FTM 191 – Drilling and tapping for inserts, Part II

How do we choose the correct drill bits and taps if we are installing threaded inserts.

This edition of the Fastener Training Minute with Carmen Vertullo was originally published August, 18th 2023 as “How do we choose the correct drill bits and taps if we are installing threaded inserts.” during episode 191 of Fully Threaded Radio.

Well hello everyone, this is Carmen Vertullo with your Fastener Training Minute coming to you from the Fastener Training Institute  and from Carver Labs  here  in beautiful El Cajon California. Today it’s a very special episode of the Fastener Training Minute because I have some help. We’re talking about drill bits and taps, not necessarily the things that you use to manufacture fasteners, but the things that you use in a machine shop when you are fabricating or maching parts. Last time we talked about generally selecting tap drills for taps this time we’re going to talk about the special drills and taps that are needed when you’re installing threaded inserts. Even though I have a lot of personal experience with this I’ve messed it up enough times to know that there’s more to know than I know. That’s why I have a wingman today with me, and that is John (Cool Hand) Butler from Martin Fastening Solutions. So John is going to come alongside and he’s going to help me make sure we get the information correct in this episode. If you are a supplier of these kinds of things, you really need to listen closely. You’re going to learn something I guarantee it because when I was talking to John about this recently I thought I knew everything and he tuned me up good in a couple of areas. So when we return it’ll be Carmen with John (Cool Hand) Butler.

Well, welcome back everybody this is Carmen Vertullo with the Fastener Training Minute and I want to introduce to you, well,  you already know him he’s been here before, John (Cool Hand) Butler from Martin Fastening Solutions.

John:  Thank you for having me on Carmen, I do appreciate your confidence in me and and having me on the podcast with you guys. Currently I’m working as a regional account manager with Martin Fastening Solutions. I cover five states. Martin is a full supplier of Industrial Products and  safety integrated, meaning vending machines, and also they have their Fastener division as well. That is the part of the company that I work for. We have a phrase that we call “all for one” so we are one company, one team, one thought. So it’s it’s a pleasure to work for Martin who handles basically the Southeast to the Midwest. From Indiana and Illinois all the way down, we have some accounts in Texas all the way down to Florida. So thank you for having me on“.

Well I’m pleased to have you John because I know you have a background in a lot of areas, but this one in particular, because you have solved some problems for me over the years, and I think the whole area of threaded inserts (and I’m going to ask you to explain what we mean when we say threaded inserts here in a minute), but they generally are  not generic things. They’re brand names for the most part, so when we throw around a few brand names or manufacturers names, it doesn’t mean we’re endorsing them. It’s just a fact of life: threaded inserts tend not to be generic, but specific by brand and part number. So John give us a quick background on why we use threaded inserts and who the players are.

John:  Oh sure. So there’s a lot of different applications. If, let’s say you’re using a plastic, you don’t want to just go ahead and drill and tap into plastic because you’re not going to have any of that strength, right? so there are manufacturers that design products (inserts) for different applications, whether it be Aerospace or Plastics. You know, say even a concrete where you have an anchor. But we’re not talking about that type of insert, we’re talking about parts that go in, whether it’s a wire thread insert, some of the major brands out there are Heli-Coil and Kato, those are two of the the major manufacturers of wire thread inserts. You’re going to get a much greater tensile strength on the product that you’re manufacturing with these types of inserts. For Plastics we’re usually putting in a stainless steel or brass insert that we can thermoset in. Meaning we use some heat and vibration to sink the insert into the Plastic. Some of the big names are TSM and Dodge, who make inserts for Plastics. These give you much greater strength.

Well that was a great intro, and essentially I loved your example of using the concrete threaded insert which we call drop-in anchors, because kind of on a smaller scale that’s exactly what these inserts do. They take a material that might not have good strength to something together, and they increase its capacity to have something bolted down to it with higher strength. So they serve a very important role in all kinds of manufacturing. So my recent experience was with what you called the helical wire inserts, or I call them generically heli-coils, even though that’s a brand name. And I discovered something about the taps that are used with helical wire inserts. The  interesting thing about helical wire inserts is that it is like a spring, so the thread pitch does not change, but some other things change. So that the tapped hole that the helical wire insert goes into is not your run-of-the-mill tapped hole. Tell us about that John.

John:  Well, yes. So when we put these inserts in we want to achieve what they call Dynamic Load. No matter what brand you’re using, it’s a diamond shaped wire, and we’re going to tap the hole, but not with the standard tap. They use  what  call an STI which is a “Screw Thread Insert” tap.  And this is a cut tap I should say Carmen, I  mean it’s not a roll-tap. So what’s the difference between the two types of taps? Cut Tap is actually going to cut away material after you’ve drilled the hole, as it puts thread inside the material, it will cut away a portion and give you a very defined, more of a diamond shape thread. Whereas a roll-thread tap, which is less expensive  because what you’re doing is rolling the thread in there and that’s going to save that tap. You can use it more often we’ll say before you’ll need to replace it. And that’s why so many machine shops want to use a roll-thread taps. But if you’re going to use a helical wire thread insert you want to use a cut-thread tap, and what that will do is to allow the insert to  fully seat itself in those cut threads. Now I mentioned before Dynamic Load, and what that is is when you put a bolt into a cut thread,  no insert at all, just a bolt, most of the tensile strength is going to be on the first few threads. So what  Dynamic Load means, is that I’m going to have that load spread out via more threads not just the highest strength of the top but it’s going to be a proportion on through the threads and with a wire threat insert you can achieve that each thread will carry a portion of the load.

Excellent and these are generally specified by Engineers right? So you want to get your part number on the drawing, whoever’s making the part. It’s a very specific part number from a very specific manufacturer that we have to buy, and  I’m in the process of sourcing this, and I’ll tell you something very interesting. Another brand name that we use a lot in our machine shop in our fixtures, is a company called E-Z LOK and I just got an email from E-Z LOK asking me if I could do some testing. I probably shouldn’t be saying this in public, but it just came in just now as we speak. It’s sort of an interesting  coincidence, and we have done a lot of work for E-Z LOK in a past here at Carver Labs. I’m excited about that but, an E-Z LOK insert is a solid insert. In other words it’s like a tube that has threads on the outside and threads on the inside, and there is  variety of those kinds of inserts.  Tell us about those solid inserts, John,  that aren’t made out of wire but are actually a full form part,

John:  Yeah, you can get different materials, you know stainless steel, carbon steel for these solid bushing inserts as a lot of people refer to them. As you said it’s a solid piece of material with threads on the outside and the inside. Many of them have keys on the outside. So when you’re thinking of like a key stock ,it’s going to go into a slot right? So depending upon the size, a key lock insert, so let’s say a brand out there is Keen-Sert, Acme is another one, they will have these keys that stick out on the top of the insert (there’s a slot that it would slide into), but those keys help drive the insert. There’s little tool that has of course indentations where these Keys would line up, and you’ll just turn the insert into the tapped hole, turn the tool over, and you hit it with a hammer and drive these Keys. An E-Z LOK insert is a little bit different. It has a slot on the top that you would use to install the insert right? So it has a tool that has a protrusion coming out that would fit right on those slots. There’s a slot that goes all the way across like a slotted screwdriver you would think of, and that would drive that insert in. The E-Z LOK has a thread-locking compound on the outside so that once it is put in place, that thread locking compound is very similar to like a micro sphere, that will lock it into place.

That’s excellent John,  and that micro encapsulated, whatever, epoxy, is very interesting because it will lock that insert into place. So that because there’s no real resistance when you screw it in, you can put those in with a screwdriver I’ve discovered. But they actually do have a special tool that makes life easier. I would say for all inserts, in my experience buy the tooling, buy the best tooling . Don’t dick around with using a screwdriver or a screw, or something that just is going to make life more difficult for you.

Well,  for one thing,  I’ll say, if I may please, is that a for lot of these you’ll want to countersink that in, or at least have it below the surface. If you are using a key locking insert, you don’t want those keys sticking out above the surface. And if you’re using a screwdriver are you going to get it to the right depth? That’s why the correct installation tool is usually suggested.

Exactly, right, and so interestingly enough, if you can imagine going back to the the spiral wire insert, the Heli-Coil insert, because every thread on the outside has a corresponding thread on the inside. The thread pitch is the same, just the larger diameter for that tap,  but the key lock insert is not the same. You can have a key-locking insert that might have (let’s say) an internal size of 3/8-16 , but it might have a 1/2-20 or 1/2-13 or some other size outside thread, which may or may not be the same thread pitch. More importantly, the tapping drill bit is going to be much larger. So with the key lock insert, and straighten me out here if I get this wrong, John, you don’t need a special tap but you do need a special tap drill bit. Tell us about that.

John:  That’s that’s correct Carmen, So with these inserts, always go to the catalog. They’re going to give you the exact measurements of what you want to do as far as your tap size. So I’m actually looking in the Acme catalog right now. It gives you the decimal point for that. Most of the catalogs will tell you actually what size drill to use, and what size tap. So of course countersinking that would be very important.

Well hey, John, we’ve been at this for 14 minutes, and that’s a record I think, even though we have not been really mumbling. We’ve been saying a lot of good stuff pure a good information all along the way and there may be more to know about threaded inserts and the Taps that go with them so maybe we’ll continue this another time but I just wanted to thank you John, because this is a watershed moment for the Fastener Training Minute. I got a wingman. I enjoyed it immensely ,and I think it’s a major step forward for us.  I hope we get to do it again,

John:  Thank you, I appreciate  it, Any time I can help.

All right signing off, thanks for listening

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