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What are the reasons for my 3D prints having large numbers of strings between parts of a layer?
I am printing a print using PLA on a Prusa i3 printer and an MK8 extruder, at 210 degrees celsius, 60 mm/sec, sliced with slic3r. The print consists of a base, with 4 tower-like projections that then join with a near-vertical overhang slope that isn't posing a problem for my printer.
However, even before the overhang begins, I am getting large amounts of strings as the extruder head jumps between the four towers in the print, leading to a "spiderweb" effect between them. How can I deal with these strings, and are they a warning that there might be something amiss with my printer, or possible other failures in other parts of the print?

Stringing is often a result of too-high a temperature, or insufficient retraction. When there is highly liquid filament in the nozzle tip, it can adhere to the remainder of the print while dripping as the nozzle moves, leading to a thin string of the filament forming. As further travel moves are performed in each layer, this turns to a web.
The high temperature causes filament to be very liquid, causing it to move downward in the nozzle chamber easily, as opposed to having to be extruded forcefully due to viscosity. The temperature setpoint of 210 was high enough to cause this to happen.
A second possible cause, insufficient retraction, can also be blamed for this issue. Retraction is a process in which the extruder reverses its movement to pull filament back up the hotend, preventing it from dripping at the tip, and forming a string. Most slicers will allow specifying a numeric value in millimeters of filament to be retracted. Remember that printers with Bowden tubes between nozzle/hotend and extruder motor will require increased retraction and priming (extrusion when starting to print after a retract-and-move). Note that too much retraction can cause other problems, such as insufficient plastic in the hotend chamber at the start of the next printing move, which can cause gaps and other issues.

Here's just a few of the things you might want to look into.

plastic - some plastic types are more stringy than others and there's also variation between brands and colors.
moisture in filament - water turning to steam tends to cause the extruder to ooze when it isn't printing, which can cause stringing.
temperature - too hot or too cold can cause stringiness.
retraction distance - not enough retraction can leave some nozzle pressure, causing it to ooze during travel moves (not sure how much retraction speed matters but I suspect it can make a difference too).
acceleration - if it's too slow it's more likely to draw out strings.
travel speed - faster travel speeds are more likely to prevent strings or make them thinner and less of a problem.
z-hop - raising the extruder on travel moves makes stringing more likely.
wipe - a longer wipe distance can be helpful to reduce stringing, especially with some of the more stringy filaments.
combing - avoiding passing over open spaces can reduce stringing in some cases
part cooling fan - more cooling might help to reduce stringiness.

There are other things too, the extruder design makes a big difference with longer bowden tubes being more challenging to tune.  The order in which the layers are printed can make a difference too in some more specialized cases.


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Are there any methods of limiting exposure of hazardous fumes and odors emitted by heating the plastics?
When using thermoplastic-filament, this can be potentially hazardous, since constant printing can emit hazardous fumes and odors that may be emitted by heating the plastics.
I understand it normally should be used in well ventilated areas. However I would like to use it heavily in the basement which is not well ventilated.
Are there any practical methods of limiting such exposure? For example locking it in some special box, covering it or suck the odors? Would that help?
Do you have any experience doing so?

Related: http://www.3dprintclean.com/

Using negative pressure ventilation and a suitable organic filter will limit your exposure to toxic compounds, but won't completely remove them from your environment.
Enclose your printer in as air-tight a box as you can manage, then use a fan to suck air out of the box.  This negative pressure will ensure that any leaks in the box will not allow gasses to escape.
The air should be blown through an organic filter.  This might be done with face mask filters for painting, for instance.
Additional filtering may be done depending on the compounds you expect the printer to produce, but the ideal situation is to set up a ventilation system to the outdoors where the products cannot concentrate and harm anyone.
Another poorer option is to simply wear a proper organic filter mask yourself.  It's not as good, since the compounds can spread through your residence or remain in the air and be inhaled when you aren't printing.

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What is the best way to connect 3D printed parts?
I want to print a model of an animal cell.
What I have so far: I managed to use different colors to print out the different parts of the cell.
My question is: what is the best way to connect plastic 3d printed parts?
Glue? Melted plastic? I need it to have a strong connection and not very visible when used well, and preferable dries fast.

What printing technology and material are you using?

I am voting to close this question as off-topic, since it is not specifically about 3D printing: as it is currently worded it is just a question about how to (generally) fasten objects, and the fact that they are 3D printed is secondary. At the very least the question should specify a 3D printing process and material so answers can focus on that.

@TomvanderZanden When prints are too large, they need to be printed in multiple pieces.  To assemble them they must be connected.  Even though this connecting not because of size, I think it is a valid question.

Moreso, this question is, at least part, about what adheres well to the ABS plastics which is alot more specific to 3D printing.  Also not this is also "rapid prototyping".

@EricJohnson My objection is that the question doesn't change if you leave out "3d printed". "How to drill a hole in a 3d printed part?" reduces to "How to drill a hole?" because the fact that it's 3d printed is irrelevant. The same goes for gluing, smoothing, painting, etc... Questions should make clear how the fact that the part is 3d printed is relevant.

Please, please, please! If you're closing as off-topic, please fill in a custom reason to explain why, inside the close reason box. This help everyone.

I disagree with closing this topic. The problem is very specific to 3D printing because of the materials that are being used that are specific to 3D printing. For example, where do you find PLA plastics commonly used other than in 3D printing? So what's the best way to connect PLA 3D printed parts together? If you have a combination of PLA objects and ABS objects, what do you do? These are not questions that would come up in a non-3D-printing forum. A person doing 3D-printing needs these techniques as part of their toolkit - choosing the right glue / cement / epoxy is extremely relevant.

I think it is on-topic, for the reasons @TonyHansen gives. However, "the best" makes it opinion-based and it might also be too broad. I suggest rewording it ("How to make a strong/durable connection") and specify the material used.

I feel this is on topic, but as it is, it might be either too broad or too opinion based asking for a best over a broad range of materials

This question, I agree, if off topic, but very similar questions would be on topic.  The examples of gluing pieces together because of machine limits would be on topic.  The example of drilling a hole would be on topic -- I've drilled holes in 3D printed objects and it is NOT like drilling holes in other materials.  Because closely related questions would be on-topic, is there a middle ground?  Can we answer with 3D printing specific information and suggest that a further answer could be better found elsewhere?

For ABS print, I recommend acetone. It is not a glue, but it will dissolve the plastic a bit and if you apply it to both connecting parts and push them together, they will stay connected after the acetone dries. However, it does not dry very fast and you have to be careful not to destroy the object.
For PLA I usually use regular super glue (Cyanoacrylate).

And you should always have proper ventilation when working with acetone.

For ABS I use a gel super glue (Loctite is my current favorite), it seems to slightly melt the ABS parts together and makes for a great bond. A slurry of old scrap ABS and acetone also works well, though I find that it will evaporate even if left in a closed mason jar over time. The small nozzle applicator and the fact it doesn't seem to evaporate makes super glue the better choice for me.
The gel super glue works "OK" for PLA but I've had parts fail after taking a small tumble. I just started using this acrylic cement for PLA. It cures very fast but seems to slightly melt the PLA in the same way the ABS options do.
For internal seams I like to put a bead of "high performance" hot glue over the seam. It's just a bit flexible and seems to do a good job taking drops.
Lastly I really like (but haven't mastered) friction welding parts together using a Dremel. Matt Griffin at MAKE Magazine did a great write up on the technique here.

I second the friction welding suggestion. It creates very strong bonds. It takes a lot of practice though. Currently I limit my use to welds I can do that will end up hidden.

After doing the processes that hroncok described, the edges of the print can be finished with a 3D printing pen.  The pen extrudes filament as a regular print head does, but is hand held.  The filament can be extruded on the previous gap between the two prints.  It will melt between the two sides and can be finished to create a smooth connection point.

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Home vs. Professional Print Quality
I've made a few 3D prints at school on what I assume are very low-end 3D printers, but they seem cheap, flimsy, and pretty ugly.  How much better quality can I expect from professional-level 3D printers (those commonly used by online printing services)?

This depends too strongly on the technology, as they can be either much stronger (nylon) or much flimsier (sandstone/zcorp). "Cheap" and "ugly" are too subjective, and we don't know what printers your school uses. If they're really that cheap, flimsy and ugly perhaps the people at your school don't know what they're doing?

Also, cost isn't correlated with quality. We replaced a $2000 printer that was a horrid mess with DIY ~$500 prints (kit, but the manufacturer "donated" to us assembly labor as we are a school). Print quality was far better after, without a huge timeframe between the old and new printers.


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How to recycle filament material from printed parts?
Is it possible to re-use ABS or PLA filament material from printed parts?
If so, what is the techniques to reform it?

There are a few options.

Machines are available which grind the used plastic into fine pieces, melt it down, and extrude it as filament to be reused. Filabot is perhaps the most well known.
Depending on where you live the local recycling programs may accept PLA or ABS. They will then shred it and melt it down for reuse.
PLA is bio-degradable so you can put it in the compost.
I put scrap ABS in acetone which results in a slurry which can be used as a glue to attach ABS parts, fix cracks, and hold parts to the bed.

A DIY alternative to the Filabot is Hugh Lyman's Filament Extruder(s), the latest is v6, http://www.thingiverse.com/thing:1199870

AFAIK PLA is biodegradable only in industrial composting facilities, not in your backyard compost heap. This is because it requires specific conditions to break down effectively.

I am sorry to say but this filabot thing has a totally unacceptable pricing. I am surprised if anyone would pay this.

If you're more interested in the recycling and reuse aspect than the re-print aspect, you could melt all the scrap filament onto a cookie sheet or into a bar (like in a bread ban).  You could then manually work the material, or use a CNC machine to carve out your next thing.
This Youtube video refers to HDPE, but the same concept will apply to other thermoplastics:

This Youtube video uses a cookie sheet and failed prints:

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Why do the corners of my ABS object lift off the bed?
I print ABS on a LulzBot Taz 5 and frequently have issues with the corners of objects lifting off the bed.
My extruder is at 230 °C and the bed is at 90 °C for the first layer and 100 °C for the rest of the layers.
I have experimented with using ABS slurry (ABS + acetone) on the bed for increased adhesion, building a foam enclosure for the printer, and varying the fan speed. I have noticed the problem is more common the taller the parts are and the sharper the corner is.
Adding ABS slurry helped for smaller parts (less than an inch tall) but with my more recent larger parts the adhesion to the bed was so good that the corners of the part lifting actually peeled the PEI tape off of the bed.
I have tried using both a skirt and a brim with no change. The skirt stays on the bed, the brim gets pulled up with the corner.

Doesn't TAZ 5 have PEI tape?

Correct sorry. I was just using Kapton at work so I had that on my mind.

What fill percentage are you using? Adjusting the fill percentage of the print should alter the rate of cooling and therefore the stresses generated by the temperature differences as you print.

50% I guess the same could be said about slowing the print down???

50% is quite high. I often use 10-15% and the print is still very sturdy - even with a single shell.

There are many different approaches to solving this issue and most of the answers already are spot-on. However, the fundamental reason for the "warping" is incorrect and inconsistent temperature across the material.
If there is too much fluctuation in the temperature across the object in this heated state can result in warping. The reason you see this mostly on the build plate is because the temperature of the first few layers of molten plastic vary much more against the build plate than against higher layers. Note that you can see additional warping mid-print using ABS and this can be a result of a draft or sudden drop in ambient temperature.
So, to help solve your problem, here are some suggestions (sorry if there are duplicates):

Completely enclose/seal your machine's build area to reduce (or eliminate if possible) draft and prevent the natural heat of the machine from escaping.
Increase the temperature on your build plate. I almost exclusively use ABS on my printer and I keep my HBP at about 112C. However, I live in the NW of the US, so my climate is naturally cooler than say Florida.
Alternatively, try decreasing the nozzle temperature to a lower point within the ABS melting range. This will just shorten the gap between the inconsistencies in temperature across layers. It is typically better to print at lower temperatures if you can help it. Obviously there are differences in the filament, so you'll have to find that "sweet spot".
Ensure your build plate is flat and your tape doesn't have bubbles. Your BP being flat should be a no brainer, but if your kapton tape (or whatever you use) has bubbles, your freshly printed plastic may not be getting the same temperature from the BP as the rest of your part. This is a bad thing as mentioned earlier.
Use extra adhesion techniques such as "ABS Glue" (ABS w/ acetone) or even hairspray. This works about 80% of the time for me, but can make it a bit difficult when removing the parts off the BP.

Most common problem with corners is to low temperature of heated bed. Set the heated bed temperature to 110°. If this will not help then try to set brim in your slicer.
The problem can be cause by other issues. You can find additional tips in following Troubleshooting Guides:

overheating (simplify3d: Print Quality Troubleshooting Guide)
differential cooling of printed object (reprap.org: Print Troubleshooting Pictorial Guide)
warping (A visual Ultimaker troubleshooting guide)
warping (all3dp.com: 16 Common 3D Printing Problems)

Adding a manually added brim with a larger bulk at the corner extremities that you can cut off after printing should help. My larger prints come off the printer looking like tents with concrete weights tied to their corners.
The 'weights' are attached to the print by very short a 2-3 layer (depending on print size) brim-like strip that makes them easy to remove using side cutters. The 'weights' are usually enough to hold the corners of my target print on the plate in conjuction with a weak slurry.

This is a common problem with ABS. You might prevent it by enclosing the printer inside a box/chamber - that will create a warmer environment and the extruded material will cool down more slowly, hence not creating such a tension.
Other option is to use PLA instead if possible, the problem is not so significant with PLA.

I have enclosed the whole printer in a foam "oven". It gets quite warm inside.

and the problem still exists?

The solution I prefer to prevent ABS withdrawal is using Blue tape on the bed, and then spread a thin layer of Polyvinyl acetate (Vinavil glue).
If your printer allows it, you can also print with the bed at 110°C.

As mentioned in the question. I have used ABS slurry to keep the part attached to the Kapton tape on the bed and the pulling up was so strong that it peeled the tape off the bed.
I guess I'm looking more for reasons the part is pulling up in the first place.

Blue tape is not Kapton tape. It is a  masking tape with heat resistance.

To answer the specific question of "why" the corners lift off, it seems it has to do with the thermal expansion (or shrinkage) and surface adhesion area.
The material is deposited hot, and even after it cools is still warm, and as it cools it apparently shrinks in size slightly. Each layer therefore produces a little bit of force, pulling upwards and towards the center of the layer as the layer shrinks.  So each layer is actually in a state of slightly tensile stress.
Over a few layers this may not cause a noticeable effect, but as more layers are added, the total force pulling on the bottom layer increases.
The reason this affects corners more than the bulk surface regions is that the total surface area holding the part to the bed is smaller at sharper corners, so less force is required there to overcome the bed-adhesion force, causing corners to unstick eventually.
Since this is an artifact of thermal expansion, attempting to maintain a uniform temperature across the print volume/printed part will probably help a lot (for example, by enclosing the printer, as others have said).
In addition to the prior suggestions, the following paper suggests that chamfering (rounding) the corners can help with this (if your design allows for that):
D. D. Hernandez, "Factors Affecting Dimensional Precision of Consumer 3D Printing", Intl. Jnl. Aviation, Aeronautics and Aerospace (2015)
"If the bottom layer does not appropriately adhere to the print bed, the cooling process and material shrinkage in layers above it will tend to pull at the smallest features, with the least surface area in contact with the bed, causing sections of the print to warp. Sharp corners at the bottom of the print pose a particular problem."
Side-thought:
I wonder if varying the bed temperature during the print (for example, slowly decreasing it to room-temp as more layers are printed) would help, since a constant bed-temp would theoretically produce a vertical temp-gradient for a very tall part.  Don't think I've seen anyone try that (presumably because Cura doesn't automatically insert those g-code commands for us).  Wouldn't be too hard to insert custom bed-temp commands throughout the g-code file though, but would take longer to temp-stabilize between layers.

In answer to the question "why do the corners lift when using ABS", the answer has to do with the coefficient of  thermal expansion (or contraction).
ABS, compared to PLA, has a higher coefficient meaning that as the temperature of you part changes the more the part will deform. With 3d printing, the material extruded from the nozzle is quite a bit higher than the build chamber. As the layers print and the extruder moves up, the lowest layers are cooler than the layers above, shrinking as time goes on.
For angular parts this is a larger problem than for round parts. With angular parts (parts with sharp edges in  X and Y axis) as they cool, the internal stresses induced by cooling increase and can't be resolved in just the xy axis and cannot move into the build plate.  The part then lifts up to reduce these stresses.
A brim or raft, is a thin layer that ideally cools at a constant rate through out which will effectively increase the bonding of your part to the build plate. Abs to abs bonding being stronger than abs bonding to whatever your build plate material surface is. For most parts this is sufficient to keep good adhesion while your part builds and cools. Raises the temperature of the build plate also reduced the stress in the brim/raft by reducing the difference in temperature.  This is why those are the go-to solutions for stopping abs from lifting.
If your part is large enough or the angles are quite sharp in XY, (think of a five pointed star for example). Then the brim raft won't necessarily be enough to prevent the warping. That's where "helper discs" "mouse ears" etc . Are helpful. These, when dispersed around the outer sharp corners, increase the surface area of the raft and also reduce the angles of the thermal contraction due to cooling.
Note, that while I'm talking about ABS specifically, this will apply to any and all materials if the part geometry, or material properties have the same issues.  Nylon for example is also a pain to print for similar reasons.
The final thing to say is that all if this is for nothing if your build plate isn't both flat and level.

I would recommend using a raft on your print.  A raft is a few layers that are printed on the bed before your print starts.
The larger you make the raft the stronger the center of it will be.  The edges may warp, but the inside where your print is will be fine.  Using a raft that is mainly comprised of lines instead of solid surfaces would allow a smaller chance of warping as it could only warp with the lines.

Another approach is to put mouse ears on all the corner parts, that you clip off the print afterward.
See Mouse ears defeat corner curling monster.

I think you answered your question in your statement. Lulzbot and ABS. Lulz does not have an enclosure.
Try using PLA for an open air system. Or build an enclosure. Following you can add glue or hairspray.
But I promise you, with any open air printer, you will face this problem. I only use ABS on my FFCPs. Even with their passive heat chambers I plan to move to PLA for all my printers.

This post is meant to share experience with products that make your products stick to the bed. This is not meant to be a promotion of the products! In other answers I've seen answers hinting to Elmer's glue sticks.
I have been printing directly onto the aluminium heatbed from day 2 of the i3 Prusa clone (Anet A8) printer and the glass beds of the Ultimaker 3 Extended and my HyperCube Evolution using a PVA based spray (3DLAC, but there are more products with similar effects, e.g. glue sticks). This sticks so well that PLA and PETG can only be removed after cooling down the bed completely. For ABS you could use DimaFix which can be used for ABS as it increases grip with increasing temperature where 3DLAC looses grip over 80 °C (according to theory). After trying DimaFix on high temperature beds for printing POM filament (very tough to get this to stick as this is bearing material!) I found that prints stick better with 3DLAC on glass.

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When should I use a raft, when should I use a brim?
Taken from the answer provided by @EricJohnson,
When should I use a raft, and when should I use a brim? What advantages does each have over the other?
Raft

Brim

A raft will allow for better adhesion for the whole print as the raft attaches to the printing surface and the print attaches to the raft. Rafts go all the way under the print and consist of multiple layers, whereas a brim is only 1 layer and on the outside of the print. Rafts are normally harder to remove than brims because of the increased contact with the print.
From my own experiences, the brim does not help a lot with layer adhesion as it is only 1 layer. I normally use a raft when I need a nice looking 1st layer that is not on the bed or when there are not enough contact points.

I find brims useful when you do have a lot of contact between the bed and the print. If you have a relatively flat object, a raft is not needed but a brim can give you something to use help separate the print from the bed. For example, I recently converted a 2D logo image from a non-profit into a simple stencil they could use for tracing. Very flat, lots of bed adhesion. The brim gave me something to use to pry up the print without damaging it. It's also useful for small boxes or trays. I use a brim whenever I don't need a raft.

A raft is used to prevent warping. Instead of printing directly on the build surface, parts are built on top of it. You remove and dispose of a raft post-print. The raft is larger than the part and so has more adhesion. Rafts are primarily used with ABS to help with bed adhesion. Rafts are also used to help stabilize models with small footprints (e.g. a pole), or to create a strong foundation on which to build the upper layers of a model. If your only concern is bed adhesion it is better to use a brim.
A brim is attached to a model and extends outward. Brims typically have several outlines and may be a few layers tall. Brims are often used to stabilize small parts of a model, such as legs of a table, because brims help these areas stay connected to the print bed.
TL;DR
The brim is only around a model and attached to its first layer, a raft is also under it.

A raft helps when the part has few points of contact with the print bed, and doesn't therefore adhere well at points within and without the part.
A brim helps when the part doesn't adhere well around the perimeter of the part.
There are very rare situations where you'll need both, but typically you'll only use one or the other.

I have been favoring brims recently; I am tired of the rafts becoming an integral part of my print, impossible to remove.


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My print is warping: how can I ensure that it cools evenly?
My print is warping and I suspect it is because of uneven cooling.
How can ensure my print cools evenly? Should I put a fan on the bed? Will no fan and a tall skirt help?
Or are my edges curling up for another reason?

This seems more like a warping question than a cooling question to me.  There are methods to fix warping that do not involve cooling.  Are you looking for only cooling solutions or any warping solutions?

Without more information we cannot address what is causing your edges to turn up. This can depend on the model being printed, the process, the material, the bed, and the method used to bond it to the bed.
As far as the initial question, a fan will most certainly ensure uneven cooling.
The middle of the print is, and will remain, the warmest.  If you want the print to cool evenly, you'll need an enclosure to block out drafts and air currents, and you'll need to bring the heated bed temperature and enclosure temperature down slowly over a long period of time.

In addition to what Adam says... Some slicers also offer a feature called "shroud", that basically prints a disposable "shell" around the print proper, and is meant to trap warm air and make the print cool down much more gently (and thus evenly).


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How can I stop my print bed tape from sticking to the filament?
I made a test print for a small gear (~ 1.5 inches in diameter) a few months ago, with a hole through the center. On the first try, the filament (ABS) fused to the print bed, meaning that I had to spend ten minutes scraping off material to loosen it. One solution to this is to use painter's tape spread across the print bed.
This yielded a good print during the next run. The problem with this method was that some of the tape subsequently fused to the backside of the gear; it was so tight that I had to discard the prototype. Multiple varieties of tape made no difference.
Is there a way to continue using this tape without having it fuse to the filament?

This can highly depend on the slicer you are using. Some software such as Makerware and Slic3r allow you to adjust the settings for the first raft/part layers. I might suggest adjusting this "Z0" point to about 1/4-1/2 of your layer height. Essentially the first layer (or two) will not adhere as well.
This is just one suggestion of many solutions. Here are some other variables I could think of off-hand:

Type of build plate tape (ie masking, painters, kapton, etc.)
Type of material. I've noticed that PLA is very stubborn if you let the part completely cool after printing and that it's much easier to remove the part from the build plate/raft right after it's complete.
Type of build plate. Are you applying too much heat (if you have a heated bp) for the material such as PLA?
Try lowering your layer height. This will ensure that each strand does not have too much surface area and therefore less chance that it will create a vacuum affect with the build plate. This can, however, result in a worse surface finish.

Note that if you do attempt to remove a "warm" print, I would make sure you use a tool (i.e. a spatula or similar) as opposed to your hand

My very first thought was you didn't re-calibrate your Z0 after adding the blue tape. It sounds like the print head was too close to the print bed to begin with, and adding the blue tape just made it that much worse.

One thing that I do to  keep it from sticking to the tape. Is to add glue from a glue stick down on the building pad in an even coat on top of the tape.


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Safety precautions when using acetone
Acetone can be used to smooth ABS prints.  What safety precautions should be taken during its use?

Related question: Are there any methods of limiting exposure of hazardous fumes and odors emitted by heating the plastics?

clarification question: are we talking chemically grade pure acetone, acetone from the home depot or nail polish remover with acetone? Safety always is a question of concentration.

There are a few main safety precautions you should consider.

Make sure the area is well-ventilated. Acetone is flammable. A buildup of acetone gas could quickly get concentrated, meaning that a single spark could lead to disaster. Using a fan is good; angle it towards an open window. This is also to prevent exposure to acetone because of its toxicity.
Be prepared to fight a fire. Should vapor ignite, you may need to fight the fire. If it is large enough, then you should clearly evacuate the area. If it appears to be small, use dry chemical powder to snuff out the fire. Alcohol foam, water spray, and/or fog may be used on slightly larger fires. Acetone is not likely to cause a large inferno to rip through the building. But there's always the chance of a small fire. Be careful.
Create a vapor chamber. This is another way to stop a potential fire from spreading. It can also reduce contamination.
Wear gloves. This can minimize any potential transfer toxic effects. However, skin exposure is unlikely to cause major issues.

Acetone is toxic, as I mentioned before, but it is not highly toxic. Exposure via the eyes and nose/mouth is the main risk. Skin effects may occur (e.g. mild irritation), but they are minor and generally arise only after long-term exposure (hence the recommendation of gloves in some cases).
Acetone exposure is only a serious problem when a person is repeatedly exposed to levels greater than 1,000 ppm (severe effects only arise at much higher levels). It seems unlikely, given a proper ventilation system, that this will be an issue
In addition to all this, basic safety precautions such as wearing a ventilator mask and goggles should definitely be taken. When working with any such chemicals with the potential for bodily harm, these should absolutely be used.

Just wear gloves...

@KevinMorse Fair point, in that case, and I suppose they can also protect from burns. I tend to dislike the associated clumsiness that comes with some gloves, but most don't have that issue. It's just my preference, and probably not the best one.

These safety instructions are incomplete. You failed to mention the need ventilation is in addition to wearing a ventilator for instance. You also left out the need to use safety equipment like goggles. In my opinion your answer should link the MSDS as a catchall for what you left unmentioned.

@EmilyM These are basic precautions that should be obvious. Nobody in their right mind would work with acetone like this and not wear goggles or a ventilator mask, just like you wouldn't take a cake out of the oven without wearing an oven mitt. I didn't think it was necessary to include them. However, I can add them in if you feel they are not obvious.

I wasn't trying to be confrontational. But when it comes to safety recommendations assumptions aren't a good idea. People are dumb, uninformed, tired, not paying attention etc. It can't hurt to be thorough. I just want people to be safe, thus my answering the question. But since you are more likely to be the chosen answer at this point, I was hoping to convince you to make an edit for the sake of safety.

@EmilyM Just some backstory, as I may have jumped off as harsh, too: Soon after I posted this answer, an error was found in my answer in comments, and so I deleted the post (because it is a question about safety), edited it, then talked more with the poster (who had been absolutely correct), before finally leaving it as is. I think I was the one who was too confrontational here; I had spent a while on this answer, and I was frustrated at myself for leaving something out. So I apologize, because I jumped on you here, quite unnecessarily.

I understand. Thank you for making the additions. No worries about the confrontation; both of us are probably to blame to some extent. What is important is the quality of the answers- we both had that same goal and thus this result (a good answer) is what we both wanted. I accept your apology and extend my own for my part in the problem, which I'm sure you accept as well. No harm, no foul!

Contrary to what the other answers suggest, the risk of fire is not that great. An acetone "explosion" is even more unlikely, since you need a ratio of 2.5%-12.8% acetone vapor to air for that: too much acetone (as would be the case inside of your smoothing vessel) and nothing happens, too little (as would be the case inside of a badly ventilated room) and nothing happens either.
Note that even if you were working in a completely non-ventilated, ridiculously small 1m^3 room you'd still need to evaporate over half a liter of (liquid) acetone to reach that bare minimum 2.5%. In any case, well before you got into the "danger zone" the air would become unbreathable.
So, then what should you be mindful of when using acetone?

It can give you a headache. Avoid breathing the fumes and ensure adequate ventilation.
You may opt to use gloves, as skin contact should be avoided (acetone can irritate the skin and possibly be absorbed through the skin). However, limited skin contact isn't a big deal: acetone is an ingredient in some nail polish removers.
Acetone is heavier than air, so if you use a sufficiently high container fewer fumes will escape.
If somehow a fire does start, it will likely be limited to your container. Having a lid handy allows you to starve the fire of oxygen, harmlessly putting it out.

All in all, smoothing using acetone is not very dangerous. Acetone isn't suspected to be carcinogenic, though it isn't something you should be careless around either. The risk of starting a fire is small. On the other hand, solvents like MEK (used for smoothing PLA) aren't as nice by far, and should only be handled with a respirator.

No fire. Acetone is highly flammable. Avoid open flame, smoking, soldering etc. near acetone or acetone fumes. Be ready to fight a fire.
Ventilate. Acetone is very volatile so the fumes will be everywhere in the room. While breathing them should not kill you, it is certainly not good for your health. It may cause drowsiness or dizziness. It is also a good idea to close the container/jar as soon as possible and do not keep it open when not necesery.
Avoid eye contact. Acetone causes serious eye irritation. IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses if present and easy to do – continue rinsing. Seek medical help if needed.

You should also avoid skin contact; repeated exposure may cause skin dryness or cracking, but this never happens me if I wash my hand after using acetone.

Safety Advice for Acetone Handling/Usage

Please remember that you handle acetone at your own risk! By using this advice you agree to hold me harmless and not sue me as a result of using these instructions/advice. Remember that I am not a professional chemist or a lawyer (this isn't professional or legal advice)!

I encourage you to research safety precautions and risks on your own to build a personal body of knowledge. The most effective safety precaution available to you is knowledge; the brain is the most important piece of safety equipment! This listing of advice for acetone handling is generated from the highlights of a Material Safety Data Sheet (MSDS) for acetone. After reading this advice you should read an MSDS for acetone directly. It would actually be an excellent idea to find and read the MSDS for all the chemicals you use during 3D printing.
Safety Equipment

Wear safety clothing! Acetone requires that you wear protective gloves, protective eyewear, and a respirator (to protect your airway). It is also highly recommended to wear protective (ideally also chemically resistant) clothing (like a smock or an apron). These safety clothes are recommended because acetone is a toxic substance which can absorb through the skin and walls of the lungs directly. Make sure to verify the gloves are made of a substance which blocks acetone absorption, also, verify that your respirator is rated to protect against acetone (many respirators are not capable of blocking acetone due to it's volatility).
Possess, prepare and understand how to use an eyewash station, a fire blanket, a fire extinguisher (rated for chemical fires), a chemical shower/dousing system and other standard laboratory safety equipment. Posting warning signs along the entrances and exits to the work area about working with a volatile, flammable and explosive gas is also recommended.
Keep an inert absorption media readily available to cleanup spills should you accidentally fail to avoid a spill. Diatomaceous earth, silica/sand and activated charcoal are all potential absorption media. Should you have a large spill or not possess absorption media (which should not happen - always verify safety equipment is present and working before handling chemicals!) then you may also dilute the spill with water and mop up the dilute solution of acetone. No matter which method you use to cleanup a spill remember to dispose of the contaminated cleanup materials according to the requirements/laws of your local area. Do not lazily dispose of the acetone down the drain without doing research on the correct disposal methods!

Control Your Environment

Ensure proper ventilation of your workspace (ventilation is required in addition to your respirator due to explosion/fire risk). If the atmospheric concentration of acetone becomes too high the risk for fires and explosions quickly becomes unacceptable (the risk is never going to be zero working with acetone unfortunately, but minimizing it is very important). Working outside is the perfect way to insure the ventilation is adequate, although that presents it's own problems and considerations. Alternatives include using a fume hood, or even something as simple as a fan blowing air through an open window.
Eliminate any and all sources of flame or spark for a considerable area around all sources of acetone (10-15 meters minimum). Take special precautions to prevent being unknowingly contaminated with acetone (which could then be accidentally transported from the work area to a flame source using you as a carrier). Personal contamination can lead to injury if you attempt to smoke during a break or at anytime before verifying you are not contaminated. It is important to provide an ignition-free environment that extends quite far away from the immediate vicinity of the acetone because acetone can ignite a vapor trail of acetone and allow the flame to travel distances via flashing over the vapor trail. Physical isolation is the ideal solution to this dangerous problem. A policy of always closing the door to the acetone work area is an example of physical separation which would hopefully prevent this vapor trail flash-over.
Avoid acetone spills. Acetone is an excellent solvent which could easily eat away the paint on your wall or destroy the finish of your table. Spills also necessitate following special precautions for cleanup and disposal, which have already been provided earlier within this list.

Acetone Chemistry

Do not under any condition mix your acetone with chemicals without an extensive analysis and understanding of the products and the risks associated with the reaction. The following list of chemicals will create an explosive compound/mixture when reacted with acetone, so do not allow them to come into contact with acetone: hydrogen peroxide, acetic acid, nitric acid, nitric acid + sulfuric acid, chromic anydride, chromyl
chloride, nitrosyl chloride, hexachloromelamine, nitrosyl perchlorate, nitryl perchlorate, permonosulfuric acid, thiodiglycol +
hydrogen peroxide, potassium ter-butoxide, sulfur dichloride, 1-methyl-1,3-butadiene, bromoform, carbon, air, chloroform,
thitriazylperchlorate.
Should you accidentally ignite some acetone, you must take additional precautions while evacuating or while attempting to extinguish the fire. Acetone is a hydrocarbon and the reaction of burning it produces products which include carbon monoxide (CO) and carbon dioxide (CO2). Essentially, humans are incapable of detecting these gases with their senses (detectors exist to measure concentration). However, these symptoms of carbon monoxide and carbon dioxide can help alert you to the fact they are present: shortness of breath, blackness along the edges of your vision, confusion, headache, unconsciousness, coma, and finally, death. Carbon monoxide is far more dangerous than carbon dioxide because often the first symptom is unconsciousness, which prevents you from evacuating, leading to death. The dangerous of gas inhalation are substantial enough that as soon as a fire becomes medium-sized you should seriously consider evacuating the area rather than staying to extinguish the fire. It is better to lose property to the fire than to die (if you die I would guess that your property is destroyed anyway!).

Risk Analysis

Acetone is a confirmed developmental toxin for females and a suspected developmental toxin for males as well. The risk of breast milk contamination is unknown, but it is a suspected toxic contaminant. Mutagenic and tetragenic effects are not known. The result of this toxicity is that pregnant or breastfeeding women should not handle or be around acetone (due to vapors) even for short periods of time.
The risk of cancer and the carcinogenic properties for acetone are not well-defined, with some declining to classify acetone as a carcinogen and others classifying it as being carcinogenic. California, for instance, has required that acetone bear a proposition 65 warning about cancer risk.
Acetone is definitely a toxic substance, but it is not highly toxic and accidental ingestion or absorption is essentially incapable of causing severe symptoms. Small exposures to acetone (like the exposure levels likely encountered during 3D printing) are more-or-less not very harmful. However, if you do get a problematic exposure to acetone, contact a poison control center.
The LD50 ("lethal dose 50%", dose where half of subjects die) in rats is 5800 mg/kg, making the predictable (humans are often similar to rats in regards to toxicity) LD50 for an adult human similarly high. With such a high lethal dose, the predicted toxicity of acetone likely causes chronic sub-lethal damage instead of causing an acute and lethal response. If we assume an average adult human (62 kg) shares the LD50 of a rat- that human would need to consume 392 cc of acetone to reach the LD50. 392 cc is nearly equivalent to 4/10 L- meaning that there is essentially no chance the small consumption of acetone caused by working with it could poison an adult human (if our assumptions are correct).
Potential effects of inhalation, ingestion or skin absorption of acetone: dry skin, nausea, vomiting, skin irritation, eye irritation, burning sensation, redness, tearing, inflammation, corneal injury, depression, fatigue, excitement, stupor, insomnia, hypersomnia, ataxia, tremors, dizziness, drowsiness, confusion, headache, muscle weakness, loss of motor coordination, speech abnormalities, narcotic effects, coma, kidney damage, liver damage, brain damage, and death.

The safety precautions you describe are completely unnecessary; you are making acetone out to be far more dangerous than it actually is. Acetone does not cause cancer. Acetone it not an explosion or fire risk given the very small amounts used. The advice to not mix acetone with those specific chemicals is unlikely to be useful to a hobbyist, who will generally not have access to those chemicals. This advice is too generic to be useful to a hobbyist looking to smooth some models. While it is good to be cautious, this answer strongly overstates the risks.

Even if it isn't carcinogenic, Acetone can be absorbed through the skin and lungs and it is toxic to kidneys, the reproductive system, liver and skin. Acetone might cause cancer though, there is no consensus (thus why I said it may cause cancer).
My list was deliberately comprehensive to insure no safety related advice was left off (I don't want to cause someone to be hurt).  Personally, I agree that Acetone is not very dangerous and that using it safely is not very difficult. Please read the MSDS since you've accused me of scaremongering- my list is directly based upon that information.

I changed the answer extensively since the comment left by Tom, so for future reader of the answer/comments, please don't assume Tom is off topic because the things he is talking about are no longer present in the form that he criticized.

Repeated exposure to acetone can lead to the skin becoming sensitised, which means that in the future it will become overly irritated at the slightest contact.
On a more mundane note, it is an excellent degreaser and dries your skin something rotten. And then your fingertips can split and take days or weeks to close up,  hurting in the meantime.

You can smooth a print with acetone using different approaches which require different precautions. In general, you should have ventilated area and use gloves (or wash your hands after the procedure).
Applying Acetone Directly
Using the print in acetone for several seconds or you can apply acetone with a brush. There is a low possibility of fire. See this video, (4) MakerBot Replicator - Model Finishing Tricks - Acetone Wash.
Cold Acetone Vapor
This process takes several hours and gives you best control of the process. Because no external heat is used there is low chance of fire. See this video, Cold Acetone Vapor Finishing for 3D Printing.
Hot Acetone Vapor
This approach takes minutes to smooth the print and there is high chance of ignition. I would never use it inside a building. See this video, Make your 3D Printed parts look professional with Acetone and a Rice cooker! - 2014.


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How to automate printing of multiple parts continuously?
I would like to print multiple parts continuously (non-interactively), so
I can leave the printer alone for a longer time. So after finish, parts could be moved somehow out from the printing area, so the next can start.
Are there any methods of achieving that with standard desktop printers without having to use multiple printers?

3D printing is not a very productive production technique for mass manufacturing (if not the least productive one). Creating several moulds from one master print is an example for a process that's simpler, faster, more stable and likely cheaper process.

Ultimaker once showed a video where they printed bracelets on an exhibition as give aways. They used the print head to push the finished print of of the build platform. It probably was just some custom G-Code,..

What portion of the process are you asking about automation, there can be many steps which require interaction, including: loading filament, selecting model to print, preparation of printing bed, removal of completed prints, and fixing when broken, maintenance, etc. And secondly, what is the purpose of automating this step? Closer to 'mass manufacturing', increased output, decreased maintenance time?

You should look into something like Creality CR-30. Its build plate is a conveyor belt. The prints stick normally when on the flat section near the print head, but upon reaching the roller they peel off and can drop into a collection bin. A decent filament changer can be pre-loaded with 5, 8, 12 spools of filament and set in mode of "continue with next spool" once the previous one is exhausted.

The only thing I can think of off hand is an old mod for the early MakerBot machines. It first was released for the Thing-O'-Matic I believe, but is compatible with Replicator 1 machines (and its knock-offs). Here's the Thingiverse page, but look up Automatic Build Plate.
Essentially, you can use the Replicator G slicing program and there is a setting for "ABP" or Automatic Build Plate. This will basically tell the ABP to run its routine after the controller receives the response that the printing program is done and roll the finished part off the edge of the build plate, then start the same program over again.
Drawbacks:

I don't think it's easily compatible with newer machines/slicers. But, it's open source
Pretty sure you have to use Replicator G, which is outdated now and may make your machine sound like it's going to fall apart (I know from experience)

Going off of @Pete's answer about solenoids. It reminded me that someone integrated a solenoid "ejector" (aka Boxing Glove) for their machine.
Update (06/08/2016):
Forgot to mention that if you choose to create your own "Boxing Glove" or conveyor belt, some software such as Octo-Pi and Repetier-Host allow plugins. So, you could interface with your hardware via customized code and integrate the functionality directly into the slicing application for the full closed loop operation.

The hardware design of the ABP is open source, but the method to use it for 3D printing was patented by Makerbot after they hired on the inventor (Charles Pax) so anyone who wants to use it (or any other conveyor-based build plate) needs to check local patent laws in their country.

An option that might be feasible for some situations (depending on your setup) is Sequential Printing - a feature provided by some slicing software, for instance Slic3r.
In short, this allows you to print multiple objects one at a time rather than simultaneously. This has some obvious benefits, but also some downsides:
Benefits:

Each object is finished individually, and you will therefore not have multiple half-finished prints when something goes wrong.
No particular printer or bed swapping mechanic is needed.

Downsides:

With most consumer printer, print area is somewhat limited, and sequential printing requires you to place objects so that the hot end can move freely between the finished objects, potentially restricting the effective usage of your print volume.
By printing objects one at a time, you limit the natural print cooling that happens when printing multiple objects at the same time. In particular for smaller prints, you might not want to print sequentially unless your print cooling solution is up for it.
Requires some setup

You specifically mention that you would like the finished prints to be moved outside the print area. In it self, sequential printing does not do this for you; however, if you fit your printer with a large, motorized print bed, you might achieve the same effect without moving into unfamiliar technology!

I like the "when something goes wrong" lol Because if you own a home 3D printer, you'll understand!

@tbm0115, indeed! I normally remember to use sequential printing only after failing a multi-print job!

It would be possible and not too terribly difficult to rig a servo or solenoid with a push plate like a plow, on top of your build plate.
However this would require another processor via raspberry pi or arduino to control it. Scripting execution when the print has completed wouldn't be terribly difficult either, but it isn't readily available and certainly isn't part of a mass produced printer.
My issue with the concept is if you push a bunch of prints off the build plate, what guarantee do you have they wont become damaged in the process?

Like this? http://www.thingiverse.com/thing:872617

I've recently seen a video of this being done successfully with almost no hardware modifications to the printer.
Unfortunately I can't find the video itself any more, but the basic idea is to use the print head/gantry to knock the finished prints off the table, likely by adding some custom commands to the end of the sliced G-code. After the print is finished, the bed moves to the Y endstop (this was done on a bedslinger printer), the head is lowered to about half of the parts' height, then the bed is slowly moved so that the part crashes into the head, gets detached and knocked off the table, then the head is lowered even further and sweeps the part away.
The only mechanical modification, namely a sheet of paper stuck to the table's edge, ensures that the part will roll clear of the bed rails, and pushes the pile of finished parts further from the printer once it's off.
In the case of that video there were three parts being printed at a time, so the motion was repeated for each of them, even though most of the time all three got successfully detached by the gantry.
This approach is likely far from universal, and probably only works with parts that are tall enough and have a small enough footprint to easily detach from the bed; I certainly wouldn't try it if the parts have really good bed adhesion and require more than a slight force to pop off. But it looks like if the requirements are satisfied it should be quite effective.
Also it's likely to be problematic on printers with box frames where it's the bed that moves in the Z direction, as the printed parts are likely to get trapped between the bed, print head and printer frame. CoreXY designs where the bed is static and the head moves in all three axes should be fine, however.

I Don't really think that it is possible without hardware modifications, or maybe some small parts that will fit in the bed of the printer all on the same time

Dan - what type of modifications do you believe will best serve the 'automation' process?

For example long foldable bed


text:
Does filament have to be stored in an airtight environment?
For standard ABS and PLA filament, most distributors recommend storing the filament in an airtight bag.  Does not doing this actually make print quality worse?  I have left mine in the open for a year and have had no noticeable problems.

You seem to have answered your own question.

I've heard of issues (more with PLA than ABS, as the PLA is more hygroscopic) when leaving filament out, but like you, haven't had any real issues after having filament sitting out for ~1 year… leads me to wonder if its really worth creating something like this.

It makes a difference where I live, and I'm not in a particularly humid climate (California).  When printing with wet filament, you'll sometimes hear it popping and see steam coming out of the extruder (it's usually only this extreme with nylon).  With most other filaments, when they're wet, the extruded filament will have small bubbles in it and the surface finish of the parts will be rougher, with breaks in the layer lines.  It can also lead to more oozing and stringing.  Air print a few centimeters of filament and look at it closely to see if there's any bubbles, if not, it's probably dry enough.  Whether the filament absorbs enough water to be noticeable in a few hours, in a day, or in a week depends a lot on the filament (and I assume the humidity too).  I'm mostly noticed problems with nylon, ABS, and NinjaFlex, less with PLA and PETG (though I avoid leaving any filament out for more than a day).
If you're not seeing any difference between, then I wouldn't worry about it.  Storing filament dry is a hassle.

Humidity may be the problem.
Humidity tends to degrade filament, making it weaker. If you leave a coil of filament out, over time it will be exposed to humidity. I have yet to hear of this happening over a short period of time - the real threat comes if you leave it out for weeks or months - but it can happen nonetheless.
Contamination with other materials is possible but unlikely. The odds of some sort of impurity developing from nearby particles is extremely low unless the filament is actively exposed to some other material.
In most cases, though, things should be just fine.

In most cases, you should be fine with ABS or PLA out of an airtight container. If you're worried about it, throw a few desiccant packets where you store your filament.
However, some specialty filaments should be stored in an airtight container. PVA is notorious for absorbing the ambient humidity around it. When it's heated, the water it has absorbed starts to form bubbles, completely messing up the extrusion.
In short, some specialty filaments, definitely. With others, it isn't necessary, but it can't hurt.

While it's interesting that PVA is nutritious, I don't think I'll try eating it. I guess you meant notorious and autocorrect got you? I was thinking of using a cheap food storage container with some dessicant thrown in.

@SpehroPefhany nice catch- it's so nutritious that it needs to be stored like food

I haven't had any other issues storing it in the open, but keeping it in an airtight environment (especially if you live in a humid environment) keeps it moisture free, which can effect print quality. Manufacturers recommend this to help keep filament dry.

Normally you should check and follow guidelines provided by filament manufacturer or please contact them for more details. It can vary as not all environments are the same. For example frequent temperature fluctuations can increase chances of making a filament turn brittle.
For example PLA can be easily transfigured at temperature ranging from 55-70°, so it should not be exposed directly under sunlight for an extended durationfaq.
PVA specifically is a water-soluble filament, so keeping it dry is absolutely necessary, because when it gets wet it can become unusable. Therefore when possible, keep them in original packaging (a sealed bag with a dessicant packet) as long as possible.
See: How should I store my filament? at MatterHackers FAQ

authors: ماجد اسماعیل


text:
Would 3d-printed objects outgas in vacuum?
I want to fabricate a sample holder and shadow masks to use in vacuum chambers. The type of printing material is not important to me PLA/ABS/PC-ABS/nylon).
I'm worried that 3d printed objects (FDM) would degas under high vacuum. Is that an actual concern?

Disclaimer: I don't work for these guys.
Take a look at MadeInSpace's 3D printer and materials... They spent a while getting a printer ready for use on the ISS and I know they spent time worrying about outgassing concerns. You might even be able to contact them directly to ask how they solved the problem.

I found much the same question at Does PLA outgas? An answer there pointed to a NASA outgassing database, Outgassing Data for Selecting Spacecraft Materials, and says that:

ABS (unknown supplier), MakerGeeks PET and Makerbot PLA have been measured and are listed in the NASA database.

Poster there recommended PLA for lower outgassing, and clear PLA because there would be fewer additives to complicate the problem.

0.56% total mass lost and 0.01% collected volatile condensable materials. Neat! So the practical answer is that PLA can be used in a vacuum.

Almost all of the FDM materials outgas even at normal atmospheric pressure, and, in fact, most plastics outgas.  Further, FDM and many other printing processes do not guarantee no internal voids - meaning that putting a 3D printed object into a vacuum may result in breakage, cracking, and possible explosion hazards.
For this reason I would focus only on SLA, as the model is printed within the liquid resin pool and should have a reduced possibility of internal voids.
Finding a resin that has a low out-gas rate after curing, though, is still going to be difficult.
For this to be answered more completely, you need to specify your tolerable outgassing rate, and the processes used inside the vacuum chamber.  For instance the answer would be completely different if you are discussing an electron microscope vs a sputtering chamber. As a start you might consider companies that specialize in engineered materials intended for vacuum use. They may be able to provide guidance as to which of their materials might be 3D printed and usable in your setup.

I agree, and also want to bring your 3D design to mind. If you have airpockets in your model, without explosion, you might create an artificial leak in your vacuum chamber. I am not aware if air pockets (however small they might be) are completely avoidable in FDM in general (I also guess this is what Adam says in the second paragraph).

I recently put PLA parts, which had a lot of internal voids due to 30% infill, in a vacuum chamber and depressurized over ~15 seconds. There was no damage or warping at all. I think it's pretty unlikely that internal voids will cause breakage or an explosion -- the total force from 14psi in a tiny void is pretty small. Plus 3D-printed material isn't perfectly airtight, so trapped gases can escape as the chamber is depressurized.

This naturally depends on the ultimate pressure you require. I have made a few tests with LEGO pieces (ABS) in vacuum and reached 10-5 mbar without problems. I did not try to go any lower.
Otherwise, have a look here: A 3D printed beam splitter for polar neutral molecules.
A Formlabs Stereolithography machine was used there, producing a material that basically is PMMA. Pressures in the 10-8 mbar range are possible with that. Recently, Formlabs has presented a resin that produces heatable plastic up to 280°C, and that can be baked to get into the 10-10 mbar range (tested here).

Are you missing a link? (tested here)

You must have a really nice vacuum pump....

At work, I put a 3d ABS part printed via 3d hubs (5*20*30), in the chamber at 1 mbar. No signs of breakage what so ever. No signs of sudden leaks.
Going anywhere below 1mbar, i.e., to 10^-infinity mbar, I think should theoretically still not cause any breakage or sudden leaks, as the expected mechanism of failure depends on the pressure difference; i.e., [1atm-1mbar] ~=[1atm-10^-infinity mbar].
Based on the above I have made some more parts to be put in a chamber at 1E-5 mbar.


text:
What type of plastic can be used to produce your own filament?
I'm considering purchasing Filabot or some similar filament maker.
What kind of plastic can I use to produce my own filament? Can I use any type of plastic or just specific printable filaments? Can I also mix different types of filament together or only one type at a time?

This question seems overly broad. "Can I produce filament from plastic X?" is a better, more focused question than "What plastics can be used to produce filaments?". Moreover, you have 3 separate questions in a single post, it's better to have a single question per post.

While I agree there are too many questions, "Can I produce filament from plastic X?" may not be possible for the OP. Not everyone is familiar with material names. So, in this case, a generalized answer might be acceptable. I don't know, however, if this hinders the scope of the site.

I think this looks like the beginning of a good, general question. But right now, it is not just one, but three questions. I would suggest that the OP would focus on only one question to begin with.

Filament manufacturers (for example, Colorfabb) also sell pellets, price per kilo would be about 10 times less than the same plastic in filament form.
Out of household garbage only ABS can be easily extruded into filament with Filabot-grade machine. PET AKA plastic bottles looks promising as well.
You can also use certain products "off-label". For example, string trimmer string (line) is simply a nylon filament and can be used as-is in modern diameter-agnostic hot end.

This question is rather broad, but your answer is rather narrow. I'm sure far more types of plastic could be used.

the price per kilo would be 1/10th the cost, not ten times less, although this comment may belong in the language SE section.


text:
Is it legal to make a fire weapon with a 3D printer?
Is there any regulation against a 3D printed weapon in the United States or Europe?
Some time ago, I saw an article in Israel where they had one that was not detected by the x-ray and was fully functional!

I'm voting to close this question as off-topic because it belongs to http://law.stackexchange.com/

It also might belong here.

I'm voting to close this question as off-topic because the legality of a 3d printed object doesn't deal with the manufacture of a 3d printed object itself, and can instead be asked at Law

I agree with @TomvanderZanden; a good case could be made for keeping this here. Laws and regulations can be a huge influence on an industry; the allowance or ban of certain products of said industry would seem to be relevant here. Remember, questions can be on-topic on multiple sites.

Related meta post: Are questions involving legal issues and 3D printing on-topic?

Sort of.
Fully plastic guns are banned in the United States by the Undetectable Firearms Act, because they can pass unseen through metal detectors - a huge problem. One way around this is to insert a slip of metal into the gun, thereby making it detectable by metal detectors. 3D-printed guns made of metal - were that possible - would not violate the law.
The UFA was originally enacted in 1988, extended from 2003 to 2013, and then again until 2023. It may seem a bit unnecessary, as all-plastic guns, like the famous Liberator have structural issues that make them extremely difficult to fire when compared to a normal all-metal gun. However, then can be used.
In Europe, gun laws vary widely by country. The European Firearms Directive is the main international agreement on gun laws, but its application varies, and it does not directly address 3D-printed guns.
I'm not aware of a country that has an explicit law banning 3D-printed guns. The only countries that ban them either unintentionally cover them or ban guns altogether.

Many countries in Europe have a blanket ban on all firearms, be it metal, plastic or cheese.

@TomvanderZanden I think I'd have to write a book to cover them all! I'm not familiar with gun bans in Europe (although I don't believe they cover 3D-printed guns), so I think I'll avoid going into detail about them all. But yes, a blanket ban is certainly the simplest.

In Canada, it's illegal to carry a weapon, concealed or not, as defined in Sections 86-93 of the Criminal Code. If a 3D printed object is designed and built to be an imitation of an existing weapon, that is also illegal under Section 85 of the Criminal Code (Obviously, water guns wouldn't be illegal, especially if you buy them at a dollar store). The only exception is when following the Firearms Act. Remember, I'm no lawyer. :)

@Zizouz212 Hm, I didn't know that! Fortunately, the question restricts itself to the US and Europe.

I just did a huge research project and my data goes along with this. If you can detect it with safety equipment, it's legal. One interesting documentary is the Vice 3D printed weapon video on YouTube.


text:
What can I use to "sand" my ABS prints?
I have a 3d printer that uses ABS filament. The software I use will generate vertical supports for my objects before printing that can be easily broken off after they have been used during print to hold sharp angles up that would normally fall.
After breaking off the stints, the print is far from smooth. Is there a material that is best suited for "sanding" down prints without damaging the print?

I have a bunch of solutions to this problem but I'm always looking for additional ideas. I usually start by slicing as much as possible off with a hobby knife. The more than can be removed before sanding the better.
For big prints I like big generic sandpaper sheets from the hardware store. Starting with the highest grit and moving down. Make sure you're discarding your sheets when they get totally gunked up (which can happen pretty fast) or you won't get much done.
For smaller nooks and crannies I have a set of needle files. They do a pretty good job clearing out screw holes and smaller features on printed sculptures.
I've also had some success sanding with my Dremel when it comes to annoying stuck on supports or other imperfections. Having some horsepower behind your sanding can be a nice break. I've also seen the wire brush attachments used for finishing Bronze and Copper-fill prints. Just keep an eye on your speed or you'll sand a hole in your print.
Lastly (and one I haven't tried) are these sanding sticks They were recommended by a friend and look like they would be pretty easy to use/swap out used sandpaper.

Addition to the Dremel: don't overdo the speed, as it might melt the plastic instead.

I use normal wet/dry sandpaper and it works just fine. If I remember correctly, I usually start with 220 and then work my way up to 400, 600, and 800.
There are also foam or rubber sanding pads available that work really well when you're sanding something organically shaped.
The grits you start and finish with will depend on how rough your surface is.

I use nail files. They're easy to get, cheap and have different grits on either side. You can lay them flat or hold them in your hand and they have some stability  making it fairly easy to sand something that is or should become flat.
Plus, you can fix any nails you damage while removing support structures.

Another method that you could try is an acetone vapor bath.
(All credit to them, by the way)
Just so you know, this is a very risky method, but the outcome is very nice. Remember that I warned you... And please, please watch cautionary videos and practice extreme caution. I cannot stress that enough.
All you have to do is get a heating pad (or anything that can heat up to the necessary temperatures) out into a well-ventilated environment.
Then, get a large glass jar that you probably won't need in the future that can fit the 3D Model and pour some acetone inside. Afterward, you should place a small platform inside, just as in the video. Place the jar onto the heating pad. Now, place the 3D Model inside onto the platform.
Now, remember that acetone is a solvent. That means that it basically melts off the details off of the 3D Model. So, if your model is moreover detailed, you should leave the 3D Model in the jar for a small amount of time (i.e. about 30 seconds at most). If your model is not as detailed, you can put it in for a much longer amount of time, such as five minutes. Remember, the longer it is inside, the less the details!
Also, make sure to take the model out without using your hands, as it could possibly be harmful. You could use a wire hanger attached to a piece of tin foil to take it out, just as in the video.
I hope this helps; be safe!
Seriously, exercise EXTREME caution while handling the vapor, as it is incredibly flammable, and can build up in poorly ventilated areas!

This answer overstates the risk of acetone vapor. It's not that bad.

Yeah... But still - better safe than sorry!

There can be problems with acetone dissolving into the ABS object.  I acetone treated a coffee mug (came out nice and smooth!), let it sit for a couple of weeks until it no longer smelled of acetone, and then filled it with hot water.  The inside bubbled as retained acetone boiled away, bubbling out through the ABS.

It should be noted that the suggested methods in other answers all have the following disadvantages:

The vapor just seems to weaken the print to much faster than print smooths.
Sanding melts the plastic pretty easily and just rips the print apart.
Filing helps but leaves blemishes that require the whole print to be sanded and/or painted.

Hi, I flagged this as a comment since it isn't quite an answer in it's own right. There may be other questions on vapour smoothing which this could be an answer to though.

@SeanHoulihane - I've edited it to clarify that this answer is pointing out the disadvantages associated with each of the other solutions provided in the other answers - which I believe was the author's intent (although I might be wrong).

agreed. The formatting makes a difference.

If sanding rips the print apart, you need to fix your layer adhesion.

I normally deburr with a deburring tool:

Then I file if needed, then I hit it with a scotch brite pad:

And then I give it a quick pass with a heat gun to darken all the areas that have turned lighter from the abrasion.
Video showing heat gun (but not scotch brite): https://www.youtube.com/watch?v=0Aj9WCabPgw

Why not add some images of the deburring tool and a scotch brite pad (instead of a link to the manufacturer) to give more body to your answer. I really like the heat gun solution! I do the same with the ABS parasol stand to get rid of the pale oxide color, only I use a weed killer gas fired heat gun :)

I've noticed if I'm printing too close too the bed or if the bed isn't level to nozzle across the whole bed the supports will leave marks on the print where the print was 'smushed' by the nozzle being slightly closer on that side. Also, in Simplify3d you can increase the vertical and horizontal distance between the part and the support, which makes a big difference as far as cleanup, too far though and the support doesn't support. I also increase the speed of support printing, since it directly affects layer adhesion. The faster the speed the less likely to bond to the model.
I use small files for small quick imperfections, and sometimes small knives for stubborn brims. For smoothing I now use a quick acetone dip on my parts. Usually 10-30 seconds completely submerged at most. Then without touching the print (it's very mushy) place it down or hang (outside) to dry out the acetone for about two hours for every hour printed or so. You can handle small parts within 10 minutes if you dipped less than 15 seconds. The acetone evaporates over time and the abs print regains its strength completely once all the acetone is gone. This can take days if it's a big part (maybe 9" x 9") and was dipped in acetone for longer than 30 seconds. If the part smells like acetone, it's still evaporating.
Don't over dip the part in acetone, you can't go back. You don't want to lose the form of your print. You can always dip again. Forget the heat acetone method or cool acetone vapor method that takes hours. Recommend doing it OUTDOORS and perhaps a gas mask and eye protection, acetone is very thin and splashes no matter how careful you are. I tried brushing it on but the results were not very consistent. ABS floats in acetone so consider how your going to get the part submerged and then subsequently out without leaving huge finger prints. Practice on a few small prints or even scrap models and failed prints. Strangely, nobody suggests this method in forums. It's much faster and easier than the other vapor methods. The dry out time isn't fast but you don't have to watch it the whole time.
Always be safe and keep acetone away from any ignition source such as an open flame and ensure proper ventilation. 100% Acetone is used in millions of salons every day, safely. Heating acetone up in an enclosed space has severely injured people so I don't recommend adding any heat source.
Acetone evaporates in water at the same rate as not in water (open air) so I'm going to try mixing water and acetone to slow the smoothing for better control and a larger bath. Even medium sized parts need a good deal of acetone to completely submerge them. Also, you can try doing one side and recording the seconds submerged. Then when it's dried out, dip the other side the same amount of time.
Edit:
Sure! I just did two scrap pieces since you asked. It's very difficult to capture gloss. These were about 15 seconds in acetone rotating them to get even coverage in acetone since the bath wasn't large enough to fully submerge them. This method can leave blemishes but these are warped or failed prints anyway. I enhanced one picture to try to show layer detail.

Maybe you could add some "before" and "after" photo's? (of the same object)

Ok added a few examples


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What is a good way to estimate the impact on material strength different printing methods will have?
I'm going to 3D print a part that needs to meet certain strength requirements, due to its usages. I know how strong a particular plastic (eg. comrpessive/tensile/shear strength) is when dealt with in a solid chunk, but not when it is 3D printed. What is a good way to estimate the change?

I am voting to close this question as "unclear what you're asking" because it does not identify a specific part, specific requirements, a specific printing process, a specific material,... We can not possibly answer this question in a useful way without knowing exactly what you're trying to achieve.

@TomvanderZanden I felt this would be less useful if I mentioned specific technologies. I don't see how this is impossible to answer in general terms.

You need to do a DOE (design of experiments).

It's hard to tell without actually testing the part. There are many ways you can 3D print a part, even on the same machine, that can yield different results.
Here are some tips to help uphold strength requirements:

Identify where your stresses are and avoid allowing the natural "grain" of the print (i.e. each layer) to coincide with the stresses of the part. For example, I just printed a part with hinges today. I set my part up to ensure that the circular profile of the hinge on each layer, instead of having the machine "bridge" the circular profile.
Make your part more solid by increasing the infill. Note that somewhere around 35% won't really provide much more strength than say 50% with a standard infill pattern (i.e. hexagonal, diamond, catfill). However, I would imagine that if a spherical infill pattern was ever designed, that would be the strongest.
An easy way to beef up small areas of a part is to increase your shell variable (how many profile layers for each layer). Again, referencing my hinge design, I made sure that my hinges were completely printed using shell instead of shell/infill.
Don't be afraid to do some post-processing such as adding epoxy/epoxies in high-stress areas.

If it's not an expensive part to print, I would suggest playing with some of these ideas yourself and conduct controlled tests to see what setups work best for your application(s).

"Note that somewhere around 35% won't really provide much more strength than say 50% with a standard infill pattern" - Where did you get that number?  I have always heard that limit is at around 60% and found it in written at least once... but I have not run independent tests to verify the info, so I'd be glad to be corrected if I'm wrong.

That's from some MakerBot reports. I suppose that statement is also dependent upon the size of the part as well. It usually boils down to the size of the "dead space" of each cell in the infill pattern. I believe my comment mostly to parts that fall within a 5"^3 space

"dependent upon the size of the part as well" - Interesting... I have to think about it.  Intuitively I would say "no" as the size only changes the number of the cells in the infill, not their dimension, so - for a sample unit of infill - the density of the material and the orientation of the tensile vectors should remain exactly the same... but I feel I may be well missing something obvious.   Thank you for the quick response anyway! :)

This is a good question, which hadn't received enough researchers' attention. People regularly print different objects, some of them with strength requirements and the need for a method of strength estimation is high.
Good experimental way to estimate the change would be to find a COTS cast plastic object, be it ABS or PLA or whatever, buy 3-5 pieces, then reverse engineer it, copy the design and print it 3-5 times in different orientations. Then you need to start destroying your objects in a manner that coincides with your needs. If your parts would be experiencing compression - crush them, if stretching - tear them apart, and measure the required strength. Then compare and get relative strength, that you can further use in your calculations. You'll notice that adhesion between FDM layers is much weaker than strength of bonds in the layer plane, so you'll have two coefficients - one for Z axis, one for XY (note, that printer settings can heavily affect the result, so every coefficient will be a function of printing parameters). Can't tell 100% reliably, but SLA may have just one coefficient - I hadn't noticed any difference between parts' strength in Z and XY directions.
If you're not a fan of thorough scientific approach, then you can just print your part and test it under your target conditions as much times as necessary. Or make a casting mold, then a solid object.

we also have problems with determining all the effects of weather on prints - high humidity or temperature might have unexpected print strengths.


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How can I set the 1st layer after a raft in Slic3r to print at 1st layer speed
When you add a raft in Slic3r, the first layer of the raft prints at the first layer speed.  After the raft is finished, the first layer of the print prints at the standard speed.  How can I make the first layer of the actual print slow down to the first layer speed?

May I ask why you want to achieve this? Also, are you willing to edit the G-code?

When I print the raft, there is a slight gap between the raft and the print itself for easy removal.  When you print at faster speeds, the adhesion is not enough to even keep the outer parts of the first layer where they were extruded (a circle turns into a hexagon).  Slowing down this part of the print fixes the problem.  I know that I can solve this by editing G-code, or manually slowing the the printers speed on the LCD for that part of the print, but I want a way that can slow down the first layer after the raft specifically in Slic3r.

I see. Very interesting problem! There appears to be a feature for running "post process scripts" in Slic3r. Might be worth having a look at.

This is still work in progress, and here is what I have so far, but first:
A useful alternative for similar problems:
A problem very similar to this would be to use different settings for different parts of a model in Slic3r. For most settings, this can be achieved through modifier meshes.
Post processing scripts:
As far as I know, Slic3r does not give you the option of setting the speed of the first layer after a raft directly, but they do allow you to run post processing scripts; that is, to automatically run a set of operations - programmed by you - on the g-code output.
Although far from trivial, you can in theory make a program that runs through the output g-code, adjusts the settings to your preference, and then saves it again at the target destination.
Tuning overall printer speed through g-code:
As it turns out, there is a simple g-code command that sets the overall speed of your printer's operation:
M220 S[some number]     ; see the link above for compatible firmware

A newsletter from Reprapwold explains that:

For example M220 S50 will reduce the speed to 50%
  of the original sliced G-code. If you want to hurry your print to the finish in time
  for dinner, use M220 S200, to print twice as fast (200%)

In other words, just like some printers allow you the change speed mid-print, you can use the M220 command to override the current speed used, either through a user interface such as PrintRun, or by fiddling with the original g-code itself.
Manipulating the g-code output to adjust speed settings:
The easiest way to achieve our goal would be to manually manipulate the output g-code file through a text editor, and insert our M220 command in appropriate places:

Set M220 S50 just before the first perimeter layer (after the raft's interface layer), to slow down the first layer of the actual model.
Set M220 S100 sometime after the first perimeter layer, to resume the normal speed settings.

In order to do this, though, we need to be able to distinguish these two points in the g-code output.
Distinguishing insertion points:
Slic3r offers a setting under Print Settings -> Output options -> Verbose G-code that - when enabled - inserts written comments all throughout the g-code files generated.
If one inspects a g-code file outputted for a model with raft, one will find the comment:
; move to first perimeter point      <- lets call this A

and
; move to next layer (x)             <- lets call this B

littered several places throughout the gcode.
It is under my impression that the first occurrence of comment A happens right after the raft is finished, and before the actual model is being printed, while the first occurrence of comment B succeeding comment A can be used to set the speed back to normal.
It should be noted, however, that the comments in the output g-code does not seem fully consistent, and I would therefore not recommend anyone to automate this logic into a script without possibly finding other, more reliable breakpoints, and thoroughly verify these through several different models.
I have not looked into the details of writing an automatic script for this task as of yet.

I've played with v1.2.9 only a little bit (I primarily use MakerWare). However, it looks as though you can just go to Print Settings -> Speed -> (Modifiers) First Layer Speed. Here you'll have the option to set the speed in mm/s or %. If you're having issues with the first layer (or two) not adhering very well to a raft, try reducing the distance between the part and the raft. Mine looks to be a default of 0.2mm. This can be adjusted from Print Settings -> Support Material -> (Options for support material and raft) Contact Z distance.
Please note that the closer the part is to the raft, the more likely the part is to sticking to the raft once it cools. So, I would recommend being close by as the part finished so you can quickly remove the raft before it cools with the part. It become especially more difficult with PLA because it becomes hardened during the print process, therefore resulting in a more catastrophic material failure if any part of the object is broken (such as a raft).
I'll also note that I primarily use MakerWare for my machine and v3.8 has made it much easier to apply these types of settings. It's similar to Slic3r's interface and no longer in a JSON file that pops up. Through the MakerWare interface, you can navigate to Settings -> Custom -> Extrusion Speeds -> First Layer to adjust the print speed. You'll also notice that there is a separate option for First Layer Raft that ensures that the two values are separate in the post-processer. I believe it still may be possible to use MakerWare for a non-MakerBot machine, just export the file to GCode and you should be able to load it directly into your machine via SD card or possibly even Slic3r (it might change some of the code though).

You shouldn't need to. The purpose of a slower first layer is to help with need adhesion. With a raft the first layer of the model is printing on the raft so it can go at regular speeds.

When the print is printing though, there is a gap between the 2 lays so the print can be removed.  if you are printing a circle or such, it will be lines instead because it only fully contacts at a few points


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What are the benefits to using 128X microstepping drivers on the X and Y axis of a FFF printer?
Assuming you have a high quality printer with a fast processor, will you see a noticeable improvement by upgrading from 16X/32X microstepping drivers to 64X/128X microstepping drivers? (e.g. smoother surface finish).  In what ways do they perform differently from the more common 16X or 32X stepper drivers.  I'm thinking the RAPS128, Silencioso, and Trinamic drivers vs the DRV8825, A4988 and A4988.

You will likely not see a noticeable improvement by upgrading from a 16x or 32x to a 64x or 128x microstepping driver. Depending on the motors you're driving and the size of the load you could actually see a decrease in quality.
Although microstepping increases theoretical resolution it does not necessarily increase accuracy. The reason is that microstepping significantly limits the incremental torque of the motor. This means that you may ask for a step but not get one because the torque of the step won't be enough to actually turn the shaft.
As an example: a motor running in full steps will have 100% of its rated holding torque. Moving to 16 microsteps/full steps drops this to ~10%, 128 drops it to ~1%.
The practical effect of this is that in high torque situations (such as printing at fast speeds) the motor may end up skipping some of the steps. In this way the increase in resolution can actually lead to a decrease in accuracy (smaller steps but they may not actually be taken).
A relevant calculation to do would be to work out what the different number of microsteps to full steps works out to in terms of horizontal, vertical, or whatever movement the motor drives. You can do this by measuring how far the stepper moves said surface in one revolution provided you know the number of steps it takes per revolution.
Example:
With no microstepping: 1 turn/inch * 200 steps/turn = 200 steps/inch or .005 inch/step (127 micron resolution)
With 16x microstepping: 16 * 200 steps/inch or .0003 inch / step (8 micron resolution)
In this example 128x microstepping would be absolutely foolish. Every situation is different and you should use this information to make a decision based on your setup. Many manufacturers have recommendations on how far their motors can be microstepped.

I think the sentence "As an example: a motor running in full steps will have 100% of its rated holding torque. Moving to 16 micro-steps/full steps drops this to ~10%, 128 drops it to ~1%." misses something important about stepper motors.  A stepper motor torque-vs-position-error curve is like a sin curve.  There is zero torque at zero displacement, and maximum torque at one full-step displacement.  This doesn't change with micro-stepping.  (cont)

Thus, if you are taking 1/128th of a full step, it will truly give you very little torque.  OTOH if you happen to stop, given a full step, at 1/128th of a step in error, you will also have a very small torque toward the correct position.

Prints benefit from higher microstepping in two ways:
Noise level
Using microstepping reduces noise from your printer's operation.
Print quality
Using higher resolution microstepping does not increase the physical accuracy of your prints meaningfully, but it can reduce surface artifacts such as moire.


text:
Do stepper motors require any maintenance?
I've had my printer for almost a year now.
Is there something I should be doing to maintain the motors?

Generally speaking you should never open a stepper motor that you intend to use again - in some of them, the magnets used will be weakened if the motor is disassembled without the use of an iron "keeper".  Further, there's a risk of getting contaminants into the small gap between the rotor and stator.  In theory, there are ways to carefully do a bearing replacement, but it's unlikely to be worth the trouble on a stepper of the sort used in desktop 3d printers.

The stepper motor itself does not.  You may want to inspect the motors for debris or dust.
Depending on your configuration you may want to check on parts of your printer that connect to your stepper motor such as shaft couplings, pulleys, lead screws/threaded rods and belts.  The stepper motor wires should occasionally be inspected for wear and strain.

Checking wires for damage could prevent something worse, but is there really any advantage to checking other parts periodically? I think that such a check is only needed when you notice a deterioration in print quality.

Never hurts to preemptively catch issues. Some of those are easy to check. Others require reviving the bed. I wouldn't bother with those since it would require a calibration again.

Especially with high speed/vibration printers, it's important to inspect screws and nuts periodically, just to ensure they don't shake themselves loose.

No, stepper motors do not require maintenance. They are a brushless kind of motor, so they do not have brushes that need to be replaced.