Tapping hole in steel by hand is hard work. Doing one or two not a problem but 10,20 or more and it get old real fast.
I have tapping heads and rigid tapping on most of my mills but on this little mill I do not have that feature.
So this method works and has been tested on hole up to 3/8-16 It you have a compressor and pneumatic wrench these this is a quick was to tap a bunch of holes without had cranking
Step 1: Drill Your Holes
Step one drill your holes and set up your tap handle. You will notice that some Hand tap handles have a hole on that fits a 3/8 ratchet perfectly you will need one of these.
Step 2: Set Up the Air Ratchet
Attach the ratchet to the tap handle connect it to the air supply
Step 3: Tap Your Holes
Carefully position the tap with attach ratchet perpendicular to the hole Taking care to use tapping fluid on each hole and on the tap clearing any chips attached to the tap from the last hole. Then set the ratchet to clockwise and begin tapping keeping the tool as straight as you can it start cutting the threads. The pulsing action of the air too will help act as a chip breaker and allow you to easily cut threads. If it stalls or feels too tight just reverse the ratchet and back it out a bit and then go again.
I have used this method to tap hundreds of hole is 1/2 steel plates and if your careful get the tap started straight it won't break taps and speed up the operation.
Any tapping oil will work and practice on some scrap material before using it on your finished work. The method works well on Taps up to 3/8 I have tapped hundreds of holes with this simple set up.