Grinding pins, also called mounted wheels or mounted points, are small wheels to which a mandrel is cemented, molded or die casted into one end [LEWI76, p. 44]. These tools are often used in hand-held operations for deburring, finishing of welds, chamfering, or dental operating procedures. A large variety of shapes exists (see DIN ISO 525) [BORK92, p. 32, DIN00a]. The long shafts of grinding pins act as cantilever und grinding forces lead to deformation of the tool. An open wheel structure with soft bonding enables favorable self-sharpening.
4.1.2.4 Long Needle Diamond Grinding Wheels
In the late 1970s, long needle diamonds were offered on the market [METZ86, p. 43, DYER79]. These long needle diamonds have a proportion of length to thickness of between 2:1 and 5:1 [TOML78a]. They are synthesized with growth direction in diamond main axis direction, i. e. crystallographic [100]-direction [TOML78a]. The growth mechanism of constant buildup on (111)-areas leads to a stepwise surface structure. Diamond cleaves parallel to the octahedric planes, so that long needle diamonds are weak in rectangular direction to their main axis. In grinding, the grits can easily break along the stepwise growth planes and a controlled grit wear is likely [JUCH78, TOML78a].
Metal coated grits
+ bonding
Body
Pressing mold (non-magnetic)
Coil
The grit size classification of long needle diamonds cannot be done via conventional sieve procedures, therefore grit manufacturers have to do physical measurements with projectory microscopes [TOML78a].
To attain the theoretical breakage behavior as well as optimum grit adherence in the bond, needle grits with ferromagnetic coating can be arranged with electromagnetic systems. The example in Fig. 4.3 works with radial magnetic field lines in cylindrical 1A1 grinding wheel die forms. The grits orientate themselves parallel to the magnetic field lines when they are filled into the die form with the resin bond mixture. Pressing and curing processes are similar to other resin bonded wheels. [TOML78a]
In grinding applications, grinding wheels with needle diamonds have a higher number of active abrasive particles on the surface than similar abrasives of the same grit size. Therefore, resin bonded long needle diamond tools showed a better performance for brittle workpiece materials [TOML78b]. However, the long needle diamond grinding wheels was not popular in the market [METZ86, p. 43 f.]. In contrast to grinding, needle type diamonds find wide application in dressing of vitrified bonded grinding wheels.