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Single-flute Gundrill Coolant Hole Configurations

Star offers three unique coolant hole configurations:

  1. Single hole – Used in general-purpose applications where coolant pressure is adequate and the machining environment presents no difficulties.
  2. Dual hole configuration – This coolant hole is recommended for cutting diameters of 0.376″ [9.54mm] and The design supports higher coolant flow, improving chip evacuation.
  3. Kidney-shaped hole – This style is recommended for cutting diameters under 0.375″ [9.53mm]. The extruded shapes help to increase coolant flow, thus allowing for better chip evacuation. This configuration should be used when lubricity is minimal or where heat is a concern.

Cutting Fluids

High-pressure coolant (HPC) aids in chip evacuation and helps keep the cutting tool cool and well-lubricated. It is a must for all gundrilling operations.

Three types of coolant (cutting fluid) are used in machining operations — straight or neat oil, synthetics and semi-synthetics, and water-soluble or emulsion-style fluids.

As a rule, straight oil provides the best tool life, provided it contains sulfur and/or chlorine. Sulfur’s anti-weld properties help prevent built-up edge (BUE) on the cutting tool, while chlorine acts as a lubricant, further enhancing chip evacuation.

Water-soluble cutting fluids contain up to 50% mineral oil, with the balance comprised of water, chemicals, and extreme-pressure (EP) compounds for lubricity. Water-solubles provide more effective cooling and have environmental advantages over oil, although its use can result in shorter tool life.

Similarly, synthetics and semi-synthetics are a chemical solution that contain little to no mineral oil. These fluids require concentration levels of at least 8%, with 10% ideal. However, synthetic cutting fluids can reduce tool life significantly compared to straight oil.


Recommended Coolant Pressures

Size (inches) Size (mm) PSI Bar
.078-.155 1.98-3.94 1500 100
.156-.186 3.95-4.72 1300 90
.187-.217 4.73-5.51 1150 80
.218-.249 5.52-6.32 1050 70
.250-.311 6.33-8.00 925 60
.312-.374 8.01-9.50 775 50
.375-.436 9.51-11.07 675 45
.437-.499 11.08-12.69 600 40
.500-.561 12.70-14.25 525 35
.562-.624 14.26-15.85 500 20
.625-.686 15.86-17.45 450 30
.687-.749 17.46-19.04 425 28
.750-.874 19.05-22.20 400 26
.875-.999 22.21-25.39 350 24
1.000 and up 25.40 and up 300 20

Star Cutter Company has developed into a world leader in the cutting tool industry. Each of our six manufacturing facilities specializes in producing a specific type of product or service: solid carbide cutting tools, carbide blanks and preforms, gundrills, gear cutting tools, and 5-axis CNC tool and cutter grinding machines.

23461 Industrial Park Drive
Farmington Hills, MI 48335

Tel. 248-474-8200
Fax. 248-474-9518