Traditional Cast Iron Plates
A Traditional cast iron scaife plate.
Traditional plates are made from a special porous cast iron of substantial hardness and high in silicon and phosphorus. The porous surface traps the diamond powder applied by the user. Normally this ‘paste’ is a mixture of olive, palm or synthetic oil and diamond. .
Preparing a plate for use
Photo courtesy Coborn Engineering Co Ltd
The precision ground surface of the plate is flat to within 4µm. The surface is scored (or ‘striped’). This ‘striped’, porous surface retains the ‘paste’. The user must work the diamond into the surface for a number of hours. This ‘opening’ is done with a large piece of boart or using Coborn DIAKISS PCD. (DIAKISS details on request).
Grade & Recommendation
Typical order code: Plate 330mm; 50mm bore; grade ‘Fine’
Diamond Impregnated Scaife Plates
Traditional cast iron plates are still very popular but increasingly, metal bonded, impregnated scaife plates are being adopted.
The diamond impregnated band (shown schematically above) forms a ring set 2mm from the edge of the plate. The band is approximately 2.5mm deep. Various band widths are available.
The plate bore size may be either 50mm or 2 inches. Plates are 330mm or 310mm diameter and 25mm thick.
Grades and Band Widths
The required band width should also be specified. Widths available: 30, 35, 40, 45, 50, 55, 60, 65, 70, 80mmT
Typical order code: Plate; 330mm plate; 50mm bore; Grade MM; width 30mm
Recommendations for Plate Installation
Both traditional and impregnated plates are precision parts. The plate surface is accurately ground as is the back face which seats onto the face of the spindle. New plates are dynamically balanced to gyroscopic limits. They must be handled with care. Any dirt or marks on the mating surfaces will result in the plate not running true.
A Coborn bronze expanding nose should be used. This automatically centralises the plate on the spindle axis.
After many months of use, plates may become ‘tight’ due to dirt solidifying in the nose area. Any attempt to hammer the plate loose will result in damage to the spindle bearings. The expanding nose can be loosened with a special key thus allowing the plate to be removed easily and safely.
The expanding nose must not be tightened without a plate in position.
Mounting the Scaife Plate
After ensuring the back face of the plate and the mating spindle face are clean, the plate should be placed over the expanding nose. The expanding nose should then be tightened gently to centralise the balanced plate i.e. until the plate just stop turning freely on its seat.
The main cap / screw can then be tightened thoroughly. Removal is the reverse of this process.
Dynamic Balancing In-situ
If the plate has been re-machined, then it is recommended that it is dynamically re-balanced using a PB1 portable balancing unit.