Today I’d like to share some tips on one of my favorite functional 3D-printing techniques: adding heat-set inserts. As someone who’s been installing them into plastic parts for years manually, I think many guides overlook some process details crucial to getting consistent results.

Whenever one is working around a design that already exists, it pays to be flexible and adjust to the unexpected. The Dremel 220 has a holder intended to clamp a rotary tool, and the original plan was to simply design and print an adapter so a soldering iron could sit in place of the rotary tool. That plan changed upon realizing that the entire rotary tool holder disconnected from the tool’s frame with a single bolt. It made much more sense to make the soldering iron replace the rotary tool holder, instead.

We can make our 3D-printed parts even more capable when we start mixing them with some essential “mechanical vitamins.” By combining prints with screws, nuts, fasteners, and pins, we get a rich ecosystem for mechanism-making with capabilities beyond what we could simply print alone.

[Thomas] only tests M5 fasteners in this video, so keep that in mind if you get ideas and go shopping for new hardware. Some of the tested inserts aren’t commonly available in smaller sizes. Self-tapping threaded inserts, for example, are available all the way down to M2, but the hex socket threaded inserts don’t seem to come any smaller than M4.

If you haven’t tried these out yet, check out [Joshua Vasquez’s] excellent guide on heat-set inserts. You’ll find this guide to the relative merits of the different types useful when ordering inserts. And if you’ve got the itch to buy a lathe now, we’ve got you covered there too.

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Use: Concrete, brick, mortar, concrete block | Type: Hammer-rated carbide-tip twist drill | Number of bits: 7 | Size range: 3⁄16 to ½ inch

Use: Concrete block, mortar, brick | Type: Rotary (non hammer) carbide-tip twist drill | Number of bits: 14 | Size range: ⅛ to ½ inch

Make no mistake; there are a handful of insert guides already out there [1, 2]. (In fact, I encourage you to look there first for a good jump-start.) Over the years though, I’ve added my own finishing move (nothing exotic or difficult) which I call the Plate-Press Technique that gives me a major boost in consistency.

These twist drill bits are built to withstand punishment. They’re machined out of high-speed steel and finished with a wear-resistant coating. Yet their tips can be resharpened. All that is good. What’s even better is that they’re made in America and yet are priced reasonably, especially when you account for the cost of the nice sheet steel bit index that they come in. We tried them, liked them, and thought enough of them to award them our coveted annual Tool Award.

We enjoyed seeing [Stefan]’s tests, and appreciate the data that can help us be informed consumers. [John] over at Project Farm does similar head-to-head tests, like this test of different epoxy adhesives.

Use: Wood | Type: Forstener | Number of bits: 8 | Size range: ¼ to 1⅜ inchesWhen you need a perfectly round hole in wood with a smoothly machined sidewall, then you want a Forstener bit. These are best used in a drill press, but the smaller-diameter bits can be used in a hand drill.

Use: Thin-gauge steel, aluminum | Type: Impact-rated step drill | Number of bits: 3 | Size range: ⅛ to ⅞ inchThey call these step drills because of their shape. Each step increases the hole diameter. You just stop drilling when you reach the appropriate hole diameter at the step that produces it. Although these bits are designed for sheet metal, they will drill a clean fast hole in heavier-gauge materials like electrical boxes and even mild steel channel, and shapes like L, U, and T.

The resulting modified soldering iron is mounted via standoffs to a 3D-printed adapter with a copper foil heat shield. [concretedog] admits it’s not ideal from a heat management perspective, but it makes a fine prototype that seems to work well for light duty. The next step would be a metal version.

Okay, by now you might be saying to yourself, “All I want is a basic set of bits for wood and metal. Got any of those?” Yes. For less than $20 you get a high-quality hex shank bit with a highly wear-resistant titanium nitride coating. And if you up your game some day to include working with an impact driver, these bits will work with it.

The usual way to put a durable threaded interface into a 3D print is to use a heat-set insert, but what about other options? [Thomas Sanladerer] evaluates a variety of different threaded inserts, none of which are actually made with 3D printing in mind but are useful nevertheless.

If this sounds familiar, it’s with good reason: we covered [Stefan]’s last stab at assessing threaded inserts back in March. Then, he was primarily interested in determining if threaded inserts are better than threads cut or printed directly into parts. The current work is concerned with the relative value of different designs of threaded inserts. He looked at three different styles of press-in inserts, ranging in price from pennies apiece to a princely 25 cents. The complexity of the outside knurling seems not to be correlated with the price; the inserts with opposed helical knurls seem like they’d be harder to manufacture than the ones with simple barbs on the outside of the barrel, but cost less. And in fact, the mid-price insert outperformed the expensive one in pull-out tests. Surprisingly, the cheapest inserts were actually far worse at pull-out resistance than printing undersized holes and threading an M3 screw directly into the plastic.

There’s a trick in the world of plastic enclosures. The threaded insert is a small cylinder of metal with threads on the inside and a rough edge on the outside. To make a plastic part with a hole for securely connecting bolts that can be repeatedly screwed without destroying the plastic, you take the threaded insert and press it (usually with the help of a soldering iron to heat the insert)  into a hole that’s slightly smaller than the insert. The heat melts the plastic a little bit and allows for the insert to go inside. Then when it cools the insert is snugly inside the plastic, and you can attach circuit boards or other plastic parts using a bolt without stripping the screw or the insert. We’ve seen Hackaday’s [Joshua Vasquez] installing threaded inserts with an iron, as well as in a few other projects.

Spade bits are made for quick-and-rough holes in construction lumber. They don’t leave a particularly clean exit hole, but in most cases that doesn’t matter. Of all the spade bits we’ve tried through the years, we keep coming back to Irwin Speedbor. They’re inexpensive, tough, and can be sharpened with a file. One set will last for years, maybe decades, depending on your use.

These hole saws are known as bimetal types because they're made from two types of steel. The body is made from spring steel and formed into a cup. Around the front edge of that cup is brazed a circular row of cutting teeth made from a narrow band of high-speed steel. The result is a light weight and durable accessory tough enough to make big holes in wood  or metal. Suppose you need to make a door knob hole in a wood door; turn to these. Use them again to make holes in steel, for a tool rack, say.

If your drill driver has a hammer setting, chuck in one of these bits and make a clean and fast hole in concrete, brick, concrete block, or mortar. You don’t need an extensive set of masonry bits; a basic carbide-tip kit like this one is a great choice. Its German-made quality should provide years of use, and its slim, vinyl wallet enables it to slip into a crevice in your tool box. Carry this and you’re prepared for tough, masonry drilling jobs without having to make a quick run to a hardware store or home center.

When the tool you need doesn’t exist, you have to make it yourself. Come to think of it, even if the tool exists, it’s often way more fun to make it yourself. The former situation, though, is one that [Sean Hodgins] found himself in with regard to threaded inserts. Rather than suffer from the wrong tool for the job, he machined his own custom threaded insert tool for his Hakko soldering iron.

Like many of us, [Sean] has embraced the use of heat-set threaded inserts to beef up the mechanical connections on his 3D-printed parts. [Sean] dedicated a soldering iron to the task, equipping it with a tip especially for the job. But it was the flavor of iron proverbially known as a “fire stick” and he found that this iron was too hot for PLA prints. As the new owner of a lathe, he was able to make quick work of the job using a piece of brass rod stock. Luckily, Hakko tips just slip on the heating element, so no threading operations were needed. [Sean] made insert tips for multiple sized inserts, and the results speak for themselves.

If you’re getting interested in woodworking, this inexpensive brad point bit set is an easy choice. The sharp tip on these bits make it easy to start the bit exactly where you need it, and their geometry—somewhere between a twist drill and an auger bit—makes for good chip ejection.

It’s almost a sure bet that when running pipe and wire in an old house, you’re bound to hit embedded nails when boring the holes. That’s where these bits come in. They’re thicker than the typical spade bit to resist bending, and they have a bevel on their cutting surfaces suitable for both wood and metal.

Have you ever wondered whether it’s worth the time and expense to install threaded inserts into your 3D-printed projects? [Stefan] from CNC Kitchen did, and decided to answer the question once and for all, with science.

There are a number of other easily-available threaded inserts, including the rivnut (or rivet nut), chunky hex socket threaded inserts intended for wood and furniture, heli-coils or helical inserts (which resemble springs), self-tapping threaded inserts (also sold as thread adapters), and T-nuts or prong nuts. They all are a bit different, but he measures each one and gives a thorough rundown on how they perform, as well as offering his thoughts on what works best.

[Stefan] also looked at torque resistance, and found no substantial difference between the three insert types. Indeed, none of the inserts proved to be the weak point, as the failure mode of all the torque tests was the M3 bolt itself. This didn’t hold with the bolt threaded directly into the plastic, of course; any insert is better than none for torque resistance.

Suppose your drill doesn’t have a hammer function or you lack a dedicated masonry drill, what do you do then? Well, if your masonry hole drilling is confined to brick, concrete block, or mortar, you can use these inexpensive carbide-tip rotary drill bits for masonry. They won’t stand up to use in a hammer drill, but they work perfectly well, if slower, in a standard drill or cordless drill driver. Bonus: Their double-flute design allows better clearing of dust and chips compared to a single-twist type. This way you can use the drill’s high-speed setting to get through the job faster. Note that there are multiples of the smaller diameters, such as the 3⁄16-inch size, which are more frequently used with masonry screws.

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These threaded inserts might be just what your next project calls for, so keep them in mind. Heat-set inserts are of course still a great option, and our own Sonya Vasquez can tell you everything you need to know about installing heat-set inserts into 3D printed parts in a way that leaves them looking super professional.

If you’re intrigued by threaded heat-set inserts, you can learn all about how to use them from Joshua Vasquez’s guide to the handy things. And should you prefer to make your own DIY press from 3D printed parts and off-the-shelf hardware, we have that covered as well.

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If you want to make serious assemblies out of 3D printed parts, you’ll eventually need to deal with threading. The easiest way is to make a nut trap that you can either insert a standard nut into after printing or even during printing. However, there are limitations to this method. If you want a real threaded part you can print the thread, cut the thread with a tap or bolt, or use a threaded insert. [Stefan] ran some tests to see how each of those methods held up to real use. (YouTube, embedded below.) He used fifty test parts to generate data for comparison.

Big HolesIf you need to make large-diameter holes—something between ¾ inch and 4 inches, let’s say. You don’t want a drill bit, you want a hole saw. Even though these aren’t drill bits, we’ve included a set of these at the bottom of this review. It’s reasonably priced and can serve both homeowners and professional users.

We like the threaded insert method where a brass insert is pushed into the plastic while hot. Special features in the insert cause the brass part to grab the plastic, making it difficult to pull the insert out or twist it within the hole. Another thing we liked was that the tests used holes printed in the horizontal and vertical plane. You can clearly see that the orientation does alter how the holes work and fail to work.

The only sure way to make consistent and clean holes in glass and ceramic tile is with a carbide bit designed for those materials. These simple and inexpensive little bits work great. The carbide tip is diamond ground to a sharp point that enables a fast and sure start, putting the hole right where you need it, instead of the bit skating off and leaving a nasty mark. The three flats ground onto the bit’s shank prevent it from slipping.

Join me below as I fill in the knowledge gaps (and some literal ones too) to send you back to the lab equipped with a technique that will give you perfectly-seated inserts every time.

How To Select a SetThere’s no sense in getting bogged down in complexities of hole making–the fine points belong to industrial users. For the rest of us, all we really need to know are the basics. That’s why we separate out bits for making holes in wood, metal, masonry (concrete or stone), and tile/glass. Some of the drill bits do a pretty good job making holes in more than one material. Other than selecting a bit based on the material you’re drilling, keep in mind the quality of the hole you’re making. That sounds odd. A hole is a hole, right? Wrong, There’s a big difference between a perfectly round and smooth-walled hole for furniture making than a rough-and-ready hole made in framing lumber to fit a pipe or cable. So think about the material, the hole itself, and how you want to make it. Choose your set accordingly.

If you’re gearing up for your first big wiring or pipe job, or if you’re a seasoned pro looking for faster and cleaner hole-making ability, then self-feed bits are the way to go. The lead screw pulls the bit through the lumber while an interior plane shaves the wood as the bit turns. The result is a fast hole and a clean one. For the sake of longevity, the plane blade is sharpenable and the kit includes two removable, replaceable feed screws, because you’re bound to hit fasteners and chew through knots.

Dremel has been helping people fit square pegs into round holes for years, and [concretedog] saw that the Dremel 220 Workstation — a piece of hardware similar to a drill press — could be convinced to hold a cheap soldering iron just as easily as it holds a rotary tool. A soldering iron makes an effective thermal insert tool, and the job of heating and pressing the threaded metal rings into plastic is made much easier when it can be done similar to operating a drill press. With a few modifications and a 3D-printed adapter, the thermal insert rig was born.

Use: Wood and steel | Type: Extra-long twist drill | Number of bits: 5 | Size range: ¼ to ½ inchSuppose you need more reach when making a hole, such as when you’re working on an old house or restoring an old car. Or in a modern house, you need a super-long pilot hole for that massive screw you’ll use to hang a ceiling fan. Enter these 18-inch bits. Built from high-speed steel and with geometry to eject metal chips, they work on wood, too (though you will have to back them out repeatedly as you go deeper to eject the wood chips).

It’s often said that you don’t need a drill bit; what you need is a hole. How you make that hole is up to you, but it’s a given that you want to make it as efficiently as possible. The drill bit, therefore, is built to match the diameter and length of the hole you want to make—as well as the material in which it works. And chances are good that you need more than one bit, you probably need at least a small set to make holes of various diameters.