text:
Which are the food-safe materials and how do I recognize them?
What materials which are commonly used in 3D printing, are food-safe?
Are there any certifications/grading process for such materials, which can help me with my cross-checking and selection?

I have been using an FDM printer.

Consider narrowing down your question by mentioning what type of printer you are working with.

@TomvanderZanden I am using an FDM printer, so is it possible to print such materials with this printer?  If yes, then I would edit my question :)

You should edit your question regardless.

Hello @Dawny33, I noticed your question has been up for a while now. Have any of the answers below been able to solve your question? If so, would you mind accepting the appropriate answer. If not, what is missing so that we may help you further? Also, if you have figured it out on your own, you can always answer and accept your own solution. Thank you.

Related, but for a specific machine and based on certification as food-safe: https://3dprinting.stackexchange.com/questions/6937/ender-3-is-capable-of-food-safe-printing/6941#6941

Food safety is a property of both the process and the material. You can't stick food-safe material in a printer that has previously been used to print something food-dangerous and expect the result to be food safe.
The only way to know if a given material is food-safe is to ask your supplier, but a lot depends on how you then process it. For instance, FDM printers often have brass nozzles, which contain lead. To print food-safe materials, you need to use a stainless steel nozzle.
Food safe materials can be identified by mean of an universal symbol.
Moreover, to ensure food-safety of a 3D printed model you may need to further process it (for instance, by vapor smoothing or coating with a food-safe lacquer). Some claims circulate on the internet that 3D printed models may have surface porosity in which bacteria can grow, but I've not been able to find a reliable source for this claim. Still, you need to be cautious.

Thank you for answering.  Are there any official grading norms by which I can make sure?  (instead of relying on the supplier's words)

From what I have seen, you really can't assume a 3d printed part will be food safe when it comes off the printer, even if you are using a food safe filament.  The best part of this answer is the final paragraph. Use a food safe lacquer, or some other food safe coating.  If the object is fully covered in a food safe lacquer, then it is food safe, regardless of what lies underneath the lacquer.

@ScottLemmon - "regardless of what lies underneath" has a hidden dependency on "provided the think lacquer layer is intact".  I would not trust the lacquer exclusively, I would rather use it as an extra precaution on top of supposedly food-safe material...

@mac, the point is that FDM is not a food safe process (at least with any consumer printers) regardless of the nozzle and filament you use.  You MUST use a sealant of some sort to completely isolate the food from the surface of the print to ensure food safety.  It's not an extra precaution, but a requirement.  This is because FDM is porous, which leaves areas bacteria to thrive, even with the most rigorous of cleaning methods.

@ScottLemmon - People have eaten and drank from wood objects for millennia (which is way more porous, and offer organic material for bacteria, fungi and algae to grow)... and yet most wood species are food safe materials (re: cutting boards). I got what you mean of course, what I meant was that I wouldn't eat from a lead plate even if coated with the most advanced of lacquers! :)

Haha. Point taken. Ideally, every part of the process is food safe.

There are 3 things that might affect food safety of 3D printed objects:

The filament - it's food safe only if it says so on the package (even if the plastic is not toxic you don't know about the color and other additives)
The hotend - the hotend and nozzle may leak metals into the filament, you need something like a full stainless steel hothead.
And finally, 3D printed objects contain little holes that bacteria can get into - so nothing printed on an FDM printer is food safe unless coated with some food safe sealing material (except for single use)

Do you have a source for the 3rd claim? Note that "hot head" is not the usual terminology, "hotend" is more common.

@tom - thank you for the correction. And sources for the 3rd claim: https://blog.pinshape.com/3d-printing-food-safe/ and http://forums.reprap.org/read.php?1,164077,168351

Food Contact Substances
There are regulatory agencies in most developed countries that regulate food containers.  In the USA, the Food and Drug Administration (FDA) regulates Food Contact Substances (FCS) which are materials that come into contact with food during production, manufacturing, storage, packing, and use.
They have many lists of FCS which are either approved for use, generally recognized as safe, regulated, restricted, or otherwise already evaluated and for which they have recommendations.
It is up to the manufacturer to ensure that FCS are safe, so the liability rests with the person making the 3D prints.  If you make something that looks like a cup and could be confused with a cup, you may be responsible for following these guidelines.
US FDA regulation for ABS and PLA
The FDA has an online resource to help guide manufacturers through these lists, Determining the Regulatory Status of Components of a Food Contact Material.
Within this, for instance, you will find the list for materials that are appropriately regulated indirect additive, under which you'll find where polymers are listed, 21 CFR 177.
Part 177, INDIRECT FOOD ADDITIVES: POLYMERS
Notably, PLA is not present in this section, or any other list that I've searched (but a more thorough search may prove productive).
ABS is included here, in section 1020, which I've quoted below. Whether your filament manufacturer is following this ABS formula or not is something you will have to determine for each ABS supplier you use, though. Additives, colorants, and other ingredients may make a specific ABS non food safe, according to the FDA.

§177.1020   Acrylonitrile/butadiene/styrene co-polymer.
  Acrylonitrile/butadiene/styrene copolymer identified in this section
  may be safely used as an article or component of articles intended for
  use with all foods, except those containing alcohol, under conditions
  of use E, F, and G described in table 2 of §176.170(c) of this
  chapter.
(a) Identity. For the purpose of this section, the
  acrylonitrile/butadiene/styrene copolymer consists of:
(1) Eighty-four to eighty-nine parts by weight of a matrix polymer
  containing 73 to 78 parts by weight of acrylonitrile and 22 to 27
  parts by weight of styrene; and
(2) Eleven to sixteen parts by weight of a grafted rubber consisting
  of (i) 8 to 13 parts of butadiene/styrene elastomer containing 72 to
  77 parts by weight of butadiene and 23 to 28 parts by weight of
  styrene and (ii) 3 to 8 parts by weight of a graft polymer having the
  same composition range as the matrix polymer.
(b) Adjuvants. The copolymer identified in paragraph (a) of this
  section may contain adjuvant substances required in its production.
  Such adjuvants may include substances generally recognized as safe in
  food, substances used in accordance with prior sanction, substances
  permitted in this part, and the following:
Substance Limitations 2-Mercapto- ethanol The finished copolymer shall
  contain not more than 100 ppm 2-mercaptoethanol acrylonitrile adduct
  as determined by a method titled “Analysis of Cycopac Resin for
  Residual β-(2-Hydroxyethylmercapto) propionitrile,” which is
  incorporated by reference. Copies are available from the Bureau of
  Foods (HFS-200), Food and Drug Administration, 5100 Paint Branch
  Pkwy., College Park, MD 20740, or available for inspection at the
  National Archives and Records Administration (NARA). For information
  on the availability of this material at NARA, call 202-741-6030, or go
  to:
  http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
  (c) Specifications. (1) Nitrogen content of the copolymer is in the
  range of 16 to 18.5 percent as determined by Micro-Kjeldahl analysis.
(2) Residual acrylonitrile monomer content of the finished copolymer
  articles is not more than 11 parts per million as determined by a gas
  chromatographic method titled “Determination of Residual Acrylonitrile
  and Styrene Monomers-Gas Chromatographic Internal Standard Method,”
  which is incorporated by reference. Copies are available from the
  Center for Food Safety and Applied Nutrition (HFS-200), Food and Drug
  Administration, 5100 Paint Branch Pkwy., College Park, MD 20740, or
  available for inspection at the National Archives and Records
  Administration (NARA). For information on the availability of this
  material at NARA, call 202-741-6030, or go to:
  http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
(d) Extractive limitations. (1) Total nonvolatile extractives not to
  exceed 0.0005 milligram per square inch surface area when the finished
  food contact article is exposed to distilled water, 3 percent acetic
  acid, or n-heptane for 8 days at 120 °F.
(2) The finished food-contact article shall yield not more than 0.0015
  milligram per square inch of acrylonitrile monomer when exposed to
  distilled water and 3 percent acetic acid at 150 °F for 15 days when
  analyzed by a polarographic method titled “Extracted Acrylonitrile by
  Differential Pulse Polarography,” which is incorporated by reference.
  Copies are available from the Center for Food Safety and Applied
  Nutrition (HFS-200), Food and Drug Administration, 5100 Paint Branch
  Pkwy., College Park, MD 20740, or available for inspection at the
  National Archives and Records Administration (NARA). For information
  on the availability of this material at NARA, call 202-741-6030, or go
  to:
  http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
(e) Acrylonitrile copolymers identified in this section shall comply
  with the provisions of §180.22 of this chapter.
(f) Acrylonitrile copolymers identified in this section are not
  authorized to be used to fabricate beverage containers.
[42 FR 14572, Mar. 15, 1977, as amended at 42 FR 48543, Sept. 23,
  1977; 47 FR 11841, Mar. 19, 1982; 54 FR 24897, June 12, 1989]

Regulation globally
The EU has a database for this, though without some industry specific experience it appears difficult to search. For instance, rather than listing ABS as an item, it lists the three monomers that constitute ABS seperately, so you have to read through the Acrylonitrile section, the butadiene section, and the styrene sections seperately to understand the food safety aspects of ABS.
Of course someone has gone to the trouble of parsing all these different regulations in different countries and created a book that summarizes much of what you can glean from individual databases, Global Legislation for Food Contact Materials J S Baughan but it's not an inexpensive resource, and needs constant update so may need to be repurchased each year to keep up with the latest legislation worldwide. It would, however, be a handy reference and starting point for a hack space or library for makers.
Conclusion
Keep in mind that these are regulations formulated by government bodies.  They may have a scientific basis (and hopefully they all do) but they do not replace your own testing and common sense.  Even if you follow these regulations, you may still be liable for any unsafe objects you create.

I have looked at this a lot, both from the standpoint of my own use, and of selling items on Etsy.
As far as I can determine, PLA and ABS are both generally safe.
The FDA lists ABS and PLA as safe plastics for food contact, although some pigments and additives can bring their own problems. ABS is nit generally safe (per the FDA) for contact with alcohol. I don't know why.
So, for my use, I make wine, beer, and cocktail containers from PLA, and coffee mugs from ABS.
PETG softens too much with boiling water and does not work for coffee and tea mugs. I've tried. It fails.
Be careful if you use acetone smoothing on ABS. The acetone enters the ABS, and even after a few days of ambient conditions, the plastic may contain enough acetone to create bubbles in the plastic when the acetone boils off in response to hot water. I had heavily smoothed this particular teacup. Perhaps if it was less exposed to acetone vapors, it may have let the disolved acetone escape faster.
I have used non-smoothed ABS coffee mugs for months without problems.
You will read about brass nozzles contaminating the print with lead. You will read about the ridges being bacterial breading grounds. This may be true.
ABS still makes a fine coffee mug for personal use.


text:
What can cause a sudden and dramatic loss in the inter-layer registration of my prints?
Suddenly, my printer has started producing prints that have a very pronounced layering. Normally, the alignment between layers is very good, and the prints look very smooth. Suddenly, the prints have become much worse and the layers are misaligned with respect to each other.

The part on the left is my "normal" quality, while the part on the right show the deterioration. Here is another picture (in which the good part is on the right):

The parts are both printed with 0.1mm layer height, and identical slicer settings/filament. I am printing on a custom-built FDM printer; the mechanism is roughly similar to that of an Ultimaker.

Can you provide before and after images of the same model, rather than two different models, hopefully with better focus on the ridges themselves?

It appears the heatbreak of my E3D nozzle had worked itself loose from the heatsink, allowing the nozzle to wobble around a bit. Because the nozzle was still tight against the heatbreak I didn't experience any issues with my hotend, but because the heatbreak was slightly loose the nozzle wasn't properly constrained and moving around a bit.
A quick turn to tighten the heatsink back into the heatbreak was enough to fully resolve the issue. My prints are as smooth as ever now.

I would suggest marking this as your answer in case this is happening to someone else. That's something that I wouldn't think to check right away. Glad you figured it out!

There are many factors, here are a few things to check:
I'd first suspect filament feeding.  This type of ridging can be caused by a filament coil that is binding occasionally, or a filament that doesn't have an even diameter or volume per length.  Binding within the filament feeder and feeder tubes can also be a cause. Bubbles in the filament, or sometimes a mismatch between the filament ideal temperature and the head temperature could create results like this, but it probably wouldn't vary so much between the layers.
Next I'd look at the print head.  If it has blockages, or poor temperature control this could result.
Lastly, I'd check the mechanisms - disconnect the motors and see if all the carriages slide smoothly without any binding, particularly the Z axis.  It doesn't look like you're missing steps, but binding here may result in greater backlash, which could result in similar ridges. Make sure any belts and gears are tight.

Nice answer, though you've not correctly identified the issue :p

@TomvanderZanden Is this ABS, and printed in an enclosure with no fans or drafts?

That is correct. The only fan is the one blowing on the cooling fins of the E3D hotend.

As with many topics in 3D printing, there can be many variables that produce this result.
Immediately, your images make me think that the belts on your machine are not tight enough. This can cause noise in every direction of movement and is more prominent in backlash areas. I would suggest going through your general maintenance checklist:

Replace Build Plate tape
Level build plate (An uneven plate or improper height can yield these results as well)
Teach your axis belts
Clean/lube guide rails
Clean drive gears

Keeping up on your maintenance (I do mine about every 5 prints) should reduce noise in your motion and ensure better quality prints, mechanically speaking.
As mentioned above, your results may be caused by your BP being leveled too low (or too high). If your build plate height is off, the filament will not adhere to previous layers very well (if too low) and can cause this back and forth "spaghetti noddle" effect on outer layers. If the build plate is too high, you might see the nozzle physically "spreading" the previous layer around as the nozzle digs into the layer.
Another possible fix for this would be to play with the settings in your slicing engine that involve the order that shell/roof/floor layers are printed. ie Start inside-out or start outside-in.

The first thing I would try is to increase the distance between the nozzle and bed on the first layer through bed leveling or auto probing configuration.

I suppose it could happen either way, high or low. I've mostly seen my machine print like this when its too low. But I've watched it was too high and seen the nozzle dig into the previous layer and spread it around.

@TormodHaugene I changed my explanation a little bit. Thank you for the attention to that detail.

Nice improvements! I think your answer is all around very good.

Have you recently leveled your print bed? By placing the nozzle too close to the bed on the first layer the first layer will seem over extruded. If there are no infill layers after the first layer, these layers will seem over extruded as well since the extra filament will have nowhere to go.
A typical sign of too close bed leveling is that the bottom layers seem over extruded, while layers after regions of infill appear normally extruded.

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sort: votes


text:
Which are the strongest and most durable materials?
I am working on a robotics project and need to print some gears. These will probably by under a LOT of pressure. Which material/filament should I choose so that the gears don't wear off easily?
PS: Newbie here...
EDIT:
According to my instuctor, it has to be some sort of plastic (not metal).
It also has to be lightweight...

What kind of printer are you using?

This question seems primarily opinion-based to me. However, maybe it would be a good question if we made it more specific. Given a few numbers on the expected pressure, and then ask if specific materials can fit the requirement.

'Newbie here'? Just saying, this site is hardly a day old :P

So, as you say you want to materials for printing robotics parts. And as you have not given any budget constraint, I would give you a list of materials which would help you achieve the task, and you can choose amongst them accordingly.

Plastics: Basically used for building prototypes. Nylon Polyamide should be a choice for you.

Polyamide 3D printing is achieved through SLS 3D printing. It offers
  strong and flexible prints. The upside of this material is that the
  printing technology requires minimum preparation of the 3D file before
  printing. There is no need for support. And it also offers the
  possibility to create intricate shapes and moving part in just one go.
  After the print the polyamide can be polished and dyed.

Metals: Metals like Brass, Alumunium and Steel should be a good choice.

But, if I were to achieve your task, I would select carbon fiber. some details about it:

Carbon fiber consists of 90% carbon atoms, each fiber is 10 times
  thinner than a human hair. Carbon is especially prized for its lack of
  combustibility and infusability but also by its incredible strength
  (stronger than steel) and ability to create flexible structure, light
  weight and corrosion resistance. Its melting temperature is 1500, this
  heat there are only carbon.

Yeah... I think carbon fiber might be able to do the job... Thanks!

You can upvote the answer if it helped you, and wait for more answers before you make a choice to accept :)

The segment you quoted applies to pure carbon fiber, but not to carbon fiber filled filament. The parts won't necessarily be stronger (especially in terms of layer bonding) than the plastic resin in which the carbon fiber is only a filler.

@TomvanderZanden Interesting!  What is your take on carbonfiber vs Nylon?   Well, that is sad. Carbon Fiber is meant to be stronger than plastic-based materials, right?

@Dawny33 going to buy a 3d printer tomorrow cuz our old one is spoilt... any recommendations?

@RahulBasu Can't recommend unless you tell us what specs, budget, etc.  And this would make a nice question in the HardwareRecommendations SE :)

@Dawny33 ooohhhh, that's a site? Anyways, budget is USD850, and I have no idea about specs...

Filaments that are intended for making parts that require strange should be rated by the manufacturer for strength and flexibility.
You need to calculate the required strength and then choose a material with higher rating
For example the rating for filaments made by Taulman are at http://www.taulman3d.com/how-to-choose.html?m

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text:
Are there biocompatible materials available to the general public?
I am currently working on parts for a custom prosthesis.
My main concern at the moment is to find biocompatible materials that can be 3D printed from a UP or a Reprap.
The piece would need to be in contact with the skin for extended periods of time, probably around 17 hours a day on average.
The main concerns I have are:

Skin reactions caused by prolonged contact
Skin reactions and bruising caused by friction
Degradation of the materials due to prolonged exposure to skin secretions and sweat
Risks of toxicity in the compounds generated by the aforementioned material degradation

Which materials can you recommend?
Any extensive data (from testing) would be greatly appreciated.

Is there any reason general-purpose plastics (like ABS, PLA) are not suitable for your application? They are used in everything from keyboards, phones, Lego bricks to drinking cups and cutlery. It seems unlikely that skin contact with these plastics could be an issue.

@TomvanderZanden I am concerned about prolonged use and reaction to skin's secretions, but this was unclear in my quesion, I will elaborate. Thanks for the input!

@AdamDavis I see your point. Would yopu feel more comfortable with an edited question stating that this question is about tests, results and observations, but not certifications and medical advice, and should not be taken as such?

There are printers designed for medical use, and the manufacturers supply them with varying levels of certification and testing, however I've not seen a filament manufacturer certify their material as bio-compatible separate from the printer. The printing process changes the material slightly in the best case (and significantly with poor temperature control or badly set parameters), so even if bio-compatible filament were found, the resulting product might not achieve the same level of bio-compatibility.
If your intent is to use hobbyist level machine for medical purposes, you might simply want to use an interface, such as a sock or a molded/cast polymer that you know to be bio-compatible between the printed part and the skin.

I guess it's still a bit early to have certitudes on these questions. Thank you for your input. I will wait to see if there are more answers out there, but ultimately will tinker with the materials myself, and make the results available to the general public.

If you want to know something about what you are questioning, it is interesting to you to read http://e-nable.org/resources/prosthetics-students-consultation/
That's a link with complementary information how to print 3D as a volunteer.
I know that is not enough information about products, but I believe Nylon is the best recommend because it is what generally printers are using, though.
This website supports information with Dr. Chang by the e-mail eagle01@rocketmail.com
but there insnt information about the components used in the prosthetics, but I know that Nylon is the best suited to it nowadays.
If you prefer there is a site with makers loging information about PETG:
https://www.matterhackers.com/news/how-to-succeed-when-printing-with-petg-filament

Hello and welcome to the stack! Please take the [tour]. Link Only answers are not what the stack strives for. E-nable is a well known program about printing external prothetics, but it is done with non-biocompatible materials, as they don't need to be biocompatible.

Your note to the mail of Dr. Chang is nice, but you might want to tell why you tell us polyamide (nylon) is best. You only added more links, tell us their contents

Thanks for your answer but we are looking for comprehensive answers that provide some explanation and context. Very short answers cannot do this, so please [edit] your answer to explain why it is right. Additionally, we prefer answers to be self contained where possible. link only answers are frowned upon (as links tend to rot) & will be rendered useless if the linked-to content disappears. If you add more context and detail from the link, it is more likely that people will find your answer useful.

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text:
Online APIs for 3D printing services
I'm interested in finding online APIs where you could perform a call to some third party service with some print preparation request with my model (i.e. "heal a model" or "set up support") and get in return GCODE file I can send to a 3D printer.
My input will be :

The 3d model (obj, stl)
My printer (makerbot, ultimaker, whatever) or a printer profile
A printing profile

This is opposed to all the classical 3D printing processes we have right now. Currently when printing in a 3D printer you would need to go through these phases:

Create/Download a model
Prepare the model for printing with some 3rd party desktop software
Export the model as gcode
Save the file to some flash drive
Plug the flash drive into the printer
Print the model with the printer interface

I would like to know if this process can be simplified to a point where you can just print your model directly from your web browser without going through all these steps.
I know I'm over simplifying things here, but I would still want to see if solutions like I suggested exist?
Thanks

For instance, an octoprint installation can greatly simplify the process. You can just upload an STL file to your printer, have octoprint handle the slicing and the sending of the gcode to the printer. Does this achieve what you want, or are you looking for something more specific?

One problem is that every printer is slightly different.  2 printers from the same company may heat to slightly different temperatures to print.  Overall you need to get to know your printer to know how it will handle different prints and slice accordingly.

This question is unclear as to its purpose. Are you asking about simplifying your process, or are you asking about online gCode generating tools? If the former, you need to change the question title. If the latter, you should remove the parts about trying to simplify your process, because that has no bearing on online tools.

This workflow might be necessary for home/hobbies printers, which are more or less "open", which has the advantage to choose a slicer of your choice for example. For commercial machines, this does not necessarily hold true. If you sell the whole package, the workflow can be hidden. I'd be surprised if commercial industrial printers do not offer integration with the most common and popular CAD and CAM software. After all, most CNC machines come with a post processor for exactly that purpose.

@TomvanderZanden, I've done already Octoprint on a Raspberry. It's a "poor man solution" since I still had to install Octoprint on some machine (R Pi, PC or whatever) and physically connect that machine to the printer.

@EricJohnson - Of course you are right, but I guess it's a matter of usage - I wouldn't use it for printing engine parts that require special handling but more home usage - stuff you can download from Thingiverse for example. I would expect that for this usage the API will be able to handle this at least for certain printers (if not all)

@MartinCarney - I ask as a developer who wants to add an online web page where a user basically drags and drops a 3D model, chooses some printing properties and gets a gcode file that he can print in his printer directly from his PC without going physically to the printer

@thethirddimension - I totally agree, I'm thinking about the common internet user that got a Makerbot for christmas and has no idea in the mysterious ways of 3D printing. He needs some service where he drags a print model and sends it to the printer, process simplicity should be more important then the quality of the print

There are a few methods to simplify your workflow.  Two solutions are outlined below and both feature a documented API you can use to further customize your workflow.
OctoPrint was mentioned by other users.  OctoPrint will allow you to configure your printer, print profiles and upload STLs for printing from a web interface.  You can configure profiles, slicers and slicer profiles for OctoPrint to use to complete your workflow.
Astroprint offers cloud slicing services in addition to features allowing you to manage printers and print profiles.

OctoPrint is nice but requires a local installation and physically connect the machine to the print.
Astroprint is very nice and closer to what I was thinking about. I'll take a deeper look and share my findings.
I'm not closing this yet, since I want to see if there other solutions like this

So they currently don't provide a developers API (though it looks like they do but I'm getting a 404 page when clicking on 'apps' on this page - https://developer.astroprint.com/dashboard). I'll be sure to follow that

AstroPrint does have an API (it technically also has OctoPrint's API).  I guess the documentation just isn't there.  You can find some of the AstroPrint specific stuff here: https://github.com/AstroPrint/AstroBox/tree/master/src/astroprint/api
Sorry, I thought much of that had already been shimmed up.

WiFi
A few of the newer machines are coming stock with WiFi connectivity such as MakerBot Replicator(s)/Z18, da Vinci Jr., Kudo3D, and some others that I'm forgetting.
However, these WiFi enabled machines essentially emulate what OctoPrint and AstroPrint provide. While wirelessly connecting might save the hassle of not saving a G-Code file to an SD card/Flashdrive, then plugging in said memory device, then selecting the program to run, the wireless solution still requires a slicer to do the work.
Both OctoPrint and AstroPrint allow building up a queue of sliced prints and I know that OctoPrint will even slice a 3D Print-ready model and place it in your queue.
The only application that I'm aware of that seems to reduce the most amount of work is MakerBot Desktop with a MakerBot Replicator/Z18. While MakerBot does not have a great reputation (as of 2016), they have produced some great software. As I understand, here's how you can utilize MakerBot Desktop:
Printing from Thingiverse

Log into Thingiverse from MakerBot Desktop
Find the model you want to print
There should be a handy Print button located in the interface
The software will preview the model. Most models that have been uploaded to Thingiverse will be in print-ready orientation/scaling
Continue by pressing Print
Now the software will slice the model and send the G-Code via USB or WiFi

Really, the only step that MakerBot Desktop skips is downloading the model from your web browser.
There are some rare cases that models found on the internet (such as Thingiverse) will also have the sliced G-Code, but you'll have to be careful to make sure it's the correct flavor for your machine.
Maybe in the future?
Currently, Microsoft is working on a new 3D printing file format called .3MF which theoretically could negate the need to slice a 3D model. I'm assuming that you would need a machine that specifically can interpret the file. This project is still very much in the works and it may be years before we see full support as the format needs to be agreed upon by both software companies like SolidWorks, AutoCAD, Catia, etc. AND the 3D printer manufacturers like MakerBot/Stratasys, 3D Systems, and other big-named companies.
If you combine the benefit of no longer needing to slice a model and WiFi/USB connection, then most of the "manual" work you describe will no longer be necessary.


text:
How do I determine whether a print material is dishwasher, food, and microwave safe?
I would like to print lunch boxes, which I can put into the microwave.
How could I determine, if the print material is appropriate (dishwasher, food, microwave safe)?

You should ask a more specific question, like "Is material X when printed using Y process Z safe"? Attempting to stuff information about all possible materials, processes and types of safety in to one question doesn't seem wise.

I am not familiar with the print materials, so I would like to ask it before I buy one. Btw this is the top voted question in the definition phase. So it is considered a good question by the community.

This is at least three separate questions.

well it won't be food safe because most thermoplastics are porous making it great for harboring bacteria. I'm not sure about the others.

This is a very nice question, with a well define scope and parameters that can be addressed objectively. Expecting "is material X when printed using Y process Z safe?" as a question is an arbitrary expectation: one could object that formulation too is too broad, as it did not ask "...with a nozzle in W material and at temperature T, post-processed with technique Q", for example.  This is a small site, with a tiny community around it.  We should work to make it relevant and helpful.  Comprehensively answering a question like "how to print functional microwave containers" would certainly help...

Although old it seems a legit and relevant question as of today. I vote to reopen. It also got above average (sadly) upvotes on this site.

This is an ancient pre-historic question (from before when the site was formed). None of the issues raised in the comments have been addressed - so it is still too broad and needs a narrower scope. A comprehensive answer would need to be many pages long (i.e. almost a thesis), needing to cover differences for X, Y, Z, W and T (as outlined in mac's comment). The OP has had 7 years to make the edits. Admittedly this could be a good and useful question. Maybe someone (else) should ask a newly formulated question (or series of questions) that addresses all of the issues in the comments.

If someone already has a comprehensive answer that they'd like to post, or an argument for opening (along with a possible proposal for a narrower edit), then maybe this should be raised in meta, as the comments isn't a good place for discussion.

@Greenonline I wanted to find printing materials that are dishwasher, food, microwave safe. Not sure how this question should be narrowed further, and then avoid being closed for "XY problem". Should I create a question for each material I find?

TBH, I really don't know. Maybe, as that is certainly narrower (maybe try and see if it gets closed?).  However, I think asking a question on Meta first, and asking what you've just asked in the comment, is probably a good idea, then you will (hopefully) get a discussion (and feedback) involving the community that could expand upon the reasons mentioned in the comments above -  and hopefully a consensus arrived at. Discussing in comments is not a good place to discuss.


text:
Can I print my own Lego bricks?
Assuming I've 3D design (or I've created one) which looks very similar to Lego bricks, I am allowed to 3D print them for my personal use?
Do I need to obtain some permission to do so, because of some patents? Or how does it work?

I am not sure this is a good question. There seems to be a dislike for law-related issues, and in this case 3D printing seems to have little to do with the issue at hand. There's no difference between this question and "Can I make my own Lego bricks? (using any method)". Votes?

I'm voting to close this question as off-topic because http://meta.3dprinting.stackexchange.com/questions/32/are-questions-involving-legal-issues-and-3d-printing-on-topic

Seriously? This is waaay more a legal question.

I think it's close enough to be ok.

This is all focused on patents, and permission, and I don't see this one as a good legal question.

To the users who would like this question to be reopened. Why do you think it should?

The patents that cover Lego bricks have expired, so you are free to print bricks using the same interlocking system. You are even allowed to offer such prints commercially.
What is not allowed (and a violation of trademark law) is to call them "Lego bricks" or use Lego's logo. "Compatible with Lego" on the other hand, would be fine.


text:
I've exported 3D models from the game, can I print them?
Assuming I've extracted 3D models from a game which I legally bought (such as StarCraft). I am allowed to 3D print them for personal use or give it to close friends?
Is there any general rule, or this suppose to be specified in the license? If so, which section/clause potentially can prevent me from doing that? Or I need to contact the company who owns the game to obtain the permission?

I'm voting to close this question as off-topic because http://meta.3dprinting.stackexchange.com/questions/32/are-questions-involving-legal-issues-and-3d-printing-on-topic?cb=1

No. Such figures are generally covered by copyright, which means that nobody but the copyright holder is allowed to (re-)produce copies of the work. Copyright also covers personal use. In the US there are limited fair use exceptions but they do not apply here.
The only way to do this legally is if it is specifically authorized in a license or if you get permission.


text:
How to print edible food?
I would like to print edible cookies or ornamentation for a cake.
Is printing with edible materials achievable by standard thermoplastic-like 3D desktop printer? Or you need to buy a special printer to do that?

Good question, but I would leave the printer recommendation out of it since that is a purely subjective matter.

You cannot print edible models using a "standard" consumer 3D printer without first installing an "hot end" capable of depositing edible - normally thicker - substances as well as a suitable extruder mechanism.
However, there are not necessarily any technical limitations in the electronics, software, slicers etc. in a typical printer that wouldn't allow you to install such an upgrade. For instance, you could calibrate your extrusion rate and nozzle width to suit batter and similar.
Some commercial printers, such as the DeltaWASP allow for upgrades that print clay, which wouldn't be very different from printing liquid food.

You can, but that doesn't mean it's very easy.
You don't have to buy a special printer, but you need a special extruder (such as http://www.structur3d.io/). Most of these systems can print anything with the consistency of Nutella. However, many parts of the printer may not be food safe.
Another option (if you simply want 2d designs) is something like the PancakeBot. It can probably also "print" with anything that has the same consistency of pancake batter.

MakerBot Industries had a mod available for their early open source machines called the Frostruder. It was basically a syringe connected to your print head. I saw this in action at the University of Washington a long time ago. Check out the legacy ReplicatorG in action!
I like to relate 3D printing as "A hot glue gun on rails". The beauty is that a lot of the home machines can easily be almost anything on rails.
So, you could always try to 3D print a solution of your own. Please keep in mind any federal regulations on food processing materials (ie ABS is not recommended for most food applications).


text:
Printing copyrighted objects as a print shop for a customer
If a person is running a print shop where there are given STL files by customers, and they print the part for them, does the legality of the printed object matter?  The customer would be supplying the file so the print shop would not know if it was legally obtained (or even what the object is).  Could the print shop get in trouble with the law for this?

I'm voting to close this question as off-topic because http://meta.3dprinting.stackexchange.com/questions/32/are-questions-involving-legal-issues-and-3d-printing-on-topic?cb=1

I might also put this site on the Legal stack exchange site because of the cross over, but I don't believe it to be off topic or irrelevant.

There are two aspects to this question that probably should be addressed separately.  This is not legal advice and I'm not a lawyer, so consult with an experienced IP attorney.
Copyright law may apply, and other IP laws, such as patents and trademarks, may apply.  They each have different requirements and restrictions.
Notably, IP law varies from country to country.  WIPO has made significant inroads into regularizing IP law across many countries, but this answer will still focus on a US-centric reading of US IP law.
Copyright law
It's already established that printed works, such as photographs, texts, and similar works will result in prosecution against the person and the company that the person outsourced the copying of the copyrighted work to.  Attempt to copy a book or copyrighted photo at a paper copy shop and they will typically refuse to reduce their liability.
Even if you show that you have rights to the work, through educational use laws, for instance, they may still refuse because they may be putting themselves in danger of a lawsuit by a particularly aggressive copyright holder.
This applies to 3D printing shops in a similar manner.  If you don't know the source of the 3D model, and that the person has a right to the model, you may find yourself liable for copyright infringement.  Even if you are sure, a lawsuit can financially ruin your business if it comes from a large corporation.
Patents
Patents apply even if you were unaware of them.  So any model you print that contains patented techniques, technology, or concepts may also pull you, as the print shop, into a lawsuit for patent infringement.
Reducing liability
A suitable contract with the person requesting the 3D print, as written by an IP lawyer, may reduce, but not eliminate, your liability. It won't completely absolve you of all responsibility, but may reduce your exposure to such lawsuits, and give you some leverage in court should someone prosecute you.


text:
Can you use PLA material with food and drinks?
I would like to print fancy plastic cutlery sets or plastic glasses.
Is it safe to do it? Or bad for your health, if so, why?

There is one brand that I know of that is undergoing FDA approval in the US. Other than that, I believe there are none.

As others have pointed out, PLA isn't specifically not food safe, but materials that have been printed previously can contaminate the PLA.
Additionally, anything 3D printed is extremely porous. Once a part is used for food, moisture and bacteria will accumulate in the pores, and can never be completely cleaned out, contaminating any food that contacts it. It can't be sterilized either, because the temperatures needed for sterilization would deform or melt the plastic.

I've also heard that while PLA and ABS might be fine, the pigment inside them used to give them some color might be dangerous, because you never know, what it is.

One alternative I've heard of to combat this problem is dipping the entire part in a food-safe polyurethane varnish, thick enough to block all food contact with the actual material. I have no idea if this is safe, but I've heard of it.

Regardless of whether the actual filament you are printing is marked as Food Safe by the provider, remember that actually printing the filament might contaminate it.
If you previously have printed a toxic filament on your printer, you cannot be sure no remains of that filament are deposited onto the model. Equally, I believe very few printers only consist of parts that are all marked as Food Safe - the parts that touch the filament that is.
Another aspect of food safety is your ability to properly clean 3D printed objects. Due to the highly structured surface of 3D printed objects, I would not be certain that they are truly clean after washing, particularly since many plastics cannot be cleaned in a dishwasher.

Related to this, the dyes in PLA are not always as non-toxic as the PLA itself, and it may be difficult or impossible to obtain a full list of ingredients for any given bundle of filament.

Having performed a quick search through all the resources at the FDA Food Contact Substance resource, I cannot find PLA in any list except an occasional notification that a specific manufacturer has obtained approval for use in specific circumstances, with the notice that such notifications are only valid for that manufacturer and cannot be used to validate another use of a substance.
There are companies that have received approval for their specific formulation and use of PLA as a food contact substance.  You may wish to discuss this further with your material supplier to find out if they have approved PLA product available.
Without specific product approval, though, PLA is not on the lists of generally recognized as safe, nor approved for food contact use.
Regulations in other countries may differ, so you may want to search the EU directives, for instance, to find out their opinion on PLA as an FCS.


text:
Why do some models appear broken in slicing software?
In my slicing software (Slic3r) some of the vertices/walls of my model seem to have disappeared, so that the inside of the model - which should be solid - is visible, while the surface appears as a thin shell.
Why does this happen? Is it still safe to export the model for printing?

My understanding is that this occurs when the object is not a true solid. Since an STL holds the triangulation of each face and spline, the slicing engine is not "smart" enough to determine if there is a gap in the model and therefore if it should be filled in and how. When the slicer encounters a gap, it will either treat the endpoint as the end of the feature or navigate to the next point on the layer, resulting in either gaps in the print or extra inclusions that don't make sense.
I've noticed that my models will fail as a true solid when I use complex solid tools such as Union, Subtract, and Trim. A lot of times there will be a rounding error in how these tools interact with the solid model that will result in a small (sometimes not very small) gap in the outer shell of the solid model. When exported to an STL, the gap is retained.
@kareem mentioned it in their answer, but Microsoft does provide online tool(s) for 3D Printing including a solid repair tool. Use Microsoft 3D Tools to upload your STL and try to automatically detect and fix issues with your file(s).

rounding error That explains a lot. I often have to add or subtract a tiny fudge factor (eg 0.001 mm) when I'm using OpenSCAD to make it unambiguous when two faces or lines would otherwise coincide. Now I know why I need to do that and why it works.

It's been a while since I've had some better CAD tools available, but I think there's an inverse correlation between price of the CAD software and how often this error occurs lol I mostly use the free version of Sketchup and this happens almost every time. I ended up downloading solid checking plugins to avoid bad prints.

Another service I use is Autodesk Netfabb at https://service.netfabb.com/

Some STLs aren't exported properly from the CAD software.
Use a repair tool or service like https://modelrepair.azurewebsites.net .
The repaired STL shouldn't have those issues anymore.

This doesn't seem to answer the "why".

That's getting into the inner workings of CAD tool export logic, which I don't know. My response to 'why' was high level and sufficient for practical purposes.

Honestly, I feel like this is not the kind of quality that we want here, especially at this time. Could you improve your answer, and add more detail? You're probably better off to have this as a comment. -1

Thank you! I had a model that was driving me insane and this site fixed it perfectly.

In the cad software, it could be that your normals are reversed or inconsistent. Recently I used Cinema4D to export some models, and the faces were acting super weird in the slicer.
What I mean by 'reversed normals' is that your polygon faces could be oriented inward. Some slicing softwares don't care about that, and treat both sides of each face equally. In those that observe reverse normals, faces may be completely invisible, or appear with a lack of shading or strange shading.
There should be tools in your cad software to align the normals, or flip them on each face at least. Alternatively, some tools like MeshLab and Meshixer I believe have tools to fix this. Also of course make sure your model is watertight and that you don't have too many errors like duplicate vertices, faces, etc.

Had similar problems with blender <-> Slic3r, modified a stl in blender then slic3r started acting up, showing strange faces where it shouldn't.
The solution was (as suggested by @tbm0115) to solidify the exported object.
Just add a Solidify modifier to the object(no need to apply), and when exporting to stl make sure to check the "Apply modifiers".


text:
What criteria do I need to be aware of when buying a 3D printer for personal use?
I'm interested in designing & 3D printing as a hobby (e.g. printing chess sets, small toys for family etc.)
Conducting a Google search has brought up a range of small, cheap printers, but beyond that I don't know how to differentiate them.
E.g. selling points include:

"liquid light-sensitive resin"
"partially assembled" with "very few parts and minor configuration"
"Wi-Fi enabled"

My question is, which features are going to benefit a small-scale, new enthusiast to 3D printing?
PS. The software I intend to use is Windows 10 3D design
PPS. I'm not a graphic designer by any means, just a new enthusiast.

I am not sure that this is a good question. Perhaps you should ask about the significance of a specific feature rather than requesting a list of all possible options?

I was in your shoes a few years back, and I strongly recommend against buying a 3D printer as a completely new enthusiast. If possible, I would suggest joining a FabLab near you to give it a try on a rented machine before buying.

When I started researching what machine to buy, I tried to absorb as much information as possible...  Luckily here in London, we have iMakr, and they run free weekly courses and information sessions.  If you are not near enough to London or NY, try hooking up on 3DHubs.com, they have a really helpful forum.

Thanks @SilverQuettier for mentioning FabLabs. I hadn't heard of them before (well, as a new enthusiast I haven't heard of much yet...), but there are some near to me (Leeds, UK)

First Questions you need to answer are:

Fused plastic filament extrusion or Cured Resin?
Fused plastic is easier and cheaper to start with.  Resin is slower and more expensive...

What size things do you want to make.
Most medium size printers will print something the size of a shoe.  For small things and parts that fit together, this will be ok.
If you want to print full masks or lampshades in single pieces, you will need larger.  (larger = more expensive).

Budget.
This will help with the question of kit version over complete machine.

Checkout imakr.com for prices in UK and US.

First off, decide on the price range of your printer, then build space and specifications but also more importantly if the printer is UI friendly.

Here are few things to consider from my point of view

Printing technology
The first thing that you need to take into account is printing technology. The most common[citation needed] right now is Fused Filament Fabrication. "Liquid light-sensitive resin" is being used in Stereolitography and Digital Light Processing - the SLA printers I found are less common and more expensive than FFF ones.

Price
Need to decide on budget. You can buy printer for 60k USD and 400 USD. Quality is somehow linked to price but that's not a rule. You can buy a shitty printer for a lot of money.

Printing area
Bigger allows you to print bigger things. You need to ask yourself how big things you really want to print. Remember that 3d printing is quite slow process - how often you will want to print big things that will take 60hrs+ to finish?

Printing materials
What kind of materials you want to print with? Some materials will need higher temperatures so check the max hot-end temperature, some will require heated bed.

Assembled or DIY kit
You can usually get kits for self-assembly cheaper than Ready-To-Print machines. However, it will require additional skills (i.e. soldering), tools and time to assemble. I am not sure if I would buy DIY kit for commercial use, but as an enthusiast I immensely enjoyed putting my Rostock Max together.

Reviews and reputation
It is generally safe to buy printer that already has some users. Beware of new magical Kickstarter printers which will "change the 3d printing forever".
Reddit /r/3dprinting suggests that your new printer should meet 3 criteria:

Printer passes the youtube test - has lots of youtube evidence that this particular printer is working.
Printer is out of the pre-order phase. This means that all pre-orders have been delivered.
Printer has a reputation of working well among current users.

I found it to be a very good set of rules.

Upgrade capabilities
That's very user-dependent, but this point is very important to me. I want to be able to change and improve certain parts of my printer. Check if you can switch the extruder, replace the hot-end etc.

Support
I think one of the most important points. See if you can find a forum for your printer and how active community is. It will be immensely helpful if something goes wrong (and it will).
Also, company support is very important. What will happen if you need a replacement part or your printer will stop working altogether?

This list is definitely not complete.
There are many more things that might be taken into account like configuration (delta or XY), multiple extruders, closed cases etc.

I think the list of masteusz is a good one but before you can decide on what you need you have to get a better understanding of how 3D printing works, like Silver Quettier said. Please be aware that printing a object is yet not as easy as printing on paper. The machines that print 3D are more like industrial machines than that they are like your inkjet printer at home.
For the curious beginner I would suggest to  first concentrate on modelling and printing technique.
Modeling
You can of course download things from ThingyVerse or YouMagine but you might be more interested in making things than printing them. I don't know Windows 10 3D design. I personally find Sketchup Modeling software a good entry-point because they have a large set of video tutorials and while you learn you can add more complicated extensions to the program. There are also extensions that help you make your model 'watertight' and 'ready for print'.
Of course you can find heaps of tutorials on Youtube for other modeling software like freeCAD or Fusion but you might find it a bit overwhelming.
Printing
As suggested in the comments, you could start with letting your objects print by others. It's worth to set aside a small budget for that.
They easiest to design for is SLS printing. You don't have to worry about overhangs etc. Buying a SLS printer is not an option but you can have it print at multiple printingfarms like Shapeways.
You soon enough find out that making a print 'light' and hollow will save a lot of cash. Shapeways will tell you if there is anything wrong with your design too.
A bit harder is FDM printing where layers of threads are stacked. Because overhangs need support, most of the time extra plastic is printed that has to be removed later.  Plastic is not expensive and insides can be printed hollow, so cost is not so much a thing you have to worry about when designing.
On 3Dhubs you can find experienced people who own a printer and want to print for you. They can tell you what is printable and what not. If you have a hub near you this is a good option to get familiar with the technique.
If you did that a couple of times you can decide to go to a fablab or makerspace where you lent/rent a printer. Make yourself familiar with slicing software like Cura before you go. There are many settings like for filling the space in the object and for making support for parts that 'hang in the air'.
When you buy a printer you probably print mostly with PLA and ABS and all printers can print that.
Even when you own a printer you might sometimes want to print a part at Shapeways because of the material options or to make something that is impossible to print.
3DHubs gives you the possibility to experiment with a large range of printer and materials. Print quality though is often influenced by the experience level of the person printing it so don't deside what printer to buy on these results. 3DHubs has a good printer-guide.
On the other hand, having a printer yourself makes it a lot easier and more fun to print objects you have downloaded. Also, making something, seeing the result and then adjusting it, is a more organic way to learn and create designs.
Welcome to 3D printing ;)

The number one most important thing about a 3-d printer is the Extruder/PrintHead component.  If these are buggy, the printer is worthless.  Seems like most printers are pretty good with everything else.  The place that they die is in the Extruder/Print Head assembly.
The second most important thing is quality of the plastic parts.  One nice thing about that is you can usually reprint the plastic parts by going to thingiverse.com and downloading them.
So, I'm on my 2nd printer.  I returned the first one to amazon and may very well return the second one.  It is a frustrating game.  On thing I notice is that VERY FEW printers have a LOT of ratings.  Some might have 4 stars, but only 8 votes...  The latest one I have had 200+ votes but a 3.5 rating.  If you have 200+ votes and anything below 4.2, you've got an inconsistent and potentially crappy product.
So, to sum up, Get details on the extruder.  Does it cool properly, is the design such that the filament is properly driven and pushed?  Is the hot head the only hot part, or is the tube getting heated too.  Does the extruder throat near the hot head have a Teflon tube inside it?
Read the ratings on Amazon, read the bad reviews and then look at the pictures of the product to verify them.
Best of luck.. I'm about to return #2 printer and perhaps part out #3.  Not quite sure yet..

One of the biggest questions you should ask yourself is: What is your end goal?

Is it to get your printer and immediately print something (pre-assembled).
Is it to learn about 3d printing by constructing a kit, encountering all kinds of potential issues getting it working, then once it is working getting everything all dialed in and then getting good prints.

The 2nd option requires less initial investment but may take considerable time and frustration. (I did this 6 months ago)


text:
Tips for not burning out my Arduino Mega or catching something on fire when wiring a Prusa i3?
I'm reading about wiring up the electronic components to my Prusa i3 using an Arduino Mega 2650 and Ramps 1.4.
I have step sticks, a heated bed, and a Switching Power Supply 12v Dc 30a 360w  (more details on that later when I can add which ones to the post).
I've heard that if you wire it wrong and plug it in, you can do anything from starting a fire to burning out your boards.
What are some tips of things to check before plugging it in? Are there any common mistakes that I can avoid?

I've actually got this question elsewhere too (http://arduino.stackexchange.com/questions/18810/tips-for-not-burning-out-my-ardunio-mega-or-catching-something-on-fire-when-wiri), but I was planning on using a different power supply at that point, so do with it what you will...

Not really an answer, but ALWAYS DOUBLE CHECK all wiring before plugging anything in.

Polarity matters, sometimes. Be especially mindful of the wires from your power supply to the board, as getting those the wrong way around will definitely cause damage. Heated beds and extruders are not polarity sensitive, and can go in either way. Fans are polarized, but will probably survive if you get them backwards - they just won't run. Stepper motors don't care about polarity, flipping the connector around just makes them run backwards.
Take special care with endstops. The endstop connectors have 3 pins (VCC, 5V and signal), endstops with 2 pins are usually connect to GND and signal. Putting a 2-pin endstop across 5V and GND will destroy the 5V regulator.
A common cause of damage is wires not being clamped in their respective terminals properly. The offending wire will arc, melting and destroying the connector. Tighten down screw terminals properly, use proper crimps if you have them. Soldering the ends of wires going into screw terminals is not encouraged, but if you do solder the ends then make sure to check after a while and tighten the screws again.
Put the stepper drivers in the right way around.
For things like the heated bed and wires going to your power supply, use sufficiently thick wires. Especially with the heated bed, a lot of current flows through the wires and flimsy wires will heat up and melt.

Good points! Why would soldering wire-ends going into screw terminals not be encourage? I always do that to avoid loose strands that could slip out and short... Though I agree that one should re-tighten.

http://reprap.org/wiki/Wire_termination_for_screw_terminals

@TextGeek use a cable-end sleeve (ferrule) instead.

@TomvanderZanden My endstops for some reason have 4 connectors! http://3dprinting.stackexchange.com/questions/1478/connecting-sain-smart-mechanical-end-stops-to-ramps-1-4

Putting a 2-pin endstop across 5V and GND will destroy the 5V regulator.

I think I've done this... at least I made some magic smoke. Would the regulator be on the arduino or Ramps board? How to test if it is dead? Thanks.

@Lemmy It's on the Arduino board. To test: apply 9-12V across GND and VIN of the Arduino, measure whether you see 5V across GND and 5V. If you see anything other than 5V, it's dead.

I'd say polarity and voltage are the biggest things -- about all you can do is double- and triple-check everything; then check again....
Be very careful about where you feed in 12V power (mainly for heaters and fans), vs. 5v (for the Arduino).
In many cases I found it unclear which way +/- went going out from the board (the inputs on my boards were at least marked clearly!). I found that if I plug in a limit switch connector backwards, that connects 5v straight to ground, which will probably make your power supply cut out (assuming it's properly protected -- otherwise it could potentially catch fire). Stepper motors, on the other hand, just run the wrong direction if you plug them onto RAMPS backwards (good design!).
Another thing to watch for only comes up if you're powering the Arduino via USB (I do that a lot, since I'm plugged in anyway to send files and such). A short can try to draw too much power from USB. In that case my Mac shuts down USB and gives a message; I don't know what would happen with other hardware.
I have heard that plugging a stepper-driver board onto RAMPS backwards is likely to fry a board, and that plugging or unplugging a stepper motor while powered is also risky. But I haven't messed those up yet, so I don't now for sure. :)
I may be overly cautious, but I never leave the power supply plugged in when I'm not around.
Best wishes!
Steve

Adding to the other answers:

ALWAYS power-off the printer completely and make sure it is not receiving any power from any source (could be receiving power from USB after you turned the power supply off).
Avoid loose wires, and before powering the printer on make sure every wire is connected in the right place. Loose wires can cause damage even if not powered if they get under the PCBs, where they can cause shorts. I fried an Arduino Mega this way.
Never mix between 12v and 5v supply/output wires. Connecting an output wire of the wrong voltage will usually cause damage only to the part receiving power, while connecting a supply wire of the wrong voltage can cause severe damage to many components at once.
Keep all wires organised. That will help you understand which wire is connected to what quickly, and will help you do what is mentioned in #2 and #3.


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How do I do multi-colour printing?
Printer: FDM printer  (FDM == Fusion Deposition Modelling).
Raw Material: Thermoplastics.
How do I do multicolor printing? What changes should I make to the printing process/to the raw material used?
(Answer in the context of printing a basic 3X3 Rubix cube)

Bonus: What are the best practises while doing multi-colour printing?   (<-- This is opinion based and/or broad, so pl add an answer to this point as an extra to your answers if you can. It would greatly help people getting started/practising with multi-colour printing)

Possible duplicate of Multi-color printing with MakerBot-like 3D printer?

@kenorb I understand that mine is similar to the one you have pointed to, but mine is more specific about the printer and the material, so it should not be closed as a duplicate the that question IMHO :)

If you think so, fine, I retracted my close vote.

Though in the context of a Rubik's cube, it's all one color, and it has stickers instead.

If it doesn't have to be printed in multiple colors, some people use cheap model paints to paint parts.

@DanielM. Yeah, I get it.  I just used it as an example!  (Seems like I've taken a bad example for my question :) )

There are a few different approaches I've seen which you could look into.
The easiest and most common is multiple extruders, each with a different color of thermoplastic. Tools like Pronterface and Slic3r have built-in support for multiple extruders. With multiple extruders you can get one color per extruder; there's no clear way to mix colors and get a color between the input materials' colors.
Another, more complicated approach is to use a single extruder with three inputs, like this one, where thermoplastic from the three inputs can be mixed in varying amounts to get color gradients between the input colors. With red, yellow, and blue filament, you could get a rainbow of colors...albeit without any control over value (white to black) or saturation (bright vs dull color).

Additionally, some printers will allow you to Pause a print, unload the filament, load new filament, the Resume the print. While tedious and error-prone, if you really wanted to get a multi-color print without separate parts, this might get the job done.

@Jeff - that's a good point and you should post that as an answer.

Here are the methods of printing with multiple colors that I'm aware of (from the most common to the rarest):

Print each color separately and the assembly/glue them together - this isn't technically multicolor printing but this I the most common solution since most printers aren't multi-color
Multiple extruders, one for each color - this is by far the easiest and mot common multi-color setup, but it won't help with a rubic cube because I don't think its practical to build a printer with 6 extruders
The multi color hotend from @MartinCarney answer that feed multiple filaments into a single nozzle - I really don't know anything about those hotends
Last, there's a trick you can use that stops in mid-print and let you swap filament, more information in this youtube video, but this also won't help with a rubic cube because you can't use different colors in the same layer

I would like to add #5, which is similar to #4 in that it involved pausing and swapping filaments. Prepare the print as if you have multiple extruders, but replace the tool-change gcode with gcode to move aware from the print and pause. This can accomplish a color change within a layer. This would be extremely tedious and impractical for a full-color print like a Rubik's Cube due to the number of swaps. I've found very little about this online, but with a little experimenting I was able to accomplish it with a design that limited the changes to just a few layers.

Design a product in such a way that it has different heights that can be seen in one plane.
By using direct drive extrusion we can easily change the material of different colours with out pausing the print to obtain colour print.

If you are trying to print something like a Rubic's Cube in the correct colors without using paint or stickers, there are only a couple of options.
Assuming that you are using a printer with only a single extruder and no fancy gadgets, you will need to print each color cube you will need to print in a lot of pieces and then put them together. You can't use tricks like changing the filament manually at a certain level for most of the cubes because most of the cubes are corner cubes with 3 colors.
Assuming that you have some sort of multi-material system, then you just use STL files that are made with the proper colors. And I'm talking any sort of multi-material system, including multiple extruders, the fancy extruder described by @Martin Carney, or the MMS from prusia3d.com which has 4 inputs to a single extruder with the disadvantage of no mixing and having to automatically waste filament when changing colors.
There is another system used by the da Vinchi Full Color 3d Printer which sprays ink onto the filament as its printing.
Since the standard STL file doesn't have color definitions, the normal thing to do is to break up the original file into several STL files each with their own color. This requires Meshmixer or a 3d modeling program.
I've done a lot of research on this, but haven't had a chance to try yet because my Original Prusia 3d and its Multi-Material kit haven't arrived yet. :(


text:
How can I calculate volumetric speed for Slic3r auto speed?
I have noticed that Slic3r offers a speed setting called "auto speed" meant to give a constant filament pressure at the extruder, which I believe could eliminate filament grinding issues at higher printing speeds.
According to the tooltip in Slic3r, auto speed is calculated from two parameters:

Maximum speed
Maximum volumetric speed

Maximum speed speaks for itself, but how can I calculate the maximum volumetric speed of my print?

Auto speed is calculated from maximum volumetric speed in mm3 per second. If you normally print at 80 mm/s, your extrusion width is 0.5 mm and you are printing 0.2mm high layers, your volumetric speed would be 80 * 0.5 * 0.2 = 8 mm3/s, which is the volume of plastic extruded by your printer every second when printing at that speed (not accounting for any die swell).

You are right about the terms: I have updated the post to reflect this. I also found a blog post discussing the math in context of extrusion width, for those interested: http://www.extrudable.me/2013/11/03/slic3r-strange-defaults-causing-qu-bd-woes/

Technically not an answer... he asked for the maximum one, you gave him how to calculate the "usual one" he already tested.

There's no fixed maximum volumetric speed that works for everyone, there's simply too much variables to account for.
By using @Ian Williams explanation you can convert from volumetric to regular speeds but you still need to test what speed works best for your setup.
Just a few of the other variables affecting how fast material can come out consistently: temperature (nozzle & heat brake), extruder motor power, path friction between extruder and hotend, material compressibility, fluidity and glass transition temperature, ..
There are interesting topics on RepRap forums, like this one:
http://forums.reprap.org/read.php?262,654085


text:
How to get consistent and accurate readings from thermocouples?
I upgraded to an Mk9 dual extruder, and it came with thermocouples installed instead of the thermistors I had before.
No matter what I did with the thermocouples, the indicated temperature jumped around by as much as 30C or more. In short, after several weeks of fiddling I never got the thermocouples to work well, and replaced them with thermistors, which have been fine.
So my question is: what is required to get thermocouples to give reliable, consistent, accurate readings? Are they just incredibly touchy?
Some things I tried include:

Of course, one must add circuitry (typically a thermocouple amplifier board such as http://wiki.ultimaker.com/Thermocouple_Sensor_Board_v1), to convert the tiny voltage differences to larger differences usable with Arduino or similar analog inputs.
Place those boards close to the thermocouples, but far enough that they are at pretty stable temperature themselves.
Have absolutely no wire extensions of splices, changes of wire types (material), etc.
Avoid doing repeated measurements too fast.
I replaced a thermocouple board with 5V through a potentiometer to the analog input pin, to rule out problems in the Arduino, pin configurations, or software, and got stable readings.
I checked for shorts-to-ground from the heater block, both sides of the thermocouples, the heater itself, etc. None found.
The thermocouple wires are surrounded by a braided shield (not common or shorted to either thermocouple wire); I tried grounding that at either end and at both ends, to the heat block, the printer frame, the power-supply ground, and the RAMPS board ground. These had various effects (sometimes large), but I couldn't find any configuration that made the readings stable (much less accurate!).

Anything I'm missing?
Thanks!
Steve

Very nice question!

Is there a big difference in cost between thermocouples vs thermistors?

Maybe $10 for a type K thermocouple, plus $10 extra for the amplifier board you need for it. $1 or less for a thermistor, judging by a quick web search.

@MartinCarney Relevant.

Just to add to this, I went through much of the same after switching to an all-metal E3D and having a thermistor fail.  I was able to print for a while using the thermocouple and then had no end to my issues.  Temperature bouncing ~20C every update and very inconsistent.  I tried several different boards, thermocouples, and even went as far as a separate power supply for the board.  I ended up removing the diode from one for some reason and that board can be found here - https://oshpark.com/shared_projects/p8Yv87Ks but I don't believe it helped at all.

Thermocouples work by passively generating VERY small voltages via the Seebeck effect -- usually a few tens of millivolts. They're literally just a pair of wires made from two different special alloys, electrically connected together at the "hot" end. That wire junction can be mounted inside whatever kind of attachment tip or lug is desired.
The fact that they're very simple and passive devices makes them extremely precise and consistent between TCs of the same type, MUCH more so than thermistors. Any type-K thermocouple in the world will give you the same accurate output +/-1-2C or so. You can even cut a thermocouple in half, re-twist the ends of the wires together, and it'll still work!
However, the very small (millivolts) signal they generate is quite susceptible to electrical noise and circuit design. The signal voltage has to be greatly amplified to be useful. So it doesn't take much EMR from your heater or stepper wires to interfere with the TC reading. A frequent problem with TC circuits in 3d printers is the dreaded GROUND LOOP -- if the "hot" tip is electrically connected to the hot block, voltage and current on the heater and motor wires can induce small currents through the TC wires that totally screw up the millivolt signal. The amplifier picks up these stray voltages and it throws off the temp read. So, there are some important guidelines for keeping noise out of the TC wires:

The TC wires must be electrically insulated from the mounting hardware (eye lug, thermowell, whatever your extruder has). You can check this with a multimeter -- you want infinite / out of range resistance from the TC leads to the mounting tip and hot block. While you're at it, make sure your heater cartridge wires aren't shorting to the hot block -- that's unsafe and can also cause problems with TCs.
Keep the two TC wires close together, and not immediately parallel to noise sources like PWM-controlled heaters or stepper wiring. If you must run the TC in a bundle with the other wires, TWIST the heater/stepper wiring pairs. (For steppers, twist each coil pair to a different pitch if possible. You don't need to twist the separate coil pairs to each other.)

Another common issue with TC circuits is the COLD JUNCTION COMPENSATION. A thermocouple doesn't measure tip temperature, it measures the DIFFERENCE in temperature between the hot tip and the cold junction where the TC is connected to either the amp or copper wiring. The TC amp has an onboard thermistor that it uses to add the temp at the cold junction to the measured signal from the thermocouple. There are a few things you need to do to make sure the cold-junction compensation works properly:

You should run TC wire all the way from the "hot" tip to the TC amp. You CAN splice it and install plugs, but only with more type-K TC wire and proper type-K thermocouple plugs. These use the same metal as the TC wire so they don't generate undesired junction voltages that interfere with the TC signal. If you splice copper wire between the TC and the amp, any temp differences along the copper will not be measured! This is a particularly big problem if you splice to copper inside a warm enclosure and then run copper to an amp outside the enclosure.
The amp should not be super hot. The onboard thermistor is designed to accurately measure temperatures reasonably close to room temp, not hot-block temps.
There should not be large temperature gradients near the amp or between the TC wire termination and the actual amp chip. Place the amp far enough away from the hot end and other heat sources (like stepper motors) that it isn't experiencing weird temp profiles.

If you do the above, the TC will output a good signal, and the amp will read it properly. But there's one more hitch. The mainboard has to know how to understand the amp's output. 3D printer control boards that are designed exclusively for TCs, like Mightyboards, usually use digital communication between the amp and the main control chip (MCU). This is high-reliability and does not require any special firmware configuration -- support is baked in. But if you're strapping an external TC amp onto a board that is expecting thermistors, you will have to tell the firmware how to read the signal from the amp. The most common technique is for the amp to output a linear voltage signal to the MCU's normal thermistor input (ADC). Then you configure the firmware to use the appropriate "thermistor table" (really a voltage lookup table) for that particular amp. Depending on your controller board, you also may need to make sure the regular thermistor pull-up/pull-down resistors aren't affecting the amp's output.
So you need to make sure:

You don't have electrical noise issues
The cold-junction compensation is working as intended
The firmware and controller board is configured correctly for your amp chip's output

If you do all that, a TC should give superior accuracy and reliability over a thermistor.

Thanks! Lots of good info there. I didn't try moving the TC wires well away from the motor/heater/limit wires, or twisting the latter; that's worth a shot. I'll post back when I try it, though since I have a working printer with the thermistors, I may not mess with it for a while.... :)

It sound like you just have a defective thermocouple. But, I just did a google search for "Why are thermocouples inaccurate" and found this article on identifying bad thermocouples and preventative maintenance. I never thought of a lot of the tips in the article, but I haven't had such drastic temperature errors either.

Thanks for the reference, good article! It would have to be 2 defective thermocouples, since I have dual extruders. And I can heat them and read a tiny voltage change with a meter directly connected to them, so they're not completely dead.


text:
What is the life expectancy of the Kossel?
I'm considering buying this package, the Kossel, as my first 3D printer.
It's not the cheapest model, but apparently a high resolution and stable, which is what I'm after.
The question is, what is the life expectancy of this printer, given the component list?
Assuming the printer is constructed properly and properly taken care of, but used once or twice a week for several hours.
Is it possible to make an estimate of how many years this particular printer could be used before it starts showing signs of wear?
Parts list:
1x Complete set of platics for Kossel Mini (PLA)
1x Kossel mini Extrusion set
1x traxxas (set of 12)
1x Carbon Tube (kossel printing arms) Set of 6
3x Square slider (40cm)
1x Megatronics v3.0 - Kossel kit
1x Heated Bed glass round 17cm diameter (Borosilicate)
1x Kapton heater mat round 16cm diameter
1x Power supply 12V (240/115V / 20A MAX)
3x Aluminum Pulley GT2
5x Timing belt 1m x 6mm (GT2)
1x E3D v6 - HotEnd Full Kit - 1.75mm
1x Hobbed bolt v1.1
1x Brass drive gear (Wade's compatible)
6x Bearing 623ZZ
125x (1 pcs) Screw M3X8 Philips
125x (1 pcs) Washer M3 normal
125x (1 pcs) Nut M3 normal
6x (1 pcs) Screw M3X16 Philips
12x (1 pcs) Screw M3X25 Philips
6x (1 pcs) Screw M3X20 Philips
10x PTFE tubing, 2inner/4outer diameter (10cm)
1x Bowden setup - J head comp. plug set (1.75mm)
1x E3D v6 - Threaded Bowden Coupling - 1.75mm
2x (1 pcs) Screw M3X40 Philips
6x (1 pcs) Screw M2X16 Philips
1x Power cable 1.8m
6x M4 Threaded rod - Custom length

I don't think it is possible, but am curious if someone else has other opinion.

I don't think this question will attract many good answers, as they will mostly contain generalities.

@TomvanderZanden This is why I mentioned a specific 3D printer and included the parts list. And supplied the expected usage.

This is definitely one of the best specified questions I've seen so far, but I still doubt anyone can give a meaningful answer, one that is more precise than "a couple of years".

@TomvanderZanden That's what you think. Just because a question may be left unanswered, doesn't mean it should really be made off-topic.

@Zizouz212 Interesting point. The question is not answerable, because we don't have good data on the life expectancy of these machines. However, it could be answerable if we did have that data, so that makes it OK. Nice point.

@TomvanderZanden I mean... Even if data isn't available, one can always make a good quality answer that stems from personal experience or the like. Let voting decide the authority and quality of the answers. But I don't see anything wrong in the question for it to be closed right now.

The most accurate answer, would likely be to email the company or find someone with that specific printer and ask.

Much like your car, the number of miles, or the number of prints that you can get out of it is entirely up to how well you can maintain it.
A 3D Printer is a machine, and a machine needs general maintenance; if you see something starting to break - or get worn out - or anything abnormal, fix it.
I am sure that if you had something like a MakerBot, it would require less maintenance then a fully home built machine, but if you are building it from scratch, I am sure you don't mind.
I am still rocking a 3 year old home built MendalMax, and have both made some improvements, and had to make some repairs along the way - but it is still in damn good condition.
For a $600 investment, I can say you will get a few years out of it if you take proper care of it. By the time the end of its life comes (5+ years), I am sure there will be much better printers available for cheaper, and you will never look back :)

Tighten all your nuts and bolts
Keep it calibrated
Keep belts properly tensioned
Oil X, Y, and Z rods
Clean of any dust and scrap plastic (compressed air can?)
Clean hobbed bolt
Clean extruder
Ensure all electronic connections are secure
Check wires at points of movement for wear

!remindme 5years

I have built a Kossel too. Got lots of tips from the Google Deltaprinter group.
Most important when using the Traxxas rod ends is to have the metal parts go into the freezer and the plastic parts in warm water(not boiling, just 60 degrees celsius or so). Then put the 2 together, due to the fact the metal crimps just a little and the hot water softens the plastic a bit, they will fit easy and will be stiff longer. These mounts tend to wear out causing play in the effector. I have printed 100's of hours on my Kossel mini with traxxas rods and still moves very nice and prints accurately.

I have downoted this answer, as it doesn't address the question of the life expectancy of the Kossel.

@HDE226868 The last sentence says that the life is at least 100 hours so it would address the question.

I would like to add that Dimitri is the person who first suggested the Kossel to me. I have invited him to this site myself. I agree with @EricJohnson that this is an answer - the Kossel stil works properly after 100's of hours. To me as a user, this answer has value.

The last sentence does address the question, I believe. Can you clarify whether the part about the Traxxas rods is because they're likely to wear out, or some other reason?

@TextGeek the remark about the Traxxas rod does address life expectancy since as i noted the way of assembling greatly improves life of the connections. Bruteforcing it together will make it wear significantly faster than is needed. The warm water/freezer method makes sure that you can enjoy your traxxas rods for a long time. I have just exceeded 200 hrs of printing on my machine this week, no wear what so ever.


text:
How can I optimize my print for casting in metal?
A fellow maker has tried printing a 3D model in clear PLA (<5% infill, 1 or 2 perimeters), burying it most of the way into casting sand, and then pouring molten aluminum. This melts and burns the PLA, and the aluminum takes the space that the printed model used to take.
There's plenty of room for improvement in his process, but I'm asking about what he can do in terms of the 3D printing process to make his prints more casting-friendly.
What print settings are (generally) best for use in this sort of casting?
What materials, if any, would work better than unpigmented PLA? (Must be a material that a typical thermoplastic FDM printer can handle.)
Any other tips or considerations?

Print a two part negative (mold) of your objects.
http://www.thingiverse.com/thing:31581
https://pinshape.com/blog/how-to-generate-a-3d-printed-mold-for-an-object/
Melt and pour wax into the mold. Praffin wax melts at only 37C, not an issue for both PLA and ABS.
Use the wax object for casting, not ABS/PLA/etc.
The mold is also reusable this way.
To prevent the wax from sticking to the mold, something might be applied to the surface. Oil maybe?

I believe casting typically uses a wax for the positive when using casting sand. So, I would suggest using wax filament in your 3D printer.
I would try to shy away from hard polymers like PLA/ABS/Nylon (all typical 3D printing filaments) if the goal is to "melt it away" because a certain amount of the plastic material will either bind itself with the metal or large chunks of plastic will cause inclusions in your part. Both of these side effects will potentially degrade the quality/strength of your part.
I haven't personally used wax filament, so I can't tell you what the correct setting are. However, you can get most of the necessary information from whichever supplier you go through. I might suggest running your machine slower when using a low-melting filament such as wax or PVA (water soluble).

From my experience with lost-wax casting for jewelry, the process is to melt the wax out, then increase temperature and burn out the remaining wax / residue. Casting wax is supposed to leave behind little or no residue after the burning process, but I don't know about PLA/ABS/nylon. I would bet that they leave behind more mess and would thus result in more inclusions.

Yeah, I would think that the hard plastics would have a hard time fully melting, depending on the metal you're using and its melting temperature.

Typical procedure on the casting is to use the lost-wax method, and using PLA is absolutely fine.

Print your part at around 101% - 103% size
Attach flues to the part (or have them part of the model)
Cast the part in a mixture of sand and plaster of paris
Once set, burn out the PLA in a furnace.
Clean the mould of debris
Pour your metal of choice

For a more detailed reference, check out the following:
https://www.youtube.com/watch?v=WWVVSZP3Au4
Regarding the printing itself, my only advice is to use a small layer height and carefully clean up the part before casting


text:
How do I calculate the cost of a 3D print once it's done?
How do I determine how much an individual print costs?
I'd like an answer including support material, failed prints, and (ideally) wear and tear / printer maintenance costs.
To clarify, I'm not asking how to predict the cost before printing, but rather how to calculate the actual cost after printing. Though predicting the cost beforehand is useful as well.

Failed prints are going to vary drastically, as will maintenance costs. It will depend on the part and the printer. The two things that will always been factors are filament cost and electricity usage. I would advise specifying the others to a better degree.

@HDE226868 See my modified question. I'm asking about calculating cost after the fact, rather than a prediction of cost before printing. I.e. you have the failed print(s) and successful print in hand to use in your calculations.

An approach we have developed in Cranfield University is presented here A System approach for Modelling AM moreover you can find the Mathematical model here FDM Mathematical Model

For FDM printing:
Both Cura and Makerbot Desktop (and perhaps others I'm not as familiar with) will give you a preview of both the length and weight of your print, including supports/rafts. Once the print is done you can weigh it on a kitchen scale.
PLA Filament currently runs about \$23/kg on Amazon, which works out to \$0.023/g. Multiplication can then give you a good estimate of materials costs for a print.
Only experience with your specific printer will give you an idea of how often you're going to hit a failed print, and how often you're going to need to replace parts. For wear and tear you could try using a depreciation model of 2-3 years, but that's only an estimate.

There are many factors that make up the cost of a print.

Filament base cost-calculate the cost per gram * number of grams used
Power used by the printer-power cost * time
Setup time for the printer-hourly cost * time
Print time (as you could be printing other objects)
Print area - you can run multiple prints at once
Chance of print failure - (1+ %of failure) * cost of materials and time
cost of printer (divided over expected prints
printer maintenance
profit margin

I disagree with including print area. You shouldn't make the customer pay for build volume that you aren't even using. The "You can run multiple prints at once" is a way to save yourself money by being more efficient. Also, please elaborate on the cost of printer variable and printer maintenance (what kind of things go into it and how to calculate). These edits would be very useful to someone in the future.

@tbm0115 I know this was a while ago you responded, but you should factor in efficiencies.  This isn't the price of the print.  It's the cost to make it.

I recently faced the problem of calculating the cost of my printed 3D models. I wanted to know what their real value had to be counted in Excel. It was really inconvenient. Then I found a program for counting, it turned out really great, even takes into account the electricity.  This is not an advertisement just throwing, maybe someone also encountered such a problem.
https://codecanyon.net/item/mcc-3d-model-cost-calculation-for-3d-printer/24033425
I was interested in the question who solved the given problem in what ways?

I looked at this app which sells for $10.  It considers several factors, but does not include printer maintenance and depreciation.  It has some compensation for failed prints, and includes electricity rates if you know them.

It includes depreciation of the 3D printer, you just need to enter its cost.


text:
What material can I use to make my own cake molds?
I would like to make custom cake molds.
I've asked about this in a few stores that specialize in cooking equipment, they said this wasn't possible.
I wonder if 3D printing makes it possible. It would require a material that is food-safe, as per Which are the food-safe materials and how do I recognize them?
However, there are two extra conditions:

The material must be able to withstand the heat of an oven or microwave, and not mix with the dough.
It should not be too difficult to remove the cake from the mold after it is ready.

The first condition is where this question is a little different from Can you use PLA material with food and drinks? - that question is about cutlery and glasses, not about things that go into the oven or microwave.
Is there a material that can be used for this purpose?

For which printer?

@kenorb Good point.. hadn't realized it might make a difference. I'd like to know in general, but otherwise: the Kossel.

I would say that FDM printing in general is out of the question for this task, ABS and PLA would both melt in the oven, and the grooves in the print from the FDM process would make it a nightmare to clean.
My initial thought was an SLA printer ( $1000+ ) which uses a Photopolymer Resin hardened by a UV light, and based on its medical uses, I would think that it is food safe - I do not know what its melting point is however.
Another idea, one that would not too easily be done in house, is porcelain.
Shapeways offers a service that you could use for this - they say just $9 per part, 125 x 125 x 200mm maximum dimms, both food and oven safe.

The biggest problem I see with using a Kossel (or any FDM printer) is that to print the mold directly you'd need a plastic with a low enough melting point you can print it and a high enough melting point you can bake it.
From this list of filaments (which admittedly shows printing temperatures, not melting temperatures) Polycarbonate and Polycarbonate-ABS are printed at 250+ C, while a brief search found cake baking temperatures from 175 to 200 C.
According to this, polycarbonate is already used for food-safe containers, though you'd still need to worry about printing in a food-safe manner and surface finishing as in the question you linked.
Those two facts suggest it might be possible to print a polycarbonate mold and bake in it, though IMO there's a much better way to achieve the same result: print a positive of the mold in whatever material you want, smooth the print for better finish quality, then use food grade silicone to make the mold from the finished print.