Anyone have an brilliant insights on this?
Came across:
which just seems amazing to me (not sure why my father’s soldering iron wasn’t in his shop when he passed away and still haven’t replaced it) and small/convenient/useful enough to justify a space in my shop…
They are useful if you need arbitrarily many cycles. But they aren’t actually stronger than directly threading into plastic. The strongest approach for small number of cycles with machine screws is to print undersize, drill to tap size if necessary (usually not), and tap with an evacuating tap (preferably a spiral-flute tap). I almost never use heat-set inserts, and threading directly into plastic has worked well. I also insert the screws by backing off until they click, then screwing them in, to avoid cross-threading. The main reason plastic threads get chewed up is careless cross-threading.
Use self-tapping screws meant specifically for plastic if you don’t want to drill and tap threads. They are cheap and readily available in assortments. After inserting them once, use the same back-off-to-start approach to find the same threads the second time.
Yeah, Michael is right. I bought an amazon kit of inserts. They’re ok at best, probably better if you put them on the opposite side of the hole.. And unless you get the size just right they either cloud the threads with material or they don’t have enough material to hold well. They do work better in ABS than in PLA, and real good in Nylon.
With that said, you could also design the part with a nut on the opposite side and heat it enough to hold it in place. or print one of the many that are on thingaverse or printables. Or design a soldering iron holder to fit onto your drill press and buy inset tips set..
I don’t have much trouble with just a soldering iron, but would use a press if doing a lot because I want them properly vertical.
Naomi Wu did a design a couple of years ago that seems quite comprehensive. There a several designs on Youtube if you want to make your own.
As to whether inserts are needed .. I’ve used the back-off technique for many years but not everybody else does. So I’ve often encountered wrecked self-tapped pillars. As a result I do use inserts if I can.
Thanks everyone!
I am probably going to continue w/ my current technique of using coupling nuts and running a fastener into it from both ends — it’s a bit pricey (unless someone has a good source for them in quantity?), and a bit fiddly ensuring that the bolts are just the right length, but w/ a full set of sizes, it can be made to work out.
I don’t follow heatset inserts vs. coupling nuts. Can you describe this more?
(I didn’t mean that heatset inserts are never useful, just that many people underestimate the value of threads in plastic, and assume that they need to use heatset inserts when they don’t.)
One thing which I’ve been doing on my CNC is making things in layers, and for a central/middle layer, putting coupling nuts there, then extending the hole all the way through (usually w/ a countersink) to the top/bottom — my thought was to replace the coupling nuts w/ the inserts (since they are cheaper and don’t need to be glued into place).
I’ve got a couple of ideas in mind — I’ll try them out both ways in CAD and see which seems to make sense, then report back — stocked up on coupling nuts anyway since I need them for a latch idea I have.
Well, the heatset inserts kind of are short coupling nuts, then!
The higher quality ones have aggressive ridges that would hold them in place if you are working in something soft enough, too. It’s an interesting idea, and totally not the use case I was addressing. 
The heatset inserts are for something other than the latches — more a general, “would this be a nice way to hold things together securely?”
My most recent use of heat-set inserts was as tiny finger nuts for holding wires onto terminal screws for a tiny, low-power ham radio “balun” to connect my radio to wire antennas, so I’m 100% on board with thinking outside the box! 
Have you thought of using sex bolts. I don’t know how small you could get them but ‘we’ used to use them a lot in the automatic door industry.
Yes, that’s an excellent option — if you know of a convenient source for them in a variety of lengths and diameters (and styles? I’m still bummed that I can’t replicate the keychain w/ the nifty design I had when I was a kid) I’d be very interested.
Sorry, what we call them and what they are listed as are different. They are binding posts..
And they are cool… Maybe they could have called them Frisco screws…
Searching a bit, I found:
which seems a reasonable variety of sizes (lengths and diameters) so I’m definitely going to use them in the Gridfinity fork which I’ve been researching.
Personally, for light to medium duty things I find the heat press inserts work fine. Quick and convenient. A soldering iron works fine, but with a press you are sure to get a perpendicular set and it’s easier to control the depth. I don’t use the inserts a lot and I couldn’t justify the space to keep a press. So I built one for my local maker space and it’s there if I ever need it.
I know them by the name Chicago screws. I like using them for a low profile strong hold.
The problem with that heat press IMO, is it’s too small to handle all parts so then which parts can you use it? Also, the insert tool doesn’t hold the inserts, it’s very loose, so you would have to use pliers to hold the insert upright while you insert the tool. yet another problem, what if the inserts are inside? I just build a machine that has IR sensors inside the shell and the inserts are at an angle because the soldering iron was too long. check out www.mothertap.com to see my bottle filling machine.
I think heat press inserts are cleaner, stronger and more professional looking than either insetting a hex nut or threading plastic holes. However, there are dozens of STL files available to make a press using a soldering iron, and specialized tip kits are also available for the iron to inset various sized inserts. This seems extremely expensive to me, as I built a press out of scrap aluminum 2020 and 2040 extrusions, roller bearings and nuts and bolts for just the cost of the iron and the above set.
Like NedMan, I know these as Chicago Screws and have used them (well, my kids have) in leatherwork. I just received this press and will likely be trying it out as soon as I source some bits that can no longer be gotten from the designated suppliers.
I find them a lot easier than doing it by hand, especially when it comes to getting things in straight.
I paid about half that price by ordering directly from China, including the soldering iron and inserts.