Micro abrasive pencils with CVD diamond coating

Abrasive pencils (burs) for grinding can be made by coating cemented carbide bodies with a rough chemical vapour deposition (CVD) diamond layer. These tools have advantages compared to conventional abrasive pencils made by electroplating or sintering of diamond grains. Different CVD diamond abrasive pencils were manufactured with tip diameters ranging from 0.06 to 2.0 mm. A hot-filament CVD reactor was used in combination with a substrate holder system having a capacity of up to 240 tools. The grain size is the most important property of grinding tools. It must therefore be adjusted carefully in the coating process. The basic influence of tool geometry and coating parameters on the crystal size is presented. By prolonging the coating time to 90 h, crystal sizes of up to 50 μm can be achieved. Manufacturing of abrasive pencils even with such long coating times can be economical, because thousands of tools could be coated in one process by industrial coating in bigger reactors. The relation between the crystal size and the roughness of ground workpieces is presented.