There are many different types of taps, and knowing exactly when to use each kind is the goal of this.
There are two types of Hand Taps:
Taper Tap
A taper tap has quite a lot of taper 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 desireable to thread most of the hole with a Taper Tap first, and then finish the bottom of the hole with a Plug Tap.
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, 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.
Power Taps
These are the types of taps you should choose from for CNC applications or for manual machining work.
Spiral Point Taps (Gun Nose or 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. But, the spiral angle on the front cutting edges helps eject the chips and the angled edge also gives 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, sprial 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.
Spiral Flute Taps or 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.
Sometime, 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!
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.
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 hole than bottom.
Form or Roll Taps (Thread Forming Taps)
Thread Forming taps don’t cut threads at all. Instead they cold form. 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. If your application allows Form Taps, they are generally the best thing going for those reasons.
Form Taps do require different feeds and speeds and they require a different starting hole size, so be aware of that before using one.
While many believe they’re only good for soft materials like aluminum, they can actually be used on the material of the hardness upto 36 HRC OR 340 BHN That covers a surprisingly wide range of materials including a lot of steels.
I will almost always choose a Form Tap over a Cutting Tap out of the available types of taps if the material isn’t too hard for thread forming.
Extension Taps (Long Shank Taps)
These are just thread taps with a long shank to facilitate reaching difficult holes that are blocked by other features on the part.
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