7

FORGE

steel are all good material choices for hand-tapping
metals. Plastics that tap well include ABS, HDPE
(cutting boards are made of this), Acetal/Delrin, and
even Perspex/acrylic if your tools are sharp and you’re
careful to go slowly to avoid cracks.

TURN ON THE TAP
Remember to go slowly! Tapping isn’t difficult, but it’s
easy to break off taps if you go too fast.
The basic steps for tapping are:

1. Measure, mark, and drill a pilot hole with the
   proper bit for your desired tap. The angle of
   this hole will determine the angle of the tapped
   hole, so make sure to drill true and square. A
   drill press works best, but you can certainly use
   a hand drill if you keep the drill square to the
   surface. Drill the hole a little bit deeper than your
   desired final depth – it’s good to reference the
   machine screw you’ll be using as a guide. You
   can mark the bit with a piece of tape to make
   sure you drill to the correct depth.


2. Clean out the hole with some compressed air to
   get rid of any chips left behind by drilling.


3. Add a bit of cutting fluid to the hole if you’re
   cutting metal – plastic doesn’t require any as
   most machinable plastics are self-lubricating.
   Tap Magic is a good general cutting fluid, but

you can get away with using WD-40 if you don’t

have a more specific cutting fluid available.

4. Put the tap into your tap handle, align it square
   and straight to the hole, and begin screwing
   it in a half turn. This first cut is critical to the
   straightness of your final tapped hole, so take
   your time and make sure you haven’t introduced
   an off angle. A bit of pressure is helpful, just
   don’t use too much! Back out the tap a quarter
   turn to release any chips from the tap’s teeth.
   You’re now on your way, cutting the threads.


5. Proceed with another half turn, followed by a
   quarter turn back. Continue repeating the half
   turn forward, quarter turn backward process.
   You need to go steadily, and slowly, and never
   force the tap if it becomes stuck – this is a sure
   way to break off a tap inside the hole!


6. Repeat until you’ve reached the bottom of the
   pilot hole, then unscrew the tap from the hole.


7. Use compressed air to flush the hole of chips.
   You’ve tapped your first hole! You can now
   thread your machine screw into place to test it.

Now that you can tap holes, you can fasten a

wide range of materials together. Get out there and

get making!

Below

The structure of the

tap allows plenty

of space for waste

material to come out

Above

Go slowly and carefully when tapping a hole, to avoid jamming

PICKING A TAP

The following common taps and drill sizes work together:

METRIC TAP DRILL SIZES

Tap Tap Drill

• M3 × 0.5 2.50 mm


• M4 × 0.7 3.30 mm


• M5 × 0.8 4.20 mm


• M6 × 1 5.00 mm

Square

Flutes

Shank

Body

Major dia.

Major dia.

Thread pitch

Teeth

Lead