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SoliForum - 3D Printing Community → Projects → Sealed smoothing station - Success!
Here's a sketch of the smoothing station I'm planning to build, pending arrival of parts. It's a small proof of concept that uses a latex balloon to separate the acetone from the vacuum pump, and keeps the acetone safely sealed in a chamber under negative pressure where it can be reused.
That is a Yoda, right ? 
I have a feeling that although the 4:1 ration of the expansion chamber you won't get enough vacuum on smoothing chamber to get the acetone to vapourise. I was only just able to get it to boil at 20 inHg so if you had much less the amount of vapor you would have would reduce significantly.
I've been following this thread with great anticipation. Being an apartment dweller myself, a fume free smoothing station would be awesome. However, just this morning a potential downside came to me. I don't know about you guys but my Yodas have a lot of air sealed inside. When the Acetone softens the outer wall, will the relatively positively pressurized print explode? I don't expect it would completely explode but I could see a wall blowing out or the print deforming due to the pressure difference. Is there a sweet spot where the Acetone will vaporize but the pressure differential would not deform the print? Could this be overcome by poking some holes in the bottom so the pressure can equalize or adding extra perimeters so it doesn't soften as much?
PS Love that Yoda is your example print in the diagram! LOL
That is a Yoda, right ?
I have a feeling that although the 4:1 ratio of the expansion chamber you won't get enough vacuum on smoothing chamber to get the acetone to vapourise. I was only just able to get it to boil at 20 inHg so if you had much less the amount of vapor you would have would reduce significantly.
Since atmospheric pressure is about 30inHg (drawing has typo--s/b inHg not mmHg), I figure the air in the smoothing chamber needs to expand threefold (leaving 10inHg pressure in smoothing chamber) to create a 20in differential. Thus, the big chamber--by my calculation--only needs to be a little more than 2x the volume of the expansion chamber to start boiling. Since it's a bit over 3x, it should be enough to vaporize the acetone.
How much? If there is, say, 0.3 liters of extra volume, I calculated before that 1ml of acetone creates about 1 liter of gas at STP, so at 1/3 pressure the same amount should expand to 3 liters of gas. So my estimate is that 0.3ltr / 3ltr/ml = 0.1ml of acetone should be vaporized by this setup at full vacuum. We'll see of course. It's also not nearly so cold in California 
When the Acetone softens the outer wall, will the relatively positively pressurized print explode? I don't expect it would completely explode but I could see a wall blowing out or the print deforming due to the pressure difference.
I don't know. It's certainly something to test. My gut reaction is that most prints are not completely air tight, and the volume inside the print would be too small in most instances to do a whole lot, but if it did, drilling an inconspicuous hole might be necessary.
Tealvince, now I understand your concept thanks to the diagram. It is very innovative.
Looking forward very much to further developments from everyone in this thread.
You will just have to use more perimeters if there is an issue with the pressure. While I don't get the true value of this system over the presto, I am interesting in seeing some examples of it in action.
I guess I should be able to test the idea of exploding items with just air in the chamber and try and get a nicely sealed print to go pop.
The problem is probably going to be with infill as there could be a load of separate compartments that all might want to cause catastrophic failure.
Well until I make something up to test, this is the setup I plan to make.
Ahem, I didn't even plan to try and draw a model, so I borrowed one off Thingiverse 
You probably don't need the valve to the pump but it does guarantee that the pump never comes near acetone.
I think I have most parts now, just need to find a good way to link the pump in to make it run as a vacuum. The vacuum hole in the casing is quite small and in a bad place.
I couldn't be bothered to wait to make the rig I have planned so....
Just printed a 4cmx4cmx2cm cube with 10% fill single outside wall, 2 bottom layers 3 top layers.
I knew the bottom 2 would make a good air tight seal but went for 3 on top just to make sure and give varying degrees of strength.
Put it in the jar without acetone and managed to get the pressure down by 23inHg and it just sat there. No bubbles in the side walls, no cracks, no squeaks.
Left it for ten minutes just to make sure it wasn't a slow process.
Nothing happened. Pretty confident that stuff isn't going to explode now.
So then I found a little glass dish to put in the jar as a standoff, added a small amount of acetone in the bottom, put the test box in and pulled the vacuum.
I was a little surprised to only be able to get 20inHg, but I think as this is the point where the acetone is just stating to boil so as I try and go lower the vapor is then filling the container, which makes sense.
I then let the pressure off and got condensation so I left it a few minutes and took the box out.
I now have a wet look test box, not really smoothed just shiny. Mildly disappointing.
I'll give it another go tomorrow, and leave it in for longer.
Need to print something more interesting to test, I won't bother boring you with pictures of a shiny green box.
Could you include a balloon with a small amount of air in the chamber? It would expand a bit when you pull the vacuum and should float on the acetone vapor. It might give you some indication of how much vapor you have, or how dense.
I'll see if I can make a small balloon out of a latex or nitrile glove finger. It will have to be small as I think once I pull the vacuum I would expect to see it fill the jar. Hmmmm, can't use superglue to hold it together that wouldn't last long.
My original idea of separating the acetone until the vacuum is pulled is seeming like it could be the answer. Pull a strong vacuum and then add the acetone, you would get more vapor in to the jar as the pressure would have been lower to start with and you don't have to worry about any vapor coming out of the pump
As I now have a random assortment of fittings from some old HHO experiments (making Hydrogen was fun) I will put something together tonight.
I want to try and reduce the amount of acetone used in the process as so little is made in to vapor it seems pointless in adding more than a few teaspoons in to the chamber. It is one downside of the Presto method that it is in the bottom of a dark container.
So I think I can bring this to a close. Sorry Tealvince.
I have been trying to use a very similar setup to my picture. I was able to block off the connection to the acetone and draw a vacuum of 23inHg. Then remove the block to let the acetone boil and the vapor in to the model chamber. The pressure dropped to 20inHg as expected
Leaving it for half an hour, just to see if it did anything showed no change. I didn't expect to see much as the acetone is still in the vapor.
Releasing the vacuum of the container so the vapor would condense gave very little signs of condensation on the glass. Whether this is due to the glass now having a residue of some sort on it to prevent condensation or that it was a room temp I can't be sure, but I then sealed the chamber again so any vapor could not escape.
Left it for another half hour.
I then removed the model from the chamber and was quite surprise how much you could smell the acetone, (not helped by having to lift the container off so the vapor flowed out, instead of lifting the model out) but even so there was clearly very little vapor.
The model was very slightly damp, and you could tell the surface was just softening, so I left it another half hour to see if anything progressed and to make sure it was dry.
After all that there is very little change. Even the top and bottom which were already pretty good still showed the print lines clearly.
I can see that something has happened but nothing close to being what you would say was a smooth model
I think this is down to the amount of vapor you get from "just" boiling the acetone. As it keeps reaching its pressure/vapor equilibrium it is hard to get much more vapor to then land on the model.
The only analogy I can think of is when a kettle boils. The instant water starts to boil there is hardly any steam, but leave it a little while and you end up with significantly more. There is no way to keep boiling the acetone as this would need you to keep pulling the vacuum, which then pulls out most of the vapor you have just created in the first place so it becomes impossible to get more vapor.
All of which brings me to say, that was all fun, but something that I can't see catching on as a smoothing solution.
and presto, we're back to where we started. Sorry couldn't resist.
Thanks for the update, did you take any pics?
The presto cooker creates a sort of convection system due to the vapor boiling and temp differentials. When the vapor is created due to a low pressure, I'm not sure that anything is encouraging the vapor to move enough to penetrate all of the surfaces. Might I suggest agitating the vapor somehow?
You could also try chilling the model to encourage condensation.
The model was very slightly damp, and you could tell the surface was just softening, so I left it another half hour to see if anything progressed and to make sure it was dry.
Thanks, Zarni, I suppose I'm not that surprised. As long as the acetone is in vapor form, it's probably not going to settle on the model, especially since everything is at room temperature, so leaving it in a vacuum for an extended period of time is probably not useful.
Instead, my plan is to use the smoothing station as a way to apply acetone evenly (or at least more evenly than a brush). This means applying a vacuum only briefly and then releasing it so it can work on the model, but keeping it in the chamber so it doesn't evaporate. I'm planning to use a venturi pump instead of a hand one, so repeating applications if necessary would not be a big hassle (especially compared to a hand pump).
And yes, Jooshs, I want to do some sort of magnetically driven fan as has been mentioned elsewhere to spread the vapors, but I haven't gotten to designing one yet.
And yes, cmetzel, I know you're proud of your presto smoothing station and it is indeed a fine piece of equipment, so I don't mean to disparage it in any way. But unfortunately, I can't use one for my personal use, as I need a smoothing station that is safe to use indoors.
Zarni, you already got a little bit of smoothing, so that doesn't sound so bad for a first-of-kind device. There are still a lot of potential improvements or similar concepts (like heating a measured amount of acetone with an expanding air bladder) that can be tried, so I'm actually encouraged by your results so far.
Sorry, no pictures as it was very dull with very little results.
I now wonder if I should have used a balloon of some type for the acetone container. That way when the pressure was released atmospheric pressure would push everything in to the chamber. Should be an easy retest.
As there was only vapor in the chamber I did give it a shake just to be sure there was no liquid present, didn't help any.
Are we trying to create something which works around the issue of getting acetone on to the model?
As I see it at present if you were to dunk the item you end up with a lots of contact but can end up with pools and runs which we want to avoid, brushing again gives the potential for uneven coverage which is where vapor comes in.
If you just had some sealed container atomisation thing could work without having any heat or vacuum.
A simple test with a spray bottle should give decent results. I'll have to rig up some more tests once I get a good setup with new rice cooker at least that way I will have something to compare against.
Sorry, no pictures as it was very dull with very little results.
I now wonder if I should have used a balloon of some type for the acetone container. That way when the pressure was released atmospheric pressure would push everything in to the chamber. Should be an easy retest.
I'm not sure what that would do. Seems like the balloon would get sucked in when pulling the vaccum and then pushed back out when released. However, I think one problem is that if the acetone reservoir is a sealed bottle with no input valve then a vacuum will develop inside it that will prevent much acetone from entering the chamber.
As there was only vapor in the chamber I did give it a shake just to be sure there was no liquid present, didn't help any.
I don't think all the acetone can stay as a vapor once the pressure is released; if it does, it probably indicates that not enough acetone was injected into the chamber in the first place. You did mention that the model was slightly wet. I think the trick is to leave the model in the chamber with the pressure released so it can act on the model in liquid form. If enough acetone was injected, the air in the chamber should be fully saturated with acetone, and thus no more acetone can evaporate off the model, allowing it to work. By taking it out, the thin layer of acetone is exposed to unsaturated air and thus instantly evaporates.
Are we trying to create something which works around the issue of getting acetone on to the model?
As I see it at present if you were to dunk the item you end up with a lots of contact but can end up with pools and runs which we want to avoid, brushing again gives the potential for uneven coverage which is where vapor comes in.If you just had some sealed container atomisation thing could work without having any heat or vacuum.
A simple test with a spray bottle should give decent results. I'll have to rig up some more tests once I get a good setup with new rice cooker at least that way I will have something to compare against.
I think atomization would be worth a try. It appears that the normal way of smoothing via acetone vapor may work not be due to the vapor itself, but due to the micro-droplets that condense on the model when exposed to the vapor. As such, any way to evenly coat the model in a thin layer of acetone might work. Another poster also suggested dunking the model in acetone diluted with water. This seems worth a try as well.
Just a thought since I have built several solar ovens. You could let the sun do the heating . My ovens gets to about 300 degrees on a good sunny day. Save a little dough on electricity.LOL I have a parabolic solar burner that gets to 900 dregees at the focal point. The cast iron pot reaches about 450 degrees.
I have a fensel lens that I've used burn things and to power a stirling engine but that isn't much use at the moment as it is rather grey outside, and in the evenings there is a serious lack of sun 
Maybe it would work if you live in California but not in gloomy England at the moment.
Speaking of atomisation though, an ultrasonic fogger could be the simple answer. The cheap ones seem to have a plastic housing but I'm sure a bit of rework can sort that out. The idea of immersing your model in to a fog of acetone and pulling out a nice smooth model sounds plausible. Another ebay purchase coming up.
All testing is on hold as the in-laws are with us and are using the spare room 
It's been awhile, but I finally got the parts I needed (mason jars, bulkhead fittings, and some misc air connectors) to try out my sealed smoothing station concept. I'm happy to report I had a successful first test!
The design pretty closely follows the sketch I included in an earlier post. Two mason jars (1/2 gallon and 1 pint) serve as vacuum chambers, with the part to be smoothed held in the smaller chamber, which is connected to the larger jar above. A balloon in the upper chamber separates the air between the two chambers and keeps the acetone from escaping when a vacuum is pulled in the upper chamber. I pulled a vacuum using a compressor-driven venturi pump that I got at Harbor Freight for $15.
As you can see from the attached video, the balloon expands when the vacuum is pulled, causing some of the acetone to boil off into vapor. After only a few seconds, I released the vacuum, and acetone condenses evenly onto the part and the sides of the lower mason jar (which you can see as the fog that suddenly appears). Since the lower container is sealed and the air in there is now fully saturated with acetone, the acetone doesn't evaporate and continues to work. I then left the part to smooth for an hour, and the results are below. The part had a nice gloss to it. It was still sticky with acetone when I pulled it out, so the smoothing would have continued if I had left it in for a longer period of time.
I used an old discarded print as a test which had a fair amount of wobble to it. About half the wobble was gone, so in the future I'd still want to use wobble-compensation and maybe some presanding, or leave it longer in the chamber.
I think your progress is really good and I look forward to seeing your next development.
On the weekend I took one for the team and chucked in a spare 30mm fan to test if it would be affected by Acetone. THe plastic parts of the fan are fine, so I suppose the only thing that could have failed would be some of the bonding parts in the circuit. So far so good.
That is a much better result than I achieved.
I am now thinking that with my setup letting the air back in was reducing the amount of acetone in contact with the model as it was being absorbed in to the air and not being deposited on the model.
Since my last attempt I have now got an ultrasonic fogger which I plan to see if that generates enough acetone moisture to affect the model. Also need to find out if it will just melt in the acetone the electronics are encapsulated in resin but the case might still fail.
I'm currently printing some treefrogs at 0.3mm as test subjects so the pictures look a bit more interesting.
Now the in-laws have left testing resumes tomorrow, I now need more acetone.
Plenty of back to back testing to come, as well as seeing what happens when you light acetone fog 
That is a much better result than I achieved.
I am now thinking that with my setup letting the air back in was reducing the amount of acetone in contact with the model as it was being absorbed in to the air and not being deposited on the model.Since my last attempt I have now got an ultrasonic fogger which I plan to see if that generates enough acetone moisture to affect the model. Also need to find out if it will just melt in the acetone the electronics are encapsulated in resin but the case might still fail.
Awesome. I can't wait to read the results of your new experiments!
As far as the fog goes, I've personally come to the conclusion that acetone vapor doesn't by itself seem to result in any smoothing, but that it has to condense to a liquid on the surface of the model first. In a normal heated smoothing setup, the acetone is heated up while the model is at room temperature, so this causes the acetone vapor to condense onto the model as liquid. In my vacuum setup, however, everything is at the same temperature, which is why I released the vacuum after allowing the acetone vapor/liquid to reach equilibrium. This caused the vapor to need to transition back to liquid, so it condenses on every surface it can find, including the model.
I'm not sure how or if this might apply to a fogger, however, so I'm definitely interested in how this will go. I'm very happy with my vacuum setup for small objects, but a fogger setup could be scaled up more easily, I think.
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