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Getting better support than Slic3r generates
I found a nice model for a ship from the game "Eve". It doesn't have a flat bottom, so it needs support material. But Slic3r generates several dozen tiny support pillars, and one by one they break loose from the build plate. As they get tall, the leverage of course increases, and since they're so tiny they don't have much area in contact with the bed, so they separate. Eventually the whole model broke free, turned a bit, and since I had gone to dinner it kept printing... see below. I think the main problem is the poor support material geometry, but the controls in Slic3r for support material don't seem to give many options.
How can I get better support material layout? Oh, this is PLA, by the way.

(appending to question to be able to put in the picture)
I tried a bunch of things, and the MeshMixer support, plus fiddling with several settings, got it to come out pretty well. Thanks to all, esp. @Tormod!

I noticed that your question has a few answers available and has been open for a while, just curious if any of the available answers was able to help. If not, then what questions do you still have?

@tbm0115 -- I've had slight improvement from playing with the slic3r support settings, but it's still pretty bad on models like this. Have also played with layer height, extrusion rate, and temperature. I still need to try out other slicing software, or designing in the support manually.

Have you addressed the issues in your printer settings? It seems premature to blame the slicer for failing when the printer is not able to accurately do what the slicer is trying to make it do. @darth pixel makes very good points below.

I know many Slic3r users - myself included - add support material to the model itself before importing it into Slic3r.
I personally favour MeshMixer for support generation, as the supports are much more predictable and easily removable. In complicated cases I also add supports in my CAD software.
Although a not free, the support generation in Simplify3D is supposed to be great, allowing for custom placement.
I also found this review that compares support settings in Meshmixer, Slic3r and Cura fairly well. Here is the summary:

Meshmixer
This support was the most efficient in material use however it required the most manual tweaking to print properly. In addition the marks it left once removed were more noticeable than Cura and (sometimes) Slic3r. While the settings could probably be further modified to improve the performance this support type appears the most limited for future improvements.
Slic3r
The support's performance was variable - by far the best in some situations (fox's head and tale) however the worst to remove with the most obvious marks in other areas of the same model. This may be down to my chosen settings and with some more tweaking I may get better results. The most obvious general flaw is that it does not leave a big enough gap between the support and the unsupported areas of the model (like the foxes legs or the lower roots of the planter)
Cura
While some of the support left marks, overall it was the easiest to generate support which performed consistently well. Once again though slight tweaks could improve this further for specific models.
Overall Cura wins my "no time to tweak - got to make it work now" award.

I would add MatterControl which I use with success. It adds very simple but stiff support material.

I just downloaded MeshMixer and tried it, and the support looks way more robust (plus looks easier to attach. Have not printed from that yet, but I'll give that and/or some of the others a try. Very helpful pointers, Thanks, @Tormod!

That is good to hear, @TextGeek!

I see more important things on your photo.

Filament layers are not sticked together, even these on the first layer (on the bed).
Next is that lines are not staight but they are wavy.

This suggests that you should try

increase HE temperature
set speed of the first layer (20% of normal speed)
decrease first layer thickness
increase extrude rate for the first layer

Of course (answering your question) there are other types of support material.
The most stable should be honeycomb but it will not work for you if you will not tune up printing parameters.

Thanks, several ideas there that seem worth trying. I've been wondering about under-extrusion too, but hadn't thought of the temperature and first-layer speed. Will post back after trying some of these.

The waviness is better after I adjusted the iGus linear slide for the X-axis -- it took some doing to get rid of excess "play" there. Only a little improvement in stability of the silc3r support columns, though (so far).

@TextGeek would you share some photos so we could see how is it going? Maybe some shots from diferent angle to see results from aside?

I have not used Slic3r very much. But my guess is that the settings should still be same.
Also, are those rafts? They look incomplete: you might want to check your leveling again.
In addition, try to increase your thickness of the support material. Make it squares or something, as that will give much better strength.
Furthermore, if there is a setting for manually placing supports, you might try that. Simplify3D had that option and it worked wonders for few of our projects.

In my point of view it seems that the bed offset not optimal.
I see that you are using the blue tape, which is better than any other tape. As a next step I would recommend to try different types of glue.
I agree with Tormod Haugene and can also recommend Cura. You can also experiment there with a lot of parameters and after a time you will get a feeling how to print your things successfully.
Just take a look at the download page at Ultimaker for the application and if there are problems with the software you can feel free to report issues at GitHub.
Regards


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Should I comment out the code for what I am not testing when loading the test firmware for Ramps 1.4?

You may want to use this code to test all the electronics before
  installing any of the suggested firmwares.

I'm planning on:

Flashing the test firmware onto the Arduino Mega 2560, then unplugging it from the USB.
Connecting RAMPS 1.4
Connecting all 3 jumpers under the X-Axis (leaving the other jumpers disconnected).
Connecting a stepper driver to the X-Axis on the board.
Turning the trimpot down all the way, and then back up 1/4th of the way.
Plugging in 1 NEMA 17 motor to the X-Axis.
Connecting 5A DC input into RAMPS 1.4 (not plugged in).
Finally plugging it in and seeing if the motor moves for 5 seconds.

Now my question is, if I'm going to do this to test out a single NEMA 17 motor, do I need to comment out the rest of the test code before loading the firmware?

There's no reason to comment anything out. It will work just fine without any modification, even if you're just testing a single motor. That said, I don't see the value of this "test firmware" over just installing Marlin.

Somebody must see the value in it, since they wrote it, but maybe it's no longer valuable, but it was at the time.

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Makerbot Replicator 2 switches off and restarts automatically
My Makerbot replicator 2 stops and restarts automatically. I lose the print and the extruder head does not move from the position. (obviously).
We have checked wiring a few times. Have not seen any issues so far.
Maybe I am missing something.
We have recently changed the ceramic tapes, fans etc. just recently.
It happens once in a while. But once it starts, it continuous, and it doesnt stop unless we shut it down for a few hours. or sometimes even days.
Any ideas what the issue could be. Or are more details required.

Have you tried replacing the X stepper and X endstop wiring? This is a common failure point due to wire fatigue, and if the +5v shorts to ground, it can pull down the mainboard voltage enough to shut down and reset the processor.

@RyanCarlyle hey thanks. I think it could be the endstops wire.
I removed the cables for both the motor and endstops, it ran for an hour.
I attached the endstops, the printer stopped and restarted after a while.
I can get the replacements from their website?

You can call Makerbot tech support on the phone and tell them you need to buy the X stepper cables. You can pay over the phone. They used to give a lot of them away for free since it's a known failure issue but I don't know if they're still doing that. Another option is Robotshop http://www.robotshop.com/en/makerbot-replicator-2-parts.html OR you can rig up something like an ethernet cable yourself.

I've heard of a few issues like this, always relating to hardware problems. If you feel comfortable opening up the hardware on your machine, confirm that all of your connections are firmly connected to your printers Circuit Cards. The issues i've dealt with I determined came from a loose connection and the gantry running would shake the connections enough to cause a loss of signal.

So I replaced the xyz motor cables. It worked for a week or so. But I'm facing the same issues again now.

Check your power supply cables. If it's shorting out it could be causing a reboot.
Make sure that there's no faulty connections on the XYZ motor cables you replaced and that they're fully plugged in (obvious I know) but doesn't hurt to check.
Also make sure that the cable routing for the motors is installed the same way it was before you replaced them. Makerbot routed the cables in such a way to reduce the strain on the connector that's caused by the gantry vibration. If its an intermittent problem odds are it's either a vibration problem or a short circuit (or both).

So we had loosened all the cables because of the terrible design.

I'll check power cables

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Hatchbox Silver PLA settings?
I have a RepRap Prusa i2. I have done the majority of my printing with clear PLA that I got on the cheap from eBay. It works just fine.
I bought a roll of Hatchbox Silver PLA (1.75 mm) from Amazon. I have never had a print go well with it. I have tried various combinations of hotter and cooler extruder and bed (180 - 220°C extruder, 50 - 78°C bed). Prints always either curl up from the bed after 5-20 layers are deposited or delaminate in the middle of the print. I print directly on the heated glass bed, and have also tried various cooling fan settings.
Does anyone have good settings (Slic3r) to use with this stuff? Or any other advice for getting a successful print?

I've been using Hatchbox 1.75 mm (but white), and settled on 190°C extruder temp, and 60°C bed. I've had trouble getting some prints to adhere to the bed, but most have been ok; I don't see a clear pattern. I don't know whether it's the fiber or my settings. I'm trying slightly higher temperatures, higher extrusion rates, and other filament brands to see if those help. Will post back if anything clear shows up...

I know the original user has probably found an answer to their question by now, but I'll add my 2 cents for the benefit of others who come across this.
My experience with Hatchbox has been that the walls and top layers were looking good at 200°C, but when I started stress testing the parts to their fail points I noticed that the internals were just a fibrous mess with no structural integrity.
So I started increasing the temperature in increments of 10°C and found that at 210°C it improved, and at 220°C there was good layer adhesion.  At 230°C layer adhesion was absolutely beautiful, but it begins to get a little too melty.  I have settled at 220°C for my machine.
Keep in mind that everyone's printers are going to be slightly different - hotends, fan setup, even the thermistor could have varied resistance from one machine to another causing incorrect readouts on temps.  That's why you have to tinker and find what works well for you and your machine.

I use a Wahao Duplicator I3 with a heated bed. I have only used the orange Hatchbox PLA with great results. I use 210°C for the extruder and 55°C for the bed. Speed is 40 mm/s which works well for me.

I use 205°C for the extruder and 60°C for the bed on my RoBo3D. I also put hot glue stick on the bed to help adhesion and use a brim if it is a small object.
I would also check the first layer to see if you need to adjust your z offset. Delamination could be a sign the plastic isn't fusing correctly, which could be both an offset or temperature issue. It could also be a feed issue from the roll itself.
You can try printing these, Print Temperature Calibration Piece, and see what temperature gives you the best result.
I have had only one delamination happen to me and I think it had more to do with a hiccup in the commands sent to the printer than the filament itself. I basically have only used Hatchbox filament.

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Stone-look surface via painting?
Has anyone tried painting a PLA (or other) print with stone-look spray paints? In particular, how does the result look compared to printing with stone-fill filaments? It looks a lot cheaper, but will it look inferior?
One such paint: http://www.krylon.com/press-room/press-releases/2013/04/add-a-touch-of-nature-to-your-next-project-with-new-natural-stone-textured-finish/?
One such filament: https://www.matterhackers.com/store/3d-printer-filament?t=LAYBRICK

Walter Hsiao has tried putting prints into a tumbler with ceramic media. http://thrinter.com/vibratory-tumbler-ceramic/

It's totally possible to achieve but the result vastly depends on your painting skills and your spray paint quality.
Your can look at this page for a concrete example.
How it compares to stone filament is fairly subjective though. Painting a 3D print usually breaks down in 3 steps :

Smoothing out the lines.
Achieved by either sanding the print or using acetone
Apply coating.
Ensures a better adhesion for the paint
Apply spray paint

If any of these steps are neglected, the final result won't look as good as using stone filament. However, if the quality of you stone filament is really bad, painting will offer a better result.


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Wanhao Duplicator i3 ABS settings
I am looking to others who have successfully printed in ABS using a Wanhao Duplicator i3.
I have tried and get a lot of warping and delamination. I tried putting a large box over the printer which did help with the warping some but I am still getting some layer separation. I used 235 °C for the extruder and 100 °C for the bed. I am printing at 40 mm/s and 0.2 mm layer height.
If someone has ABS and PETG settings for this printer, your help would be appreciated.

What kind of models are you experiencing these warping problems with? Some things (large and flat models) just can't be printed in ABS regardless of settings, and you should just use a different material. There's a lot more at play than just your settings.

They were corner brackets for an acrylic enclosure, maybe 1.5 inch square with slots for the acrylic to slide into. The other was an L bracket about 1.5 inches long printed on end. This is where I got the separating layers. I am pretty new to 3d printing and have done well with PLA but want to learn other filaments as well.

I had the same issue and fixed it by printing a little slower (25mm/s IIRC) and using some kapton tape on the bed. You might also want to lower the bed temperature over time, like described in https://filaments.ca/pages/temperature-guide#abs. I printed at 90 with a longish model and lowering the bed temp stopped my separation.

I just tried ABS for the first time. I was having issues and I don't have a glass bed. My first four prints failed at the start, so I used Scotch wrinkle free glue stick and my print is working just fine. lol. Thank you Scotch Wrinkle-Free glue stick.

I am an official Wanhao Distributor
By experience I can recommend you to print with this settings:

Extruder 230 °C
Heated Bed 65 °C
Have a glass surface
Use hairspray over the glass
Continue to enclose the printer or at least put it where there is almost no wind
Print at 45 mm/s

Note that this settings vary a lot depending on humidity and other factors related to where you are printing, so it would be very useful to know where in the globe are you experimenting.
Also note that humidity is very very bad for 3D Printing Filaments so keep them sealed while not using them.
Please do  comment if you have any more doubts.

I've had hit and miss success, but nothing I would consider great. I was using Hatchbox ABS with the extruder at 230 °C and the bed at 65 °C and a homemade enclosure.
One thing that did help was making sure the HVAC vents near the printer were closed.

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Which endstops are most precise?
I have seen mechanical (micro switch), optical  and magnetic(magnet + hall sensor) end stops.
Are there any differences in how exact they switch at the right location? If so which are the most precise?

There are some different criteria that we should use to select a switch type:

Precision / repeatability: does the switch trigger at the same place every time? How much spread is there in the trigger position? Do environmental changes or machine setting changes affect the trigger position?
Contact distance: does the switch register with enough clearance to its hard-stop that the homing axis can stop before colliding with something?
Noise-rejection: does the switch ONLY trigger when it is supposed to?

It's important to ask, how much switch precision do we actually need? A typical 3d printer drivetrain using a microstepping stepper motor can only accurately position the moving load within +/- one 1/16th microstep (even if using finer microstepping than that) due to error-inducing effects like friction torque and magnetic detent angle error. That's around +/-0.01mm for most printers. The homing switch only needs to be as precise as the motor's positioning! Nothing is gained by having, say, 0.001mm precision endstops.
This precision of +/-0.01mm is achievable for all types of endstop switches, with proper switch selection and configuration.
Then there are three "standard" switching types in use in consumer/hobbyist 3d printers:

Mechanical switches, typically dual NO/NC limit switches, which either pull up or pull down a signal pin by connecting an electrical circuit when triggered
Optical switches, which use transistors to detect when an obstacle ("flag") is blocking the window between the emitter and sensor
Hall effect switches, which use transistors to detect when a magnetic field exceeds a particular field strength cutoff

Mechanical Switches
Precision/repeatability depends on the switch quality, length of lever arm attached (longer increases contact distance but is worse for precision), and impact speed of the carriage with the switch. It's possible to have a good mechanical switch or a bad mechanical switch. This is typically a reasonable default choice because it is simple and cheap.
A small mechanical switch with a short lever arm (or the lever arm removed) will generally achieve the required +/-0.01mm switching precision. Very cheap switches, high contact speeds, and long lever arms may provide inadequate resolution for Z homing or probing, but will still be adequate for low-precision X and Y homing purposes.
Where mechanical switches tend to cause issues is in noise rejection. Different controller boards use different ways of wiring the switch: some use two wires and only send a signal when triggered. When not triggered, the signal wire is left floating or weakly pulled up by the microcontroller, while attached to a long wire that acts as an antenna to pick up EM noise. It is VERY common for heater or stepper wiring to emit nasty EMR due to the PWM current control. Two-wire endstop cables should always be run away from stepper and heater wiring. Shielding and twisting the conductors is a good idea too.
A more robust approach is to use three-wire switches that actively pull the signal line high or low depending on the switch position. These will tend to reject noise better.
Very cheap mechanical switches may fail within the life of the printer. However, most limit switches are rated for millions of cycles, which is unlikely to occur over any normal printer's lifespan.
Mechanical switches are easy to align and easy to trigger by hand during troubleshooting.
Optical Switches
These rely on a flag blocking a window between a light emitter and a detector. This is non-contact and can be quite reliable, but introduces some challenges. The exact trigger position (and thus precision) may depend on ambient light levels in the room, because the sensor is monitoring for light to decrease below a specific intensity. So it may be very repeatable/precise in the short term but have some drift if the sensor moves in and out of the sun through the day.
Switching tends to be more consistent and reliable if the flag enters the window from the side, rather than the top.
Optical switches will actively pull the signal line high or low, and thus have good electrical noise rejection.
Hall Effect Switches
These measure the intensity of the nearby magnetic field and trigger when it exceeds a certain amount in a certain polarity. This is highly precise/repeatable (better than +/-0.01mm) and extremely resistant to noise and environmental conditions. (Unless your printer is next to something that emits large magnetic fields, anyway.)
The hall switches I've seen have an adjustable trim pot to tune the trigger distance. That's a nice feature when trying to manually calibrate a Delta or a Z-bed for first layer height.
The primary downside to hall switches is that they need a magnet to trigger the switch. This can be difficult to trigger by hand during troubleshooting, and requires attaching a magnet somewhere on the moving carriage. Glue works fine... but don't glue the magnet in place backwards!

I don't see the "Precision / repeatability" answered for the different switch types. You name the effects that have influence though. I think the question is if a good mechanic switch is more precise as an Hall Effect switch. Or if ambient light makes an optic switch less precise than  bad mechanical switch. And what are the variations anyway. Are we talking millimeters in difference or µm? Some ball park values of the achievable precision would be needed to compare the three end stop types.

It simply depends too much on the specific switch used to give a concrete answer. In particular, two different mechanical switches can have very different precision. A cheap limit switch with a very long lever arm might be +/-0.5mm with a speed-dependent trigger position, but that's unusually bad. My experience is that all the "typical" endstop switches (hall, optical, short-throw mechanical) are equal or greater precision than the positioning resolution of a typical stepper motor drivetrain (+/- a 1/16 microstep or thereabouts) and thus the exact trigger position repeatability is irrelevant.

Let me add some detail to the answer to clarify this a bit.

Nice answer, however, do you have any source for the precision of (common) switches being this high? The statement "use transistors to detect" is a bit superfluous since just about everything uses transistors and transistors aren't really key to their operation. RE large magnetic fields; have you considered that the stepper motors themselves emit quite a bit of magnetism. I found that once triggered, my hall endstops stayed triggered due to the magnetic field of the motors, and that to get them to "untrigger", I had to add a magnet of the opposing polarity close to them.

Repeatability is far more important than precision.  The word "precision" indicates, roughly, how small a distance difference can be determined, and you'd think there's no point in exceeding the stepper motor limit -- except that the bed itself can be adjusted far more precisely w/ the four corner bolts. So if you can get super-tight repeatability, you can "home" the bed itself to that position.

Carl, within the realm of science, engineering, and switch specification, precision and repeatability are more or less synonymous. The precision refers to the spread in the measurement values from measurement to measurement. What you're thinking of is resolution.

You've missed the induction sensors. No, those are not Hall Effect ones.

One should also consider how many cycles before failure. In this regard, optical and hall-effect sensors outperform mechanical sensors greatly (in similar price ranges).

@RyanCarlyle Repeatability and precision are not more or less synonymous. Precision is how far are your measures from the target regarding to an scale. Repeatability is the spread of the measures according his own target. R&R studies can help to determine if tha part can meet your goal. However many electric parts can give  that required repeatability unless the mechanical part gets damages or dirty during usage, but most of them has a limit more than 100,000 clicks as life span and much more. I work as Quality Engineer (30 years)

Thomas Sanladerer performed exactly the comparison you ask. Check the whole video.
The result is that inductive sensors are the most accurate, but they are highly dependent on the bed material chosen.
Mechanical switches (bare, no metallic arm) are about as accurate and keep the same accuracy with every bed material (however you need a mechanism to retract them, which may or may not decrease the accuracy).
Other sensors are less accurate.
In any case, most of them are already far better than required, since anything below 50 microns is fine and basically all of them reach that accuracy.
Choose based on other factors such as weight, installation, price. Inductive, after a calibration based on your specific bed, may be the easiest since they need no retraction, but they are bulky. BLtouch is probably the second choice, mechanical microswitches the third one.

Good find of an old question and a good summary of Tom's tests. He did not test an optical breaker circuit though - where a light always hits a photodetector and the moving part pushes a wall inbetween. This setup is very precise.

I'm not sure it can beat the other ones: as written in another answer, that kind of endstop is based on the light reaching the sensor dropping below a certain threshold. Since it's a measurement based on (infrared) light, the ambient light will impact it. It can be accurate in a specific environment but not immune to various changes to the environment.

I am talking about light barrier type optical sensors. An LED sends full bright power into a sensor and a "wing" moves in. Such endstops were not tested by Tom but are used extensively in heavy machinery as they are rather foolproof and a broken light source or any item falling into the sensor trips an emergency halt.

@Trish to explain better: in those sensors the light is converted to voltage, then when the voltage crosses a threshold, the output is triggered. However the threshold will depend slightly on the environment temperature, and since a small change in the threshold translates in a much larger change of trigger height, they may not be better/much better than the other systems. Oh, and you still need retracting them when not in use, which add an additional mechanical component which will decrease accuracy. For example, a 4 cm ABS holder will expand by 80 microns over a 30°C temperature difference.

Thomas' video was about bed levelling rather than the OP's question about end stops. however it did show the accuracy of microswitch without lever vs relevant alternatives.

I don't think there is a simple answer.
In my opinion, for a home sensor accuracy doesn't matter.  Firmware usually allows setting an offset between the indicated position and the actual position.  What really matters is repeatability.  Every time the sensor indicates position, the position is the same.
Mechanical Switches
I have found through testing several mechanical switches that the "make" event is less repeatable than the "break" event.  For best results, I move toward the position that closes the switch, then move in the opposite direction until the switch opens.  If I remember correctly, I got "make" repeatability of about 0.02" (0.5 mm), and "break" repeatability of about 0.005" (0.13 mm).
Optical Switches
For a delta 3D printer, I use optical sensors.  Optical sensors have a built-in illumination and sensor, usually on opposite sides of a forked structure.  The sensor side has a slot which masks the light being received, helping to shroud it from ambient light.  The slot is along an axis which is either aligned with the fork or normal to it.  The flag you use for the interrupter should completely cover the slot, and for good repeatability edge of the flag must be parallel with the slot.  In other words, some sensors expect the flag to enter from the side while other expect the flag to enter from the top.  Either will work, but you need to choose the right sensor for the configuration of your machine.
Ambient Light with Optical Switches
Perhaps ambient light could be a problem.  If so, it could be addressed by shading the sensor.
Let's assume that the LEDs in the sensor are the same efficiency as the ambient LED lights.  For reference, here is a spec sheet for a typical optical interrupter used in optical sensors:  http://www.isocom.com/images/stories/isocom/isocom_new_pdfs/H21A.pdf  The package of the optical sensor is designed to reduce susceptibility to ambient light.
Light intensity falls off as distance^2, and the illuminators in the sensor are very close.  How much effect does room light have on the sensor?
In my shop, I use 8-foot LED replacement bulbs for the fluorescent bulbs.  With this, I have 72 watts of LED lighting, which, let's say, illuminate evenly the semi-sphere below the ceiling.  A full sphere is 12.56 sr (steradians, or stereo-radians), so the half sphere is 6.28 steradians, for a power of 11.46 W/sr.  At the sensor, this must be divided by the square of the distance, let's say 8 feet.   This gives us (11.46 W/sr)/(96in^2) = 0.119 W/area.
The illuminating LED has a power (typically) of 1.2 V * 0.05 A, or 0.06 W.  The light cone from a typical LED is about 30 degrees, which is 1 sr, for a power of 0.06 W/sr.  Scaled for an estimate of the distance between the emitter and sensor of 4 mm or 0.157", is (0.06 W/sr)/(0.157in^2) = 2.43 W/area.
It seems unlikely that general ambient light will be a problem.  If it were, the sensor mounting could be designed to shield the sensor from direct exposure to ambient light.
It is important with optical sensors to be sure the interrupting flag is actually opaque to the illuminator light.  As I found, red PLA is not especially opaque to infrared light, so I needed to paint the flags with a black pigmented paint.
Hall Effect Switches
I have no experience with Hall effect magnetic limit switches.  Other answers here have praised them because they have an adjustment which can be used to set the precise detection point.  I don' t like adjustments because they drift.  Pots are subject to wear, oxidation, and both slow and fast variation in their resistance.  I would prefer to have something unadjustable and repeatable in hardware and use software to hold the calibration.
Example of Hybrid Choice
On a 6-axis delta architecture CNC machine I build, I use a hybrid approach to sensing home position.  Mechanical switches indicate a position that is close to home, and the index pulse of a rotary encoder defines the precise home position.  The homing firmware moves toward home until the mechanical switch closes, then away until it opens, then back toward home until it detects the index pulse.   As there are six axes, there are six sets of these switches and encoders.  Using a mechanical switch for the rough homing made sense for this machine because the index sensor is hit once per revolution, so it is not a unique indicator of home, and this machine creates a lot of dust and chips, which could block an optical sensor.
So, without an absolute answer, my preference is for optical switches for repeatability.

The precision values you got for mechanical switches appear to be extremely high. Granted, they are not perfect, but if mechanical switches only had a repeatability of around 0.5 or 0.13mm, then nearly every print on those well-known cheap Chinese 3D printer kits would fail, which is clearly not the case.

The link has unfortunately died... do you happen to know the title of the document, so that we could search/google for it?

This link may serve: http://pdf.datasheetcatalog.com/datasheets/105/55275_DS.pdf

I think there are several factors involved in which sensors are best, but the general ordering for me would be Hall, Optical followed by mechanical. All of the types will be subject to some drift due to vibrations and changes in the printer over usage. Therefore it's the ease of adjustment as well as the accuracy of the stop which counts in the assessment.
In my experience the hall effect sensors are the most accurate and easiest. They don't rely on physical switching (as with the mechanical) meaning there is no "wear and tear" on the component and the point of switching will remain fixed. They have a potentiometer which can be adjusted to make the position of the stop change without any mechanical intervention allowing very fine tuning. They can be very accurate.
Optical are similarly accurate but usually have a fixed component that cuts the beam to switch on/off the sensor. The adjustment of the stop will usually be mechanical because the mount points will need to be adjusted - this reduces their accuracy. There are various adjustable mounts to alleviate this on thingyverse or the like.
Mechanical switches are similar to optical in terms of adjustment with the added inaccuracy of the actual switch mechanism which may degrade over time.

If you take a look at the RepRap Wiki, they briefly explain these three switches:

Mechanical

"Mechanical Endstops are the most basic form of endstops, made of an ordinary switch, two wires. Changing the switch state signals the electronics.

Optical

"These Optical Endstops observe the light level and reacts to sudden changes."

Magnetic

"These endstops; Hall effect sensors is a transducer that varies its output voltage in response to a magnetic field. Hall effect sensors are used for proximity switching, positioning, speed detection, and current sensing applications."

In regards to your question, it's dependent upon your circumstance. However, most of the time a good 'ol Mechanical Switch is repeatable and serves its purpose well.
I, personally, would place both optical and magnetic switches in the category of a multifunction component. Meaning, both of these types of switches (generally) provide a valuable range for object detection. This can potentially lead (depending on your machine) to a pushed command that tells your machine to slow down when it comes close to the soft stop.
Again, personally, I would be wary of using an optical endstop with potential white light noise from ambient room lighting or other sources. I could be wrong in my concern for some modules that address these kind of issues.
So, if we narrow down between mechanical and magnetic:
 - Magnetic would provide a gentler approach, reducing (potentially) the amount of wear
 - However, I'm assuming, magnetic switches require "dialing in" depending on the components used in the sensor. This could lead to an undesired range that the sensor is triggered.
 - Mechanical switches are simple. They're either touching or not touching (on or off)
 - A possible pro (or con) is the ability to manipulate the trigger manually, more easily. I've run into a situation a few times where I needed to manually trigger the endstop as part of a troubleshooting step. But, if you accidentally bump your endstop while the machine is running, no good.

Do you know if this "pushed command that tells your machine to slow down" is used on any machine?

I don't know of a real world use for 3D printing, that's why I said it's a potential option. I have seen similar setups in traditional CNC machining with a third party sensor. The sensor does its thing and essentially pushes a G-Code command to the machine's controller. Typically the command is a subroutine that performs multiple functions like moving the machine to a safe distance, stopping, and notifying the operator. Look up Caron Engineering for an example with their TMAC setup.

This doesn't answer the question, which asks "which endstops are the most precise?". There's nothing in here that addresses that - this answer mainly seems to be theorizing about a "gentler approach" which isn't even supported by any firmware.

@TomvanderZanden I'm purposely staying away from answering that part of the question as it is primarily opinion based.

You could answer that part pretty objectively if you looked in some datasheets for the repeatability characteristics of various endstops.

A separate issue not addressed in other answers is that the end stops for X/Y axes have different requirements than those for the Z axis.
X/Y Axes
When the printer offers XYZ calibration (like Prusa i3 MK2), the properties of the X and Y switches play a role, since for the Z probing the probe should be centered above the fiducials (copper circles) in the bed. The XY part of the calibration measures the position of the fiducials relative to the end-stop trigger point. Then the Z calibration measures the height of each fiducial.
When the XYZ calibration is not offered, there's usually no need for very repeatable positioning relative to the X and Y travel ends, and on most printers you could simply move the motors until they start skipping steps and call that a day - it will be accurate to within a few steps.
Z Axis
The Z axis always has a high requirement on accuracy and repeatability, and there are two general approaches to determining its position:

No end-stops on the Z-axis drive system, a probe is mounted on the print head and is used to detect when the head is a certain distance above the print bed. This can be used for 9-point calibration of the bed shape and thus removes the need for bed levelling.

End-stops used on the Z-axis drive system. No sensor on the print head. The bed needs to be separately leveled in reference to the nozzle - thus the bed leveling screws.

Delta Z
For Delta, you essentially have three Z axis drivers, and similar to the Cartesian XYZ drive, you don't need any end-stops if you have a probe on the print head. You can also perform multi-point bed leveling with such a probe.
Other Approaches
X and Y endstops become unnecessary once you use closed-loop stepper control, such as Mechaduino or linear digital position sensors (e.g. as used in CNC machines).
The Z probe is still useful if you don't want to perform bed leveling manually.

While these are interesting points about endstops, it doesn't address the actual question at all.

Do you have any references to a delta running without endstops?  I'm fairly certain endstops are required to establish axis position otherwise the motion gets screwed up.

Kinematically they are not required. Similar to a double-Z-axis Prusa mount, you start with a "fairly" middle-of-the-bed position, then all three Z axes move down until the probe detects the first fiducial. It's a large circle (e.g. 1 inch dia) and establishes the Z and radial origin (think of the bed in polar coordinates). Second fiducial is a narrow sector and establishes the angular origin. Now you can find further small fiducials to perform full Z calibration (or full XYZ calibration after assembly). For XYZ cal you need a Prusa-like custom bed. For Z only a circular metal plate will do.

@KubaOber Could you please explain how you would decide where "fairly middle-of-the-bed" is on a delta without any sensors? The initial position could be literally anywhere...

You can't. You do it manually, or you use a mostly metal bed where the fiducials are negative, i.e. gaps. The inductive sensors are good at detecting those. This would also help detect the edge of the bed so you don't need any additional sensors at all other than the inductive one. I run a delta like that.


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Slicer/Printer Origin
I am very close to buying a 3D printer and have started to do some preliminary design work from the things I'd like to make, but I have a question: Which corner of the print bed corresponds to the origin (0,0,0) in slicer software? Is this the same across slicers and printers?
The reason I ask this is because of the difficulty some have in removing items from the bed. It seems to me like I'd want to print small items closer to the front of the printer to make access easier, but it looks like most slicer hosts only show a box representing the build volume with no real indication of what's "front".

It really doesn't matter what is really front for your printer or software. You can always rotate your object before printing and you can always reposition objects on the bed. All applications (which i know) allows rotating and repositioning and all printers doesn't really care what is where. So you don't have to worry about the problem you've described. nevertheless whatever printer you'll choose and whatever software you'll use you have to get used to it and find your own technics.

Depending on what kind of printer you have, the build table origin and slicer origin (0,0) are usually either the front left corner, or the center of the build plate. This can be changed by the end-user in most open-source printers. There is no standard or requirement for a particular origin location. The important thing is merely that the slicer and printer coordinate systems match, so parts actually come out where your slicer thinks they should.
In practice, it's usually quite easy to tell what's "front" in your slicer's build volume. When you open the program, the bed usually appears as it does when you stand in front of your printer. It is rarely an issue.
In terms of difficulty removing prints from the bed, a removable build plate is an excellent solution. Plastic has a higher coefficient of thermal expansion than most build plate materials (like glass), so throwing the print+plate in your freezer will generate large separation forces and help remove the part for you. Non-removable build surfaces are a deal-breaker for most serious 3D printer users I know. Either don't buy such a printer, or add a removable plate yourself.

Normally the home position of the printer is the front left corner of the bed.  The slicing software will ask you where this is so you can than position your object anywhere on the bed. The slicing software will make all the necessary adjustments for you. You normally would print the object in the middle of the bed, especially when heated, so it would be the most consistent in temperature.
Personally, I have more of an issue keeping the object stuck to the bed than getting it off. Once the bed cools, the objects are easy to pop off. My experience using PLA and a glue stick.

On Cartesian printers, the origin is usually the front left corner.
On Delta printers, the origin is in the center.
If you are having trouble getting prints off the build plate, maybe consider a removable flexible build surface, such as the Easy Peelzy.


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Alternative 3d molding techniques at home
i have seen formbox http://golem13.fr/formbox/ and it uses heat and many materials like PVC. Is there any way to do this with paper or paper derivatives(like egg carton)? If the answer is yes, how can i do that?

You have a bit of vagueness to the question. Does your reference to paper-like material mean the substance used to create the positive form or are you suggesting that the paper-like material would be formed around the positive form? Does your scenario include a previously constructed vacuum box?

Working principle doesnt matters. i want to make mold of different things by using paper. İt should copy form like a skin

This question isn't about 3D printing, as such I'm closing to vote it as off-topic.

@Tom van der Zanden  So explain what is 3d printing. Is it only abs and pla?

No, FDM (using any material) is just one example of 3D printing. Other techniques include, SLA, SLS, DLP, Binder Jetting,... Roughly speaking, 3D printing is any process in which a model is built-up additively, layer-by-layer. What you've linked to just isn't 3D printing, it's vacuum forming.

So also you can apply paper layers additively. First of all form than combine different layers. I think you should change your vision.

There is now a meta question to discuss the validity of this topic

Forming kinda blister out of paper is possible but not the way it's formed out of plastic. Paper is not elastic, it's bendable but not strechable. It's the issue of how cellulose fibers are formed and how are they entangled.
Anyway - you can create a form out of wet mixed paper pulp. Wrap it around your model and then wait until it's dry. It will form amazingly stiff form. You can do it also out of wet handkerchiefs.
You could build a vacuum machine as in the formbox to squeeze the paper pulp the get water out of the material but the cover should be done out of light silicone film so it would be treated by vacuum.

wet paper is quite well suited for making molds in the manner you describe. The original model should be treated with some form of mold release to ensure a clean break from the model. It is of course dependent on the material of which the model is constructed.
Fiberglass molding is done by wrapping the model, called the plug with fiberglass saturated with a resin, then encasing that in the equivalent of a plastic bag. Removing the air causes the fiberglass to match precisely the surface of the plug, creating a good mold. It would work with paper pulp too.

@fred_dot_u removing model from the form is always the case. Formbox or "blistering" in general is easy as the blister itself is flexible somehow. So model can "exceed" general rules. paper form is not as such.


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Glue sticks for print bed
I would like to get a green tombow PITS adhesive stick. On Rakuten, it costs \$1 (USD). On my 3d printer's (XYZ) retailer's site, it costs \$20 (USD). Due to the costs and the fact that Rakuten does not ship to my country, I need an alternative. I am currently using Davinci 1.0 for my bed, which I believe is a glass bed. So, my questions are:

What glue is best for PLA plastic?
What glue is best for ABS plastic?
Is there a glue that functions with both types of plastic?

The glue sticks I saw in use were normal office supply sticks. So probably optimized to glue paper ;-) So I would recommend to use whatever your local office supply store has. You can also try hairspray.

@LarsPötter hairspray is ok but it sprays (spread) around. paper glue is way better as it can be applied on exact place on the bed.

@MithunKalan please refrain from using phrases like What is the best.... These types of questions typically fall under the category of What types of questions should I avoid asking?. Thank you and welcome to 3D Printing SE!

As mentioned by Matt - PVA glues work perfect for both filaments.
It works well because it's softening temperature is between 45..85C so it's more or less temperature of HB.
Advantages:

cheap
easy to apply on HB
can be applied on cold as same as on hot HB
sticks model very well
non toxic, no solvent, odorless
easy to wash (from HB) (just wash it under water or scrape with sharp tool)
works very well even with old and dry layer of glue

Disadvantages:

quite hard to detach model (I use paper knife)
first layer is not glass-perfect
after detaching, model is a bit sticky (first layer)

I use Scotch Glue Stick by 3M.

This answer focuses on one specific type of glue, while there are countless ones that work. A "these types of glues work"-type answer would be significantly more valuable than this answer, which is essentially a product endorsement/review. (Like the one given by Matt, except a bit more detailed).

@TomvanderZanden you are absolutely right! But isn't it what Mithun Kalan was asking for? I'll edit my answer of course to make it more general.

I use glue Sticks from Staples. It works. Anything else is over thinking :-)
I use it daily on PLA and ABS on 3 out of 5 printers. Printed 5 lbs this week in plastic so far.
Following my flashforge creator pros use this amazing mat, that even after months of use still work great (so long as I clean it with alcohol every so)
Some use hairspray. Tried it, mix results, got sick of breathing the stuff in. Also it wont work on both plastics as gluesticks do.

Most PVA glue works well for both (Poly Vinyl Acetate).
There are different brands in every country.

Are you able to elaborate a bit more on the glue and what makes it a good choice?


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3D printing using OctoPrint on Linux Ubuntu desktop
I'm trying to set up OctoPrint on my Linux Ubuntu 16.04 desktop to work with my Micro3D printer. The printer works fine on Mac and Windows:

I've installed OctoPrint with the M3D Fio Plugin Manager. I can see the files in ~/.octoprint/ fine and I can even turn the printer fan on/off, move the extruder, etc. through OctoPrint:

But when I press the blue "Print button", there is no response. Also the files in the "upload" section are greyed out. Must I download a slicing program or something? I'm new with 3D printing in general but not with Linux. Grateful for help!

I just discovered that OctoPrint only reads .gcode files for printing (apparently, unless you have a slicing software embedded in it), so I installed Slic3r separately, and ran
./slic3r mystlfile.stl

to generate a .gcode file (in the executable directory).
Then I uploaded the .gcode file to OctoPrint and things got moving.

For me it sounds like you've missed to install the CuraEngine for slicing, but I'm only guessing, as I'm not using OctoPrint at all.
Instead I'm using Cura directly and save gcode to a SD or use USB printing for quick/small prints.
Regrads ;)

Yeah I think it comes auto-installed on other systems but not in my case

On Ubuntu you can install it easily via APT. It is available in the Ubuntu repositories. Additionally it is possible that you'll need a specific version of the engine. You'll find a repository for it on OctoPrint github page.

Ah, and if you like to use Cura (incl. CuraEngine) provided by Ultimaker you can take a look at my PPA (https://launchpad.net/~thopiekar/+archive/ubuntu/cura). Remember, that it might be possible that the newer CuraEngine there does not work with OctoPrint.

I'm now using CuraEngine slicer with the M3D plugin on OctoPrint. Works great. Thanks for suggestion. Yeah there is a limit on supported version of cura.


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Auto Bed-Leveling with Inductive Proximity Sensors and Magnets
I recently decided to upgrade to auto bed-leveling using an inductive proximity sensor and an aluminum build plate on my Prusa i3. I also wanted to try to secure the build plate using neodymium magnets at 4 points, with the magnets being secured with bolts to the Y-carriage, and steel washers glued to the bottom of the aluminum build plate (since aluminum is not magnetic).
I would like to know if anybody has attempted this, and what the results were, as well as any issues incurred. My primary concern is a possible interference between the small magnetic field that is created by the magnet, and the sensor when probing the plate. I fear this question may sound a little open-ended, but I would just like to know if this could work. Please feel free to ask any follow up questions to details I may have missed. Thank you.
P.S. I would also like to note, in case there is any relevance, I do not plan on using a heated build plate, since I have a heated build chamber.

My main concern would be the strength of the glue when the heated bed is on.  When I use Elmer's glue on my abs models to hold them to the bed, it softens when the bed is heated.

Good question. The magnets from the build plate will almost certainly interfere with your inductive sensor, the movement from the carriage will induce a current in the inductor as it approaches the magnet and may cause it to trigger. If you're looking for a mag build, I'd suggest looking at: http://www.3dprintermods.com/prestashop/index.php?id_product=9&controller=product
I'm just about to get into auto-leveling myself, with this particular build there are a few ways to get around the issue. If you plot your auto level to occur as far from the magnets as possible (x,y location wise), then you might be ok. Otherwise you might consider investigating optical and touch probes.

You might use the magnets themselves or additional ones on top for the leveling process, as partly discussed in this thread:
http://forums.reprap.org/read.php?1,479795
A mechanical or piezo switch might also solve the issue for you with a lot less guesswork and trouble.


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What setting do I need to change to get rid of this gap between the shells and the inside?
I've noticed that some of my prints (mostly square-ish objects) are coming out with gaps between the outside shells and the inner parts. This gap is visible even in the 2D sliced preview of the layers so I think it must have something to do with slicing settings, but I'm at a loss for what I need to change to fix it.
See below for images of the issue. On the orange piece near the right hand side you can see light shining through the gap. The black cube has it at the top, though it's not deep enough to let light through like with the orange one. There is also an image of the layer preview which shows the same gap.
I have a Rostock Max v2 (stock hot end). I am using Matter control using mostly stock settings, I've tweaked around layer height, speed, and temp but I don't think those are the cause.
.
Images of the issue:

Hi, FoamyGuy! I edited your post by adding the images you refer directly to the post. This way, you don't need an additional click to see the issue, and the images will be available even if the link goes bad.

@TormodHaugene ah thank you. It slipped my mind that you could embed them. Thank you for bringing them in to the question.

It's generally called infill overlap.
In terms of first layer it's good to set extrude rate to 120% or even more so infill will overlap perimeters and itself. There is also the issue of "overlapping" layers which is not managed by any specific parameter. it's the issue of layer thickness and HE temperature.
Unfortunately Matter Control has kinda bug or at least an issue with extrude rate. If you set higher  extrude rate then overlap will be automatically reduced in some way. So it's good to increase extrude rate manually during printing and then set it back to normal. this will cheat slicer.

Ah! Thank you. infill overlap was set to 0.1. I bumped it up to 0.3 and at least on the layer preview there are no longer the big gaps visible. I'll try a test print to see how it comes out.

Ok, the test print is finished. using 0.3 did remove the gap between the infill and the shells. As you noted, it seems to be somehow tied to the extrude rate setting. Even though I didn't change rate it seems to be extruding slightly less now. Maybe I can find some happy medium with them.
How would I manually increase the extrude rate? Edit the gcode file that comes out of the slicr before letting it run on the printer?

@FoamyGuy On the bottom of control panel there are two sliders. One drives print speed and second drives extrude rate. These two canbe set during print. This is what i meant to say. Good to here you've managed the problem.

Oh, Thank you. I see those now. I'll give a shot here a bit later.


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Travel Mug Woes
I have a 30ish year old travel mug from Sheetz that I intend to model and print using my OpenScad skills.   The fact that it is an insulated mug means that the inside is hollow to an extent.
What reccomendations do you have toward turning this into a foodsafe, leakproof success?

Hi! Do you intend to use this mug for hot liquids or cold only? Many thermoplastics will start to soften between 50-100C, which might limit your options considerably.

Both, though it is intended to be a coffee mug primarily

Why do you want to 3D print a travel mug? It will be almost impossible to get satisfactory results, a store-bought one will be both vastly higher quality and vastly cheaper. Insulated mugs also tend to have a vacuum on the inside, which is something you definitely can't print.

You should mention what printing technology you're using. On this site, it's common practice to presume it's FDM but for the sake of clarity (and for future reference, when other printing processes might be more common) you should mention explicitly what printing technology the question is about.

I noticed that your question has not had much activity lately, are you still looking for an answer to this question? How might we be able to close some gaps?

@tbm.  Sure. xxx

You cannot make a safe coffee cup using home FDM printers. There are no printable thermoplastics available to consumers/hobbyists that will reliably AND safely contain coffee/tea temperature beverages.
Even though some plastics may appear mechanically suitable at first sight, there are long-term issues with using thermoplastics for elevated temperature service. The material becomes weaker and less dimensionally stable under load as the temperature approaches the glass point of the polymer. For example, here is some Stratasys test data for ABS strength versus temperature:

Even if the plastic survives a few uses, it may creep and warp over time. And that might be fine, depending on your needs! People have printed working coffee cups out of ABS before. For some definition of "working" you can make print a working coffee mug. It's just not going to work at the level of longevity and reliability that people typically expect from hot beverage containers. (Imagine if the handle breaks and pours scalding liquid in your lap.) PLA in particular tends to give out abruptly due to its unusual ability to creep to ultimate failure with very low elongations.
Then there is the question of whether ANY FDM printed part is ever safe for repeated food service use. One-time uses (such as throw-away cookie cutters) might be perfectly fine, but repeated use introduces additional problems because FDM parts are porous. They contain a microscopic void/grain structure that is perfect for trapping food debris and sheltering bacteria. Every FDM part is similar in that regard to an old, scratched, wooden cutting board. They are difficult to effectively sanitize. A high-temp dishwasher cycle will do the job, but that imposes significant thermal stress on thermoplastics.
Here's an example micrograph I took of voids in a printed part (strands all aligned the same way to highlight the shape):

These voids will also allow liquids to leak unless careful print settings are used. Over-extruding with multiple perimeters, or doing some kind of post-print sealing can make water-tight parts. It's not hard, just takes some experimenting.
There is also considerable anecdotal evidence that much of the cheap filament from Asia is full of nasty, toxic substances that may leach into hot beverages. Heavy metals like lead, strontrium, and cadmium are often found in thermoplastics as processing aids, pigments, or simply from unscrupulous companies disposing of industrial ashes by mixing them into dark-colored filaments for export. US-made and EU-made filaments seem to be better in this regard.
Now that the basic issues are out of the way... Here is the breakdown of specific materials you might want to try:

PLA blends used in 3d printing will soften and fail almost instantly on contact with hot beverages. (They contain melt-reducers and viscosity modifiers and polymer molecular weights specific to FDM filament and will perform differently from injection-molded PLA products.) It is possible to anneal PLA to survive higher temperatures, as this increases the crystallinity of the polymer and thus makes it more heat-stable. However, that is highly experimental and results will vary considerably with filament provider, color/pigment, and annealing process used. Even annealed PLA is unlikely to survive long-term against very hot beverages and dishwasher use.
ABS will become fairly weak at hot beverage temperatures. It may survive use for a while, but is quite weak and will slowly creep with very hot beverages or in a high-temp dishwasher. ABS IS approved for food use in many contexts, despite what many people think, but hot beverages are not one of the approved uses.
PET blends are chemically a pretty good choice -- soda bottles are PET -- but generally have glass points around 70-75C and thus will be weak or fail outright at hot beverage temperatures. It is also important to ask what is being blended into the PET. For example, PETG is "glycol modified" but filament vendors do not share any details about this or reveal how it may affect the polymer's leaching behavior.
Most nylons will creep under load at surprisingly low temperatures, perhaps 50-55C depending on the blend. Nylons are also attacked by acids and will absorb stains and smells from coffee. Nylons also tend to swell/shrink quite dramatically on exposure to water, so mechanical fit and general shape of nylon parts may not be stable enough even for cold beverage service. Taulman's 910 is probably a good candidate for hot beverage service due to its high working temperature, but acid attack from coffee exposure may still be an issue in the long run. It's worth trying.
Polycarbonate is thermally stable even in boiling water, so mechanically it is fine, but PC leaches BPA (one of the monomers left over from manufacture) into hot liquids.
High-temp exotics like Ultem and PEEK aren't printable by consumer/hobbyist printers at the size scale required for a coffee mug. They simply warp too much unless you have an oven for a heated build chamber.

In summary, you can make a working coffee mug via FDM printing, but it isn't a great idea. Your best bet for 3d printing a coffee mug is ordering ceramic printed from an online service bureau.

Did you get the graph from Stratasys' website? I've been trying to find information like this for a while now.

@tbm0115 Yeah, it was in a white paper they posted on their site a while back.


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What is causing these artifacts when the extruder moves in one direction?
I have a Prusa i3 that I am mostly happy with. However, I am seeing these strange artifacts when the extruder moves along one axis in one direction - in particular from the back of the printer towards the front. The extruded lines look uneven and the surface is quite rough, but only in that area and only while the extruder moves in that direction.
Here is a recent print that shows this happen. The pieces were printed side by side, and both of them show this on the left hand side, while the right is okay.

I am thinking maybe the extruder tip is slanted (not perpendicular to the bed), which causes some sort of scraping while extruding? What do you think?

What material are you using? Is there a possibility that it's warping/delamination?

Does the printer sound the same when moving along both sides? Could this be some kind of self-resonance?

@tbm0115, this is PLA. There is some warping going on, but it's very minor and I don't believe this is it (it is mostly evident on lower layers).

@TormodHaugene, it sounds the same to me, but I won't pretend that I am musically gifted or anything. I don't hear anything anyways, I just see this poor result on one side.

I noticed that your question has not had much activity lately, are you still looking for an answer to this question? How might we be able to close some gaps?

In case of such difference in printing in different directions you can check if;

for x and partially z axis

filament is blocked and cannot be pulled as it should
spool is blocked

for x and y axis

rods on which caret/HB is sliding are parallel
timing belt idlers are parallel and they are in a line

Shape of the nozzle or its perpendicularity should not be the case as it's hot and it wipes layer itself.
You can also check if it's not an issue of cooling fan. It can vibrate as such.
Eventually it could be an issue of cooling itself. Let's assume you have cooling fan at the back and it pushes air to the front then when caret moves from the front to the back then cooling time is longer than when the fan goes in opposite direction.

Those are some very good ideas. I recently had problems with the pneumatic connector on the extruder, so I will check (and probably replace) that, maybe it is affecting the filament feed. My x & y rods are fine though, so are the timing belts. Cooling fan might be it, as well. I will try it tomorrow and report back.

@Catsunami double check your timing belt idlers. Look closer if they don't  twist your timing belt not at all. Such little twist can cause that teeth touch flange and cause "jumping". Everything almost not recognized visually.

@Catsunami: If you have a "wind shade" on the left side of your prints from a cooling fan on the right side of the prints, then that is most likely be the source of your issues!

In my case, there were some artifacts only on the right side, and the problem was that the screw was partly out of the pulley under the bed. I would suggest moving the bed to the back and checking the pulley. You might also consider cleaning and lubricating the rods, which is what I was doing when I discovered it.
Here is an example of the bumps when the pulley was loose (using TPU):


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How to open .max files
I need help opening a .max file a friend sent me. The thing is, I don't have Alias Maya. Well, a copy of Alias Maya that works anyway.
Are there any other file openers that I can use? Or do I have to get Maya to open the file? Would Alias Maya open the file? I don't want to get download 1.3 GB and discover that there is 15 MB file opener.
Is there a file converter maybe? That converts .max to, maybe, .obj?

I believe the best tool for such conversion is 3DMax itself. I also tried google which returned me some worth-to-check results.

If you want to use it for 3d printing then I suggest you to ask your friend to export it to STL format.

You could try import it with blender. It's a free software which should be able to import the files.
First thing is to go the the File->User Preferences->Add Ons tab. In the Import-Export section, enable the 3DS Add-on.
After that you can export it to the desired format. Before exporting you must select the model/mesh you want to export. Otherwise nothing will be exported. The obj exporter is enabled by default in blender.

So I must export the file in Maya first?

Or import in Blender?

Blender should be able to import the .max file directly after activating the shipped 3DS Add-on ;)

Ah. I see. How big is blender?

Blender is about 100 megabytes at the moment. So not to big in my opinion

Oh woah. I was expecting it to be atleast 1gb. This is the whole file right?

Jep. In the 100 mb download is everything you need. Just don't forget to activate the 3DS Add-on. I use blender a lot in my 3d printing projects...

Oh great stuff. Thank you for the insight. I will try it and let you know.

Tell me something. Is a .max file the same as a .3ds file?

These are two different file formats from the same company (Autodesk). But blender should be able to import both

I installed blender, and went to add ons, and saw the .3ds file plugin was already on. I then looked for my file and didnt see it. Any suggestions?

Is there another plugin?

Have you had any luck importing .max files in blender?

Let us continue this discussion in chat.

.3ds is not .max. Try converting online


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Are there any services that offer 3D scanning?
So, have a plastic car part I want to duplicate because the driver side part is broken (I have the passenger side part) and It isn't sold anymore. It's a small piece that would be an excellent candidate for a 3D printed replacement. I know there are companies I can send a 3D model to that will happily print it for me, but I also need to create a 3D model from the part. Is there a company or service that I could mail the part to that would return it along with a 3D model of it?

The right Google (or other) search should do the trick. I've provided 3D Printing services via 3D Hubs and MakeXYZ and some people do provide 3D scanning services. If you can't find 3D Scanning, you could try talking to a local machine shop. They might have the tools to be able to reverse-engineer the object, or know another place that can.


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Print paper or cellulose - any recyclable filament?
I know there is a 3d printing technique, where sheet of papers are cut and glued. Like the ones Staples has in their stores. But this sort of paper isnt recyclable, because of the heavy use of glue.
Is anywhere filament available, which is made of cellulose or other recyclable and bio-degradable material? Or do you know if research is going on in this area?
edit: added bio-degradable

maybe laywood... I know it's not recycled but maybe it could be, but generally it uses cellulose as it manages wood... with one eye closed... MDF is also wood :)

thanks for this hint. I read a little about it aaand it is 40% cellulose and rest is bonding agent. for me it looks like the cellulose is for the "taste" or "look" only. But not as the main material....

I believe the 3D printing technique you are talking about is Laminated Object Manufacturing (LOM)?
Could you please specify: is your goal to find any recyclable 3D printing filament for FDM printers? In that case, could you perhaps be looking for any kind of PLA material (which is bio-degradable)?

Filament made of Polylactic acid (PLA) is usually made of biological materials (such as corn), and can therefore be considered bio-degradable in most cases.
Whether the filament is 100% bio-degradable (and non-toxic for the surroundings) will depend on the specific formula used by each individual filament manufacturer. (Many manufacturers include various additives to achieve particular effects, such as glow-in-the-dark, metallic finish or extra strengh.)
Woodfill PLA-like filament might be of extra interest to you, not only because it typically is bio-degradable, but also because it will give you the look and feel of being bio-degradable.
Hope that helps!
PS: there are multiple other filament types that are either recyclable, bio-degradable, or both, although PLA might be the most commonly available of them all.

Check Green-TEC by extrudr.eu is made from lignin (wood)
or perhaps Algix Dura. They are both bio degradeable.
Green-TEC ist my favorite because of less warping and fast printing.


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How to enlarge a Sketchup Model
I have moved forward with the whole .max thing. It's on the back burner. But not as critical now. I have found a Sketchup model of the model I want. But it is ridiculously small (0.17 m long by 0.10 m wide!).
How do I enlarge it to fit my dimensions as a whole?

You could try the scale function (try s on the keyboard). There's probably a metric conversion issue, so try applying the 25.4 rule to your model. If the model is in mm, but your environment is in inches, then multiply by 25.4. If reverse, divide by 25.4.

I would not consider 0.17m (=17cm) to be ridiculously small. That's pretty large for 3D printers. The ".max thing" seems wholly irrelevant to the question.

I included the .max thing because the original model I wanted was in .max format, but I found the same model in a sketchup model.

You're right. 17 cm is quite large for printing. I wanted to upscale the model because it is uncomplete.

Use Cura middle button in bottom

Ah. I see. Thats what I needed. Now I can work on my model nicely now =D


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Open Source 3D scanning
I am trying to make a structured light 3D scanner using single camera, light projector and a turntable.
After days on Google I did not find any reliable open source project which I can get to work.  SLStudio really seemed a good choice but did not compile properly.
I was wondering if anyone knows a good open source which they have used with the same kind of setup? Any help would be really appreciated. I am blocked here.

In this video I've seen something, but I'm not sure if it's the source of open source https://youtu.be/_LyuTwJ2vsY

I got some really useful resources here but I got rid of structured light approach because of lesser resources.
I used VisualSFM(.exe) , VisualSFM(source) with the turntable for the purpose and got some pretty neat results. Works well and easy to use.

I did find only one 3d scanner which uses structured light. There is many projects using a laser diode. And these systems are completely opensource.
Structured Light
Structured Light 3D Scanning by kylemcdonald

http://www.instructables.com/id/Structured-Light-3D-Scanning/?ALLSTEPS

Laser diode
Sardauscan

http://www.instructables.com/id/Build-a-30-laser/?ALLSTEPS
https://github.com/Sardau/Sardauscan
http://www.thingiverse.com/thing:702470

ATLAS 3D Scanner

http://www.freelss.org
http://www.thingiverse.com/thing:1280901
https://www.kickstarter.com/projects/1545315380/atlas-3d-the-3d-scanner-you-print-and-build-yourse/posts/1475722

Ciclop

http://diwo.bq.com/en/tag/ciclop/
https://github.com/bqlabs/ciclop

3D(ollar) Scanner

https://hackaday.io/project/2021-3dollar-scanner
http://www.instructables.com/id/Lets-cook-3D-scanner-based-on-Arduino-and-Proces/?ALLSTEPS

"Super Make Something" Tutorial On How To Build a Simple 3D Scanner

https://www.youtube.com/watch?v=-qeD2__yK4c
http://www.thingiverse.com/thing:1413891
http://diy3dprinting.blogspot.de/2016/04/super-make-something-tutorial-on-how-to.html

Different method
$15 3D scanner consists of a tub of milk and a smartphone
Interesting idea of using milk and phone.

http://www.instructables.com/id/GotMesh-the-Most-Cheap-and-Simplistic-3D-Scanner/
http://www.3ders.org/articles/20160423-this-3d-scanner-consists-of-a-tub-of-milk-and-a-smartphone.html

I have also been looking for some free or paid software for doing 3D scanning and the closest I have found to something that might work is thishttp://wedidstuff.heavyimage.com/index.php/2013/07/12/open-source-photogrammetry-workflow/
But it isn't Structure from light (doesn't use a projector)
If you want to stick with Structured Light then I would suggest looking into openCV (http://docs.opencv.org/trunk/d1/d90/group__structured__light.html#gsc.tab=0) I havn't looked into this much but it looks like you might be able to get something working with it.

Thanks user802599, OpenCV solution looks good, wish I had it earlier, will look into it anyway as i have worked with openCV
I got rid of structured light approach because there weren't enough resources and made one using VisualSFM. its really good and fast.

You can use a Kinect sensor for Xbox 360 OR Kinect sensor for Xbox One. That sensor allows you to get a true 3D surface with its SDK. You can connect these devices directly to your PC using USB (I have one).
Even the Xbox One model, in its SDK, has an example that allows you export your captured mesh as STL files.

Try Brown University School of Engineering: Projector-Camera Calibration / 3D Scanning Software.
I have not tried it myself, but give it a look.

I have given it a try.... didnt seem to work then... ill work on it again and get back to you.. thnx :)

@hamza I just wonder why you arent donate the answer with a +1 ? It actually gave you worth

I definitely will.... sorry that i didnt earlier..... :)

It is not structured light. This uses a laser:
https://hci.rwth-aachen.de/fabscan
But it is completely open source software / open source hardware.
See also here:
https://www.thingiverse.com/thing:14198
https://www.youtube.com/watch?v=hBueeqDJ6rQ

Thanks Lars, seem like really good resources, ill look into each of them...
I got rid of structured light approach because there weren't enough resources and made one using VisualSFM. its really good and fast.

BQ Ciclop 3D Scanner

Scan Volume: Bigger than 5 cm x 5 cm and smaller than 20 cm x 20 cm
Scanning Precision: 0.5 mm

All the necessary parts for Ciclop are included in this DIY kit, which comes unassembled.
This Ciclop 3D Scanner Parts List:

1 x Plastic parts( 1 set with 11 pcs)
1 x Arduino Uno R3 with USB cable
1 x ZUM Scan Shield
1 x A4988 Stepper Driver
1 x C270 HD camera
1 x Nema17 stepper motor
2 x Laser
1 x Power supply adapter
1 x 16014 ball bearing
1 x M8 threaded rod (9 pcs)
2 x Acrylic panel
1 x 8mm spiral wrapping band
1 x Set of screw and nuts

Note to mods and reviewers: Whilst this is technically spam, it is rather descriptive and not malicious spam (unlike the two deleted answers). The info actually supplements one of the options given in Amra's answer. For this reason, it has currently be left in place. Maybe the link should be removed, and user account destroyed.


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FlashForge Creator Pro Tool Failure! Temp limit reached
After printing successfully for a while I received an error saying:
Tool 0 Failure!
Temp limit reached
Shutdown or restart.
The front panel is not responsive and doesn't allow the printer to print at all. If I quickly go to monitor mode it shows tool 0 temperature in the ~700°C range; which made me think it was the thermocouple.On the motherboard I unplugged the thermocouple and the same error occurred, I then swapped the other thermocouple and put it in its place and got the same error except the tool 1 temperature showed "NC".
I had recently taken apart the extruders to change out the nozzles and thought I had possibly smashed the wires when putting it together but now I don't think that's the case.
I'm on the phone with FlashForge's tech support but wanted to see if someone else has had the same experience for cross reference.
What's the underlying issue? Is there a quick solution to this that can get me printing right away (I'm under a deadline)? What's the end solution?

It's possible the sensor wire has been damaged. I've heard of sensors being damaged, resulting in the machine continually "increasing" the extruder temp, but usually it will timeout.

It sounds like a failed TC amp chip. But we need to rule out some other stuff.
Some important facts about the Creator Pro temp sensor:

If you smash and short the two thermocouple wires together, the printer will simply read room temp.
If you cut or disconnect the thermocouple wires, the printer will report NC for "not connected."
The thermocouple lookup table in the firmware only goes up to 300C.

Seeing a number over 300C means either a bad thermocouple amp chip, or excess voltage on the TC wires due to a short to something else in the hot block. (However, such a short will usually fry the entire controller board to smithereens.)
To rule out stray voltage entering the TC wires, completely detach both thermocouples from the hot blocks and lay them out not touching anything metal. Do you still get an unusually high reading on tool 0?
To rule out an issue with the specific thermocouple, swap thermocouples between tool 0 and tool 1 and see if the problem moves with the TCs.
If the TC is not touching anything, and the problem stays with the tool when you swap wires, and you STILL get >300C reads, the thermocouple amp chip has failed. It is possible to replace the chip if you have (or your friend has) a hot air rework station and some experience soldering. Or you can get a new mainboard from FlashForge.
The next question is why this problem happened. You don't want to fix the symptoms with new parts but have an underlying issue cause the same failure to re-occur after you swap out parts. With the printer on but the heaters off, use a multimeter to check for voltage between the hot block and the printer's ground. Certain types of heater cartridge failure can short the hot block to +24v. This is highly dangerous and needs to be fixed before you continue using the printer. So make sure you check it before trying to repair anything else.

Still get the same error after removing both thermocouples completely and swapping.
I noticed a lot of static when touching the chassis. Could be the root cause of the issue.

Yes, static could potentially fry the TC amp.

Is there an instruction set on how to check voltages around the device that you're aware of?

Hmm, not a manual or anything. I would flip the (powered up) printer over on its side, put one multimeter probe on a V- terminal on the PSU, and poke the hot block for tool 0 (right extruder) with the other multimeter probe. If it's 24 you have a bad cartridge. Make sure you're hitting aluminum and not insulation. Another thing you can check is whether the tip insulation on the TC itself is damaged... disconnect the TC completely and measure resistance from the tip to either of the wire terminations. Should be infinite / out of range. If it's low, you need a new TC.

Static is a big deal..

To StarWind's point, after replacing the motherboard I continued to have problems with printing large flat surfaces where the printer would go past its intended boundaries. Problem was linked to X/Y stepper motors needing replacement after being exposed to stray AC voltage. Stray AC voltage came from unknowingly using an ungrounded receptacle in my garage.

In my case, the resistor in-between the relevant thermocouple jack and MAX6675 chip was visibly fried.  I haven't yet fully repaired the issue, but I was able to return the printer to a usable state by unsoldering pin 7 (look up the MAX6675 datasheet to see which pin is #7).  This forced the temperature reading to 0℃ for the afflicted hotend, allowing the other one to operate without being interrupted by a false "temp limit reached" from the unused hotend.

Oh yeah my printer had that. Specifically 2 Flash Forge Creator Pros, Replace the thermal couple. Done. Really fragile thermal couples they use.
Edit I see you tried shorting the TC. Wouldn't shorting the TC, produce the same error?

To whomever is down voting, please post comments so we can improve the answers.


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Would a steel, instead of an aluminium, plate be reasonable?
I have a Flashforge Creator Dual.
One corner of my print bed is warped down.  I am thinking about having a steel print bed made so it would tend to stay flat.
Has anyone tried this?

Whether you should use steel or aluminum depends on the construction of your print bed stack. Either will work, but there are trade-offs involved.
Various considerations that may come into play:

A flat sheet of aluminum has better stiffness/weight ratio than a flat sheet of steel. If weight/mass is a concern, such as with a Mendel style moving Y-bed, aluminum may be superior to an equivalent stiffness steel sheet. On the other hand, steel has the superior stiffness/thickness ratio, so if the total thickness of the plate is constrained, such as by the printer's mounting hardware, steel may be higher performance. In short, for sheets of equivalent stiffness, aluminum will be thicker but lighter. That may or may not matter for your specific printer.
Differential thermal expansion can be an issue, depending on what the plate is attached to. For example, rigidly bolting a steel sheet to an aluminum sub-frame will cause the structure to warp when its temperature changes. Likewise for bolting an aluminum sheet to a steel sub-frame. Bed mounts that "float" will not cause warping in either case.
All kinds of rolled sheet metal may have a tendency to warp when heated/cooled, due to residual stresses and grain alignment effects from manufacture. When people want extreme dimensional stability for the flattest and lowest-warp print bed possible, an aluminum cast tooling plate material such as MIC 6 is usually used. The MIC 6 sheet is then precision ground to be flat. Of course, that adds cost.
Neither aluminum nor steel is a particularly good bare print surface. Either will need some kind of adhesion layer, like Kapton tape or gluestick. The adhesion layer matters far more than the type of metal underneath.
Aluminum sheets are often used as heat-spreaders to even out the bed temperature of heated beds. This is very important when heaters are smaller than the total bed size, or have hot spots. (Most heaters do have hot spots.) Steel is a relatively poor conductor of heat, so the surface of the bed will take longer to heat up and will be less even. That may or may not be an issue, depending on the printer and desired materials.

So, it's really a holistic design decision. Aluminum is far more common because of its thermal properties and lower weight, but steel print beds (particularly with permanent adhesion coatings) are often used too.

+1, this answer has helped me in my design. However, en lieu of the Kapton tape, or gluestick, a PEI sheet could be used, as used in the Prusa i3 MK2. 12"x12" PEI sheet is available for around $15 (Amazon) to $20 (eBay). It can be secured using either bulldog clips or 3M 468MP adhesive sheet.

I would consider getting another aluminum build plate for the following reasons:

Lightweight. Aluminum is a very lightweight metal, making it suitable for most machines that have injection molded platform arms. This reduces potential sagging of the arms and overall load on the -Z- axis stepper motor.
Conductivity. Referring to this simple Google search for heat conductivity, aluminum is significantly more conductive than steel (205 vs 43 respectively) with copper at about double that of aluminum.
Availability. Aluminum is already a widely used material for 3D printing, so finding one will be relatively easy and probably cheaper than having a steel build plate custom made.

In conclusion, I personally would not recommend using steel for your build plate as aluminum seems to have the most benefits. Yes, steel will be more rigid and durable, but I don't think that these should be variables that are significantly more beneficial over aluminum.

This doesn't really answer the question "can I use steel instead of aluminium?". It just lists some advantages of aluminium, but that doesn't rule out steel as an alternative. I would imagine you can quite happily print on steel.

Updated my answer to elaborate. Technically, the OP could use steel, but my personal opinion is that it is not a good idea. I tried to avoid expressing my opinion by highlighting the benefits of continuing to use aluminum.

If you are talking Stainless Steel, it is a HORRIBLE thermal conductor (AL is 20x better).  It might make the heated bed almost useless.


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How to choose printer with dual extruder?
I use Prusa i3 with one extruder for some years and I would like to print from one material in two colors or from different materials for one model. Therefore I'm lookig for new printer with dual extruder.
Is there some way how to measure and/or compare quality of printers with dual extruder on the market?
For example to create 3d model - ask the seller(s) to print it - and then compare? - what details to focus on?

Without some type of budget, answers are going to be all over the place and I doubt any company selling under $1000 is going to print you a sample.

@tjb1 I agree it can be hard to make such deal with printer producer but it seems to me pretty realistic to ask one of 3D hubs as suggested by tormod-haugene below

Hi! Did you consider simply upgrading your prusa i3 to have dual extruder instead?

As you suggest yourself, ordering test prints of some model is one way to do it.
3D Hubs and MakeXYZ allows you to get your model printed by hobbyists and small businesses for a fair price. Both sites also allow you to order prints based on printer type, which I believe is what you may be looking for.
On 3D Hubs, visit on of the trend reports, and select the printer you want a sample from. Similarly, on MakeXYZ, search local makers for your desired printer.

"Make" Magazine compares 3-D printers in a way that is as scientific as possible to help determine the strengths/weaknesses of each 3-D printer compared to others. The link to the November 2015 comparison test is available here: http://makezine.com/comparison/3dprinters/ I was unable to find the ability to compare among dual-extruders, however.


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Extrusion adjustment
I recently started to use Simplify3D! It is great software, but I have a problem with adjustment of amount of plastic extruded. I have a slight under extrusion after I adjusted amount of plastic extruded using  perimeter test (Printing a square with wall thickness of one layer, measuring, adjusting extrusion multiplier). I suggest that there is under extrusion by looking at top layer (there is distance between layers) and there are gaps around holes as well. I'm using Ultimaker two and colorFabb filament. I can resolve problems by increasing extrusion multiplier, but then I have incorrect layer width :/
I have also attached picture. http://postimg.org/image/keghmu075/ On a right side, there is a part with correct extrusion multiplier (under extrusion).
Maybe you guys have some ideas?

SHORT ANSWER
You're not supposed to do the single-wall perimeter thickness test to calibrate Simplify3D. That screws up the extrusion volume. The correct volume calibration procedure for S3D is:

Measure actual average filament diameter and input that
Print a 100% infill calibration cubes
If the print is over-extruded (top or sides bulging), decrease Extrusion Multiplier by about 0.05 and try again. If the print is under-extruded or looks clean, increase Extrusion Multiplier by about 0.05 and try again.
Repeat as needed to dial it in. The correct value of Extrusion Multiplier is the largest value that does not produce over-extruded prints. This produces minimum void volume and strong parts.
In the future, that specific material+extruder combination will always have the same extrusion multiplier. You only need to measure and input filament diameter and you will always get accurate volume output. (And if you use high-quality filament with consistent diameter, you don't even really need to measure the diameter.)

If you really want to measure perimeters, you can do 3 perimeters and divide the measurement by 3. That takes into account most of the overlap and will be much closer to accurate than a single-perimeter measurement.
COMPLETE ANSWER
The goal here is to fill the print volume as completely as possible (at least in the "solid" parts of the print like perimeters, roofs, and floors). Empty space between strands doesn't contribute to part strength. In fact, voids act as failure initiation sites by concentrating stresses. Because extruded strands come out with rounded edges, they have to be overlapped to squeeze plastic into gaps and minimize "corner voids." That looks like this:

Where the bulges overlap, the excess plastic gets pushed into the corners to mostly fill the voids. It's very difficult to get 100% packing density, but you can get pretty close if you calibrate volume correctly.

You DO NOT want to space the strands without overlap. That makes very weak prints and looks like this:

To get the right amount of strand overlap, the slicer has to do some math and make some assumptions about how you're calibrating it. This is not uniform between software packages. So it's important to understand what "extrusion width" means to different slicers. For a couple prominent examples:

Slic3r treats "extrusion width" as the measured outside dimension of a stack of strands. Adjacent strands are then positioned closer together than the nominal width according to a somewhat complicated equation to get sufficient overlap for bonding.
S3D treats "extrusion width" as the average width of the stack of strands, which is the equivalent width if the plastic strands were extruded as ideal rectangles instead of a stack of ovals. Adjacent strands are positioned 1x nominal extrusion width apart. That provides the correct amount of overlap without any extra math. But each individual strand is really somewhat wider than the nominal "width."

Both of these techniques can produce the exact same output if calibrated properly, but they require different calibration techniques because they calculate the plastic volume and adjacent strand spacing different ways.
It's important to understand that S3D spaces its strands 1x extrusion width apart. When you use the measured perimeter thickness to calibrate Simplify3D for extrusion width setting = measured thickness, you get under-extruded prints with no strand overlap. S3D's strands must measure wider than the "width" setting to get the correct overlap.
In practice, S3D's code is smart enough to know how this affects print dimenions, and will adjust perimeter positions to get accurate overall dimensions. But single-wall test boxes will be thicker than expected.
The downside to the way Slic3r calculates volume is that it is only accurate for strands that are shaped like ovals. And that is only an accurate assumption when [extrusion width > nozzle width + layer height]. The strand must be wide enough for molten plastic to flow sideways and develop the circular bulge cross-section. So people almost always print with wider strands in Slic3r than is strictly necessary. The volume calculations don't work all that well with thin strands. Whereas S3D's volume calculation method works fine with pretty much any extrusion width greater than layer height and greater than nozzle diameter.
There are pros and cons to both systems. You just need to understand the correct calibration technique for each.

Thanks for your answer, it is really great! Don't you think that approach of S3D is less scientific, because there we need to relay on our eye, but measuring perimeter in Slice3r we can get nice exact calibration result, which can be used by software to get really precise prints? Another think, I'll need to explain students how to calibrate amount of plastic extruded and it will be pretty hard for them to suggest when it is good enough to go.

Slic3r's method assumes a specific extrusion strand shape, which is only 95% correct under specific combinations of slicing settings, and not correct at all with other combinations of settings. It will push the wrong volume of plastic in those conditions. S3D's method is empirical but works great over a wider range of conditions. It's a trade-off.

Whether the top of the cube bulges up is a pretty easy metric to explain to people, I think.


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Pros to UV printing
This is related to Cons to UV printing and focused on Ryan Carlyle's answer, mentioning:

"...resin-curing SLA/DLP printers are industrial or commercial tools that are really not suitable for home desktop use."

So, my general question is what are the pros to using a DLP printer in an manufacturing environment?
My experience with 3D printing in manufacturing has shown me the necessity of understanding material strengths as well as how to utilize the 3D printing technology (FDM mostly) to produce a structurally strong part. Most of what I've made has been fixtures with small to moderate forces applied to them.
In short, are there any technological advantages to using a DLP printer in a manufacturing environment?

Would you mean "are there any technological advantages..." rather than "advances?"

Now that this question is nearly 6 years old, I would love to see an update based on the technology changes since 2016.

When using a DLP 3D printer, a projector (or other UV light source) is shining on a layer of resin.  As the light source shines on a whole layer at a time, it is able to print at a rather constant linear vertical rate. This rate is normally around 2.5 cm (1 inch)/hour
When comparing this to a standard FDM printer or a single laser system (such as the Pegasus Touch. The printer takes more time on more complicated layers. If a you were able to print the same 2.5 cm (1 inch), at 0.3 mm layer height, it would be a total of ~85 layers. This would allow for ~42 seconds per layer. Most layers would take longer from this (from personal experience).
With the constant layer rate, multiple objects can also be printed at once because if the printer has to print the layer for the first object, it is not taking more time for it to cure resin in another location on the print bed.
In addition to this, DLP printers can have much better resolutions than FDM printers.  A DLP printer such as the Titan 1 has a 37 μm XY resolution while a Prusa i3 has a resolution closer to 300 or 400 μm.