Do you even need threaded inserts? Strength tested! 

I think it could be interesting to see how the number of perimeters around the hole and the type of infill (geometry and density) affects the strength of the insert (using CNC kitchen ones for example)

Surprised you didn't try nut pockets (what prusa does with their printer parts). That creates a nice solid wall that isn't distorted by brass teeth. I typically use wood screws if it's a one time use, and the inserts if it's a part that may need dis-assembly (also looks more professional). In injection molding it's exactly the same, if it's a one time assembly then self-tapping, if it needs to be serviceable there better be inserts included.

Flip the camera inserts to the other side of the printed piece. That way you have a larger flange you are pulling against the print. Essentially acting as a larger backup washer.

Test it with a regular hex nut countersink in a hexagon hole from the back on the part or a square hole in side the part and push the nut in from the side. I do this all the time and it works perfect and does not require any special nuts.

Just a FYI, spiral fluted taps are much better suited to tapping plastics and soft materials like aluminum as they evacuate the chips while tapping.

Friendly tip - for anything starting at M4+, I am not using inserts for plastic, but inserts for wood. They have larger diameter of the metal part. And I am heating them up and screwing them to the plastic - significantly increasing the contact area. Works much better. And the best part - you can then screw in the bolt from the other side, make the insert invisible and even stronger :)

Perhaps consider printing a 100% infill 'doughnut' of say 10mm around each insert/tap/thread point to eliminate some of the variability caused by your part flex and infill interface, along with using an omnidirectional infill like Gyroid. It would improve pull-to-pull consistency and more accurately demonstrate the ultimate/average strength of each method.

LOVED the Blondihacks "Yahtzee" nod with the lathe part-off 😂

I typically use self-tapping 3mm screws in 2mm holes with no printed thread. Even for parts that need occasional disassembly and re-assembly they work great. And let's not forget that lots of injection molded cases do the same thing. And in my experience PLA parts survive unscrewing and rescrewing better than the industrially produced ABS parts. As I'm writing this I'm printing 3.5" to 5.25" mounting adapters that I designed today (because the ones on Thingiverse are all just imitations of mass produced parts and these designs work poorly for 3D printing) and the means of fastening the adapter to the PC case is by means of 3mm self-tapping screws. I always use the longest screws that will fit.

In combat robots, we all use plastite screws. They have triangular lobe coarse threads. You just screw them into the plastic, no tapping required. A common failure mode we see are heat set inserts pulling out, but the plastite screws fare much better. We also tend to use a lot of walls since we’re printing for strength. Usually 3mm walls or more. Plastites are also lighter than inserts.

Would be more interesting to test screws made for screwing into plastic, like "plastite" instead of screwing ISO screws directly into plastic. Right tool for the right job!

Love the machining work and the Quinn reference, yahtzee! Would like to see your mill and lathe setups more!

For extremely small screws (M2, M2.5, M3) I tend to just screw directly into an oversized printed hole; basically the tapping method, but skipping the tapping step. I get fine results, but I'm also never designing parts for strain, just assembly.

Did you test torque-out at all? Because that pull-out test is honestly almost entirely pointless as that is just not the way you use them in, dare I say it, almost any case.

A handy tip for increasing the number of perimeters around just a hole: You can put an infinitesimally thin annular gap spaced out a few perimeters lines from the ID of the hole. This will force the slicer to an extra set of perimeter lines around the hole without having the increase the number of perimeters everywhere. I'll actually put these phantom gaps anywhere I need to add solid perimeter lines in an area that would otherwise just be infill.

I'd be really interested in seeing the results of different infills as the failure mode was always to rip the connecting walls, I think that'd be much more useful for figuring out how to get the strongest output for each usage case!

I usually embed nuts inside the print by modeling a cavity and pausing the print at the top layer of the cavity. Nuts are usually a lot easier to find for a particular size than threaded inserts, and more broadly useful. If you need even more strength, modeling in space for a steel washer between the nut and the inside wall of the part increases the engagement with the plastic part by quite a bit.

For the past 5-6 years I’ve just self-tapped into a tighter printed hole and had excellent results that way. Yes, occasionally I’ll use a nut on the back and once or twice inserts but for 90% of the loads I put my prints through (including my CNC machine), the self-tapped printed holes seems just fine.

In my experience the screws for wood work much better. The hole in the printed part should be a bit bigger than the core and since these screws have a very deep and sharp thread, they usually connect very nicely with the part. The failure point is typically the connection between the printed hole and the rest of the part. For tapping the thread into PLA i found that a decent lubrication makes the process almost perfect. I typically use some grease since it does not flow away unlike oil. By the way adding a little of grease on woodscrews eases the joint process a lot. Cheers

Please also test the strength of self tapping screws. The "threads" of those, are spread over several layers, and seams to make a quite strong bond. It's a way quicker solution to use, that I have had good succes with.

My favorite is the wood thread insert with spikes on a flat washer on the back of the part. Also always add some extra walls around the thread and it won’t pull out but generally I’d print a section of 100% infill there anyways. If you can get 4x diameter on the hole depth, printed threads chased with a forming tap are wicked strong. And like others said, burying a nut in the print in some way is always a super good option. If the nut is near an edge, you can add a keyhole slot on the side to slip the nut in and then screw through the front. I had to make a super tricky assembly once and used a thick 3mm washer tapped for an m4 bolt and slipped it in through a side slot that got plugged with epoxy to hold the threaded washer and plug in.

This is a fantastic video! You mentioned that you solder lead free. Could you make a video on how you do this and what solder you use. I have been trying to use lead free solder for a while and I just can't get the solder to cooperate.

I like to use “alternate extra walls” and “connect infill lines” to really boost the strength of printed parts. The perimeters become interlaced with the infill structure and resists pullout and deformation. I use grid for faster prints but prefer gyroidal for strength in all directions or for parts susceptible to warping.

I personally think, the Torqueout Test won't give completely comparable results, because of different coefficients of friction (galvanized steel bolt - PLA/brass/Nickel plated brass). A pullout test would give indefent results, sadly requires a test machine. But I think the "ranking" would be quite similar. I tend to use woodscrews for simple "once" connections, Bolts in printed threads if the simple connection needs to be a bolt for other design reasons. Sometimes printing only the first few millimeters and let the Bolt cut the rest by itself (friction stops unwanted rotations). Heat inserts only when I need wear resistance, if even more is needed Ensat-Gewindeeinsätze. Really strong threads I get by designing in massively longer threading depth or a nut placed inside during the print.

First year Uni manufacturing here in Australia taught me that a bolt has a un-threaded shank portion where as a machine screw (not a wood screw) is threaded all the way to the head. Love the testing videos, keep up the great work.

Two ideas I have are creating a wide ring in the middle of the screw hole that acts like an anchor in the shape of a washer. Or creating a recessed area on the backside to actually install something like a fender washer to spread the load out if you really need the strength.

This video needed to be made, thank you. Please test nut captures and the strength of inserts from the opposite side. Tapping holes with a hand drill is something I never do regardless of material as while it takes a little longer I find that doing it by hand results is less damage to the threads especially for fine pitch threads.

Great video 👍 something that people don't often talk or think about is that in many cases threaded inserts aren't necessarily "stronger" than direct threading...but in applications where you need to often remove a threaded fastener (eg. a thumbscrew) they are a must (for example helicoils in aluminum).

Few other types of threaded inserts: "thin wall threaded insert" and "helicoil" both would be interesting to have in the comparison. As another comment mentioned, would be interesting to know print settings and do a review on things to improve the joint. I would also love to see how using a "matching" grade of screw would affect the strength of joint (i.e plastic screws). Ace video as always Tom, loving the new clean feel of the production.👍

Thanks for the time and efford to test this for us!

Yes! i've been waiting for more videos on this subject. Thanks Thomas

I would love for you to test the direction of pulling out, AFAIK, Voron parts sometimes have you thread in the direction of installation and sometimes opposite. Taking your thread adapter into consideration, the large flange on the end would take a LOT of force to pull out in the opposite side of the install. Also it would be nice to know how much the different techniques of linking the perimeters to the infill would work! Great video!

What about wood screws? They are made to hold on to the wood fibers that are weaker than metal. They are also very cheap

You might try adding extra wall thickness in the slicer… 🤔

@MadeWithLayers I could watch you 'make chips' all day! So glad you finally have a workshop you deserve. Can't wait for more chips to come!

Super interesting. Personnaly I usually extrude the shape of the nut from the other side of the part. thats my prefered solution as you often get the nut provided with the bolt, you dont have to buy plenty of insert or spend the time inserting them. Maybe you can do an addon video and compare to these results to this method, that would interest me a lot. Thanks !

I prefer cut threads for everything below m6. I use 3d printing mainly to prototype parts that eventually get machined. 99% of the time some cheap PLA is sufficient for my needs. usually I print with 3-5 perimeters. I usually use alcohol as cutting fluid. few drops of cutting oil dissolved in the alcohol works even better. also aluminium taps work way better then normal ones (the ones that have every other tooth missing to reduce friction) through hole whenever possible, bottoming taps that push the swarf up only when really necessary. ...in 3d printing I can make the hole super deep or all the way through the part even if I'm not going to do that on the machined part for obvious reasons. a final note: for embedded nuts: get some square ones - they work better in every regard I can think of compared to hex nuts when it comes to incorporating them into 3d prints. (don't rotate as easy, easier to design the pocket/slot, usually better bridging if pocket has to be upside down...)

It would also be cool to see a resin version of this test, with different resins, of course.

awesome video, we got printing, machining, a great ad spot and knowledge, thanks Tom!

Please test with 100% infill

You should be able to test for lead content of the Alibaba inserts using a swipe test. These are marketed for use in testing house paint and toys, but would work for this purpose too.

This is a valuable contribution to 3D print engineering, Tom!

A very interesting and broad ranging study that was very well executed.

Test the pull from the backside. It theoretically should be stronger.

I am just saying this before watching... I print all my threads on my designs and don't have an issue, so I am very interested in the results. EDIT: now having watched it I can see how the inserts would have a benefit but unless there is a need for more strength I'll stock with printed

Yea, dont power tap plastic dude. Especially fine threads. This is the second video of this channel I've seen today where your process is severely flawed because you have no idea what you're doing. How about doing some research first. Blind leading the blind.

I switched from stocking machine screws to self tapping plastic-threading screws a little while ago and have had a fantastic time with them! Most of my parts aren't particularly load-bearing, but need to be held together... They're just so simple to add to a design!

I see you teased the rivnuts. I've been using rivnuts as inserts for a while. I design for them to be inserted from the back side so that the flange can act as an anchor. The resulting connection is more robust than typical inserts.

you are washing your hands too much with harsh alcohol hand sanitizer ? you need to moisturize !

For the love of god please moisture your hands 🫣🥲

Large diameter steel washers can spread the load over a wider area of the plastic when used in conjunction with a steel not. A thread for the screw can be included in the hole so that a lockout effect can be achieved with the steel nut.

Tom, I doubt you'll even see this but, we need a machining channel from you. I also see you for your blondiehacks reference! Been watching for a decade or so. I can't thank you enough for the knowledge you've shared.

There are thread inserts for wood that would work similar to the "tripod" adapters, but give more variety of thread sizes.

I mostly use the modeled threads, but if I need the strength I will use a normal nut pressed in the back of the part. Where I think the inserts shine is with parts that need to be disassembled many times. The modeled threads are only good for a couple assembly cycles and a nut can sometimes get out of place if the press fit is not great.

Fascinating! And the thread adapters are an eye-opening option.

This was super interesting! And shows that there are different options based on the use case

I would like to see different materials used such as nylon and abs, however you did a wonderful job with this video keep up the fantastic work.

excellent video, love the threaded holes made with layers

Usually, a screw is tapered to a point at the end, and a bolt is the same diameter for the entire shaft.

I have had good luck with the injection mold inserts with resin prints for my drone. Even experimented with camera threads printed directly into the resin. Surprisingly it worked out very well.

Thomas, in tru holes you are blessed with having the possibility of using the insert from the backside of your workpiece. which creates the fact you have to pull the insert not only out but also tru the complete printing. And a bit of a hassle but you can also demonstrate the "print in place" possibility, if someone might be interested. possible with an ordinary nut.

This is the type of video i love to see from you. Suggestion for the next one. What is the best way to use screws with 3d printing. There will be different use cases, lid that you screw and unscrew. a load bearing part(multiple directions), etc.

The vast majority of installation torque (80-90% in steel nuts and bolts) goes into overcoming friction so it's not a good way of measuring pull out force. Once installed the assembly strength is determined by bearing and pullout strengths, not twisting of the insert.

I've also tried a two stage hole, which does the same thing CNC is trying to accomplish with his section on the insert before the grips. This seems to work better with inserts that don't have that feature, when using an iron to put in the insert. My main problem with iron installed inserts is they don't get in straight or in the right location, unless just pressed in from the other side. I think that STL files provided online should allow the insert to be pushed in from the other side or at least have a two stage hole to help start the insert in with an iron.

Hi Thomas, first at all thank you for your always excellent videos. If this video, you are in fact testing resistance vs. torque which is fine to know how the attachment will resist to an over torque. But according to me, should you be able to test resistance vs. axial force, this will provide tremendous inputs on how these fixtures resist under load. And we could have some surprise with plastic tapping. And should you be also able to test self-tapping screws at the same time, this will give us a whole overview of attachment resistance.

Thank you for putting in the research work! Since you asked what to check next: Self-tapping screws, wood screws, inserting nuts, use of washers (larger area might not pull out as easily?), using the inserts from the other side (pulling through the entire part instead of pulling them back out where they inserted) and of course more walls / more infill / both...

One thing, you didn't mention would be a rivnut. Slipped into the hole from the other side. And since it doesn't have the rotation ribs, you can use a bit of glue if you don't want it to rotate. You can match the rivnut length with the part thickness, or recess the back side to match the rivnut length.

It would be interesting to see options to improve the strength of the printed part around the threaded inserts.

USSA woodworking channel uses threaded inserts for wood in their designs. They also insert it from the back of the part so the chamfer helps spread the load. Would be interested to see how they perform. I only use inserts for parts that need to disassembled fairly often. Normally I just undersize the hole by the thread thickness, and let it self tap.

I've found that friction threading fasteners into unthreaded holes works quite well.... What you do is you rapidly turn the fastener in about a 1/4 turn then back out a little less than 1/4 then back in a 1/4 until the fastener is seated. The friction from this rapid back and forth heats the fastener so it doesn't cut rather it melts it's thread into the plastic. If you size the hole correctly it will take a little bit of muscle to seat the fastener and you will be able to feel the resistance slightly lower when the fastener starts melting it's way in.... The result should be a tight thread with it's layer lines fused together. Something you will not get from a printed tread. Also this method of threading does not clog the hole or remove any plastic. The plastic is pushed outward into the walls, if anything leaving the wall thickness slightly higher.....I've used the word fastener in this description over bolt because I've used this method with screws as well as bolts up to 1/4-20. Other than that if I just need a thread in my print where the bolt will be repeatedly adjusted I heat set an ordinary nut into the print. Which is cheap strong wears good and I don't have to order anything online to complete my project. With heat set nuts I print a hexagonal recess in the hole slightly smaller than the nut and push the nut in with soldering iron set to as low a temp as I can where the nut will still push in. Like with fiction threaded fasteners no plastic is pushed down into the hole. The plastic is instead also pushed outward increasing the wall thickness. So far I have had zero issues with pullout of friction threaded fasteners and heat set ordinary nuts have only failed in bad designs and when over torqued.

I would love to see this tested with some PETG-CF or PC-CF and varying infill/overlap settings. I'm super curious to see whether the results will vary depending on materials chosen too.

My favorite part about your videos is building the test setups.

I once tapped E-SUN cf-nylon and was amazed by how well it worked. It almost felt like tapping aluminum the way the chips came out!

Thanks for another great test. This was basically already the conclusion that I have come to over the years. If I only ever intend to screw something together once, I may just size the hole so the screw bites in and cuts threads, or use a nut. Same for quick one-off prototypes. However anything I intend to unscrew or use multiple times, gets inserts. I made myself a custom profile in openscad for the inserts that I use so that the hole is a little wider where the insert goes, so that a little less plastic is pushed down but there is still plenty to melt around the brass and make a tight hold.

As you hinted at I'd like to see how much better it performs if you modify the 3D printed parts to improve the strength of the connection to the rest of the part.

"Should I test ... or ... or ... or ... or ..." Yes 😁 Very interesting test, and great presentation!

Was glad to learn about the threaded adapters. I’ll be trying those. But I do have good results printing a coarser thread in soft materials like we have with 3D printed parts. In particular I frequently use #10-24 printed threads for small part assemblies.

Great video ! Yeah I would like to see a test with the alternate extra wall option from cura, it seems to fit this usecase perfectly.

thx for the test

I'd be interested to see the comparison between threaded inserts and embedded nuts

Thank you!

I have threaded inserts (somewhere) & have never used them. Screwing into the bare holes in the print has worked just fine.

Cheers for the work. I really like it. Would you try - as well as Stefan did - screwing the bolts directly into the through holes. No tapping beforehand. I myself use this all the time with so many different materials and have super results.

For the injection moulding inserts, to make the plastic pushed away less of a problem I insert a bold into the insert and then put the soldering iron on the bold...like that the area that needs to remain free for the bolt is clear

Another thing which is worth noting, is loosening of the screws over time. Having a metal threaded insert allows you to use a more diverse range of threadlockers (e.g. Loctite 222 or 243 etc). I designed a custom hotend shroud and ended up simply under-sizing the holes and forcing machine screws through as "self-tappers" which holds pretty well, but the screws do end up getting loose (I think it's because the bowden tube puts varying pressure on the hotend as it travels across the x-axis). Something else worth testing, is instead of using machine-screws, use actual thread forming screws meant for self-tapping into plastic. They tend to have a sharper, more coarse thread and are often seen in injection molded parts.

Great video! Thank you for doing the research and testing. I wonder if this means we are better off saving some money with cheaper fasteners. 🤔

Wonderfull sunday morning, waking up with science, especially with your and @cnckitchen work, I'm a huge fan. Regarding your questions, I do use another option due to design/thicknesses of the part compromise. I either leave an insert space for a nut or a vertical hole to hide the nut inside the part. This keeps the part thin and strong because the nut itself is the thinner I could get while not compromising the strength (usually speaking of M3/M2). Also, I use more infill, more walls, and ASA.

I would love to see some more in depth how different materials and slicer settings impacted the strength.

Why not place nuts in to your prints (or on the back)?

Whenever the design allows it, I press hex nuts into the back side of the part with a clearance through hole to screw in from the other side. Make the nut recess compliant to avoid splitting the 3D print. PrusaSlicer has a couple of tricks that help. Modifiers allow more perimeter layers and/or more infill to strengthen the 3D part around the threads. PrusaSlicer also has negative volumes that can increase part strength in a particular direction that can be useful to support loads attached with threaded fasteners. There are slicer tricks for bridging over the top of the inserted nut pocket, with RU-vid demonstrations. For smaller inserted nuts, typically M4 / #8 or smaller, using square nuts instead of hex nuts will help prevent the nut from spinning in the 3D printed part.

Thinking about it, for parts where you have enough depth to use a nut+washer and have it covered up by the top layers that might be the strongest combination of things. Alternating extra walls makes a pretty big difference in my experience, and so does making sure there is enough material there by adding an extra wall or two. Most slicers also have a wall overlap setting that gets them welded together more.

I would be interested In seeing you explore how best to model the insert locations/holes

Great informative & practical segment. I designed a hole with fins (negative cut-outs) extending into the infill area, increasing the hole perimeter material and the engaged surface between perimeter & infill. They are arranged radially around the hole. In my example for a 5mm hole, the fins are 0.5mm wide by 3mm long, with 8 in the radial array. I start & end the fins 0.5mm inside the object surface so that they're not visible from the outside. Since the area around the hole is where the failures are located, this should increase strength substantially. This also would provide space for the excess material to go with thermal insertion. I haven't tested or even printed this design yet - wish I could send a screenshot of how it looks in the slicer.

Great test, thank you. Please also showcase you prepared wood-inserts, “nieten”-inserts and maybe a regular hex-nut in the opposite side..

I'd be curious to see how inserts compare to captive nuts, and how different wall and infill strategies alter the properties for both. Great video, as always. Thanks!

I printed some tool heads for my Dillon 650 Reloading Press. I did it just for low-stress depriming only, so very light loads. I dabbled with printing threads, but what worked best was printing 20 walls in the holes, and running a 7/8-14 tap through the holes. Yes, it was messy, but it worked, and continues to work.

Thumbs up for the machining montage!

My daughter in law's father and I both had the same thought when we got our 3d printers. "Now I can print a hexagonal pit in the 'backside' of a terminal strip, and trap plastic between a conventional hex nut and the screw head." He 3d printed a threaded hole thru the rest of the pla from the bottom of the pit holding the nut to the other surface. I just drilled and tapped mine.

i tap ASA all the time. holds great. great vid, thanks

The 1/4" - 20 adapter seems similar to just imbedding a nut inside the print. I had a print that added a 1/4" - 20 flange nut to make a tripod mount.