Gluing 3d printed parts
This is a tutorial based on a previous blog post showing you how to glue our White, Strong & Flexible material. White, Strong & Flexible is also known as nylon 12 or polyamide 12 and comes from an EOS 3D printer using the selective laser sintering(SLS) process. EOS calls the material PA 2200.
This tutorial is only for our White, Strong & Flexible material, other materials have different properties.
We would advise people to not glue parts unless you have either broken one or want to build something that exceeds our SLS build envelope of 20 by 25 by 23 cms. For this little demo we have taken my little SLS stress ball. I've carried it with me for a month or so to show people our materials. The ball itself is based on a design by Shapeways member George Hart, you can check out his site here.
Breaking rapid prototype parts is either easy or hard, it really depends on the design and the material. If you make a thin tail-like structure such as our monkey's have, then a good push with your thumb will break off the part. If the structure is less limb-like a hammer might be needed to break it. SLS is a strong Nylon and it is resistant to impact. When it does break it tends to shear. The rhomboid structure used in the ball meant that this was a robust enough structure to withstand weeks of bouncing on the streets of Amsterdam and Eindhoven but sadly all that wear and tear built up. The coup de grace was an unfortunate incident of some careless oaf stepping on it.
Super glue is also known by its much less marketable name of Cyanoacrylate. The glues of this family are ethyl-2-cyanoacrylate, n-butyl-cyanoacrylate and 2-octyl cyanocrylate. Ethyl-2-cyanoacrylate is most commonly marketed as Super Glue(secondelijm(NL), sekondenlijm(DE)). The other two families are used as medical glues so you will probably not find them at your local stores. All of these glues can be used to repair or stick together Nylon 12 parts.
The second type of glue that you can use is Araldite, an epoxy resin. You can check out the Araldite website here. We chose to use Super Glue for our little repairs.
Please take into account all the warnings on the packaging such as using a well ventilated room and keeping these products away from children. And don't glue your eye, because that would just be terrible.
I applied glue sparingly and removed any visible left over traces with a paper clip. The glue of course becomes a different color to the material so any excess glue is ugly. The glue bonds very well to the part and sanding is not necessary. Cleaning a surface beforehand though does improve the bonding of the glue. As you can see from the picture the ball healed well. There was a tiny hairline fracture visible but generally you did not notice it. Indeed my Nikon lens was unable to pick it up on this picture but you might be able to see it on the left.
Gluing does not always work
Glue is not a catch all though. A problem arises because the material properties of the glue and the 3D printed part differ. Nylon 12(or Polyamide 12) is flexible the glue , not so much. This means that although the glue repaired the part well and indeed restored the bouncy ball qualities of my object, sadly this did not last. After a half an hour of bouncing, the glue pressured by the forces acting on the sphere let go. So even though super glue works well to repair ornamental parts there are limitations as to how much functionality can return to a part. So, I would not assume that things such as live hinges and springs can be returned to their full previous functionality once broken.
Paint plus glue is a no no
Once you paint a model that has been glued in some cases the paint accentuates the hairline fracture and the glue itself. If you look at the picture of my pretty red ball it looks great.
I painted it using a standard Tamiya Colour Spray paint. It took seconds and was fun to do. However when using paints the paint sticks to visible glue left overs. Strands of glue that you did not see previously will also become very visible now. It is very important that you use very little glue and have next to no left over glue before you paint a model. On my model my near invisible fracture now looks like this:
Some delicate work with an unfolded paper clip meant that I could quickly remove the paint that had built up in the openings. The roughness on the outside though is still visible.
So I would recommend that you use glue: only when necessary, as little as possible on visible parts, take care of leaving behind glue residue. I would also warn you that it is difficult to glue live hinges and springs while maintaining their functionality and to be extra careful with glue when you intend to paint the part afterwards.
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