What is Thread Tap?
Thread taps are especially designed tools used to cut the female portion of a mating pair of metal fasteners. A die, on the other hand, is a tool used to cut the male portions. Basically, taps are used to cut nuts and dies are used to cut bolts. Taps are also used to cut threads into a hole so that they will receive a bolt more effectively.
There is a difference between threading and tapping. Both threading and tapping produce screw threads. However, threading produces external threads whereas tapping makes internal threads.
There are many types of thread taps including hand taps, plug taps, spiral point taps, and power taps. These are just a few out of many different thread taps.
A tap is used to make (cut) new threads or clean out (chase) existing threads in a screw mechanism. Though this tool is most commonly used by machinists and engineers, automotive technicians may also have a tapping set in their toolbox. There are dozens of situations where having solid knowledge and appreciation for the science behind tapping threads into a piece of machinery can prevent hours of troublesome work and hundreds of dollars in replacement parts.
So what are the types of taps? There are 3 main taps you should be familiar with and they are Taper, Plug, and Bottoming Taps.
Types of Thread taps
Below is a list of ten types of thread taps for you so that you know what they are for. With the information that we arm you with, you will have the power of making informed decisions to decide what type of thread tap you need.
1. Hand Taps
You can buy hand taps from your local hardware store. These are common but are not for CNC work. Compare hand tapping to that with thread taps from the store. You will see that your money was a good investment. The store-bought one performs much better.
There are two kinds of hand taps: taper tap and bottoming tap. They are the following:
The taper tap can be identified by the visible and pronounced tapering of the cutting edges. This provides a very gradual and less aggressive cutting action. The distinct feature of a taper tap is the 8 to 10 threads that taper from the tip to the full cutting force diameter. A taper tap is most often used as a starter tap for difficult blind holes.
The gentle taper of the cutting edge is the most forgiving when tapping by hand and allows for a straight hole to be cut in especially hard materials.
A taper tap is rarely the final tap used before completing a project, however, as the taper leaves incomplete threads cut at the bottom of a blind hole.
Bottoming taps have 1 to 2 tapered cutting edges before the full cutting force is engaged. Though this tap is extremely hard to start threads with, it is capable of cutting threads all of the ways to the bottom of a blind hole. Bottoming taps are best used after a taper or plug tap has been used to cut the initial thread.
2. Plug Tap
A plug tap has a less pronounced taper to the cutting edges. This gives the plug tap a gradual cutting action that is less aggressive than that of the bottoming tap but more aggressive than a taper tap. Typically, the plug tap will have 3 to 5 tapered threads before the full cutting diameter is engaged.
Plug taps are great when used with through-holes, as they are almost as easy as taper taps to start, but also offer a more complete set of threads.
3. Power Taps
If you have manual matching work or CNC applications, then this is the right type of thread tap for you. The above tips are generally referred to as hand taps since they are manually operated. During operation, the machinist must periodically reverse a hand tap to break the chip (also known as swarf) that forms from cutting. This prevents the cut material from crowding and breaking the tap.
The most common type of power-driven tap is the “spiral point” plug tap, also referred to as a “gun” tap, whose cutting edges are angularly displaced relative to the tap centerline.
This feature causes the tap to continuously break the chip and eject it forward into the hole, preventing crowding. Spiral point taps are usually used in holes that go all the way through the material so that the chips can escape.
Another version of the spiral point plug tap is the spiral flute tap, whose flutes resemble those of a twist drill. Spiral flute taps are widely used in high-speed, automatic tapping operations due to their ability to work well in blind holes.
4. Spiral Point 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. But, the spiral angle on the front cutting edges helps eject the chips and the angled edge also gives a superior cutting performance.
Hence, they’re really the least expensive thread tap you might consider using for power tapping and can be run at slightly higher speeds than hand taps.
Like hand taps, spiral point taps can be had as a taper tap has a tapered end, or a plug tap (intended for blind holes) has much less taper.
They’re cheaper than the other two types, but I typically prefer the other two. The primary disadvantage of these is they push the chips ahead of the tap–down into the hole in other words. This is not a big deal for through holes but is a bad idea for blind holes.
5. Spiral Flute 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.
Sometimes, take a spiral flute tap and a regular hand tap and tap a couple of identical holes by hand. You’ll be shocked at how much less effort the spiral flute tap requires. Choosing the right types of taps really helps!
6. Interrupted Thread Tap
These thread taps only have a tooth for every other thread. The idea is to provide improved chip extraction. Removing every other tooth helps break chips and also provides more room for the chip to escape and for lubricant to come in and do its job.
7. Pipe Taps
As you might expect, Pipe Taps are the types of thread taps used for tapping pipe threads. There are both straight and tapered pipe taps depending on whether the pipe thread is intended to be straight or tapered. The photo shows a typical NPT Thread Pipe Tap. You can see the taper of the NPT thread profile.
Taps for tapered pipe threads have to work harder because you can’t drill a tapered hole. There’s quite a lot more material they must remove at top of the hole than at the bottom. Use a pipe taper reamer to taper the hole so the tap doesn’t work so hard.
8. Forming tap
A quite different kind of tap is a forming tap. A forming tap, aka a flueless tap or roll tap, simply forcefully displaces the metal into a thread shape upon being turned into the hole, instead of cutting metal from the sides of the hole as cutting taps do. A forming tap closely resembles a cutting tap without the flutes, or very nearly just like a plain thread.
There are lobes periodically spaced around the tap that actually do the thread forming as the tap is advanced into a properly sized hole. The threads behind the lobes are slightly recessed to reduce contact friction.
Since the tap does not produce chips, there is no need to periodically back out the tap to clear away chips, which, in a cutting tap, can jam and break the tap. Thus, thread forming is particularly suited to tapping blind holes, which are tougher to tap with a cutting tap due to the chip build-up in the hole. Forming taps only work in malleable materials such as mild steel or aluminum.
Formed threads are typically stronger than cut threads. Note that the tap drill size differs from that used for a cutting tap as shown in most tap drill tables and that an accurate hole size is required because a slightly undersized hole can break the tap. Proper lubrication is essential because of the frictional forces involved; therefore, lubricating oil is used instead of cutting oil.
9. Extension Taps
Extension taps have long shanks. This allows you to get to hard-to-reach holes. “Long shark tap” is another name of this thread tap.
10. Punch Taps
This thread tap uses the technology of Audi and Emuge that allows tapping cycle time to fall 75%. It’s a great tool to have for your thread tapping needs.
How To Use a Tap and Die Set
Step 1. Determine the Threads Per Inch
Tapping is when your threads are cut into a hole. A die set is used to cut threads onto a cylinder (bolt). To use a tap or a die, first determine the number of threads per inch (TPI) of the part to be fixed. A gauge system that has a number of different pins can be used to calculate the TPI of a bolt or nut.
After determining the TPI of a bolt, choose the die that corresponds to it. A tapered die will tell which side to begin using. The die fits into a special wrench that holds and guides the die.
Step 2. Create New Threads
To use the die to create new threads on a worn-out bolt, place the bolt into a vise to hold it as the wrench is turned over. Cutting metal with metal can create heat, so put some cutting oil on the bolt to lubricate it.
Place the die over the bolt and hold it horizontally. Turn the wrench. The die will catch on the threads already cut into the bolt. Every couple of turns, reverse the wrench about a half a turn to clear the threads so that the die will cut better. Also, re-apply cutting oil throughout the process. Turn the wrench until the bolt comes past the top of the die.
Step 3. Turn a Steel Rod into a Bolt
A die set can also be used to turn an ordinary steel rod into a bolt. To do this, the rod must have a beveled end. If necessary, chamfer the end of a rod on a grinder to get a bevel. The die will not work very well with a flat-ended rod.
Lubricate the rod often, as when cutting into a worn bolt. Make turns slowly. Have a little bit of patience with this process to achieve the desired results.
Step 4. Use a Tap
To use a tap, choose the size that is appropriate for the size of the bolt or the hole you want to thread. Place the tap into the special wrench and tighten it in. Then, place the cutting end of the tap over the hole and turn. Use cutting oil to lubricate the tap. As with the die, once the tap is started, make a slight reverse turn every now and then.