Lapping Problem Solving

Problem: Concave Parts

Concave Parts Solution

  1. Concave parts are produced by convex lapping plates.
  2. Check the lapping plate flatness using a Straight Edge or Kemet Flatness Gauge.
  3. A Straight Edge will show the plate is high in the centre.
  4. A Kemet Flatness Gauge will show + on the dial indicator.
  5. Correct the Kemet Plates shape by using the reconditioning procedure.
  6. Check that any pressure applied to parts is balanced and even.
  7. Are the parts fully sweeping the Lap Plate during the process.
  8. Move the Dispensing Bar or Bars closer to the centre of the Kemet Plate
  9. Adjust the Conditioning Rings to nearer the centre of the Kemet Plate.

How to Correct a Concave Cast Iron lapping Plate

Problem: Convex Parts

Convex Parts Solution

  1. Convex parts are produced by concave lapping plates.
  2. Check the lapping plate flatness. A Straight Edge will show the plate high on its outer edges.
  3. A Kemet Flatness Gauge will show - on the indicator.
  4. Correct the plate shape using reconditioning procedure.
  5. Adjust the Conditioning Rings to an outer position.
  6. Ensure that the pressure being applied is evenly balanced.
  7. Ensure parts move across as much of the plate as possible during lapping.
  8. Adjust the Dispensing Bar to the outer area of the Kemet Plate.

Correcting a convex lapping plate

Problem: Parallelism

Parallelism Solution

  1. To lap parts parallel ensure the lapping plate is flat.
  2. Ensure the machines Hand Pressure Weight is lapped flat on the plate.
  3. Do not use Felt Pads or Non Skid Faced Weights.
  4. For best results lap uneven number of parts i.e 3,5,7 etc. Use dummy parts to make up number.
  5. Turn parts over and lap at least 3 times.
  6. Use only short lapping cycles.
  7. Check parallelism and flatness regularly.
  8. When using special fixtures, ensure they are balanced for weight.

Problem: Conditioning Rings not rotating


  1. Reduce the amount of lubricating fluid being applied.
  2. By repositioning the Dispensing Bar, create a running condition where the outer edge of the Kemet Plate is running slightly drier than the centre area.
  3. Ensure Kemet Liquid Diamond is being stirred and the diamond dispensing jet is not blocked.

Problem: Scratched Components

Scratched Components Solution

  1. Is the correct type of Kemet Plate being used? (Kemet Copper XP and Kemet Tin are the most popular polishing Plates).
  2. Is the correct grade Kemet Liquid Diamond being used? (micron sizes 6 and below are considered polishing grades).
  3. Is the plate too wet? Best polishing results are obtained with “just moist” Kemet Plates.
  4. Are the parts being polished of a soft material i.e. Brass, Copper, Aluminium, Soft Steel etc? If so, consider a 2 stage process finishing with a polishing cloth such as Type ASFL-AW and 1 Micron or 3 Micron Kemet Liquid Diamond.
  5. If using a polishing cloth are Ceramic or Plastic Faced Conditioning Rings being used? (Cast Iron Rings cause scratching).
  6. Is the polishing machine being used in a suitable working environment i.e. away from grinding and other similar machines.
  7. Are the parts clean before lapping?
  8. Were the parts cleaned between lapping operations? This is important to avoid cross contamination.
  9. Have the parts been de-magnetised after grinding?

Problem: Blocked Dispenser Bar

Blocked Dispenser Bar Solution

  1. Remove screw from end of Dispensing Bar and remove jet assembly. Clean ultrasonically, if possible, otherwise clean using an airline.
  2. Do not use the Dispensing Bar to apply Kemet Type K Liquid Diamond followed by Kemet Type W Liquid Diamond, without first cleaning the Bar thoroughly.

Problem: Electronic Dispenser not working


  1. Check the electrical connection with the lapping machine.
  2. Check the 2 fuses on the Dispenser.
  3. Change the circuit board inside the dispenser if routine checks fail to show the problem.
  4. Check the timed power supply and continuous power supply to the Dispenser are the same voltage.

Problem: Electric Stirrer not working


  1. Check the fuse on the back of the Stirrer.
  2. Check the plastic tube leading from the bottle does not interfere with the rotation of the magnetic paddle.
  3. If problem are experienced with creating a vortex in the liquid diamond, turn the unit off and restart slowly.

Problem: No Stock Removal from Lapping Machine Dispenser


  1. Is Diamond Stirrer turned on?
  2. Is there a strong vortex in the Liquid Diamond Bottle?
  3. Is the Liquid Diamond Bottle as close as possible to the Dual Dispensing Bar?
  4. Do all Conditioning Rings have chamfers on their outer edges?
  5. Is the Dispensing Bar blocked on the diamond side?
  6. Is the correct pressure being applied to the parts being lapped?
  7. Try a larger micron Kemet Liquid Diamond.
  8. Reduce the amount of lubricating fluid being applied.
  9. Try a water based (Type W) Kemet Liquid Diamond.
  10. Increase the Electronic Dispenser settings for Kemet Liquid Diamond.
  11. Remove anything from the surface of the Kemet Plate that is not required for the specific lapping process being performed i.e. spare Conditioning Rings, Workholders etc.

Problem: Difficulty in cleaning parts after lapping


  1. Do not let components dry out after lapping.
  2. Consider changing to a Kemet type ‘O’ Liquid Diamond (oil based) particularly if ceramic parts are being lapped.
  3. Always try to use an Ultrasonic Cleaner after lapping. A hot water based detergent will usually remove lapping residue.

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