7

Workshop Basics: Creating screw threads

SCHOOL OF MAKING

ou can use a hand tap to easily cut

machine screw threads into metals

and plastics, providing yourself with

a great way to fasten parts using

standard machine screws. While

there are lots of ways to join materials

such as rivets, screws, and nuts, these can be

difficult to use with thick materials or enclosed parts

where drilling a hole all the way through the work is

impractical or impossible. Tapping a threaded hole

internally into a pre-drilled pilot hole in the work is a

terrific alternative that enables easy assembly and

disassembly. Thanks to the high tolerances of taps

and screws, you can then match this hole with the

same size machine screw and you’ll have a perfect

fit, making it easy to securely fasten your parts and

materials. Plus, it’s very satisfying to make and use

professional-looking precise threaded holes you’ve

cut for yourself!

TOOLING UP TIPS

• Taps are spiralled cutting tools that are fluted to
  allow cut material to pass.


• The body of the tap has a tapered lead with
  cutting teeth, followed by teeth that keep the
  tool positioned properly as the lead is screwed
  down into the pilot hole.


• There are flutes between the toothed ‘land’
  sections to allow for chip removal.


• Tap shank has a squared end for securing into
  the tap handle (i.e. tap wrench).


• Major diameter measures the widest depth of
  the threads being cut.


• Minor diameter is the narrowest section of the
  cut, slightly wider than the pilot hole.


• Thread pitch is used to measure the distance
  between thread crests, and corresponds to the
  coarseness or fineness of the screw threads
  you’ll use.


• Tap handles hold the tap securely and give you
  leverage to turn the tap in the hole while you’re
  cutting threads.


• A note about dies: you’ll often hear the words
  ‘tap and die’ used together. A die is in inverse
  of a tap – instead of cutting the threading into a
  hole as with a tap, the die is used to cut threads
  onto the outside of a rod, thus turning it into a
  machine screw.

A GENTLE TAP

It’s good to get a small set of taps in the sizes you’ll

most commonly use, such as M3 × 0.5 (this second

number specifies thread pitch), M4 × 0.7, M5 ×

0.8, and M6 × 1. You’ll also need tap drill bits that

correspond to each tap. These are used to cut a pilot

hole slightly smaller than the minor diameter of the

tap’s teeth. Store your taps and tap drills together so

they’re clearly labelled and easy to find. Extra points for

making your own index with cardboard and gaffer tape.

You can use a hand tap on different grades of metals

and plastics. Aluminium, brass, and softer grades of

John Park

johnedgarpark

John Park is a maker
who builds creative
technology project
videos and tutorials for
Adafruit Industries.

Above

A tap and hole

ready to add a

screw thread

Bolt straight into metal using taps

Creating screw threads

WORKSHOP BASICS

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