Vapor polishing 3d printed parts

[NWChen]

On vapor polishing/smoothing 3D printed parts, i.e. with acetone vapor: can anyone speak about the change in sturdiness and tolerances of the part? Did you use it on a robot and/or experience any issues with it?

Pic below for reference (right: untreated, left: acetone vapor treated)

[techhelpbb]

Originally Posted by NWChen

On vapor polishing/smoothing 3D printed parts, i.e. with acetone vapor: can anyone speak about the change in sturdiness and tolerances of the part? Did you use it on a robot and/or experience any issues with it?

Since you specifically mention acetone probably best to mention that trick only works on ABS. I haven't done this trick with FRC parts but with interlocking pieces the effect changes the part dimensions inconsistently based on how the vapor gets into the all the nooks and crannies. Since this is partly dissolving the ABS it actually makes the inter-fused-layer bond a bit stronger at the price of tolerances. Personally I'd still be more careful in how you handle the effect of the fused layers during the design phase because the effect tends to be 'skin deep'.

If all you want is to make something shine - you can sand the pieces and get a nice shine back with shellac. This trick does actually work with PLA as well. At least with sanding you can control which surfaces change tolerance and you don't risk any part warping because it started to dissolve.

[jagoldman]

I have my own 3D printer in my house that I sometimes do this process on. It only works with ABS plastics.

To start off, when looking at what kind of filament you want to use, I would look at what the parts you are making will be used for and what stresses they will under go. For example, PLA is stiffer and can withstand more pressure than ABS, but PLA is more brittle while ABS is more flexible.

Moving on to your question, the process dissolves away the ABS plastic. When all the vapor exits the part, the part regains full strength. However, while the acetone vapor is still in the part, it continues to melt away at the plastic and make it weaker. This means that even if the part doesn't look done while you have it in the chamber, it will be ready to take out. Be careful when removing parts from the vapor chamber because if you press too hard, you can deform the part. Additionally be this process can make things sag.

In the past, my team has used PLA on our robot without any problems, and if the tolerances were off, we would use sandpaper, files, and drill bits to correct. I see no real purpose of polishing a part like that or any reason to use ABS instead of PLA.

For personal items this is a really cool way to make random objects look cooler, and its also fun to experiment with the times, temps, and amount of acetone used.

Good luck with your printer and your projects.

[MrBasse]

As has been mentioned before, the shape will change slightly. However, the material isn't really being dissolved, it's more akin to melting. You will be left with the same amount of ABS unless a chunk drips off before you remove it, but in my experience by the time it gets to that point your part no longer resembles your part anymore...

If you orient things properly to allow gravity to pull as straight down as possible, you shouldn't have issues with maintaining tolerances on holes and locating pieces. But they definitely have a tendency to lose round a little.

Start small and play with it, it takes some effort to make a chamber that I would feel safe using around kids on account of flammability issues of acetone and the heating of said flammable liquid. On the upside, when it does start on fire it is a pleasant slow burning flame that gives you time to move before too much goes bad. That said, take a lesson from me and don't do it for the first time in front of a class full of students over carpet. Ours went fine, but we learned that this process works very quickly and continues to work after you are done with the vapor bath.

What do you want to smooth out and why? If it is just for appearance, you can't go wrong just trying it. If it requires holding dimensions it will take some trial and error to find the right times and heat, then very good consistency to repeat results.

[jagoldman]

There is a lot about this on other 3D printing sites but if you are concerned with how much you are melting off and hazards, there are multiple methods that you can use. Heating the acetone will be faster, a lot faster, but that releases noxious fumes. You can also not heat the acetone and get a more controlled melt and no fumes.

[NWChen]

Originally Posted by techhelpbb

If all you want is to make something shine - you can sand the pieces and get a nice shine back with shellac. This trick does actually work with PLA as well.

Originally Posted by jagoldman

In the past, my team has used PLA on our robot without any problems, and if the tolerances were off, we would use sandpaper, files, and drill bits to correct. I see no real purpose of polishing a part like that or any reason to use ABS instead of PLA.

Originally Posted by MrBasse

What do you want to smooth out and why? If it is just for appearance, you can't go wrong just trying it. If it requires holding dimensions it will take some trial and error to find the right times and heat, then very good consistency to repeat results.

Thanks so much for your help. I'm looking into smoothing a structural PLA piece for appearance purposes, so tolerances still apply - I didn't know acetone vapor polishing wouldn't work for this application.

[techhelpbb]

Tetrahydrofuran and M.E.K. can smooth PLA. I've used M.E.K. but it tends to take a long time with Inland generic PLA spools (there are different formulations of PLA so be aware that not all PLA is the same). I would strongly urge anyone considering these chemicals to use them near ventilation

I should add - Tetrahydrofuran and M.E.K. make short work of latex gloves. Were suitable gloves when handling.

[Design mentor]

There is one use of Acetone vapor polishing that I can recommend that is quite useful:
When a part is used in conjunction with rubber, maximum friction can be obtained with smooth rubber contacting a vapor polished part. This process was used in the production of a squeeze actuated slip-clutch ratchet-like screwdriver that I invented and licensed to Sears. The screwdriver handles were machined on a lathe then run through an acetone vapor chamber. This drastically increased the friction between the inside of the rubber grip and the acetate handle. The grip was slightly oversized and mounted on snap bushings over the handle - when the user squeezed the rubber grip it deformed and contacted the screwdriver handle. Even with the grip contacting only about half the normal contact area of a handle that a hand would have, the friction was so great that the overall torque of the screwdriver was about one and a quarter times normal.