This article deals with the most important factors to consider when using taps with internal coolant holes: the filtration system and coolant discharge pressure that need to be carefully configured to achieve the best performances of the process.

Keep an eye on the filtration system

When using a tap with coolant holes, Yamawa recommends to always maintaining a high degree of filtration to ensure the removal of any dust and chips. Check the built-in filter of your machine: a mesh of 20~50 μm should be used.
Sludge or fine chips may be stuck in the tap’s coolant holes, clogging the holes and reducing the coolant flow. When the amount of coolant supply decreases, a tap breakage may occur. To avoid clogging, timely replace the coolant filters to maintain the filtration accuracy below 100 μm.

The role of discharge pressure

The level of coolant pressure depends on tapping conditions. The coolant pump must supply enough coolant to the cutting edge chamfer of the tap and — if needed — it must be able to forcibly discharge the chips. In some cases, the use of a higher coolant pressure may be required.

According to Yamawa’s best practices, tapping achieves the maximum benefits when using the higher coolant discharge pressure. Be aware that the coolant discharge pressure limit for a standard tapping holder is 6.5~7 MPa.

The coolant discharge pressure of a CNC machine is usually an optional setting at the time of purchase. Herein some reference values:

  • Around 1.5 MPa – basic/standard coolant pressure specification
  • Around 3 MPa — high coolant pressure specification
  • Around 7 MPa — super-high coolant pressure specification

To sum up, here there are your practical tips when using taps with coolant holes:

  • Use filters with a mesh of 20~50 μm.
  • Regularly replace filters
  • Keep coolant discharge pressure around 1.5~3 MPa
  • Consider using specific taps such as HT, SP, PO taps with specific flute design that facilitate chip evacuation.