Plate in-situ on the Bench. This does not replace the need to Pre-Balance the Plate, before mounting., but can eliminate almost all vibration from polishing system. Visit here for more information

PS Series Brochure

Coborn Planetary Scaife Series Brochure


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