In the next example below, this insert was set without using the plate-press technique. Notice that nasty “bulge” of excess material that beads up around the insert. That’s precisely the bulge that we can remove when we use the final plate-press technique. To accommodate displaced material, I suggest increasing the hole depth by about 50% of the insert length. This change ensures that the displaced plastic has somewhere to go and doesn’t fill up the cavity where the insert should be. Now that we’ve got a handle on designing and prepping parts for inserts, let’s get to the installation procedure. Heat-set inserts work by softening the surrounding material as they’re being installed. Once installed, removing the heat-source causes this molten plastic to re-solidify around the inserts’ knurled feature, holding it in place. Let’s consider thinking about this process in terms of heat transfer. Installation holes are smaller than the inserts themselves (they’re undersized), so we can’t install inserts by hand force. Rather, we first heat the insert and then conduct that heat into the surrounding material such that the hole deforms, accommodating the larger shape of the insert.

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. With a design ready-to-go, I’d recommend tweaking one 3D-printer Slicer setting first, namely the perimeter layers. Slic3r defaults to two perimeter layers for hole features. I’d recommend bumping this value up to at least 4 perimeters for two reasons. 4 perimeter layers for added structure and reduced sink marks Steel / Stainless (EN 1.4305 Equiv. / EN 1.4301 Equiv.) / Stainless Steel (EN 1.4016 Equiv.) / Brass If all went well, you should have a nice-looking insert that’s flush with the part surface. In the image below, I used the iron to seat these parts most-of-the-way in and then cooled them flush with the plate-press technique.

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. First, make sure that your soldering iron has completely reached its set temperature before using it to install inserts. If we try installing an insert while the iron is still rising to its setpoint, the process just takes longer, and all that heat from the iron is spending more time diffusing into our part, causing it to warp. Next, with the insert positioned in the hole, apply heat to the insert. Let the weight of the soldering iron tool itself apply the gentle force needed to push the insert into position. Gravity should be doing most of the work here. This process takes about 10-15 seconds. Keep applying heat until your insert is about 90% seated into your part. You can find inserts on McMaster-Carr (pn: 92160a115) or on Tindie. (I admit that I use the McMaster-Carr one for 4-40 and M2.5 inserts, but also with M3, M4, and M5 inserts without any issues!)

Other guides suggest adding a small taper to the hole feature. This is a nifty feature that enables inserts to seat themselves into the hole before installing them with heat. Some inserts are themselves tapered, which has the same seating effect on an un-tapered hole. Adding this tapered feature (or buying the slightly-more-expensive tapered inserts) isn’t necessary, but it does make the installation process easier. Slicer Settings: 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.Finally, my last tool for this process is a small square of thin sheet-metal, about 150x150mm (6″x6″). This sheet becomes a “flat” reference that I’ll discuss in the process later. Designing for Inserts: First, we want to make sure that our installed insert is still “grabbing” onto material after we install it. An installed insert displaces material outwards during installation, so adding layers improves the odds that we haven’t melted through it upon installation. This final step of the process seems odd, but it’s critical for two reasons. First, it seats the insert so that it’s both vertical and completely flush with the top of the printed part. Second, it flattens any bulging material that flared up while we were installing the insert.