Taps and dies are tools used to create purpose screw threads, which is called threading. Many are cutting tools; others are forming tools. A tap is used to cut or form the female portion of the mating pair (e.g. a nut). A die is used to cut or form the male portion of the mating pair (e.g. a bolt). The process of cutting or forming threads using a tap is called tapping, whereas the process using a die is called threading.
Both tools can be used to clean up a thread, which is called chasing. However, using an ordinary tap or die to clean threads generally removes some material, which results in looser, weaker threads. Because of this, machinists generally clean threads with special taps and dies—called chasers—made for that purpose. Chasers are made of softer materials and don't cut new threads. However they still fit tighter than actual fasteners, and are fluted like regular taps and dies so debris can escape. Car mechanics, for example, use chasers on spark plug threads, to remove corrosion and carbon build-up.
Types of Thread Taps
Straight Flute Taps (Hand Taps)
Hand taps, typically bought at the local hardware store, are the most common types of taps, but they are generally to be avoided for CNC work. The straight flute is the standard style of tap, designed for a range of different common tapping applications.
Spiral Point Taps (Bull Nose Taps)
These thread taps have a spiral cut with relief grooves. They’re common and look like most of the hand taps you’ll see around. However, the spiral angle on the front cutting edges helps eject the chips and the angled edge also gives superior cutting performance. This feature, and the excellent shearing action of the flute, make spiral point taps ideal for production tapping of through holes. In general, they’re really the least expensive thread tap you might consider using for power tapping.
Spiral Flute Taps (Gun Taps)
Spiral Flute Taps have an open spiral just like an endmill. Their primary advantage is they eject chips up and out of the hole. They’re always preferable over spiral point taps when you have a blind hole. They’re also preferable for an interrupted hole where another feature intersects because the spiral helps restart the threading past the open feature. Commonly available in slow spiral (18-30° helix angle) or fast spiral (45-52° helix angle).
Roll Form Taps (Thread Forming Taps)
Thread Forming taps don’t cut threads at all. The tap is chipless. Threads made this way are often called “rolled” threads. With this process, the metal is pushed out of the way and compressed into position rather than being cut. There are no chips to remove. As a result, the taps themselves are less likely to break and the threads they make are stronger. While many believe roll taps are only good for soft materials like aluminium, they can actually be used on materials up to a hardness of 36 HRC, which is about 340 BHN. That covers a surprisingly wide range of materials including a lot of steels.
Tips for Buying and Using a Tap and Die
If you are just starting out, then a basic 20- or 40-piece tap and die set should be all you need. It will come with the most common sizes and types of taps and dies, which will allow you to complete most projects. However, if you have a specialized project or you know that you will need a certain type of tap or a specific die, then make sure that you get a set that includes the pieces that you need.
Another important factor to remember is that for most metals, the manufacturing process can make them very hard, but it also makes them brittle when they’re stressed on the wrong points. So when using the tap and die set, make sure to take the time to clear the metal and wood shavings after every full rotation to prevent the tools from breaking.
- Make sure that you buy a set that includes the types of taps and dies that you need.
- Invest in a tap and die set that can easily handle the materials you frequently use.
- Taps and dies are brittle, so always take your time to clear the excess metal or wood from the flute during thread cutting to prevent breaking the material or your tools.
Taps are available in many types such as Hand Taps and Pipe Taps. The most commonly sold taps are hand taps (sometimes called bolt taps) and they are appropriate for tapping the vast majority of materials in through or blind holed conditions. Taper Style: Starts the thread square with the workpiece. Plug Style: Generally used in thru holes. Bottom Style: Generate the thread to the bottom of the hole.
Dies are available in Round and Hex Dies Hex Dies are for dressing over brusied or rusty threads, they are the most cost effective rethreading tool available. No special holder is required for this type of die, any wrench large enough will suffice. Ideal for maintenance in the shop or field. A Round Adjustable Die is desired for improved wear life. Round Dies are chamfered on both faces. One side has a 2 to 3 thread chamfer for threading, the other side has a 1 to 1-1/2 thread chamfer for threading close to a shoulder. Adjustment is obtained by a fine pitch screw which forces the sides of the die apart, or allows them to spring together. The slot is beveled so that when the dies are used in a machine holder the adjusting screw can be removed and adjustment made by the adjusting screws in the holder.