FTM 192 – Thread-Cutting Taps, Part III

How to choose the correct thread-cutting tap for cutting a thread into a hole. Part 3

This edition of the Fastener Training Minute with Carmen Vertullo was originally published September, 21st 2023 as “How to choose the correct thread-cutting tap for cutting a thread into a hole. Part 3” during episode 192 of Fully Threaded Radio.

Well hello everyone, this is Carmen Vertullo with your Fastener Training Minute, coming to you from Carver Labs in beautiful El Cajon California, and from the Fastener Training Institute.

Today our faster training minute is the third and maybe the last, we’ll see, in our series about Cutting Taps. Now these Cutting Taps that we’re going to be talking about are used for tapping holes. You drill a hole and you tap it. These aren’t any kind of Taps used for manufacturing nuts mass production in the industry. These are the things that you either use in your hand with a tool or maybe you put them into a CNC machine or a drill press with a tap matic to tap holes. We’re going to talk about the most common types of Taps and maybe a little bit about special taps and to help me with that I have a guest who is one of our great Fastener Training Mentor Program mentees, his name’s George Munos. He’s from Ababa Bolt, here in El Cajon, which is the place I got my start in this industry. When we come back I’m going to introduce George to you and we are going to talk about cutting taps.

Well hey everybody, welcome back to the Fastener Training Minute. Today we’re talking about Cutting Taps and this is the third in the series, and I have a good friend here, a guy I’ve known for a long time. I worked with him and his name is George Munos. George tell us about where you work and what you do there. “George: Hey Carmen, I work at Ababa Bolt we are a wholesale fastener distributor, cutting tools, cutting fluids. I’ve worked there seventeen years. I’ve done a little bit of everything in the warehouse, in front counter, inside sales. We sell taps there.” And when I worked Ababa Bolt, I sold taps too, and throughout my working life,  all the way back to shop class in eighth grade, when I first learned about Cutting Taps, I’ve used them. Interestingly enough there are a few things to know about taps, so I’m going to start off by asking George, and I remember there were three pretty basic types of taps that people would ask for, or at least if they knew what they were doing they would ask for, and you might counsel them.

Tell us about those three types of taps, George, in terms of the type and what the differences are between them. “George: Sure. So yeah the very basics. There are three different types, different flutes, I think they’re called. There’s a bottoming tap, which is used for blind tools commonly, a plug tap which is the most common one, and the taper tap which I think gives you longer cutting surface usually for harder Alloys .”  And so when someone would come into the front counter and they would just come up to you and say, I need a 1/4-20 tap and they don’t know anything about those, what would you ask them to help them tune in on which one of the three types they might choose?  “George: What you’re drilling into, what’s it for, basically trying to figure out if it’s gonna be a bottoming hole or through hole“.  So the bottoming tap would be used in a bottomed hole,  like a hole that’s not all the way through, so you can get closer to the bottom? “George: Yes sir”.  But it’s not so good at starting threads because it doesn’t have much of a taper to it? “George: Not much of a taper at all, about one or one-and-a-half threads.

So I know also from my work in the CNC machine shop, that there are some other types of taps that can sometimes be used by hand, and one of those is just spiral point tap or what’s called a gun nose or bull nose tap and it wouldn’t be typical that you would find those in the fastener supplier tap section would it? “George: Not usually like in commercial fasteners. you could special order stuff. Somebody who kind of knows what they’re doing, what they’re looking for.” And that’s popular for us in the CNC world. Now one of the issues that you have is when you’re going to tap a hole, the chips have to have somewhere to go, right? or else you have to pull the tap in and out to clear the chips. And I know our world, in the CNC world we have a tap that’s called a spiral flute tap, and describe that for us. “George: The name kind of says it. It’s a spiral, big spiral I think, it’s for ejecting the chips when you’re cutting.” That’s right it will make the chips come out of the hole instead of going into the hole. And the cool thing about that is if you have a blind hole those chips don’t get packed in. It’s not a hand tap, though  I’ve seen people use them as hand taps ,and I’ve used them as hand taps, but they break very easily. Ask me how I know. You look at them and they just look spindly. They look like there’s no metal or meat there, and they look kind of like a weapon, like a mace or something. They’re just gnarly looking tools, so you have to have great control to use them properly, and that control comes from the CNC machine tool. And I’m going to talk about one more type of tap that is very interesting to me ,and this is called the roll-thread tap or the thread-forming tap.  You look at that tap and it has it could it could not have flutes, but it does not cut any material. Therefore we must have a hole that’s  larger than the normal tap drill, (remember a couple of episodes of go we talked about tap drills), And with the roll-thread tap you need a larger hole because we’re moving material both outward and inward, and one of the biggest mistakes we see people make as they use the normal tap drill for the Cutting tap with the roll-thread or thread-forming tap. And these don’t work and all materials, you’ve got to have a reasonably ductile material. But their claim to fame is that they don’t break as easily, and they last a really long time. So if you have hundreds or thousands of holes to tap in your CNC equipment or even by hand or the tapmatic, it’s the way to go.

Now that’s the very basics of taps, and I would say there are some other types of taps, there are taps for tapping pipe threads for example, and there are taps for oversize holes. We have this thing called “H limit” right, George? “George: Yes sir commonly what you’re going to see in commercial stuff is a”2-H”. Once people who really know what they’re doing they’re going to change them, there’s “3-H” up to “7-H”.” And that refers to the size the thread is going to be within the limit of what that thread is allowed to be according to its class. It doesn’t make the tapped hole in or out of limits, it just simply decides where within the thread class that you’re making, the tapped hole is going to be. And this comes in handy when you want a little bit larger hole for assemblability or a little bit tighter hole for whatever reason. Maybe you want a higher strength internal thread and  actually it goes all the way up to “H-11” which is a very over-sized hole.  The typical fastener distributor that sells taps probably would not have that type of tap, but they could order it for you, because all of the tap manufacturers make all of those H-Limit taps. I’m not going to mention who they are, you all know who they are . “George: Commercially you’re just going to see like “2-H” is what common stuff that the home stores are going to have .” You go into the Home Depot or some equivalent and you’re going to get a “2-H“.

So I think that’s about enough to know about the common types ofc hand taps for right now.

Also of course, there’s a product called the threading die, which makes the external thread that you would have on a bolt. It’s  very difficult to use, in my opinion. Most people use them to repair or chase damaged threads ,but you can make threats with them a lot of care and a lot of preparation. If you have an issue with using a threading die, giving me a call or email me. You know how to get a hold of me, and I will tell you all the things you can do wrong with threading dies, because  I’ve done all of them. All right, well George, thank you for joining us, and it is my pleasure thank you for participating in the Fastener Expert Mentoring Program. By the way, by the time you read this probably will be fired up.

This has been Carmen Vertullo and Jorge Muniz from ABABA Bolt with your Fastener training minute, thanks for listening.

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