Introduction: Add Metal Threads to Your 3D Prints - Make Them Functional!

Picture of Add Metal Threads to Your 3D Prints - Make Them Functional!

Connecting mechanical components can be a challenge with 3D printing. Tapping functional holes in plastic that can support a load is nearly impossible. I want to share an easy method I've found to add metal threads to a 3D print that you can do with just a soldering iron.

This Instructable is entered into the Full Spectrum Laser and Hack Your Day contests so if you think it's a winner for either one, I'd appreciate your vote! Thanks!

Step 1: Materials and Tools

Picture of Materials and Tools

You will need heat-set metal inserts for this. I purchased mine from McMaster-Carr.

The only tool you need is a soldering iron.

Step 2: Design Your Model

Your will have to have the right size holes on your model to fit the inserts. On McMaster, they list two tapered hole diameters. Find the sizes for your insert. The largest of the two is the diameter you will need to make your holes in your model. I usually oversize the holes in my models a little to accommodate for the 3D printer's tolerances. Mine usually prints holes smaller than they should be but yours may be different.

Step 3: Assembly

Picture of Assembly

The next step is to 3D print your model. Once you've got your part made, then you can start assembly.

1. Heat soldering iron. Wait at least a minute for it to get hot. Remember to always be safe around heat!
2. While it is heating, you can position the inserts so that they rest on the holes.
3. Once the soldering iron is hot, place it inside the insert and push down gently.
4. As you are pushing, the insert will slowly sink into the plastic. You may have to wiggle the soldering iron back and forth to straighten the insert.
5. Continue applying pressure until the insert is flush with the plastic. Remove the iron from the insert.
6. Flip the part over and remove any extra plastic with a small knife or screwdriver.
7. Repeat for all other inserts.
8. Wait a few minutes at least before using the inserts to make sure the plastic is fully solidified.

The inserts will still be hot for a few minutes after so be careful not to touch them right away.

Step 4: Finished!

Picture of Finished!

Now you've got some fully functional parts ready to go!


nateinvestor made it! (author)2016-05-27

I used this tutorial to make my own. Thanks for posting this.

artmez (author)2016-03-06

In step 2 says to use the LARGER of the two dimensions for the hole size. That seems counter-intuitive as then there is no plastic to melt and hold the insert. The McMaster list is equally confusing about the process. Shouldn't the design's hole use the SMALLER dimension?

adamgw (author)artmez2016-03-06

The McMaster list isn't very clear on the matter. I used the larger of the holes when I made them and there was plenty of plastic to melt onto it with some that came out the other end. The tolerances on my 3D printer when printing holes seems to print them on the smaller size so I usually oversize my holes by at least 0.01". The smaller size would work too.

I find its easier sometimes to look at the CAD drawings on McMaster for clarification.

mjammal (author)adamgw2016-05-13

Hi, from what I understood from Mcmaster, and after I measured the insert, my guess would be that the holes have to be tapered, with the smaller diameter towards the tightening direction. Otherwise, I do not see much contact if the hole is straight.

adamgw (author)mjammal2016-05-14

Once the insert heats up, the plastic melts around the insert and when it solidifies it should hold the insert in place. If the hole is smaller than the insert, there will be extra plastic to remove at the end of the insert.

jclerico (author)2016-03-12

I wonder uf you could just bevel a brass nut with a grinder and make your own inserts...

adamgw (author)jclerico2016-03-14

That would probably work. I would probably rough the sides with sandpaper so that the plastic has more surface area to bond to.

PhoenixP (author)2016-03-13

I've never needed an iron to use screws with my prints before. Does it make them more fixed or something? I'm now curious!

adamgw (author)PhoenixP2016-03-13

Using the soldering iron on the inserts makes the plastic melt around it, making a super strong bond.

jsherwin9856 (author)2016-03-12

It may be good to know that the inserts are available with a larger diameter flange. This is helpful in the event that you could pull the threaded insert out of the plastic when tightening anything to it. My company learned that the hard way.

darrenhall (author)2016-03-04

Hi - is that the recommended way to fit the inserts?? - if not then that is a very cool method - I don't use a 3D printer as yet ( no real need for one ) but any builds that could do with a solid thread will be getting your method shown here.
Great INST

ThomasK19 (author)darrenhall2016-03-04

You can also leave the space to fit a normal nut which can be either glued or melted as above.

dhylands (author)ThomasK192016-03-12

I've also left holes for nuts, put a pause in the gcode and stuck the nuts in and then 3D-printed over top of the nut (leaving the bolt hole). It's nice to have options.

adamgw (author)darrenhall2016-03-08

Yes, that is the recommended method. McMaster sells special soldering iron tips for it but they aren't necessary.

fergio (author)2016-03-07

ottima idea bravo. Così si risparmia tempo e lavoro

SoLongSidekick (author)2016-03-07

For step 2, you usually over... what? Over what???

adamgw (author)SoLongSidekick2016-03-07

Thank you, fixed it. I oversize the holes a little because they print smaller, at least for me.

SoLongSidekick (author)adamgw2016-03-07

Ah that makes sense, I guess that depends on each person's printer. But it's definitely a good thing to include to get people thinking about how their particular printer prints. Thanks for the awesome tip, I have the McM page saved for the next time I need something like this.

DavidK60 (author)2016-03-07

This thing gives off fumes so do it outside OK

tisaconundrum (author)2016-03-06

This is genius :D

NormanK2 (author)2016-03-06

I have done this, I also found that having a 3d pen helps as you can weld the inserts in with it if you need

adamgw (author)NormanK22016-03-06

That sounds like a great idea, wish I had one of those.

DIY-Guy (author)adamgw2016-03-06

I have not tried one of these pens, but here's a link to some fair prices.

pholy (author)2016-03-06

What materials have you embedded these inserts into? Is PLA strong enough to take the torque of tightening a screw into the insert? I'm guessing that ABS plastic works well, but the printers I can use only use PLA filament.

adamgw (author)pholy2016-03-06

My guess is that it would be able to at least tighten a screw but it would depend what kind of loads it would hold. PLA is strong but has a lower yield strength than ABS. Might be worth a try!

Tardisrepairman (author)2016-03-04

If you have a pillar drill you can achieve great accuracy and even without one you can have more control if you get a threaded rod to fit the insert and screw it in. You could use another insert as a locknut.
Wrap paper neatly round the end of the rod and insert it in the pillar drill. The paper acts as a heat insulator so you don't have to heat up your whole pillar drill! :-)
Heat the bolt near to the insert and you will be able to press it into the plastic part keeping it lovely and straight. The heat sink effect of all the metal also means that once it is in place it can be cooled quickly by removing the heat source.

I had to look up "pillar drill", as I'd never heard the term before.

For Americans, etc. this would be called a drill press.

Good idea, whatever you call it.

AviationMetalSmith (author)2016-03-06

I need to try this on the bottom of a digital camera, where it meets the Tripod... But IDK if it will burn up the camera... thinking about it...

brian32768 (author)2016-03-06

Oh my, that is so elegant, I will try this! I have thus far been so jazzed about my ability to print 6 sided holes for hex nuts that inserts did not occur to me. Now that I have seen this method I fear nothing else will do for me.

For those of you who need to acquire more tools to get rid of your extra money (I was there once), if you go to the McMaster page the author lists, look at the page for these heat set inserts on the right hand side, each insert has a matching soldering iron tip for (just) $15. Nothing satisfies like having the Right Tool. (Wellll... having space to keep the toolbox organized and tidy is satisfying too.)

zirt57 (author)2016-03-06

Oh, p.s. Sorry, nice article and idea though. I will just have to find another outlet to buy the inserts. Thanks.

bmaverick (author)2016-03-06

Nice write-up. I use dodge or PEM nuts similar to this. I do like the heating solder method. Will have to try that with the Ulterm material next week.

shapespeare (author)2016-03-04

That's a nice elegant approach which gives you a very professional looking result. Good Job.

I sometimes make a space in the model for a regular hex nut and add a pause command to the g-code so I can drop the nut in at the right time. If you plan things right the nut is completely encapsulated in the print and forms a threaded hole. Another option is to make your prints out of nylon which is strong enough to be tapped directly.

Kuuran (author)shapespeare2016-03-05

What pause command do you use? I have only found M codes that are not recommended to be added to gcode files.

I then tried G4 to dwell for a few minutes, but that needed too much nursing. Finally I realized that I could split my gcode in part1.g and part2.g, so I get to take a nap during part1.

Kuuran (author)Kuuran2016-03-05

I get it that M codes can be placed in gcode files, but searching for pause in the reprap gcode page I could only find M25, which clearly states it should not be used in a gcode file. Instead it points to M226, which is not supported by marlin.

I never would have guessed that we can resume from a stop. What gcode does that? I have no lcd or keypad on my printer.

shapespeare (author)Kuuran2016-03-05

I'm using a LCD controller which makes it easy, you just push a button to restart. You might be able to take it out of pause with the host software. It is different for every setup so you have to experiment.

shapespeare (author)Kuuran2016-03-05

M Codes are part of G code so most printers don't have a problem with them, although they aren't all supported the same. You have to experiment a bit to see what works on your machine. M0 usually works on Marlin based systems although it is supposed to be a stop it works like a pause. You can also add a G1 immediately before the pause to move the extruder out of the way so you can reach the part and so it doesn't drool on it as it waits. Most slicers are using absolute locations so when you come out of pause it will automatically go back where it left off.

watchmeflyy (author)2016-03-05

Smart idea; thanks for sharing. :)

peabody1929 (author)2016-03-04

I print a hexagonal depression on the back of the plastic part and place a hex nut in the hole. it then becomes a normal screw threaded into a normal nut.

mtairymd (author)2016-03-04

Interesting approach.

Another option is to use a tap and thread the insert into the plastic. I've used key locking inserts to prevent backing out.

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