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Are there any software packages that can open and edit 3MF?
I am trying to find programs that can import and export 3MF file formats. I know that Cura 15.10 beta can open 3MF formats, but I am looking for a program that open, edit and save 3MF files. I am very interested in finding a more portable file format for my 3D designs.
If you are not aware the 3MF format promises to provide a "replacement" for STL files that contains the complete model information, theoretically allowing us to slice and edit the same file.
http://3mf.io/

I forgot to add the link for the Cura 15.10 Beta https://ultimaker.com/en/blog/17294-cura-1510-is-now-available-for-open-beta-testing

Semi-related: have you looked into AMF?  3MF is similar and newer format.  Both are XML based.

Microsoft 3D Builder should have support for this format.
Solidworks 2015 has support too. A software adoption list is placed on 3mf pages.

It looks like you're right. Unfortunately 3D Builder appears to windows 10 only are you aware of any that might work on Windows 7?

Unfortunately not. You have to wait for several moths.

3MF consortium is developing a library: https://github.com/3MFConsortium/lib3mf  The repository started to be more active recently. According to open issues transport to other platform is not done yet. After then 3MF support starts to emerge in open source SW, I assume.


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Heatbed control with Pronterface
I'm having trouble getting my MendelMax 2's heatbed not to heat up when I want to print without it. I don't get how multiple sources of control relate to each other (same with extrusion temperatures, actually):

Slic3r (1.2.9) has settings under Filament Settings / Filament / Bed, for First layer and Other layers (and groups of settings can be saved).
The pronterface GUI (Printrun-Mac-10Mar2014) has an "Options" panel where you can set "Bed temperature" (actually, two settings, one for PLA and one for ABS -- though I doubt the software can test which filament is loaded!)
The pronterface GUI also has a menu/fill-in labelled "Bed", which works fine to adjust the bed when nothing is printing. The menu there lets you pick from a manually-entered value, "0 (off)", and (apparently) the settings for PLA and ABS from the options panel.
Marlin's Configuration.h has settings for bed minimum and maximum temps (the non-zero minimum seems to be to prevent running the bed when the thermistor isn't working, to avoid unlimited overheating).

I recently tried to print some PLA with no bed heat (using blue tape on the glass build plate). I sliced the model with bed heat off in Slic3r; changed the PLA bed temps in the printerface options panel to 0; and picked the PLA setting in the GUI main screen (and also tried setting "0 (off)" manually.
When I started to print the object, the bed turned on and stayed on, maintaining 60C.
I thought of just unplugging the heatbed, but then I expect the print would never start, since it would try to heat up the bed and never succeed.
So how does the decision about which temperature setting to use, really get made? I have the same question about extruder temps, speeds, accelerations, and other things, too -- whose settings are really in charge?

Can you generate some g-code and put it in pastebin or somesuch? Does your bed heat up right after you turn on the power?

I should be able to grab the gcode, will try. Heatbed doesn't come on immediately, so it'd not just bypassing all control; and it maintains temp correctly at 60V...

3D printer get the temperature settings from g-code file. The firmware settings for min and max temperature are just safeguards.
You should verify instructions within the g-code file. If you are not familiar with g-code, take a look to wikipedia. List of g-code instructions for marlin firmware is here.
Instruction responsible for setting bed temperature are M190 and M140. Open your g-code file and search for lines containing them. If you delete these lines then the bed temperature will be not set during print. Additionally it means that it is set by your slicer.
In Slic3r you should check Printer settings → Custom G-code → Start G-code if it contains one of mentioned instructions and possibly remove it.

Sli3er will control the bed temperature during a print. The options in Pronterface can be used to pre-heat the bed and hot end, or to adjust the temperature during a print.
The slicer will put the temperatures you set in the filament tab settings into the gcode at the appropriate layers. As the printer reads these codes it will adjust the temperatures. If you manually change the temperature, it will stay at your adjustment until it encounters a line in the gcode file that tells it to change again. Usually this only happens at the start of a print, or at the transition from the first layer to the second layer.
When you change the filament settings in Slic3r, they do not save automatically, so if you changed them, closed the program without saving your filament settings, and opened it later, the changes would be lost.
The other place where temperature can be changed from is in the custom gcode settings, where you can specify operations to be performed at the start of the print, in between layers, or at the end of the print. Take a look there and make sure that there are no codes to change temperature in any of these fields.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/

sort: votes


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Show generated support structures in Cura
In Cura, when you enable "Print support structure", is there a way to see what it will look like?

Select the View Modes Button in the upper right hand corner, and select Layers.

Works, looks kind of weird though.  Too bad there isn't an option to show the support structures in normal mode.

Cura generates support based on the outlines of the layers which will be printed, rather based on the triangles of the 3D model.
It is therefore not possible to show the generated support in the solid view.
You can view the support in the layer view however.
In Cura 2 that's on the left bottom of the screen.

Support is classified as a helper part in the legend of the layer view.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


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Proper settings for printing rubber and rubber-like materials?
I am struggling finding how to print complex shapes made of rubber, tpu, tpe...
Are there any clear guidelines on how to print those materials without deforming and uncontrolled retraction?
The printer is not a problem, I can print on:

Delta WASP (the one I am specifically looking advice for)
Makerbot 5th
MB Z18
Sharebot NG
Ultimaker 2

Thank you!

Just an idea for anyone interested in getting elastic objects from 3d printers: making moulds and pouring 2 part silicone or another material is also a way to get an elastic object ( https://www.youtube.com/watch?v=J1jDaZX6PCk )

First off, you need the right extruder design. Specifically, the filament path between the drive gear or hob and hot end must be extremely well-constrained. 1.75mm TPE filaments (thermoplastic elastomers) will buckle in an instant if given the chance. That means they will try to squeeze out of any little opening in the filament drive path rather than being forced through the nozzle.

Is there a gap >1mm anywhere between your extruder drive gear and hot end? Including the groove in the drive gear itself. If so, either change extruders or print something to fill the gap. Many popular extruders already have Ninjaflex conversion parts uploaded on Thingiverse or Youmagine.
Are you using a 1.75mm bowden drive? You probably shouldn't bother with the softer TPEs like Ninaflex. Harder TPEs like Semiflex may be ok, but it's still difficult. 3mm bowden drives may perform ok. Direct drive extruders are highly recommend.
TPUs (thermoplastic urethanes) in particular can be sticky in the filament feed path between the spool and extruder. Try to minimize corners and turns (even inside PTFE tubes) between the extruder and spool. As a general rule of thumb, don't exceed 180 degrees of cumulative tube curvature in the entire path from the spool to the nozzle.

Once your filament feed path is fully enclosed, the filament will be constrained and unable to squeeze out the side or wrap around your drive gear. That's the most important step.
The next problem is simply loading the filament. Purging out PLA or ABS with a soft TPE can be challenging because of the force required to purge the old material. Many default loading routines are actually too fast for TPEs and will cause the TPE filament to bunch up rather than purging the previous material. It tends to extrude better when there is nothing else in the way. Some tips:

Do some cold-pulls to clear out the hot end as much as possible before loading the TPE. (Nylon is ideal for this. Preheat to nylon temps, run through some nylon, let the extruder cool to ~180C, and then forcefully pull out the nylon. If you can't pull it out, pull hotter. If it leaves nylon behind, pull colder.)
If you have a high-melting plastic like PET or nylon in the hot end, purge with a lower-melting solid filament like PLA first. This will reduce the viscosity of the old material when inserting the TPE.
If your printer has a fixed loading speed, consider making a gcode file with nothing but a preheat and very slow extruder move as a custom loading script.
If you fail to load and jam up the TPE, try again! Sometimes it takes a few load/unload cycles to get the old material purged and a clean feed going.

The final issue is print settings. You ever hear the saying, "you can't push a rope"? That's kind of what you're fighting with TPEs. With a properly constrained feed path, you can push rubber, but not very hard. So minimizing extrusion force is the name of the game.

Print SLOW to start. Like 10mm/s. You can dial it up once you're getting good results. This will minimize nozzle back-pressure and reduce the amount of "pushing a rope" that the extruder drive must do.
Retract as little as possible. Turn off "optional" retractions in your slicer, such as during layer changes. Some people even print with no retraction at all, and use high travel speeds and coast/wipe features to minimize stringing. That's overkill, but it can help with marginal extruders. I personally add about 50% to my normal ABS/PLA retraction distance.
Print on the hotter side of the recommended range to start, then dial down the temp as needed to reduce stringing and oozing. Printing hot will reduce nozzle back-pressure.

With all that, it should be possible to print the softest TPEs with reasonable success. But if you really can't get it working right, plenty of higher-durometer TPEs are available now that are significantly easier to extrude.

Thank you @Ryan for the exhaustive answer. I will try your suggestions ASAP and get back to you.


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Heat sensor problems with Makerbot Replicator 2X
We have a Makerbot Replicator 2X at our school.  I have a class in the computer lab and one of our focuses is using the printer. Currently, it is not printing properly.  We are using PLA at 210 degrees Celcius.  The built plate is not heated (using Build Tak).  This has worked very well in the past.  The problem is that when the extruder goes to lay down plastic, the filament is too hot and curls up in a clump around the extruder.  This is characteristic of when we first tried PLA at a higher temperature.  I think that our heat sensor is not working properly.  Does anyone know how we can fix this problem?  Is there a way to calibrate the sensor is should we install a new one?

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?

@tmb0115 I selected the proper answer.  We replaced the thermocouple and it started working again.

Overall, it is unlikely that the problem is temp sensing accuracy. There are only a few things that will throw off the thermocouple's reading:

Poor thermal coupling between the tip and the hot block, such as if the tip has partially pulled free of the brass thermowell crimp (this will make the hot block hotter than the reported temp)
Loss of electrical insulation between the tip and the hot block, plus some ground loop noise or stray voltage on the hot block (this will typically add noise to the reported temp)

You should be able to visually check for the first, and test for the second with a multimeter. The resistance between the board end of the thermocouple leads and the brass thermowell at the tip should be infinite / out of range.
To actually check the thermocouple calibration, you have a few options:

Easy: Look at the behavior of the printed plastic. PLA that is too hot will smell of pancakes/waffles much stronger than normal, or even smell burnt. The printed material may be more shiny than usual. It will string and ooze more as you print.
Moderate: Secure another reference thermocouple (such as might come with a digital multimeter) tightly to the hot block with some Kapton tape, somewhere the aluminum block is exposed. The external TC should read within a few degrees of the printer's TC. (Assuming you get it attached well enough.)
Hard: Place the tip of the TC in boiling water to check if it reads 100C (or slightly lower if you live at a high altitude). Repeat with well-mixed ice water to check if it reads 0C. Both measurements should be within a couple degrees. You will probably need to dismantle much of the extruder to detach the thermocouple for this test.

But, again, the problem probably isn't the TC. It's more likely either a bed tramming issue (eg too much gap between nozzle and surface) or the BuildTak is degraded and not adhering. This can happen if you do a large number of prints in the exact same place, or get the surface oily, such as with fingerprints. Try a fresh sheet of buildtak or cleaning it with rubbing alcohol and moving the print to a different location.
In some rare cases, low-quality filament or filament stored in very high humidity may not stick well. This is pretty rare though. For the most part, if your nozzle gap is right, any extruded plastic will stick to Buildtak.

The temperature is fine.
In my experience the filament curls up only when the extruder is extruding way up, far from the plate: are you experiencing this while actually printing?
If yes: recalibrate the printer so that the extruder is closer to the build plate and this shouldn't happen. For the filament to curl up it means you are way higher than you should be.

"Recalibrate" meaning adjust the leveling screws using the built-in leveling script from the LCD, or by printing a level check STL.

Also, if the problem is really about the distance between plate and extruder, and not the temperature, I would suggest editing the question title accordingly.

Could also be finger grease on the Buildtak.

It wasn't the distance between the plate and extruder. Will be trying more options soon. @gcatalfamo

Could you post a very close-up picture of the filament curling up while printing? It might help us understand your problem better :)

Yesterday our teacher started getting heating errors and sure enough, the thermocouple is shot.  Thank you for your help though! @gcatalfamo


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parts for autoleveling Prusa i3
I am following this video series to add auto-leveling to my Prusa i3.  https://youtu.be/awsI9bMndJA
I have printed the parts I need and have the servo and ss-5 endstop in my cart at Amazon.  What I need to know is what wiring I need to connect the endstop to the RAMPs board?  I bought this printer as a kit and all parts were included so I am learning slowly.
The switch
http://www.amazon.com/gp/product/B00HPLBAYW?psc=1&redirect=true&ref_=ox_sc_act_title_3&smid=AZHZ102UTKBMA
Thanks!

You just need some wires, nothing special about them. You can use any wire that's flexible enough. For the endstop you'll need 2 wires, for the servo (if you need to extend the cable) 3. The connectors on the end are known as dupont connectors.

Thanks.  I am new to 3D printing and electronics in general but I have always been interested.  I went on Amazon and bought connectors, crimper, wire (different colors), soldering iron, etc.  Now I will be unstoppable!

Let us know how it works out -- others (including me) will be interested in perhaps doing the same.

@TextGeek I bought the stuff and became a connector-making fool.  I ended up making many extension cables as I keep moving things around.  Then i started soldering them and using shrink tubing instead. :D


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Which hotend does not clog and is good to use with a Bowden 1.75 mm setup?
I'm building my own 3D printer (custom design, made by me and cut using a water cutting machine) but I have always had problems with the hotend clogging.
I have had four hotends:

a J-Head;
a full metal;
a full metal made by me and;
my current hotend which is just a block of aluminium with a plaster cold-end 100% homemade with no precision at all.

Believe it or not, this hotend is the only one that has finished a whole print (about 40 minutes), all of the others, with or without fans, haven't managed to finish one!
Well... this hotend has a 1.5mm hole so I guess that that's why it can print.
The problem with all of the others was that the 1.75mm PLA that I'm using clogged the hotend after two minutes.
Now I would like to buy a new, more precise, hotend. I'm using a Bowden extruder, can you suggest a good hotend?
This is my printer:

Please consider reconstructing your question. At this point, it is unclear what direction to look in to answer your question. Perhaps provide clearer information on your machine design and/or what issues you're having with your current extruder?

OK, my question is: what do you think is a good extruder that does not clog and that is good to use with a Bowden 1.75mm setup?

@FormentiMatteo, I agree with tmb0115 that your question is very diffuse  at the moment. I would consider rewriting it to better build up what you are wondering about. Also, please try to ask the question in such a way that it isn't primarily opinions based since such questions tend to have a very short lived value, without any definite answer.

Have you considered that the problem isn't the extruder, but rather the filament you're putting through it? Is it kept clean + free of dust? Has it been exposed to air? If you know for sure that the filament is good, then yeah, look at your extruder.

Actually  no... It has always been exposed to moisture and dust... Is it a big problem?

Please also be precise with the vocabulary, since hunting around what people might have meant is unnecessary work for everyone involved. In this particular case I guess by extruder you actually mean the hot-end itself, right?

For what it's worth, 100% of my nozzle jams have been caused by the PTFE tubing not butting up to the threads of the nozzle when screwed into the heat block.  You could be using $500/kg filament and having that gap would still cause an issue.  I now assemble my hotend "backwards" to ensure it's correct.  I put the PTFE tubing into the throat until it's flush with the edge, then insert the throat into the block, then the nozzle, then the heatsink and fan.  I've not had this problem since.

To make the suggestion of Martin Carney a real answer and shift things away from comments:
Yes, moisture and dust can be a problem. Find elaborations on the moisture here:
Does filament have to be stored in an airtight environment.
Also, dust getting into the hot end won't make extrusion easier. (link with suitable information needed). There are filament cleaning 'devices' for print on thingiverse, have a look at things with the tag: filament cleaner.
There are some other things that are mostly discussed in relation to hot-end clogging, which are printing speed, retract setting and what I would call hot-end resistance. For all of those, read through this thread and refine your question according to what you tried and what the results were:
Repeatedly Clogged Printrbot Simple Extruder.

To add to kamuro's answer, with respect to the dust aspect, the page Filament Not Extruding/ Clogged Hot-End makes a couple of relevent points:

Dust collector not applied around the filament:  Filament attracts a lot of dust, which can potentially all come into the
  hot-end. In some dusty environments this could cause a clogged hot-end
  within a few hours.
Clog from the inside of the hot-end: It could be that a big dust particle is inside the hot-end tip blocking it from the inside.
  This can be solved by handdrilling the nozzle from the inside with a
  2mm drill provided in our webshop.


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Does anyone have a Simplify3D configuration file for a Lulzbot TAZ 5 with a 0.5mm nozzle?
I've been searching, but I'm coming up empty-handed. They have a file for the TAZ with the 0.35mm nozzle, but I'm not certain if I can just change the nozzle size and be done with it.

Have you tried the configuration assistant under the "Help" menu?

From S3D 3.0.2
And yes, you can just change the nozzle size in the process "Extruder" tab and be done with it, if you're using auto extrusion width. If you're using manual extrusion width, also change that to be equal or greater than the nozzle size.
S3D will handle everything else. It's not a bad idea to recalibrate extrusion multiplier (with 100% infill 20x20 calibration boxes) but it isn't strictly necessary.
General tip for switching to a larger nozzle: while you get used to it, make sure you preview your sliced files carefully looking for areas with gaps or missing details smaller than the extrusion width.

That pushed me in the right direction, Ryan. I still need to play with it more and I wish that S3D had a profile for the TAZ 5 with the single 0.5mm nozzle, but starting with the dual 0.5mm and removing the extruder at index 1 made for a nice start.


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Settings to change when upgrading from Smart Extruder to Smart Extruder+
I am optimizing a collection of slicing profiles and in the process of upgrading some profiles from the classic Makerbot Smart Extruder to the new Smart Extruder+.
What are the parameters that should be changed with the new extruder?
Are there any params to which the new extruder is more "sensitive"?
Thank you!

There are no "sensitive" params here. You just need to set it up like the regular Smart Extruder.
Like the original design, the Smart Extruder+ is supposed to make Replicator printers simpler to use, more reliable, and more future-proof. It automatically detects when the printer's filament runs out and pauses the job, notifying users via a desktop or mobile app. It also can be quickly swapped out upon wearing out or becoming obsolete.
Additional improvements include faster print start up and refined build plate leveling, the process of calibrating a 3D printer. The smart sensors within the extruder have been enhanced for better performance and to streamline the printing process from start to completion.
Improved components include:

A better thermal management system
Extended PTFE tube to feed the filament into the nozzle
Faster print start up
Refined build plate leveling and calibration

The enhanced smart sensors are a big part of the story here though in that they allow for better speed, along with savings on the bottom line too, keeping users informed about print status from beginning to end, whether from the PC or mobile app.


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default axis steps per unit Makerbot replicator 2
I can not find anywhere default steps per unit for Makerbot replicaor 2. I'm using Ramp V1.4 instead original board and need to know default steps :/

The Replicator 2 and 2x use 18 tooth GT2 pulleys, 1/16 microstepping, and 200 steps/rev steppers. That makes the proper steps/mm value 88.888889.
Note that Makerbot used ~88.56 steps/mm in their defaults, which is the value you get if you calculate from the belt+pulley pitch diameter from the Gates GT2 specs. But this is the value you use for calculating belt length required in a closed loop, not for steps/mm. The 88.88... number is more accurate.

Hey once again, what about z axis then?

Z is 400 steps/mm. (8mm lead, 1/16 microstepping, 200 steps/mm motor.) Sidenote, make sure you don't over-drive the Z stepper with plug-in drivers, it's only rated to about 0.4A.

@RyanCarlyle FYI minor typo above, you say 200 steps/mm for Z but I think you mean steps/rev since you already state Z is 400 steps/mm. Thank you for accurate numbers though!

I've been referring to this answer for years and it worked until I switched to Klipper where rotation distance is calculated using microsteps. Using 1/16 moved double the distance. Microstepping is 1/8 on 2 and 2X ("Replicator 1 is double that due to 1/16th stepping VS 1/8 but both use the same pulleys") according to: https://groups.google.com/g/makerbot/c/zWllJKQMrZY. Setting microsteps to 1/8 and not changing rotation distance (36 worked, and is close to the default, 40) made Klipper move correctly.


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Laser cutting on RepRap
I have seen some lasers attached to the RepRap platform for cutting but most seem to be cutting paper, balsa wood, or merely etching.  If I were wanting to build a platform for cutting wood, similar to the wood framed or boxed 3D printers on the market, what power laser would I need for that?  I assume that a lower powered laser would have to travel slower but going too slow would add the possibility of catching the wood on fire (not good).

Please do not go down this road. First, not all lasers are equally absorbed by the material and the energy converted to heat to vaporize the material. The light not absorbed is reflected right back into your eyes. This is especially dangerous because it doesn't make you go blind instantly, fooling you into thinking there is no harm. You got the other part right, the lower the laser power, the less turned to heat, the longer it takes to cut, the longer you risk exposure to your eyes. That's right, a low powered laser is MORE dangerous than a big one. Next, the only way to properly cut is with air assist. This means a stream of air blows away the vaporized material so the laser can keep cutting deeper. This also prevents fires. The thing we haven't even touched is a proper safety enclosure, proper bed design to not reflect the laser beam back into the laser killing it and your eyes, and finally smoke/particle exhaust.
Simply put, these cheapo DIY lasers are dangerous, and are also illegal.

Thanks.  This all makes sense. Can you expound on the legality of them?

Most civilized countries have power thresholds (based on speed of eye/tissue damage) for laser products that dictate conditions under which they can be sold. Your typical red laser pointer is <1mW and basically unregulated. Whereas something like a 200mW Blu-ray burner laser will require a safety interlock to prevent exposure to users, such as by shutting off power when the door is open. https://en.m.wikipedia.org/wiki/Laser_safety

Strapping a laser to a cheap robot made with flammable plastic parts and no enclosure is stupid in the extreme. Don't do it. Seriously, just don't. RepRaps are not suitable for laser conversions.
You have to worry about reflected light damaging your eyes, and for the blue diode lasers currently growing in popularity, causing skin melanomas. You have to worry about mechanical vibration from jerky motion loosening fasteners. You have to worry about the workpiece catching on fire. You have to worry about the fumes being generated from etching and cutting. You have to worry about firmware freezes locking the laser on. It's dangerous to you, anybody in line of sight of the machine, and your property.
Many of the lasers currently being sold for RepRap conversions, particularly from Russia, violate US and EU safety regulations related to power and safety interlocks and should not be on the market at all.
The people posting videos of their RepRap laser conversions are almost always ignorant of proper laser safety requirements and regulations. It's downright scary how much blue flare you can see the camera picking up in a lot of these videos. Don't follow in those people's footsteps.
More directly answering the question details, most people doing light etching or paper cutting type work are using small 0.5-2W diode lasers. These are particularly dangerous because they have poor focus and because they don't have the power to cut cleanly and quickly. That means more fumes, more fire risk, and more damage to the workpiece from edge charring.
Slowing down the laser is not a good solution: dwell time is your enemy. You want a beam powerful enough to near-instantly vaporize the material, not slowly burn it away.
An entry-level proper lasercutter for cutting things like plywood and acrylic is more likely to use a 40w CO2 laser. It should have air assist and fume extraction, and a safety-interlocked enclosure that 100% reflects or absorbs the CO2 laser light wavelength. That basically means a dedicated machine.

This is really good advice.


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How can I improve the overhang angles my printer can successfully print?
Using an FDM printer and PLA or ABS, without adding support material. What modifications can I make to improve how steep an overhang my printer can print before it starts having problems?
The obvious first answer is to add a cooling fan, increasing the airflow over the freshly-extruded material ensuring it solidifies. What other things can improve it?
Does lowing the temperature help? Raising it?
Does speeding up or slowing down the print head help?
Does increasing/decreasing the extrusion diameter, or layer height help?

The two most important things you can do are:

Provide adequate cooling to solidify the plastic quickly
Minimize layer height

Cooling is really obvious. You need the plastic to solidify before it has a chance to sag. PLA in particular has to shed a lot of heat before it is fully solid. A fan and air guide setup using a "squirrel-cage" radial blower around the nozzle is optimal. A little 30mm or 40mm axial fan will not provide optimal performance.
Low layer height when slicing is less obvious, but is extremely effective. When you use thinner layers, two things happen:

There is less melted plastic per pass and a higher surface area to volume ratio, so the fresh material cools faster.
A larger percentage of each strand in the overhang is supported by the previous strand. If you do 0.2mm thick by 0.4mm wide, half of each strand is unsupported. But if you do 0.1mm thick by 0.4mm wide, only a quarter of each strand is unsupported.

When you combine these two effects, it is possible to exceed 70 degree overhangs with good surface quality.
Another lesser factor is printing shells/perimeters inside-out rather than outside-in. This helps anchor the outermost strand a little better as the overhang is built. This is pretty minor though.

The layer height explanation helps a lot, thank you!

There's an answer here that holds some of the same concepts. Regarding your questions:

Does lowering the temperature help? Raising it? : Yes, lowering the temperature can help. I've found that it is best to stay closer to the lower end of the material's melting point and just a bit above the point. Not only does this help with potential over extrusion, but also shortens the time it takes for the material to cool (refer to the link above). However, this could cause clogging if your temperature is too low. Keep an eye on your drive gear to see if there is too much friction while at lower temperatures. Increasing may keep the drive gear from "eating" your filament.
Does speeding up or slowing down the print head help? : I prefer to print slower, most of the time, to allow the material to cool a bit more to avoid curling/warping (I primarily print with ABS, so it matters more). You might be able to give and take between temperature and speed. Consider if your nozzle is cooler and your speed is up, bridging gaps might yield the same results as if you proportionately swap these two values. This concept may only matter if you are in a pinch to get the part done. Again, I prefer slowing my machine down as it allows current/previous layers to cool more before continuing. This can be especially helpful with overhangs when paired with lowering your nozzle temperature.
Does increasing/decreasing the extrusion diameter, or layer height help - I assume that extrusion diameter equals layer height (not difference in nozzle diameter, aka swapping nozzles). I'm not completely sure, but I think this depends on the part as well as slicing engine settings. For me, MakerWare is pretty good about proportionately adjusting extrusion steps with layer height, so I see an equal change in the width of the extrusion. I would think that in general, a larger layer height would yield a larger extrusion width. This would be helpful when printing overhangs, but may not be helpful when printing bridges (a larger strand will retain heat longer than a smaller one).

Hopefully this helps, please comment if you need more information/clarification.

@jwpat7 good catch, fixed now

By extrusion diameter, I do not mean layer height, nor even necessarily changing the nozzle out for a different size. In Slic3r, you can specify the width of a "line" of extruded material. It can be wider or narrower than the nozzle's actual opening, with different results. In another question, I asked if I could print 0.6mm extrusion with a 1.2mm nozzle. I tried it out and it's possible, but it's prone to problems.

@MartinCarney That's a very cool feature! I'll need to check if MakerWare has a similar parameter. What sort of problems have you encountered?

Well, I only tried a few prints, and never measured them to check precision, but there were problems in print quality that are hard to describe. See my question on the subject. Basically, your layer height to extrusion diameter ratio must still be "good" if you want to have any success extruding smaller than your nozzle diameter.


text:
Printerbot printing stringy
My Printrbot is always printing stringy, despite changing the setting on my z probe by entering command M212 Z-.1 through Z-1.5, with and without a heated bed. My prints look roughly like the one on the left. How do I fix this?

What do you mean by stringy? Stringy as in underextrusion? Stringy as in strings between islands (problems with retraction)? Without pictures or a more detailed explanation, it's impossible to help.

Please elaborate on the conditions. What have your tried? You're question, in its current state is unclear or too broad.

The most common cause of print issues like this is incorrect first-layer gap between the nozzle and bed. You can tell if that's the problem by trying to print with a raft and/or letting the print continue for a while. If the raft helps and the print eventually "heals up" and only the bottom few mm are bad, then you have a bed leveling / nozzle gap issue The bed must be leveled to the nozzle properly, or nothing will work right.
When using a probe, you need to follow the manufacturer's instructions for how to configure it. For example, are you adjusting the Z offset in firmware configuration.h or in EEPROM? Printrbot should have a guide for this.
If the nozzle gap is fine and the stringiness continues farther up the print, there are two main causes:

XY or Z movement is larger than intended due to incorrect steps/mm value or wrong microstepping setting
Severe under-extrusion

Of the two, under-extrusion is far more common, and unfortunately has lots of possible causes:

Printing too cold for the material
E-axis steps/mm is incorrect for the extruder drive hardware and microstepping
Extruder stepper current is too low
Extruder hardware is misaligned or jamming or the teeth are full of plastic dust
Partial nozzle clog or damaged PTFE tube in the hot end
Commanded flow rate through the nozzle is too high, such as if you're trying to print big, fat strands at high speeds
Incorrect slicer calibration (eg extrusion multiplier is too low) or inappropriate slicer settings (eg extrusion width too large for the nozzle size)
Excessive filament feed path drag between the spool and extruder drive

The first under-extrusion tests you should start with are:

Preheat and try to push filament through the hot end by hand. Can you get a strand to come out without a ton of force? Does it go mostly down, or curl back up to hit the nozzle?
Remove the hot end from the extruder drive, and command 100mm of filament motion through the extruder. Measure how much travel you actually get. It should be close to 100mm.
With the hot end removed, command some filament motion, and try to stop the filament from moving by hand. Does it take some significant force to get the extruder to stall or slip?

Based on these, you should have a better idea of what needs to be fixed.


text:
Stainless tip for thermistor
I would like to secure my hotend thermistor in a more reliable way (now it is just thermistor plugged in the hotend :D). I want to have a stainless steel tip for it to fix it inside hotend with a screw (The same approach as used for the heating cartridge). I have thermistors, but I cannot find any tips to buy separately.
Maybe you have some links for this kind of stainless-steel tips? Or some keywords I can use to search them?

The main problem here is that the hot block has to match the temp sensor. There are a couple available commercial options for hotblocks with cartridge-and-setscrew temp sensors, but they're not thermistors:

E3D PT100 RTD -- requires a special amp (http://e3d-online.com/V6-PT100-Sensor-Kit)

Carl Raffle Tecto Heater Block with thermocouple -- works as-is in Mightyboard-based printers, but requires a thermocouple amp for boards that use thermistors (http://shop.raffle.ch/shop/tecto-heater-block/)

Other popular options for thermocouples include a brass thermowell crimped onto the tip of the TC (Makerbot and FlashForge) or an eyelet lug crimped onto the tip of the TC (Wanhao).
The best off-the-shelf solution for most printers is probably to use an E3Dv6 hot block, which uses a screw and washer to clamp the thermistor leads so the glass bead tip can't pull free of its pocket.

Thanks man, "brass thermowell" is exactly what I was looking for. I just didn't know how to call it (maybe because I'm not native English speaker). Other things are really interesting too, thanks for your help. That is the link to thermowells I found: http://www.alibaba.com/product-detail/thermometer-with-brass-thermowell_1780646847.html?spm=a2700.7724838.0.0.vhGi41

Or this link: http://www.aliexpress.com/item/3-30mm-Stainless-Stell-one-End-Closed-thermocouple-Pt100-protection-Tube-thermowell/32307713415.html?spm=2114.01010208.3.119.bjO0ZF&ws_ab_test=searchweb201556_1,searchweb201644_2_505_506_503_504_10020_502_10001_10002_10017_10005_10006_10021_10003_10004_10022_10018_10019,searchweb201560_1,searchweb1451318400_-1,searchweb1451318411_-1&btsid=6d095233-1baf-4d07-95da-c21fd0d660a9

I am not too sure what you're searching for, but I imagine it to be a kind of thermistor housing to distribute pressure from the screw while maintaining good heat conductance.
I first have to say that I'd be afraid to damage the glass droplet of the typical thermistor design by putting pressure to them, especially including later thermal expansion. However, I never tried and we might find some valuable experience on that in other answers here.
If what I assumed in the first paragraph is true, I would suggest forming some housing yourself with copper foil or copper sheets, since the heat conductance of copper is good and it is more or less soft.
However, as a more simple solution, you might just cut the metal part of a 'wire ferrule', if you got some lying around. (Wikipedia has no english article for this, so I link the german one for the images: Aderendhülse)
Additional info: Can't you clamp the thermistor the way it is done in the E3D V6 hotend, see this image?

Thermal contact should be quite good and you don't have any problems which could lead to damage of the thermistor.

You understand me 100% right.The think is that it is much chipper for me to buy these enclosures than to spend my time for it. I was sure that such a think exists, but I did't know how to call it. That is exactly what I was looking for:http://www.alibaba.com/product-detail/shanghai-brass-thermowell_60362628006.html?spm=a2700.7724857.29.339.kY5eXu

The idea with screw and washer doesn't sounds nice for me because hole is twice as much bigger then thermistor, so I was not sure about thermal conductivity, which can change because of position of sensor.

My thermistors came with a small spring surrounding them, which seems to work pretty well for this (see also E3D Thermistor Alternative). It's pretty close to the size of the spring in an ordinary pen, so you could just try one of those, or you could wind one from copper wire. I always use thermal grease as well, just like you'd use for heat sinks.
image from B3 Innovations - Thermistors (Gen1)

Can you take a picture please? I don't really understand how it can work :/

Here's a link to the picture from B3 Innovations, where I bought mine: https://www.b3innovations.com/wp-content/uploads/2013/12/Pico-Hot-end-e1417577727405.jpg This shows it installed on a hotend, but they sell the "thermistor assembly" by itself, or as mentioned you could do something similar.

Aha, looks really nice. It can prevent wire from banding, good idea. Thanks a lot man.

Your link to the image has expired, it would have been a good idea to include the actual photo in your answer (in case of the inevitable link rot). I have had a search, is this what the photo was of? If so, would you like to edit and add it to your answer? image from Thermistors (Gen1)

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Is 3D printing feasible for a coaxial rotational joint?
In a design that I need to prototype, I have a coaxial, rotational joint between 2 cylinders connected to another coaxial rotational joint between 2 cylinders by a hinge. I have attached the individual part files as well as their assembly where you can use your mouse cursor to check how they move.
Click here for the SolidWorks parts and assembly files
Initially when I 3d printed them by splitting them in half, the outer tube did not close, even after filing the inner tube sufficiently.

Could you tell me an alternative method to get this complicated joint working? I need to 3D print them. I plan to use ABS for the 3D printing.
Thanks for your patience :)
EDIT:
Lubrication: I plan to use grease to lubricate the sliding surfaces.
Clearances:
I printed them without clearances initially (this is my first ever 3D print and I wanted to know how accurate it would be). I then used Dremel and filing tools to file away about 0.5 mm of both the surfaces. It should have been enough for mating the parts. The gap between the edges of the outer shell while trying to close it around is 3-4 mm which doesn't suggest 3D printing inaccuracy. I suspect that the outer tube isn't circular enough in cross section. It meets the inner tube at the the two ends of the semicircle and not inside its belly (you can see it in the picture). I have already tried the obvious, which is removing material from the surfaces wherever the parts touch. The model seems to be too warped for any success. The parts were printed upwards from the bottom, so it is not the warping due to gravity.

Can you just attach photos to the question? The google drive links require permission to open.

Fixed it. Thanks. You would be able to see the picture and the other files now

Is your issue that the two halves of the outer part are not mating up? What kind of tolerances do you have in the model? It's normal for FDM parts to be oversized by ~0.1mm in X and Y.

Simple question, but I sometimes forget when I'm designing. Did you account for mating tolerances? As Ryan suggested, you may consider creating a "machining model" that accounts for the capabilities of the process. In the case of FDM, shrinking the part by about 0.007" might help as well as generally giving yourself about 0.005" between surfaces. I wouldn't expect much accuracy beyond that though

I have added some more details in the question (under 'EDIT'). Sorry if I wasn't clear.

Consider ball bearings
Depending on the requirements for your joint, I would consider making a design that utilizes ball bearings. With ball bearings, your join will not wear down as quickly, and also move smoothly.
Handling dimensional inaccuracy
The topic of how to achieve dimensional accuracy of FDM printers has already been discussed in this question. You might want have a look at Ryan Carlyle's answer for a specific routine on how to calibrate a Cartesian printer.
From the question linked, a summarized approach for handling dimensional inaccuracy could be:

Add any desired tolerances into the joint in your CAD model, without regarding the inaccuracy of the actual printer you will use.
Tune your printer and slicer to reproduce those dimensions set by your CAD program.

Generally speaking, the printer settings should handle filament independent dimensional accuracy, while the slicer should be used to account for different characteristics in each filament type. Correcting size through your CAD model is ill-advised, since you should be able to use the same model for multiple printers.

Good points. However ... there is some latent inaccuracies in most FDM printers (especially desktop-styles) that are basically impossible to rectify using slicers / printer settings without upgrading hardware or (depending on the resolution required) changing processes as @fred_dot_u mentioned.

@SRDC, are you thinking of the extrusion width's effect on dimensional accuracy? I agree with your comment, and see how this conflicts with the ideal scenario where you shouldn't "fit the model to the printer". Still, for most people, I believe a well calibrated FDM printer gets close enough. If that is the case for the OP, however, I cannot tell. :-)

Have you considered to use a service to have the part printed? You can print almost anything in one "pass" using selective laser sintering, typically done in nylon. I am currently un-boxing an SLS printer, so I cannot currently offer to print it, but the capabilities of SLS are substantial for parts of this nature. I've read of entire planetary gearboxes being printed, fully assembled, with appropriate clearances for operation, once removed and "dusted," or cleaned of residual powder.
The printer I hope to be assembling soon has 80 micron powder, so the resolution is quite high, although I forget at the moment the x/y/z figures.
Do you think such a method would suit your purposes?
Edit (add):
because FDM printing by nature causes "oozing" especially in the x/y directions, I would not be surprised to learn that your outer piece has a smaller inside diameter than your design has specified. You may have to make adjustments to the design to compensate. Those adjustments would be specific to a particular printer/filament combination as well. Calibration prints would make the task slightly easier.

SLS could work. I need to check if I have facilities nearby which can do it. It was not a problem of oozing, since I have removed about 0.5mm on both mating surfaces. I suspect the outer shell isn't circular. You can see in the picture that the outer tube meets the inner tube at the the two ends of the semicircle and not inside its belly

I can now see that the ends of each "arc" are contacting, while the centers of the arcs appear to have air gaps. If force is applied, do the ends join and do the centers contact the inner cylinder? If so, I'd suspect that the outer parts are distorted from a proper cylinder.
I've done cross-section prints of a 3d model in order to determine tolerances and clearance without printing the entire project to find something went wrong.
If you can slice the bottom of all three pieces and print them, you may find that you have distorted semi-cylinders that have to be compensated/adjusted.

Depending on your tolerances and how many you need - and how valuable your time is - you can 3D print in ABS with a regular FDM printer, then clear out support material and do an Acetone vapor treatment or vapor wash. It will be smooth enough for most prototypes.

I wouldn't recommend a vapor treatment on something that is tightly toleranced. There are too many variables in the process that can throw to part out of tolerance.

I would agree - perhaps I should have been a bit more specific ... depending on your tolerances. If you need machine-type tolerances, don't bother with vapor treating, as tbm0115 said. However, if all you're needing is a first pass to try and see/feel/explore how everything works together and if it's really doing what you thought it would, then vapor treating could be great - especially if you have relatively large features compared to your filament size / resolution.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
Print sketchup files (STL) on makerbot
One of the local libraries has a new small Makerbot 3D printer. I have been submitting Sketchup files converted to STL files for printing.
The tech guy who runs the printer for patrons is having trouble getting a project of mine to come out to be the right size. I need this item go be 2 inches wide. The tech guy sizes the item on the screen to 2 inches. I watched him do it. But, the item is printed with a base of 2 inches, and the item itself comes out smaller.
Does anyone have suggestions about this? I can get more info if someone can give me the right questions to ask. The tech is open to taking suggestions. He wants to get the printer running smoothly for patrons.
I submitted a file with my own base with supports made in Sketchup. But, the tech guy said he needs to set the printer to create it's own base and supports.
Additional info:
When I printed it by letting Makerbot create the base and supports, it came out to be 1 3/4" as shown here:
https://flic.kr/p/EashnD
Printer: Makerbot Replicator with Smart Extruder (not Plus).
(I am now at the library with the technician.)
Here is a screenshot of what I am trying to print. It is a replacement clip for a messenger bag. So, it has to be 2 inches across.
https://flic.kr/p/EtdM6s
Here is the printer:
https://flic.kr/p/E5F1M6
I used a website to convert the DAE file exported from Sketchup to an STL file. It was GreenToken.com.
If I open the object's STL file in Tinkercad, the object appears two inches wide. And, if I open the file in one of the 3D printer websites in Tinkercad, the object appears two inches wide (in cm).
The security on the library's computers do not allow me to apply plug-ins to Sketchup. The library's Tech staff is going to eventually put the plug-in in there.
If it is resized to 2 inches wide in the MakerBot software to be sent to the printer, why is it printing the generated base 2 inches wide and not the object? Are there some settings the tech guy in the library is missing in this set up window?
Additional notes:
The library now has the latest version of SketchUp on Macs. They are working on installing the STL plugin. (Security issues)
My process for producing an STL file to print is now this:

I create something in SU and export it as a DAE file.
I have found that meshconverter.com produces better STL files than greentoken.
I then upload/fix the STL file at the netFabb website.
I then import the STL file into TinkerCad to view it. If there are problems in the file, I can see them. And, I run it through netFabb again. I can also modify the file in TinkerCad. It is no where near as sophisticated as SketchUp. But, it doesn't claim to be.

I have found that there is a way to export the STL file to 3D printer hubs through TinkerCad. You can see the prices, the material available and the location of the company/person doing the printing. You can contact the printer ahead of time and they can look at your file to give you advice.
Update
I just wanted to add that the netFabb website does not export STL files after it fixes them. It now gives you a 3MF file format when you upload an STL file. I am not sure why this happens. But, this has put a big wrench in my process. I can no longer fix SketchUp STL files with netFabb. When I bring them into TinkerCad, I see errors in the object. It seems like there are issues with complex curves.

How far off are the dimensions? Which Makerbot printer is this?

Also, can you upload a render of your model?

What are you using to do the export to STL
I use this with great success https://github.com/SketchUp/sketchup-stl

I'd second KevinMorse 's suggestion with using the Sketchup-STL pluggin. I've used it for years now with a MakerBot Replicator (1st gen). The trick with sketchup is making sure the right units are output. The pluggin mentioned above allows you to specify the units regardless of the SketchUp template. When you export using this pluggin, select the output in metric millimeters to have everything jive with MakerWare/MakerBot Desktop (MakerBot's slicing engine). Let us know if this helps.

tbm0115 and Kevin: Thank you very much for this. As things develop, I will add to this post.

@TwoJuncos Have you been able to resolve your issue or are you still looking for more help?

tbrn0115: Thanks. The library now has the latest version of SketchUp on Macs. They are going to install the STL plugin, too. I have found a better converter website: meshconverter.com. It seems to produce better STL files than greentoken. I use the netFabb cloud software to cleanup/fix my STL files. Sometimes, when I import an STL file (from SU) into TinkerCad, I can see that some areas are messed up. netFabb fixes them.

tbm0115 You can look at some things I have created here:     https://www.flickr.com/photos/ken-a/    The orange hinge was created completely in SU and run through meshconverter.com and netFabb. The red woodpecker/tree profile was made in Inkscape, imported into TinkerCad (SVG file) where I added the base and rings made in SU. The yellow cup with leaves was completely done in SU. Unfortunately, it is too tall for the printer. The library is working on printing the red woodpecker.

tbm0115: Note: The red woodpecker profile/pencil holder has been giving the library's printer a problem. The base created by the printer keeps separating from the base of the object at the start of the print. From looking online, the tech guy found that the glass plate needs some type of sticky material to keep the object in place. He read that hair spray might solve that issue.

Note on the clip for the messenger bag: I found that the plastic used by the printer is not strong enough for the prongs on the clip. The tips of the prongs keep breaking off even though I have modified the design several times. The plastic is too brittle. I have found some online 3D printing websites through TinkerCad that use more flexible plastic.

When exporting from SketchUp you have options for what units you want to export the STL as. Pronterface and Slic3r use millimetres so for these you should export as millimetres.
You can run into issues when designing a part in inches and then pulling it into printer software which might be expecting millimetres. In this case you may have to scale the part by 25.4 in all three axes.
As an example, if you have a 1" test cube and you export it as mm the STL will have six faces that look like this
facet normal -1.0 0.0 0.0
  outer loop
    vertex 0.0 25.4 25.4
    vertex 0.0 0.0 0.0
    vertex 0.0 0.0 25.4
  endloop
endfacet

You can see there are no units anywhere. If you import this into a program that is expecting inches you will get a test cube that is 25.4 inches cubed. Scaling by 25.4 can fix this OR you can just tell SketchUp to export as inches.

It appears that you have scaled the object after the raft and supports were added. As you can see in your photo of the raft, the clip is approximately 7/8ths (1.75/2) the size of the raft.
Edit: As a side note, STL files don't actually have a concept of units. Each axis is defined in arbitrary units. That's why when you export and import it you have to set the scale appropriately.

ArkTekniK;  Thanks. I can tell you that the tech guy at the library opened the file in the Makerbot software, selected the object, brought up a menu that allowed him to size it by entering numbers and selecting either mm or cm. He then added the raft and supports somehow when I wasn't there.

I´m using sketchup 8 and I had the same error under makerbot, and some times with slic3r. After testing some programs to fix mesh I realize that some faces are inverted on STL file, so this can be detected on preview under pronterface, or simplify3D. before sending to print is needed to check this point; not all STL from a repository is working or is with the right size. If you detect a GRAY surface is time to invert that face to get que correct fill.

My advice is to use a micrometer (i.e., sliding dial caliper) accurate to within .001" and measure the printed object.  If it is 1 7/8" for example, you would open the STL file in Makerbot software and use their scaling tool to scale the object to 1.0666666...., which is what you get when you divide the desired size (2") by the actual printed size (1.875").
I have found that it is much simpler to do that than to reinvent the wheel and try to figure out what each software engineer was thinking on each program and each conversion process and try to make it work right every time.  Chances are that the same conversion factor might work right for any file originating from the same source and going through the same conversion software package.  Also,
3D printers in general don't like edges that aren't completely "welded", or continuous seams.  With Sketchup if you keep zooming in on an edge you almost always get seams that are stitched at intervals determined by Sketchup algorithms.  They are "unwelded" seams.  Some 3D printers can handle them.  Many don't.  I have used various 3D software packages, including Sketchup, and the best one so far has been Rhinoceros 3D.  It handles multiple complex curvaceous planes and can radius adjoining curved edges and can "weld" them.  Aeronautical and boat building companies use it for CAD/CAM applications.
...
The STL file converter you mentioned is probably taking the Sketchup file and "cleaning it up" so Makerbot likes it.  You would almost have to know exactly what algorithms each developer uses. to try and 'fix' it mathematically
Like I said, do your own measuring and scale accordingly.
BTW, it's better in my opinion to let Makerbot do the rafts and supports.  Their engineers typically do a pretty good job.  Where I have had issues is on things with a shallow angle (almost horizontal) hanging out into empty space.  If you can re-orient the object in the makerbot software so those types of angles are minimized, the print is alot cleaner.

Makerbot automatically puts in rafts, and supports at preset intervals so the plastic won't sag.  You  can override Makerbot automatic settings, but I don't recommend it until you've printed dozens, or even hundreds of objects.  If you're not confident that you know more than the designer of the Makerbot printer, leave the rafts and supports up to the engineers.  The Library tech aide doesn't have the skillset to change the raft and support presets.  I have messed with them and ended up with piles of stringy plastic on the rafts.  I have had some success, but Makerbot algorithms are superior.

A "sliding dial caliper" is not a micrometer.

Not true, technically.  All micrometers fall in the family of 'calipers'  https://www.merriam-webster.com/dictionary/micrometer .Most dial, digital and verniers are technically "not" micrometers, because a "micrometer" is one millionth of a meter.

For the purposes of this thread, any relatively inexpensive caliper, either digital, dial or vernier (including the barrel and "C" clamp style micrometer), would be more than sufficient to get the accuracy desired.

Not endorsing these products.  These are inferior quality and wouldn't work in most machine shops, but for this thread, any of these would work if used and taken care of properly:
https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore%2Cf%2CEAFeatured+Weight%2Cf%2CSale+Rank%2Cf&q=digital+caliper


text:
Why does MakerBot Replicator heat the extruder and platform separately?
I am using a MakerBot Replicator 2x, and when it is heating the platform and extruder, it begins by heating the platform, and then after that is at 110C it goes on to heat the left extruder to 230C. Does anyone know why it does this, since it has enough power to heat both? It seems like it would take less time to heat both at once.

It really doesn't quite have enough power to heat everything at once. Initially bringing the bed up to temp takes a lot of current and so Makerbot's start sequences decrease stepper current and hold off on heating the extruder(s) until the bed is preheated. Once preheated, the bed's power draw decreases to a lower "holding" level and there is available capacity to do everything else.
The start sequencing decreases the max average power draw by a pretty substantial amount. The decrease is about 0.6A each for the XYAB steppers and 1.7A each for two hot ends, totalling 5-6A of avoided peak power draw. (Even lower if you preheat with the steppers disabled rather than idling.)
The history here is that one of Makerbot's design decisions with the Replicator 2 and 2x was to utilize off-the-shelf UL-listed power bricks (like a laptop might use) instead of an internal power supply. This made engineering and safety certification much easier, and completely eliminated mains-voltage wiring inside the printer, which is a big safety plus. However, the largest readily-available 24v power brick had slightly less current capacity than optimal. So Makerbot came up with a software workaround for the hardware limitation.
If you want, you can replace the stock power brick with a ~350w PSU and preheat everything at once. Sailfish firmware builds intended for printers with properly-sized PSUs (eg FlashForge Creators) will allow simultaneous preheating.


text:
Settings for CuraEngine
What is the proper way to give printer settings to CuraEngine? Is it possible to put all these settings into a file (like Json formatted)?
CuraEngine.exe -v -o "c:\3d\test.gcode" "c:\3d\test.stl"

I think the easiest thing is to use the Cura application together with CuraEngine.
If your printer is not supported, you'll need to add it manually by adding a JSON here: https://github.com/Ultimaker/Cura/tree/master/resources/machines
But when you are done you can easily choose all the features you want. For example: generating supports, printing order when printing multiple models, etc.
Cura and CuraEngine are developed at the same time, so you can expect that all features supported by the engine are accessible by the UI.

I'm not sure if it's possible, but on github is code for setting CuraEngine up. Maybe you'll find this link,  CuraEngine/src/settings/settings.cpp helpful.
The latest release has more speed customization. You can change first layer speed, outer shell speed, inner shell speed, infill speed, and top and bottom speed.
You can cut objects, its just a little wonky. In the advanced tab there is a "cut off object at Z height" that you can use to cut objects in half.
Theoretically, you can put all settings into a JSON formatted file.

First, try
CuraEngine.exe --help

The proper way is to first load in settings from the .def.json file of your printer. However, the formulae in the machine definition file are not being processed. CuraEngine only uses the default_value.
Then you specify setting overrides to set specific settings to a specific value. The specified settings are applied to the last provided object/extruder and otherwise globally.
CuraEngine.exe -v -j machine.def.json -s global_setting=global_value
    -e1 -s setting=extruder_value
    -l object_to_be_printed_with_second_extruder.stl -s setting=object_value
    -o output.gcode

One-at-a-time mode is done by adding --next commands between each group:
CuraEngine [general settings] -g [settings for the first model] --next [settings for the next model]


text:
What are the advantages/disadvantages of using synchromesh cables instead of belts?
Some 3d printers use synchromesh cables instead of belts. For example, the Deezmaker Bukito (http://bukito3d.com/) and a number of RepRap conversions.

Photo from http://christophergranz.com/?p=449
Are they significantly better than GT2 belts? What are the challenges?

https://groups.google.com/forum/#!topic/deltabot/9BFg8H5eq3o

Yeah, I saw that, just curious if anyone here had different thoughts. Terence's answer is a load of crap. (Metric firmware? Yeah right. Gcode coordinates are floating point so it's irrelevant whether the steps/mm is integer or not.)

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?

Really need to get Whosa Whatsis or someone from Deezmaker to answer. Or I could just answer it myself.

One big advantage would be the ability to located the motors below the build chamber, thus removing a heat-sensitive component. In the future, this could enable higher build chamber temps, although since the syncromesh cable is currently spec'ed at no more than 80C that doesn't provide a lot of net gain.

Looking at the specs for both the GT2 belt and the Synchromesh I'm very hesitant to recommend a Synchromesh over a belt.
The first thing that sticks out is that there are both error and cumulative error specifications for the Synchromesh. For a device like a 3D printer, I don't like the idea that of my axes can accumulate up to ±0.16 in. of error over 100 pitches (the pitch is between 0.12 in. and 0.25 in. so that is 12 to 25 in.).
Contrast this to a belt where the only way you have a cumulative error is if you skip a tooth and I think the winner is the GT2.
Looking at the non-cumulative pitch error both products are comparable but again the belt wins. For the Synchromesh we have an accuracy of ±0.002 in. versus ±0.0003(1) in. for a 2 mm GT2 belt and ±0.0012(1) in. for a 3 mm GT2 belt.
Note: I can't be certain about exact values for error since there are no numbers for the GT2 - only a stupid chart. I also have a hard time believing that error is not a function of total length for both the Synchromesh and the GT2 belt but I'm not the manufacturer. However, since both products are made by the same company I wouldn't be as concerned about them trying to oversell one product over the other.
In conclusion, I don't see of any reason to choose a Synchromesh over a belt if your physical layout is compatible with both. As pointed out in the marketing material for the Synchromesh, it can be routed along 3 axes whereas a belt works best along a single axis. The Synchromesh seems to be a product designed for a very specific application...
Sources
http://www.sdp-si.com/PDFS/Technical-Section-Timing.pdf
http://www.sdp-si.com/PDFS/Synchromesh-Cable-and-Attachment-Inch.pdf

I've heard from people that use synchromesh that the cumulative pitch error doesn't actually cause any issues. They say the pitch is consistent and much tighter than the spec, so it doesn't cause any issues at normal printer scales.

@RyanCarlyle, I don't doubt the product may perform better than specifications but choosing components based on "may perform better" does not seem like a wise decision unless there are other motivators. You asked "are they significantly better than GT2 belts?" I answered "not according to the specs".

It's a fine answer, I'm just pointing out that the people using its end to  think it's better than GT2, and it would be nice to talk about why that is.

@RyanCarlyle It's possibly a psychologic thing...


text:
What are the appropriate ranges of gear ratios for 1.75 mm and 3 mm filament extruders?
Most 3 mm (mostly are actually 2.85 mm) filament extruders have some kind of gear reduction. Many 1.75 mm extruders are direct-drive / ungeared but some do use gears. What kind of reduction ratios are suitable or optimal?

$ \frac{(2.85\ mm)^2}{(1.75\ mm)^2}=2.65$ which is the reduction you would want assuming a 1.75 is direct drive.
In this answer I am comparing the amount of filament flowing though the extruder by using $ \pi \times r^2$.  Dividing the 2 values gives the ratio of the 2 speeds.  A gear ratio is them used to change the speed.

Sure, but most 3mm extruders use more reduction than that. Why? What are the drivers?

Eric, could you please elaborate on how that formula works, or perhaps add a link to it?

Eric is calculating the ratio of the two cross-section areas of the filaments, assuming (probably corretly) that the force needed to push the filament through the hotend is linearly proportional to this cross-section area. This also assumes that the finally pushing hobbed bolt or gear has the same diameter. The answer hence is highly incomplete and lacks all explanations.

What you actually mean, but do not explain correctly, is that when compared to a 1.75 mm direct drive, the 2.85 mm extruder needs the calculated amount of gearing to achieve the same force.

This basically depends on the torque your stepper can produce! A high torque stepper (the bigger the height of the stepper the more powerful the stepper) can push filament with much more force than a stepper motor with less torque. To increase the torque you employ a gear ratio to reduce the speed. As torque and speed are inversely proportional, a reduction by half in speed doubles the torque.
If your stepper is powerful enough, you can use a direct drive (no gearing) to push the filament. However if you want that same stepper to move filament of larger diameter, you might not have enough torque to do so. This means that you will have to increase the torque by employing a gear reduction. Using direct drive extruders thus require high torque, and thus high mass stepper motors, this causes the mass of the hotend carriage to increase considerably. Using stepper motors with less torque (often called pancake steppers because of their reduced height) for such applications is often seen together with a gear reduction. A drawback of reducing speed is that you also decrease the maximum print speed ability or max speed filament retraction speed. To reduce the speed you can use a gear reduction using gears or use pulleys and belts. A major advantage of a belt reduction is that it operates without much less noise than using gears.
Let us assume that you have a stepper that is powerful enough and want to extrude thicker diameter filament. The following guideline can be used to calculate the gear ratio. Also if you express the value in an actual torque, you could work your way back to calculate the gear reduction for a pancake stepper you would use to replace your current X-value torque motor, that is left as an exercise.
From 1.75 mm to 2.85 mm
Under the assumption that the force that the nozzle exerts on the build plate ($F_n$) is constant for different types of filament size, you would be able to calculate the ratio of force for the extruder ($F_{e}$) and nozzle of any filament diameter using the pressure in the nozzle using:
$$ p=\frac{F}{A} $$
Where, $p$ is the pressure, $F$ the force and $A$ the area.
$$ p =\frac{F_e}{A_e}  = \frac{F_n}{A_n} \\
F_n=F_e\frac{A_e}{A_n}=F_{e_{1.75}}\frac{\frac{1}{4}\ \pi\ d_{1.75}^2}{\frac{1}{4}\ \pi\ d_{n}^2} = F_{e_{2.85}}\frac{\frac{1}{4}\ \pi\ d_{2.85}^2}{\frac{1}{4}\ \pi\ d_{n}^2}
$$
Where $d$ denotes a diameter of the nozzle or the filament. Subscripts $e$ and $n$ denote the extruder and the nozzle respectively.
Note that the force that is generated by the extruder is derived from the stepper torque $\tau$ directly, or through a geared drive (gearing ratio $R_{gear}$ ):
$$
\tau_{e} = R_{gear}\times\tau_{stepper}
$$
Note, a gear ratio of 1 denotes direct drive.
The force would then be calculated by dividing the torque by the radius ($r$) of the extruder gear:
$$
F=\frac{\tau_e}{r}
$$
Combining equations gives us:
$$
\begin{align*}
&1.75\ {filament}\ \Rightarrow F_n=\left (\frac{1\times\tau_{stepper}}{r_{e_{1.75}}}\right )\frac{d_{1.75}^2}{d_{n}^2} \\
&2.85\ {filament}\ \Rightarrow F_n=\left (\frac{R_{gear}\times\tau_{stepper}}{r_{e_{2.85}}}\right )\frac{d_{2.85}^2}{d_{n}^2}
\end{align*}
$$
Which can be rewritten to:
$$
R_{gear} = \frac{d_{1.75}^2}{d_{n}^2} \times \frac{d_{n}^2}{d_{2.85}^2} \times \frac{r_{e_{2.85}}}{r_{e_{1.75}}}
$$
Note that each $d_{n}^2$ is applicable to the nozzle size of the extruder. Hence, for similar nozzle sizes, the $d_{n}^2$ term cancels out:
$$
R_{gear} = \frac{d_{1.75}^2}{d_{2.85}^2} \times \frac{r_{e_{2.85}}}{r_{e_{1.75}}}
$$
This means that if you go from 1.75 mm to 2.85 mm filament, for the exact same extruder gear radius (which is not likely as you probably need a different extruder gear/hobbed bolt that can accommodate the larger diameter filament), the gear ratio is $1:2.65$ and therefore you need to reduce the speed accordingly.
The reason that you see different gearing ratios can not only be explained by differences in the extruder gear/hobbed bolt diameter differences, but also in stepper torque values.
For 3 mm filament the ratio will be in the order of $1:2.94$ for equivalent extruder gear radii and reuse of the same stepper.
A similar calculation shows that for a 0.2 mm nozzle on a 2.85 mm filament extruder a gearing ratio of $ 1:5.3$ is required. This "extra room" for extra torque to fit smaller nozzles also explain the larger gear reductions. What is optimal is not only defined by the nozzle size and filament diameter but very dependent on the stepper motor and the torque it can produce. Gear reductions should be limited so that they do not minimize overall print speed or cause problems with retraction (this latter I experienced myself, a too high retraction speed caused the stepper to miss steps on my custom designed 1.75 mm to 2.85 mm bulldog extruder conversion. I'm using a $1:4$ speed reduction to produce enough torque with a stepper that is normally used for direct drive (of 1.75 mm filament). Note that within the aluminium bulldog housing, a different sized extruder gear is used to accommodate the larger diameter filament:


text:
Point Cloud to STL File
I had a friend request that I print out the Bathymetry of Lake Michigan as a gift for her PhD adviser. I went to NOAA and the site had a few files for the Bathymetry of Lake Michigan.
Files and types are located here: http://www.ngdc.noaa.gov/mgg/greatlakes/michigan.html
I am trying to convert this into an STL file to print in my 3D printer however I am having no luck in converting this into a mesh I can use. I have tried multiple approaches with the different files that are listed but cannot seem to get it to properly convert to a mesh. I have tried the following so far:
-Import an .xyz file into MeshLab to convert it to an STL. After I import it looks like nothing imported and I can't navigate around in the file
-Import an ASC file into MeshLab to convert it to an STL. After I import it, I get no errors but the output is a long, thin mesh that looks nothing like lake Michigan
-Just for a test, I imported the .xyz file into Autodesk ReCap just to see what would happen. I noticed that the points were in a long thin area similar to the ASC import but as I browsed around I noticed that the each layer of dots was the actual Bathymetry contours.
I have tried multiple approaches and software beyond these but can't seem to get the files to convert into a printable mesh that I can manipulate to send to my 3D printer.

http://www.cadforum.cz/cadforum_en/how-to-convert-a-point-cloud-to-an-editable-3d-cad-model-mesh-tip9512

I took a quick look at the .xyz file. It seems to contain a grid of points overlaying the lake. They are in the format of Longitude, Latitude, Altitude, and are arranged in rows by Latitude. The northern most latitudes, 46.00-46.09 degrees, have NAN for altitudes. This probably broke most the software. The dataset extends from -88 to -84.5 long and 41.62 to 45.99 lat which nicely covers the lake https://c1.staticflickr.com/3/2682/4036834071_74d19b6327_b.jpg

In order to properly get an STL file out of a point cloud, you'll need some tool to help triangulate the points to create proper shell surfaces. The shell that is created in an STL is what the slicing engine will "slice".
I'm not as familiar with the full potential of MeshLab, but I would think this tool is best suited for files that at least have most of shell already in place. Essentially best for fixing STL's.
In the past, I've used (the very expensive) Unigraphics NX8. This CAD/CAM software is very powerful and has tools for creating meshes out of point clouds. I believe it was the sew tool that allowed me to do this in the past (I no longer have access to the software). Other CAD programs such as SolidWorks, Rhino, AutoCAD, etc. might have similar features.
Alternatively, I think it looks like you might be able to convert a 3D point cloud in SketchUp. If the cloud is layered by height and each layer had points on the same -Z- plane, then you might be able to automate creating lines between the nearest points on the same plane. Then it might just take a little bit of manual labor to "fix" the model to become 3D printing ready. Also check out this forum post, it looks like someone had luck in converting terrain point clouds.
Completely alternatively, have you considered converting an image to STL? I've done this many times before and it turns out quite nicely. If you can find topographical map of the lake, you could alter the image into grayscale (play with it a bit). Then use software to convert the grayscale image to STL.

Thanks TBM! I'll check into these tonight and let you know. I appreciate you giving a little bit of background as well.

No problem! Hope it helps. Please keep us updated on the project, it sounds like a cool print! It'd be nice to see how you end up getting this to work if you are able to convert the point cloud.

Just an update.
I went through various methods last night and the links you provided and I tried "CloudCompare" to import the point cloud. It originally had the same issues as MeshLab until I realized that the z-axis is elongated for some reason on the import. I fixed this and I actually saw the bathymetry but had some odd noise on the land portion of the lake. I'll continue tonight and may revisit MeshLab now that I know the z-axis has that issue and how to fix it.

You pointed me in the right direction. I used CloudCompare to import the cloud and then I rasterized the cloud and exported it to an STL file. Thanks for your help.

So, was CloudCompare able to clean up the noise you found in the point cloud? Thanks for the update, I'll have to start looking into CloudCompare for future projects!

I couldn't use the noise reduction feature as it would bomb my computer out. I got rid of a majority of the noise by cutting off the import at the shoreline. I then imported into MeshMixer to clean up what I could in  the leftover data.

I was able to download the file collection from the link you posted, although I used none of the Grid files, as they seemed inappropriate to this task. The shape files were then imported into AutoCAD using the trial version of  Spatial Manager.
The resulting drawing indicates that it's in 3D. When the 3D orbit tool is selected, the image rotates a flat drawing.
I saved the AutoCAD DWG file and imported it with SketchUp, ostensibly not the smartest program for this sort of thing. The result was a flat image, not a 3D one.
I suspect that the resulting flat drawing IS the image and cannot be 3D printed, unless you have reason to believe otherwise.

You can do this using MATLAB, or possibly Octave (the open-source version of MATLAB). I'm doing this right now to print a globe with exaggerated topography and bathymetry. MATLAB has tons of tools for importing data. I'm sure you can import the Lake Michigan bathymetry data, though you may have to hunt for an importing script on the MATLAB exchange.
As long as you can get your data imported as a 2D matrix of X, Y and Z values, you can use the surf2stl() function by Bill McDonald, available here:
https://www.mathworks.com/matlabcentral/fileexchange/4512-surf2stl
This creates an STL you can use. Note that it's just a surface, so you'll need to give it depth some other way so your printed object isn't paper-thin.


text:
PETG Collecting on the Extruder
I have recently bought a spool of eSun PETG. So far I really like the filament. My only complaint is, I get lumps of charred filament deposited on my object. The slicer I used is Craft Ware and I have played with the Far Travel -> Elevation settings. I have noticed that this helps but then I have little to no adhesion to the print surface and my supports do not stick to the raft. Does any one know how to mitigated PETG from collecting on the extruder?

Different brands and blends of PET filaments seem to do this to different degrees. Esun's PETG is definitely one that tends to glob onto the nozzle. Basically, the nozzle plows through the top surface of the filament and lifts up some plastic, much like the bow of a ship lifting up some water at high speeds. PET's viscosity and stickiness seem to amplify this effect more than other filaments.
Some things you can do to minimize the globbing:

Calibrate extrusion volume on the low end of what you'd normally use for other filaments (how you do this depends on your slicer)
Use your slicer's "Z-hop" or "avoid perimeters" feature so you don't do travel moves across printed surfaces
Invest in an anti-stick coated nozzle, such as are sold by Micro Swiss or Performance 3-d (these don't eliminate globbing, but they do reduce it and make the nozzle much easier to clean)
Play with slicer settings such as extrusion width, layer height, and infill/perimeter overlap to reduce the amount of "excess material" that sticks above the print surface

Again, this is a common problem with PET blend filaments. Anecdotally, some brands seem to glob more or less than others, so switching to a different vendor may be worth trying if you want to do a lot of PETG prints.

I have never printed any PETG so far, but could this also be an issue related to extruding temperature? I would assume that a less viscose extrusion could help extruded filament bits to not stick to the nozzle.

Nice answer. I would like to add "calibrate your first layer height" as one of the countermeasures - in particular for small, compact models.

For me, none of the classic solutions to PETG zits worked; these include extra retraction, slower/faster retraction, lower extrusion width, lower extrusion multiplier, avoid perimeters etc. It was especially disappointing to see lower extrusion multiplier making no difference whatsoever in reducing the zits, but only resulting in a mechanically weaker and even spongy result. What made all the difference is to disable z lifting during retraction which my slicer profile has enabled by default. This setting alone eliminated nearly all zits and most stringing (i.e spiderwebs).
Of course, the amount of zits and stringing will heavily depend on the particular filament you're using and the particular model you're printing.
Additional note: I was getting extra zits/overextrusion on a particular model I had that was exceptionally thin and tall when attempting to print with PETG. Lower extrusion multiplier made no improvement but weakened the part and resulted in spongy structure. I was successful in printing this part along with another part that was of similar height. I'm suspecting that printing the part alone but much more slowly to help with cooling would also succeed.

PETG strings at working temperature to different extents depending on brand. Some of the thinner strings are flying in the air due to the fan or mechanical stress, and are finally captured by the hot end.
I feel, PETG has two modes

Too cold: Less to no stringing, but sometimes underextrusion and weak layer bonding
Hot enough: Stringing (from weak to strong) but good bonding

Things which do not help (at least least on my printer with direct extruder), but which I tried out individually

Retractions past 1.5 mm on my direct extruders
Reducing minimum distance
Retraction speed 30 to 60 mm/s
Z-hops
Fan speed 30% to 100%

Things I have not tested

Maybe minimum layer time could be increased

Things that worked

Coasting seems the only thing which helps, but you still have very thin strings at sufficient temperatures

Other things to consider

As mentioned the PETG brand has a certain impact
The worst Co-Polyester I tested were (by far) the XT-Filaments (pink and green)
All regular PETG filaments were better than XT in nearly every aspect, but still tend to string to a certain degree


text:
Threaded rods to create frame/axis connection. Which improvements can be made and are they needed?
I am building what I dub Frankenstein's printer from various components I could find in the electronics dumpster to print the proteins for a P3 Steel (toolson edition).
I want to elevate a scanner bed with an attached DVD drive motor for X-Y movements of the hotend. I plan to connect this by threaded rods to a base that also hosts the heated bed on a stury z-axis mechanism. To make this as stable as possible, I plan to conncect M8 threaded rods in the 8 edges in wooden blocks.
I am planning on 4 vertical rods and 2 crossing rods along the diagonals of the backside of the system. Additionally each side is planned to have one diagonal connected by a rod.
We're talking about a height of about 30cm and M8 rods. Will this introduce lots of vibrations and is it possible to avoid easily? Are there any better connection ideas or improvements I can make to this design?
*edit: here is a really bad hand-drawn sketch:

do you have a schematic, 3D model or image that you could include in your question? That would certainly be of help to better understand your situation.

up to now i have successfully avoided getting into a CAD program (next on the list). I will include a pretty bad drawing (my skiills here are as well developed as the CAD ones) as soon as I have the time.

Even a pen-and-paper sketch would help enormously.

That sounds ok for light duty; the main thing I'd worry about is that threaded rods are weak under compression and flexion. That might mean you end up with vibration, or just inaccuracy. Perhaps consider substituting something more rigid (angle stock, T-extrusions, etc) for some or all of the places where stiffness is important?

If I understand you correctly, compared to a Mendel RepRap you are using:

M8 threaded rod (the same kind of rod used in the Mendel RepRap frame)
roughly the same lengths of rod as in the Mendel, and
cross-braced with more diagonals than the Mendel design.

So I expect less vibration and the same print quality as a Mendel.
Rather than put one block of wood at each corner with holes drilled at a bunch of weird skewed angles,
the "1X2 split vertex" looks like it is a lot easier to construct.
I've heard several people claim that lots of threaded rods and associated corner connectors can be replaced with a few big sheets of wood in a 3D printer.
See Mendel90, RP9, SGBot, WolfStrap, etc.
Looks like a very educational project. Good luck.

To split the blocks up into their angular parts is a great idea. I was stuck with one block since I had the minimization of vibrational possibilities in mind. I guess when screwed tight the vertex should easily do the job. This was really helpful input, I didn't know about the 1X2 design...


text:
z-axis hard to move in some areas - what could be faults, how to improve?
I have a z-axis which follows schematically the same principle as the makerbot one's (threaded rod and two leading rods with linear ball bearings carrying a level). It is from an old experimental lab doing physics or chemistry.
The axis move gorgeously about 5 cm, but then it get's stuck on either sides of this way. Both driving threaded rod and the leading rods seem perfectly fine and should be able to allow for further movement. This is as far as I can see by eye.
Where should I look to find further issues and how could I improve the performance? Do I need to take the construction apart?

There could be a few issues at play.

The smooth rods are not parallel which is causing the bearings to bind the further you go up.
Part of the thread is damaged not allowing it to pass through the nut.
The threaded rod is bent significantly to where it either doesn't pass through the nut or bind the assembly. (Is the end of the threaded rod opposite the motor constrained?)
Even less likely is that the motor could be damaged.  Since you said it moved 5mm I would have to assume that is several revolutions of the motor so this is unlikely but possible.

The easiest way to find the problem would be to unhook/remove the threaded rod and see if you can move the carriage up and down the rods by hand, if so you just narrowed the problem down significantly.

I had to remove the coupling to the threaded rod to find out that the smooth rod arrangement was not the source of the problem. The threaded rod was probably not used for some years and probably never at all in certain areas. A thorough cleaning beyond visible clanliness brought everything back to life.

X stage binding like this is almost always caused by parallelism issues with the rods and/or screw. The two-rod-plus-screw arrangement is quite over-constrained and thus requires good alignment to move smoothly.
Some basic troubleshooting steps:

Make sure the screw is not constrained at both ends. It is very difficult to manufacture a screw that is perfectly straight and then mount it so precisely that it can rotate with zero runout. Screws in light-duty linear motion applications should be allowed to "wobble" freely so any bend or runout doesn't apply side-load forces to the Z stage. This can be accomplished by putting a misalignment-tolerant coupler (like an Oldham coupler) on the driven end, and/or leaving the non-driven end free without any support bearing. A motor mount with a small amount of compliance (like a rubber stepper damper) can help when the screw is captive to the motor.
Lubricate the screw and bearings and make sure everything is clean and in good condition.
Allow the Z carriage to self-align the rods and screw. The proper technique for this will depend on the Z stage, but the basic idea is to loosen the rod and screw mounts on either end, run the Z carriage back and forth a few times to push the rods into position, and then only re-tighten the top and bottom hardware when the carriage is at that end. It may also be necessary to loosen the screw nut and bearings on the carriage to get everything aligned properly and smooth-running, but that does not enforce parallelism like loosening the rod and screw mounts, so is really a secondary step. It may be necessary to leave some "float" in one rod or the bearings on one rod (with gravity preloading out any resultant slop) if the hardware has major alignment issues.
If the stage still binds after doing the above, it may be necessary to check if the linear hardware is bent (such as by rolling rods on a flat table) or use a file or Dremel to loosen up the mounts or whatever feature is causing the misalignment.


text:
What's the advantage of two z motors?
Some RepRap models use only a single motor for the Z axis, others use two.
For example, there is the 3drag that has only one motor and a smooth rod on the other side. There are modifications that add a threaded rod on the other side that is connected to the motor axis with a belt - which seems to be a really good solution.
Other printers, like the Prusa i3 or the Mendel90 have two Z motors. And after playing around with a two motor model, I find it pretty annoying when they get out of sync and I need to calibrate the axis and the print bed again. So two motors seem more like an disadvantage to me.
Could someone please shed some light on why most RepRaps have two Z motors (nowadays)?

There are three main options here for Mendel style ZX gantries:

One Z screw and motor, which is similar to a cantilevered design but somewhat more stable because of the opposite smooth rod
Two Z screws and two motors
Two Z screws and one motor, with belt synchronization of the two sides

Of all of these, running two screws off one motor is clearly superior in reliability and user-friendliness. There is no risk of the two sides of the Z stage going out of sync. One motor running at higher current will generally out-perform two motors splitting one driver's current via parallel wiring, because one motor with twice the torque can push much harder when one side of the gantry binds up or hits a rough spot.
The only real downside to the single motor, double screw approach is that it requires more engineering and parts. A closed-loop timing belt must be run between the two screws, with associated pulleys, tensioner, and support bearings. In comparison, using a separate motor for each screw is very simple. It adds a stepper and a shaft coupler, but saves a lot of vitamins and design complexity.
Two-motor, two-screw solutions are lower-cost and simpler to design. That's why they're used. End of story.
One-motor, one-screw Mendel style printers are quite rare. The passive side of the Z mechanism does add a little bit of stability to the X stage, but not a lot. It's possible to rack the X stage out of square with the bed and bind up the gantry. In order to work at all, they require a very wide/tall bearing footprint on the driven side to resist torque exerted on the driven side by the weight of the X stage and extruder carriage. So it's true that they don't have synchronization issues, but additional design challenges and undesirable flexure modes are introduced. It's much more common for one-screw designs to simply cantilever out the X stage, like a SmartRap or Printrbot Simple.

Thank you for the good explanation, I'll mark this one as the solution, as I think that it answers my question best and matches my experience. So you think it could be good decision to replace the second z motor on a Mendel90 (or a Prusa i3) with a belt? Both have a smooth rod and threaded rod on either side anyway. Btw, the belt design I meant for the 3drag is this one, couldn't find it before. I thought I could use that as a rough template.

I would add that having screws on both ends also lets you reduce the mass of the whole carriage, because of the much lower required stiffness. That should let you crank the speed/acceleration up higher, though that's less important for Z than for the other axes.

As an Ender 3 user, I can second that "one motor, one screw, two rails" is frustratingly error-prone if you mess anything up. It does work quite well if assembled correctly, though.

The general concept is to provide additional stability during the print. In the case of the 3drag machine you mentioned, you could run the risk of the -X- axis sagging due to the weight of the print head and/or additional wear on the rod or bearings on the one side (smooth side) as a result of the off balance weight. However, you may find "hacks" like this can potentially help reduce the affects by providing a bit more stability.
Having two -Z- axis motors with the threaded rods can help ensure stability of the -X- axis during print and can, overall, reduce wear on the mechanical components.

First up: I'm no expert. All of the below is guesswork.
I think that the main reason is that it makes for a simpler design.
If you hold the X-Axis only on one side, you have to keep it level through rigidity. (Especially if you have the extruder motor on that axis.) If you try to control the sagging, you have a problem because the torque changes depending on the position of the extruder.
For stepper motors to go out of sync, one has to miss steps. Regardless on whether you have one or two or seventeen motors, if you are missing steps, you need to debug it.
I got lots of missed steps in both X and Y, and I tried everything. Until I found out that I was actually missing steps in Z, and the nozzle was hitting the build.