Correcting a Convex or Concave Lapping Plate on a Kemet Diamond Lapping Machine
On any lapping machine the lapping plate flatness is key to producing flat components, in this video we hope to give you an explanation of how to control and correct lapping plate flatness. A lapping plate will usually wear convex or concave, most lapping machines will use control rings to control plate flatness, these run against yokes which can be moved inwards or outwards to bias the wear rate of the plate.
Before checking plate flatness, the lapping plate must be cleaned, we use Kemet CO-42 cleaning fluid, the plate must be completely clean or the gauge readings will not give a true indication of plate shape.
The Kemet flatness gauge, is a gauge with a calibrated hardened steel gauge block, first sit the gauge on the gauge block and zero it, then place the gauge onto the lapping plate and note the gauge reading. this plate is 4 microns convex, take a number of readings to confirm the plate is truly convex. Small variations in flatness can be corrected whilst processing components, but for larger variations we use the internal abrasive system.
To correct a convex plate, position the abrasive drip wires inside the control rings, select the conventional abrasive system on the abrasive selector switch on the machines control panel. The conventional abrasive pump and tank are situated inside the left rear corner of the Kemet machine, this must be filled with Kemox 0400s abrasive slurry, because our plate is convex we position the rings towards the center of the lapping plate, this will bias the wear rate at the center thus flattening the plate, set the timer for 15 minutes, start the machine and ensure slurry is dripping from each slurry feed. At the end of the cycle remove the rings and again clean the lapping plate ready for rechecking with the flatness gauge. The gauge now shows the plate is flat.
If the lapping plate is concave, position the rings so they over hang the outside of the plate, this will bias the wear rate towards the outside area, make sure the rings cover the whole plate or a lip will be formed, remember when correcting a concave plate it will correct approx 3 times faster than a convex plate.