What is Thread Tap?
Thread taps are specially designed tools used to cut the female portion of a mating pair of metal fasteners. 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.
These are used by hands with a tap handle or with the help of a wrench and are also used with the help of drilling machines.
A number of small parts are joined to complete a machine. Mostly nuts, bolts, and different kinds of screws are used for this purpose. Taps are made of high carbon steel, high-speed steel, alloy steel, etc. These are hardened and tempered. Their shape is almost like a headless bolt with full threads. The upper portion is square and four flutes are made on the entire part in which threads are there.
Types of Thread taps
There are different types of thread taps that are used for a variety of reasons and purposes. Below are some of the most common types of thread taps and their basic description:
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:
- Taper Tap: A taper tap has quite a lot of tapers to help it ease into cutting threads gradually. Typically, the first 8 to 10 threads are tapered. Taper Taps are the most common types of taps and are typically what you’ll have in a Tap and Die Set.
- Bottoming Tap: A bottoming tap has almost no taper at the end because it is designed to thread all the way to the bottom of its reach. Only 1 to 1.5 threads will be tapered. Bottoming Taps are useful for threading blind holes. It’s desirable to thread most of the hole with a Taper Tap first, and then finish the bottom of the hole with a Bottoming Tap.
2. Plug Tap
Plug Taps are in between Bottoming and Taper Taps because they have 3-5 threads tapered, which is more than a Bottoming Tap and less than a Taper Tap. Unfortunately, the terminology is not always consistent. Some vendors call these “Second Taps” and refer to Bottoming Taps as Plug Taps. Check to be sure what you’re getting and using.
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.