Acetone vapor polishing issues

[Ryan Carlyle]

Alright, so I got a cheap crockpot and am trying some ABS acetone vapor polishing. I'm mainly just looking for smoother surface finish so moving parts will slide better.

Problem is, I'm getting crazy bubbles and it's ruining the surface finish. My best guess is that acetone is sealing up the surface, then heat from the crockpot is expanding air inside the part and making bubbles in the soft surface layer. Anyone have any advice?

My cheapo vapor polishing setup, just for preliminary testing:

Surface finish bubbles:

If expansion of the infill air is the problem, then I can switch to a cold forced-air acetone vapor polishing setup instead of the hot crockpot option. But it would be nice to do the crockpot since it's so dang easy.

[Scottbee]

I don't know about a forced-air ambient temperature system..... but this method is really easy and gives great results: http://microfabricator.com/articles/view/id/529447399aad9d1e13000008/7-steps-to-a-shiny-porcelain-finish-on-abs-parts-with-acetone

[Scottbee]

I should add that some folks use a large inverted glass jar so they can monitor the progress....

[Ryan Carlyle]

The goal is delivering a large amount of acetone vapor to the surface of the part. There are three basic ways to do this:
1) Use heat to boil / increase the vapor pressure of acetone (crockpot or jar+HBP methods)
2) Use a combination of high surface area (such paper towels lining the chamber) and long exposure times
3) Use a fan to circulate acetone-enriched air over the part

Of these, the forced-air method is the only one that really guarantees even exposure. Acetone is heavier than air so it tends to affect the bottom of the part more than the top unless you stir the polishing chamber.

What I'm realizing is that heat-accelerated methods cause problems if the part is not solid AND the vapor is able to create an impermeable skin before thermal equilibration with the air inside the part. Maybe if I heat the part first or drill a small air relief hole...

[Scott D]

Ryan, the bubble are usually caused by over treatment. And they will only get worse over the next 6 to 12 hours as the acetone still has a chemical reaction after you remove the parts from the pot.
As I'm sure you know acetone naturally will expel vapor, the heat is to not only speed up the process but to get enought vapors over the top of the parts since the vapors are more dense then air.
With that said, what I have found is when I was looking to use a crock pot the natural vapors would over treat the bottom of the part as the pot was working on heating the acetone to evaporate more vapors to built up hight enough to treat the top of the parts causing bubble on some sections on the part.
I found put this is because my pot had a heating element on the sides and took longer to heat the asetone. I switched to a deep fryer that had the heating element on the bottom. This would heat the asetone fast evaporating the vapors up over the part evenly. Since the fryer I have is not variable I plug it in for 3 to 5 seconds until I hear a sizzle sound, unplug it for 30 seconds, plug back in for 3 seconds again until I hear the sizzle. At this point I would start to vapors on the lid indicating the parts have good vapor coverage.
I'll let it sit for one minuite and pull the parts out. Depending on the quality of the print you may need to repeate this process one more time? I had used a bunch of failed parts I kept around for making ABS glue as test subjects before I got tho correct.
You time for exposure to the heat may be different depending on the wattage of the heating heating element in your pot.

If you pot is heating up on the sides it may be taking longer to evaporate the acetone causing over exposure to some sections of the part being treated.

[Jetguy]

This is just my experience but another "rookie" mistake is putting too much acetone in the chamber.

My first "experiment" with acetone vapor polishing, I used a large container and my largest heated bed (Reprap 200x200mm) and stupidly put a rather generous amount of acetone in the bottom. I incorrectly assumed that I could control the process with time of exposure. What results is a blob of a part that stays soft for a month because a huge amount of vapor enters even the infill areas of the part and works from the inside.

What I've learned is that a tiny capful of acetone is all you need, let the heat evaporate the controlled amount and still limit the overall exposure.

You must control both aspects, the volume and concentration of vapor cloud and the exposure time.

[Scott D]

Thanks jetguy, I forgot to mention that aspect. I made the same mistake in the start, but not as bad as a big blob for a month.

[Joseph Chiu]

This would be a good time for Kurt to explain how too much acetone vapors can cause a catastrophic failure a looong time after the treatment is done...

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[David Clunie]

My set up uses a large glass jar from world imports, i think it cost $20 and is a 1 gal or 2 gal jar. I put a piece of steel mesh in the bottom to keep a piece off the bottom, though you should insulate it from heat transfer, i was using gutter mesh, which i think comes in plastic and or coated metal that might be better suited, or most often I just hang a piece using flower wire (for shaping and securing flower arrangements).  I then use a small computer fan that rests under the lid, which i just set on top so the jar doesn't explode.  I mount the computer fan using the metal screws it comes with and some magnets so that its elevated off the lid on the inside and using magnets on the outside to hold the fan in place as well.  I then use a 9v battery to circulate the vapor.

Acetone is volatile and doesn't need much heat to vaporize, your low setting should be enough to do the trick on a stove or heating element.  I have a wire mesh that i place the jar on (a chrome cooling rack) above the electric heating element on my stove so the jar isn't in direct contact with the stove's heating element.  

One tip that I stole from the "big boys" and I think is KEY for a even vapor polish is to put your item in the FREEZER for 15 min prior to polishing.  (do it while you heat up the jar/device and circulate the vapor.) then when your ready take it out of the freezer and put it into your vapor polisher, the vapor will immediately condense on your object and create a smooth vapor polish.  just make sure to NOT over do it.  Just like with cooking there is what I call "carry over cooking" from when you remove your object from the vapor polisher it will continue to "smooth" until the vapor has dissipated enough.  So if it looks "done" in the jar, it'll be OVERDONE when you remove it and let it "rest".  So its better to take it out early and have to do another run to take it out late and have it dissolve/collapse into a gooey heap.

Next time I do some polishing I'll take pics and video and show how I do it and throw it up on my blog www.dbclunie.com .

-david c.

[Kurt @ Gmail]

Hey Joseph - sorry for such a slow response. I don't check my Gmail account often - and didn't see this till now.

For my issue - I suspect you are talking about the Dragon Disaster - with the Melted section. Although, in this case - its Quite different from what these guys here are talking about. As mine wasn't a vapor treatment. In my case - I attempted to add weight to part of my Dragon - since the head part was so heavy - that the Dragon kept trying to tip forwards. I put liquid black plastic - with some stones - in this one "U" shaped section. But - my Bad. Problem is - after I did that - I finished up repairs - and sealed the whole dragon back together. In doing so - it left NO Way for the Acetone vapors to escape - and thus harden the liquid plastic. Instead - it stayed Liquid - until it proceed to Melt and Droop this whole section of the Dragon - and the Dragon Head ended up lowering all the way down in the Pain & Agony of the poor dragon!           :-)

-K-