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Coolant Thru Tapping w/ TER

It is possible to seal taps for high pressure coolant thru operations.  The success or failure is dependent on the tap length and flute lengths ground into the tap.

Using Coolant Caps
Coolant Caps can be used to seal collets if there is 5mm or 1/4" of shank ahead of the collet face.
 
This position allows the o-ring of the cap to seal against the shank.

From my research tap manufacturer's are anything but consistent.  There are hundreds of shank and square combinations, relief grind lengths very inconsistent batch to batch this makes sealing taps more difficult than it needs to be.

Long tap shanks is the best condition for using coolant caps and sealing for high pressure coolant up to 750psi.

When Coolant Caps do not work

Both taps below are standard 1/2 hand taps.  If you look at the flute on the top picture it extends into the collet.  The picture on the bottom the flute stops just before the front of the collet.
These tap production issues effect both Coolant Caps and Sealed Tap Collets.