Incorporating Nut Inserts Into Your 3D Printed Parts

Machine threads are one of the most common components used for fastening parts in an assembly or attaching your part to another substrate. Here are a couple ways to incorporate screw threads into your 3D Printed ABS or PLA parts.
Threads directly from your 3D Printer-
The pitch and helical profile is critical for incorporating threads into a 3D part. Typically, large pitched threads, like ones on hex head bolts found at your local hardware store work well for prototyping or fit testing as long as the forces are relatively low.
Nut Traps-
Another option is to use a “nut trap”, a hexagonal hole that you put a nut into on the other side. They are tricky to get the right size, but very satisfying when you get it right. They stay in place, and very strong as long as they are not torqued down too hard. Some slicing software will allow you to pause the print, insert a nut then continue printing the remainder of the part.
Tapping a printed hole-
Threads can be created by tapping a hole, either directly into a hole with an area filled solid around the hole for support, or into a designated fill area made for drilling.  Bulking up the drilling area is recommended so threads will hold together better throughout the layers. ABS is a bit soft for machine screw tapping, PLA is probably better but may be a bit brittle for self-tappers and need a bigger pilot hole.
Threaded Inserts-
In the photo below I show a few different varieties of threaded inserts. Blind Nuts are used with soft material such as wood and the screw enters from the opposite side, when tightened it pulls the nut up against the material. Nut Inserts are often threaded into holes and the screw enters from the same side. When shopping for threaded inserts, you will find a few different varieties, they are inexpensive and most work well. Nut Inserts are easy to install and work well for tensile loads. They can withstand some torsional loads, but tend to spin out at high torsional stresses. These work well when you want to be able remove and replace the screw, otherwise self-tappers are good for one off insertion and they work fine in printed parts.
Print the part you want with a suitable sized hole. Place the insert on top of the hole and then use a hot soldering iron to push it in.
Retro Nut Press-
There are a couple different ways to press your nuts into your plastic parts. Using a pencil soldering iron works well, but found that there was a lack of control.
Thinking about some kind of simple press, I remembered an old Dremel Drill Press that I had stuck up in the rafters. Being a vintage item, I didn’t want to hack it up, so I designed a clamp that replaced the body of the Dremel and held a pencil soldering iron. Brass is easily machined allowing me to make a couple adapters for different size inserts.
The old press ended up working out well, you can set the stops for precise depth on repeated parts. Once the iron is hot it takes seconds to heat the insert and press it in. With this particular press, the table moves up and down and the head/iron is fixed.