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How Fine to Filter Coolant

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How Fine to Filter Coolant

Relationship Of Particle Size To Machining Tolerances

  The machine coolant should be filtered to a particle level that is 10% of the tightest desired tolerance.


If the top line is 0.001" specification you need to filter to 0.0001", which is the bottom line.
The two lines are 0.0001" apart in this scale.



1. The tool has to make a cut that stays within the big line and the little line.


2. You should filter machine coolant to the size of the little circle .

(Circles are 10, 25, 50 and 60 microns in relative diameter. 25 microns == 1 / 1,000 inch)

The second smallest particle is more than enough to deflect the tool.


Particles in the coolant get between the tool and the work during machining. The carbide is hard but it chips. As the tool edge rotates into the work it traps a particle. The hard particle then micro-fractures the edge of the tool. This is like chipping obsidian with deer antler to make a knife or like cutting diamonds. A large amount of force is concentrated in a very small area and the material fractures.

  • A chipped edge takes more energy to cut.

  • A chipped edge makes rougher cuts.

  • A big part of the reason carbide gets dull is micro-fracturing and micro-chipping.