The engineers trust of Peter Smith, Tom Power and Barry Kirkham have been at it again and have rebuilt the old flat lap machine from a wooden framed truck tyre based machine into a new shiny stainless steel “smicko” machine. Stainless steel has been used on all of our work surfaces now to make maintenance and cleaning easier for members.
A flat lap is available to make polished faces on larger rocks like the one shown in this photo.
Using the 150mm diamond wheels for any stone larger than about 50mm is not permitted in the club. The reason for this is that it causes excessive wear on the diamond wheels which are expensive, and on a technical level, it is not possible to get a perfectly flat surface on a curved wheel. The only way to achieve this is either manually on a piece of glass or using the flat lap.
There are several laps provided with the machine, but all grinding from coarse through to prepolish are achieved using a rotating steel disk to which an appropriate grade of silicon carbide grit is added. Water is dribbled onto the disk to make a slurry and then the rock is held firmly against the steel disk with the silicon carbide being an abrasive element to the task. As the rock face is flattened, finer and finer grades (from 80, 200, 400, 600 up to 1,200 grade) are used to get rid of all scratches and defects on the surface of the rock. Important! Between each grade of grit the steel disk and the rock need to be thoroughly washed to remove all traces of the coarser grit.
Once grinding has been completed and everything washed thoroughly, the polishing process can be commenced. For prepolish, a copper lap is provided which should be used with 3,000 diamond paste.
To polish, a leather faced lap is fitted, to which a damp slurry of tin oxide is added to this lap to complete the polishing process.
Peter has provided a user manual, with which members should be familiar before using the machine.
When next in the club, have a look at this machine, adjacent to the saw room.
A big thank you to Peter, Tom and Barry for their efforts in providing top quality machinery for club members to use.