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A need arouse to drill and tap lots of blind 1/4-20 holes in 3/4" thick hardox 45-50RC hard plate.

So if you ever need to do this use:

Tap hole: >0.202" or bigger.  5/8 deep.
Drill used: Tialn coated carbide drill.
S=1418 RPM
F=2.6 IPM
NO Peck, No Coolant

Tap: TIALN coated 4Flute PowderMetal tap from OSG.
Rigid Tap Peck:0.05"
Depth: 0.40"
Used MAsters Cutting oil. Pretty standard for tapping.


Was able to drill/tap 16 test holes. After inspection tap did not show sings of severe wear. So its safe to assume you could make around 30 holes this way.

If you ever have to do this- GOOD LUCK Innocent

Tapping Hardox Rc 45-50
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