How To: Bond Your 3D Printed Parts
If you’ve ever split a 3D model larger than your build plate into smaller pieces so you can print it, you probably found yourself trying to reattach all the pieces. Sometimes, the pieces don’t butt against each other as cleanly as you’d like to, or there’s a huge gap between the seams that you can see through. If you have wanted to print a model larger than your print volume and you’ve never done it before, check out the article by our MatterHacker Pro, Scott, here.
There are several post-processing methods to help hide those seams or to reattach each piece with a cleaner seam, although some are more noxious than others.
There are two steps to this process: attaching and blending. Attaching each piece will be done with adhesives or solvents and blending will use various putties to actually fill it in.
Before you get into adhering your parts together, you’ll want to rough up the two surfaces you are going to stick together. This will give just a little more surface area for the adhesive to stick to, allowing for a stronger bond. With whatever grit sandpaper you have on hand (it really doesn’t matter as long as the surface feels rough when you’re done) sand the 3D print until it’s noticeably rougher than the clean sides.
For most materials (like PLA, ABS, or PETG), cyanoacrylate (or superglue) is going to be the most common and easiest way to keep two pieces together. Some more flexible materials, like TPE, TPU, or nylon, aren’t very reactive to superglue. While superglue’s biggest advantage is that it almost instantly cures, that’s also it’s biggest curse.
Any mistake you make with one edge not completely lining up with the next or any drips will solidify and stay there. Sometimes it’s beneficial to have that immediacy in gluing your parts together, so you aren’t holding or clamping parts together in perpetuity. An unfortunate characteristic of super glue, however, is that it is harder than most putties or filaments, so any drips of superglue or seams that superglue spilled out from will be that much harder to hide. When you try sanding the seam, the surrounding area will start getting sanded before the seam, leaving you with a drip shaped island on your print.
An alternative to super glue is a 3D printing pen like Crafty Pen. You can utilize a Crafty Pen as a welding tool, using either the hot end to melt the two sides together, or using filament from it to fill in some of the larger holes. You can even use the Crafty Pen to bridge holes if your prints aren’t quite as flush as you planned them to be.
JB Weld or 5 minute epoxy works well too. I personally find 5 minute epoxy is most helpful to back seams that are superglued together, to give it that extra bit of rigidity to keep the two parts together. Of course, this is only viable if the back side isn’t visible or doesn’t need to look pretty. Either of these two are applied in basically the same way; mix up the two part of the epoxy and smear it onto each side of the parts that are going to be adhered, or spread on the JB weld onto both sides.
Bondo Body Filler, filler primers, Evercoat Body Filler, Bondo Glazing and Spot Putty, wood filler, and 3M Acry-fill Spot Putty are all excellent choices to fill in the larger gaps or discrepancies between the two halves. Only consider using these putties and fillers on your 3D prints if you intend to finish and paint them, because not only will it be a significantly different color than your print, but it will also have a smoother finish than the layer line striations of a 3D print.
Hopefully this gives you a good headstart on printing some really big projects on smaller desktop printers, because you don’t need to be limited by your build volume. Of course, there are many different resources out there, so if you feel like I’ve missed any that you feel are important, feel free to leave a comment down below.
Now, these are all adhesives, which means an adhesive force is what holds them together. Chemically, there are still two distinct parts with a sticky third material holding them together. 3D Gloop is different: it starts dissolving the plastic when it is applied, and when they are pressed together and time passes, the 3D Gloop evaporates and the plastic rehardens, leaving one part. There are a couple different formulations specific to 3D printing filaments, so make sure to use the PLA formula only on PLA. First thing's first: wear proper PPE like a respirator and goggles with adequate ventilation. To fuse parts simply apply 3D Gloop!, press and hold together for 15-30 seconds to achieve a strong tack hold. Bonds will achieve 80% strength after an hour and full strength within 6 hours of application.
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