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Brass rails, bunting bearings ok for x,y axes?
new to 3D printers and to this community :)
Would a 1/4" brass rod with bronze bunting bearings for sliders and SAE 30 oil suffice for X and Y axes with moving extruder instead of print surface?
I'm gathering cheap/scavenged materials for a first time build, as a learning experience, and it doesn't need to work very long.
I just have no idea yet how heavy the extruders are, generally. I'm thinking of threading the rod so I can pull it tight for straightness under load.

The brass rods don't sound like a great idea for the long term.  If you have them on hand and want to use them for a week while you wait for case hardened steel shafting to come in, sure.  Trashed (paper) printers and copiers can be a nice source of shafting and bushings, especially if you are 3d printing whatever they mount in and so able to customize for them.

Extruders tend to be quite light. An E3Dv6 complete with fan, shroud and wires is under 100g. Unless you use a Bowden extruder, you also have to add ~300g for a stepper motor. In any case, it will be quite light.
Sintered bronze bushings can definitely be used in a 3D printer; they're used in the (quite popular) Ultimaker 3D printers. I can't tell whether your particular bushings will work well, but I think the most important consideration is that there isn't too much play between the rod and bushing (but I'm assuming you took care of that). 3D printers don't place high loads onto the motion system.
"Proper" LMxUU bearings aren't very expensive either (reasonable ones can be had for less than $2) so if the bushings don't work out, you could always try those.

The rod and bearing fit almost perfectly with maybe an average of 0.05" play. I'm looking at using a belt driven system with optical encoders. I've already tested the encoders and steppers with my driver and its compatible.

.05" is a huge amount of slop in a 3D printer. The general goal is <0.005". And 1/4" brass rods will be very floppy unless the span is very short (like <6" maybe).

@RyanCarlyle Thanks, that was one large concern as part of this question. This is just a throwaway build for learning, do you think it will work for that purpose? I will go for much tighter tolerances in the next build. As long as it extrudes the filament far enough out to make up for the play, I'm not concerned with making it pretty. I just don't want it to not function at all. I guess that depends on my speed :/ and the slop in the rods will hopefully be taken care of by the rod tightening. It's only going to be about 8" of travel

Someone correct me if I'm wrong, but having about 0.05" of slop could inhibit the carriage's movement and potentially damage the stepper motors with the amount of extra load you'd be putting on them. The slop could take the rails out of parallel which has more of an effect the longer the rails are. So, I guess it depends on how large of a machine you're talking about for the first test 6"^3 might be okay, but anything greater would be risky. Also note the answer explaining rod length here


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Carbon fiber instead of smooth steel rods?
I have a long 8 mm smooth steel rod of about 55 cm long. This rods bend easily due to the length. If I replace them with 8mm solid carbon fiber rods, will the bending reduce? Will the bearings wear off the carbon fiber rod? I couldn't find too much information about this.

Are you talking about Bambu Lab X1-Carbon?

Steel is the best material for a linear rod when you have a fixed cross-section. It will have the least flex of any rod (aside from some exotic metals) of the same size.
Carbon fiber's material properties might seem superior at first sight, but the stiffness is very anisotropic -- it's very stiff along the grain and not very stiff across the grain. So multi-axis stresses like bending aren't necessarily going to perform up to the theoretical specs. Carbon fiber has exceptional stiffness-to-weight ratio, but the stiffness-per-area isn't necessarily superior in this application.
People do occasionally use carbon fiber for linear rods/rails, but only in much larger sizes than 8 mm. Think >25 mm.
And that's really the problem here. 8 mm diameter at 550 mm long is well outside what's reasonable for bending stiffness. Bending deflection increases with the CUBE of length, and this is simply far too long for the size of rod. The general rule of thumb for precision motion applications is length < 25*diameter. That's a conservative rule, but it's the right ballpark. You really shouldn't be going over 200-250 mm or so with an 8 mm rod.

Thank you very much for the info! 2020 V-Slot extrusion should behave way better (that is, the bending should be almost negligible) right?

I could only add that you can try to use kinda print leveling feature. That's not the solution for bending rods of course but you can decrease the influence of it.

Yeah, 2020 is fine for ~500mm spans. You might want to upsize a bit for longer than that. The 25:1 rule works pretty well for dual steel rods (diameter) OR single aluminum extrusions (nominal thickness). The deflection math just works out convenient that way.

I agree that steel is the best material for rails but the info provided on carbon fiber is just wrong.
When making a carbon fiber part, whether a tube or any other shape, you lay the fabric in the orientation you need for the direction of the forces. If multi-directional strength and stiffness is needed then the fibers are laid in multiple directions. Nobody who knows what they are doing lays all the cf in one direction...
In general, carbon fiber is stronger than steel by both the strength to weight ratio and by volume. I say "in general" because parts need to be designed in the right way. A poorly designed carbon fiber part or a low quality steel can easily be weak.
There is a great video on YouTube showing a strength and stiffness comparison of a carbon fiber drive shaft vs the same part made in steel. The steel drive shaft bent and snapped with 3 times less force while the cf drive shaft had no visible bending until it snapped.
The main reason why steel is a better linear rail material is surface hardness. Linear rails have bearings traveling up and down continuously. The rails need to be hardened to prevent them wearing out too quickly. The surface hardness (how easy it is to scratch or penetrate) of cf is far lower than steel. There is no comparison.
Cf is great material for the frame but not the rails. For stiffer rails, I suggest buying some square THK rails. 15mm the rails will be plenty stiff enough for most 3d printers.

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Is there a lubricant that can be used for linear bearings, bronze sinter bushings and threaded rods alike?
My printer will feature LM8UU bearings/threaded rods for the z-axis and bronze sinter bushings on the x- and y-Axis.
As also, but not only, written here http://reprap.org/wiki/Lubrication, I know that one should:
 - use machine oil for sinter bearings, if anything at all,
 - grease on the 'more fluid' side for the linear bearings so that the lubricant stays eqally with balls on the upper and lower side
 - and probably PTFE grease for the threaded rods (as for example provided by the Ultimaker UM2)
Is there a way to unify this or at least only use two lubricants?
I do not have the slightest idea about lubricants, I would not know what to actually buy if the combination would e.g. be machine oil and low viscosity grease. Do you have specific recommendations of what to avoid?

A mid-weight PTFE grease like the popular Superlube will work in all the cases you mention (bearings, screws, and sintered bushings). 3D printer service conditions are quite light-duty as far as lubricants are concerned. You really just need to keep everything a little bit "wet" with oil or grease and performance will be adequate.
The main downside to using grease with sintered bushings is that they will likely stop being "self-lubricating" after the first exposure. The grease tends to clog the pores that allow the sintered bushings' factory oil impregnation to maintain a nice oil film on the sliding surfaces. So the bushings will forever-after require regular re-greasing, just like the ball bearings and threaded rod.
In comparison, a light machine oil like 3-in-one will maintain the sintered bushings' self-lubricating properties, but if used in ball bearings and screws will require very frequent replenishment. And that is certainly an option -- oil DOES work on bearings and screws -- but odds are good that you'll eventually over-oil the bearings, get drips on the build plate, and bang your head against a wall trying to figure out why your prints won't stick all of a sudden. Grease doesn't need to be applied as often, and it tends to stay where you put it rather than dripping. So grease is generally preferred to oil if you have to pick just one lubricant.
Again, the most important thing is to keep sliding and rolling surfaces wet with something. You'll just have various maintenance trade-offs with different options.

I ended up buying teflon (ptfe) grease as you suggested, from a hardware store around. But I will additionally buy a machine oil for the sinter bushings for optimal lubrication.

I needed to grease up my machine and had no access to specialist materials.  So I researched, and ended up using Vaseline.
I now have a small tub of it as part of my machine maintenance kit.

As for me...  I used the oil I use to lubricate my Trombone slide!

... and which oil would that be, or do we have to guess?

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Why are the STL files for the Ultrascope telescope at 45 degree angle?
I began printing the parts for the Ultrascope DIY telescope designed by the Open Space Agency.  See http://www.openspaceagency.com/ultrascope.
All of the STL files for the 3D printable parts are canted 45 degrees.  Brackets, tubes, everything I have seen so far.  Is there a reason for this?  I printed one part last night and simply rotated the part so it would lay flat because I didn't want to deal with supports.  I am relatively new to 3D printing -- Am I missing something I should know?  Is this a thing?

The orientation of the part in the STL file depends on the Software that creates the file. I had a software that would export the parts standing upright instead of laying flat. Depending on the CAD software it can be beneficial for the creator of the model to create in in a different orientation as the one you want to use for printing. Also not all CAD Engineers know (or care) about the best orientation for printing a part.
So my guess is that this is an issue of file export/ STL file creation.
It is totally normal to rotate the parts into a position that is best for printing.

i see 2 other possible reasons (both intentional)

parts were oriented to be printet together so such position conservers space

printer for which these file were created had the bed oriented in such position (rot45deg)

@darthpixel: Seeing that the TO wrote 'simply rotated the part so it would lay flat', both of these options do not seem reasonable to me.

@kamuro: that was just an option as it could be potential asnwer, that's all :)

Actually @darthpixel might not be wrong.  My print bed is 200x200 and if I lay the hexagonal tube parts flat and rotate 45 degrees on z-axis, it will JUST fit the bed.  Unfortunately, no matter how hard I've tried, the points closest to the edge curl up.  Today I am testing leaving the hexagonal part at 45 degrees (fits the entire space way better) and using supports.

@zkent i want to add offtopic comment. It seems your bed's not warm enough. I don't know what's your printer but maybe you can add a coat underneath something similar to this. This will warm up your bed quicker and heat distribution will be better.

@darthpixel, I will give that a try.  I am using a RepRap Prusa i3 variant but I know these PCB heat beds are hit-and-miss on distribution.  I have also thought of enclosing the entire printer in a box to keep the temperature up.  The parts, when laid flat can be over an inch thick, so that doesn't help either.

@zkent enclosing whole printer seems to be sophisticated ;) and harder to do and it can have influence on parts dimensions and can eventually harm your printed parts (if you have some in your prusa). Coat is quite easy to install and has great effect. You can even try to create your own coat with 2..3 layers of your old white 100% cotton T-shirt, aluminium foil and some cardboard. Stick it with kapton tape and voila :)

Layer lines are failure lines.
Sometimes I choose to print a part in a weird or sub-optimal orientation just to minimise the load across layer lines when in use.
That may mean more support material and longer print time, but a completed part that fails is no use at all.


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What are the ideal print conditions for polypropylene?
I'm having a lot of trouble printing polypropylene right now, and I think it may have to do with the conditions. I'm using a very thin coat of ABS on the base plate (just as you would do when printing with ABS) in order to promote sticking.
In this following first picture, I attempted with a 240°C tip and a 150°C bed (above PP's Tg). Oddly enough, one side actually looked somewhat decent while the other clearly had trouble sticking. The print speed on this was 1500 mm/min.
In the second picture, I was printing with the tip at 220°C and a 50°C bed. What's interesting in that print (you may be able to see it) is that the polymer extruded with little blips of material followed by a more stringy section, rather than a steady, even filament. (Print speed on this was 2100 mm/min)

Does anyone have suggestions for doing better prints with PP?

Polypropylene CAN be printed with excellent results, you just need a good filament roll and good printing setup.
A few days ago I read this topic and was kind of afraid of testing it, now I am so happy I tried it.
I am printing the PP filament from the brand Smart Materials 3D (search on google).
I am using a Prusa i3 Mk2, bed heated to 70ºC and hotend to 210ºC. I ventilate the printer as much as possible: room windows open and fan at 100% after second layer.
IMPORTANT: apply some cheap brown packaging adhesive strips to the bed, where the part is going to touch the bed, with adhesive facing down. I tried many other solutions but none worked.

I have printed so far at 20mm/s constant, with 0.2 mm layer heigth, 0.4 mm extrusion width, 0.8mm retraction, flow 125%. Still optimizing setings.
Parts come out very nice, with good flexibility and amazing inter layer bonding. Density is a bit lower than ABS, so excellent, and impact resistance is awesome.
Check some parts I printed today:

Awesome hints, it worked like a charm! I almost gave up on PP after reading Ryan Carlyle's post (which is definitely helpful too), but in the end I had less issues than with ABS. Only thing I changed was 240ºC on hotend, but that may be due to a different manufacturer/material.

I am using that same tesa brown tape; but it sticking rather too well. Even as I drop the temperature, I cant get the tape off consistently; and its not like this stuff sands very wel... tried another newer roll of tesa tape and its responding rather different; letting go a little better; though still not great. Strange!

Polypropylene is a bear to print. There's a good reason almost nobody does it. The main problem is that it's a semi-crystalline material, which means it doesn't follow the normal rules for warping prevention.
An amorphous polymer like ABS or PET is able to slowly flow or creep until it cools below the glass point, Tg. This means the stresses caused by thermal contraction will "shake out" above Tg and only start accumulating when the print cools below Tg and fully solidifies. That's why heated build plates are usually set around the glass point for amorphous materials -- there's minimal warping stress in the print at that temp.
However, when you extrude semi-crystalline polymers like PE or PP, crystallization starts as soon as the temp drops below the melt point, Tm. A crystalline polymer will not flow or creep at a rate that is meaningful over the duration of an FDM print, so thermal contraction stresses will simply build up more and more as the plastic is cooled farther below Tm. And there's a loooong way to go when cooling from Tm to room temp. As a result, you get HUGE warping stresses with these plastics compared to more typical FDM materials.
It is simply not possible to pick a heated bed or heated chamber temp that entirely eliminates the tendency of PP to warp. The normal rules we use for amorphous polymers don't apply. And, greatly compounding the problem, PP is a very low-surface-energy material with adhesion behavior fairly similar to wax. It doesn't want to stick to much of anything except itself.
High warping stress + poor adhesion = bad times.
So, the simple answer is, polypropylene does not have the correct polymer behavior to be favorable for FDM. You will always be fighting warping. Think carefully about whether you want to struggle with PP or switch to a more suitable material that could accomplish the same design goal for the printed part. Do you really need to use PP? PET blends have similar hardness and chemical resistance, nylon blends have similar toughness, and TPUs can handle living hinge applications. That covers most of the reasons you'd want to use PP.
If you absolutely must use PP, you're going to need to pull out ALL the tricks people use with traditional high-warp materials like ABS and PC and nylon.

Use a build plate made of a close relative of the material you're printing. For example, people have successfully printed HDPE on a PP build plate, so I would imagine that a HDPE build plate should work for PP.
Or, use a perfboard build plate with a raft so the initial layer will get embedded into the holes.
Or, use a coarse fibrous surface like stiff cardboard or fiberboard.
Get the build chamber enclosed and as hot as you can without damaging the printer. 50C is usually reasonable for motors, extruders, etc unless you have PLA printed parts to worry about. (Heated build plates only really help with the bottom 5-10mm of the print if the printer is not enclosed.)
Use helper disks / mouse ears on corners.
Really mash the first layer down onto the build plate.
Print low layer heights, like 0.1mm. Smaller layers mean the thermal contraction applies more shear stress between layers, and less of the large-scale aggregate bending stress that lifts corners.
Higher print speeds may also help due to some complex strain-crystallization effects, but that's only currently proven in nylon to my knowledge.

Another option, if it meets your functional requirements, is to use a fiberglass or carbon fiber composite PP. CFR and GFR plastics usually warp less than virgin plastics. The fibers have a low coefficient of thermal expansion, which makes the composite material contract less as it cools, which reduces warping stress. The most successful PP printing I've ever seen was GFR-PP. But that stuff is hard to find and may not work if the part needs to be flexible.

First picture clearly shows that temperature was too hight, second one suggests too small extruding speed (too little) which is connected to your printing speed.
35mm/s is quite slow :)

I've improved the print a little by increasing the print speed to up to 3500 mm/min, but I'm still having issues. I re-coated the baseplate with ABS, and adjusted the temperatures as well but still haven't got this optimized. Thanks for your suggestions, though I'm not out of the woods yet.

Yes. These settings work for Ultimaker as well.  Set the printer to print PLA, and put brown tape on the bed under the print.  Set the layer to 0.1 mm, set the initial layer to 0.1 mm.
Don't over heat the PP or when it cools it will shrink tons making it want to peel off. PLUS if you don't let the PP go below its Tg (80°C) by making the bed too hot it will stay molten and eventually stick to the nozzle making a truly pants print, and probably detach itself.
I have been making tiny detailed little components with PP this evening, just about to put 21 on to make and then off to bed!
Update:
Sorry, PLA settings on the UM is 210°C for Hotend. I am making round PCB spacers, so these are best with a 100% infill and a concentric fill pattern. Also, I recalibrated the platform with a very thin post-it note which is about 50% of the thickness of the UM calibration card. It makes sense to just get the PP soft enough to extrude, in fact I am seeing turbulence at the beginning when the extruder runs some material through the molten material has a curly cable appearance. Like this the material beds itself right into the tape. Lovely.

Hi and welcome to SE 3D Printing! Thanks for posting an answer.  However, it would be a very good idea to edit your answer and post the additional information in the answer itself, rather than the comments. Not only does this contain the information in one "block", but also comments are rather ephemeral and are generally used for queries, or clarification requests, and as such can end up being deleted.  Many thanks :-)


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Tetrahedral honeycomb?
I have an idea for a 3D printed project, but I'm a total noob in this area and need someone to reality check it for me.
Basically what I want to do is a tricopter frame made of a tetrahedral honeycomb.
The whole model would be within 30 * 30 * 10 cm, the honeycomb edges would be approximately 1mm thick and about 15mm long and it would be printed out of nylon with SLS.
I have found Shapeways' design guidelines and my idea seems to fit it, but still it feels slightly more extreme use than what they had in mind.
Is this doable? Does anyone else use a similar method? Is there some software that I can use to generate honeycombs like this, or do I have to write it myself?
Edit:
This is how two layers of the honeycomb look like:

In the actual model there would be several layer of this on top of each other and the shape would be kind of carved out of the honeycomb (+ some finishing to avoid spiky surface)

consider designing and printing only corner connectors and then assembling the structure with match sticks or drinking straws. that will reduce the price significantly

For designing your part, especially considering the repetitive mathematics involved, I would consider to learn to use OpenSCAD. I've learned the program and it fits your modeling requirement quite well. I feel it's easy to learn and is somewhat easier for folks who have a programming background. I don't have one, but it's still a logical progression to learn this program.
Regarding the SLS aspect, that also jumped out at me as a suitable answer. Solid shapes require to have "drain holes" to reduce the amount of powder consumed by the process.
I am assembling a Sintratec SLS printer and your model is the sort of thing I would enjoy to create with the printer. I've not yet listed my Sintratec printer on 3dhubs to solicit business, simply because it's not yet a fully assembled printer!
I did a quick Google search for "openscad tetrahedral honeycomb" and found this link:
http://forum.openscad.org/Beginner-Honeycomb-advice-needed-td4556.html
The result is more a polygonal honeycomb, not a true 3d tetrahedron, but it's a start. The file that created it is fewer than a few dozen lines of code.
The post is old  enough that the internal links no longer work but the OP posted his module code and that does work:

I'm not sure how personal contact works in stackexchange, but I'd be willing to work with you regarding creating your code and if the printer ever gets assembled, printing out your part.

Adding a picture again, to show the latest revision, based on the updated information:

Thanks, that would be awsome. I just (very roughly) calculated how much it would cost to print at shapeways and came up with a value of about 1k USD. That's way out of my budget :-).
For modelling I thought of doing the shape in SolidWorks, exporting to stl, and then replacing the volume with tetrahedrons using some script, but I'll have a look at openscad.
You can find my mail address by following the github link in my profile :-)

I've added to the original answer as I don't know how to generate an image here in the comments. How does this new image compare to your objective?
It's sometimes challenging to determine what anothers' thought picture represents. The above model is 1mm high, 15 x 30 mm although OpenSCAD is measurement agnostic, mostly.

I added a picture of part of the honeycomb to the question. I couldn't do more because my computer started slowing down a lot.

Is this doable?

It has been done, therefore it is doable.
I agree with fred_dot_u that OpenSCAD is a good system for programmatically generating highly repetitive 3d procedural content like this space truss 3d structure.
p.s.: A few links to people 3D printing various space trusses:

Parametric Space Truss Platform
smoothed2 octet truss flats
Micro Truss Toy
Materials by Design
"Nano octet truss materials synthesized"
"Computer-Aided Design and Rapid Prototyping"
"Octet Truss Construction Kit, v2"
"Octet Truss Memory, Time and Dollar Costs"
"3D Printed Isogrid and Octet Truss"
"Ultralight Cellular Materials"
3D printable "octet truss" models
STL finder "octet truss" models

In short, I don't think printing the full tetrahedral honeycomb design is a good approach considering the application of the part. Here are few things to note when attempting to 3D print the tetrahedral honeycomb:
I wouldn't recommend trying to 3D print this with a an FDM/FFF printer as you will most likely need supports and there would not be enough strength laterally. You may be able to print the design using SLA, but handling would be very difficult before post-processing as the part is very brittle post-print until a heat treat or curing process is done to chemically solidify. The post-process of the SLA could determine how strong the part is (ie. stainless steel powder, infused with bronze in a heat treat process would be good for such a part).
While SLS may be the best method for 3D printing this type of design, for that size part (30x30x10cm) you're looking at an expensive print regardless of whether or not you print it yourself.
Instead, I would highly recommend finding (or designing your own) a joint connector that would allow you to join wood/plastic dowels in the tetrahedral honeycomb shape. Not only will this be cheaper for you in the long run (easier to replace a few broken segments than an entire 3D printed model), but it could provide more structural strength for something that could potentially get banged around, like a tricopter.
For example, this model on Thingiverse (not my model) shows an example of how you can utilize 3D printing complex or custom joints that allow you to connect dowels in the shape you're looking for. It'd kind of be like building with K'Nex.
As far as designing said joint, you could model a single "inner" joint that has 18 connectors (8 on XY plane, 6 on YZ plane, and 4 on XZ plane). Below is a crude example of what I mean drawn in Google SketchUp:

The post specifically asks about SLS, so what's the point of mentioning FDM and SLA?

I'll update the answer to include SLS. But to summarize my answer, I don't think that printing the full design makes sense either economically or structurally. SLS has the best chance, structurally, alongside high definition DLP, but that's a major expense still.

Thanks for the answer. I roughly calculated the cost and it would definitely be too expensive. The underlying idea of what I was trying to accomplish is to make somehting fairly strong and very light using minimal amount of manual work. Vertex connectors and (probably wooden) pins would work, but it would kind of defeat the purpose :-)

Are you completely sold on the frame being made out of a tetrahedral honeycomb? Even a basic truss should suffice if you're making a hobbyist tricopter, unless you're going for cool factor. If you go with a basic truss, your overall weight could go way down and the cost too if you print several panels of trusses and join them with lightweight dowels.

If one creates a connector custom to this project, especially if done with an SLS printer, one could use carbon fiber rods for strength and light weight. Even a large quantity of connectors would be a reduction of cost to print via SLS, as well as fitting better in the build volume.


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Marlin move axis issue
I have problems with setting up Marlin for my new printer. Each time I rotate the dial, axis move to the same amount. It doesn't matter how much I moved it, to 1mm or to 20 mm (according to screen), axis move to the same really small step. It happens with all of axis. I tried to change step per unit to much higher value and it still does the same. Maybe you have some ideas guys? :)

Did you check the stepper current? Maybe the stepper tries to move, but doesn't succeed.

I figured out that problem was in my endstops. I solved it but still almost the same behavior. Already a bit better, but still not fine. I do not even know how to describe this behavior. Axis move but really weird, direction is correct but amount is wrong and quite random. I'll try to check current as a next step :)

Update. Jumpers were inserted to 1/16, but stepper chip I have (9488) could not handle that many micro steps. I changed it to 1/8 and now it works good.


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Is there a way to convert a file to .dwg?
I can download a file from Tinkercad as any of these:
.STL
.OBJ
.X3D
.VRML

Is there a way to convert any of those file types to .DWG?

I found this site and tested it a moment ago. I uploaded a simple .STL file (crystal) and had to register as a user (free, unremarkable) in order to perform the conversion.
http://www.cadforum.cz/catalog_en/stl2dwg.asp
The downloaded file was in .DWG format and opened without a problem in AutoCAD 2013 as a 3d object.
Note the placement of the pivot point in Meshmixer (first image) and the corresponding location in AutoCAD.

I managed to download the file as a .DXF. Will that open in AutoCAD?

It should, as well as open in many other CAD type programs. DXF means drawing exchange format.

There are solutions with instant delivery/conversion, and others that take some hours to send you the file.
I found solutions varying from free online conversion to pricey service.
You may need to do some touch up on the files converted from automated platform before you send it to a CNC or other CAD/CAM machine.
You can check on these platforms:
http://cadmesh.com
https://www.convertcadfiles.com/
Have in mind that, the higher is the model complexity (shape) the harder is to convert the model.
If trying to convert a 3D scanned model, make sure to have a closed mesh and a high-density mesh definition.
Good luck!


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What brand of 3D printing materials is the most famous/popular?
I am new to 3D printing and have read there is a fair bit of knowledge required to use the right product for printing.
In search for a good quality brand to start with, what is the most used filament based on sale volume worldwide?

A potentially more appropriate question for the SE network might be What effects filament quality?, then track down how a particular supplier processes the material.


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Strength of 3D printed Objects
I am new to 3D printing and need to know if I use steel in printing, do I get the same strength (compression and shear) as steel profiles manufactured in a factory?

Can you provide which technology you are expecting to use to 3d print using steel as the material? I am aware of laser sintering for metal as well as additive welding processes for steel.

Just any technology that works is fine.

This question is far too broad. You really need to narrow down what printer, process and material you're using.

I agree with @Tom, there are far too completely different types of 3D printing to give a simple answer. You could, however, rephrase the question to ask something like: "Are there currently any 3D printing technologies that can produce prints that match the strength of steel profiles?". If you also have an actual issue you want to solve, adding a 3D model or sketch, and a more detailed problem description would also improve your question.

A laser sintered part typically uses what could be described as surface bonding, as it does not melt particularly deeply into the powder. It would not have the same strength characteristics as machined steel or otherwise processed metal. A part constructed from 3d printing using feed metal/welding methods would have more strength, but would not necessarily have un-modified steel strength, due to the heat applied during the process.
Using a metal which responds to post processing, as in tempering, will likely improve the strength, but I believe that one is unlikely to reach the same values as "ordinary" steel. Compression along the lines of the construction layers would be reasonably strong, but forces applied in other directions are likely to match only the characteristics of the bond. The same consideration applies to shear strength.

If you want to improve (spelling of) the author's post, then consider leaving a comment or making the edit yourself.

Fred_dot_u do you know whether it is possible to use gold for 3d printing?

I've not seen any references anywhere to using gold in 3d printing. It's a great idea, but would be astonishingly expensive to prototype a machine. Probably the least expensive method would be gold-infused PLA, but even that would be hundreds of dollars per gram.

I've seen gold powder bed printing. Shapeways also provides gold "printing" but I'm pretty sure it's stainless steel infused with gold. So the part is printed in stainless powder and a post-print heat treatment infuses the gold with the stainless steel to solidify the part and introduce the desired material.

In terms of FFD plastics:
Using metal infused filaments for FFD printing; definitely not.  The properties mixed into the filament will have some affect on the final piece, stronger, heavier, etc for BronzeFill, but still the majority of the print material will be plastic.
However, you can use PLA plastics (and new Moldlay wax like filament) for lost wax casting so all of the plastic is replaced with the molten metal.
In this case, yes, all the plastic or filament is replaced with the final casting metal and it's at strong as any other cast item.

I wanted to make a tensile testing machine or very simple version so that I could optimised the strength of my printing (rather than the appearance).  Haven't done it.  I printed some herb holders for a door and they are not just not quite strong enough so two broken out of 24 in a year


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Can a sandstone 3D print be printed as a solid object?
I've been asked to prepare a 3D model for 3D printing in sandstone. I've been told that it needs to be 3" tall and the walls have to be at least 2 mm thick. It's an absolute pain in the neck having to make sure everything is the right thickness. So, I was wondering, can the whole model just be printed as a solid object, with 100% infill, and does that work for sandstone?

Why you have to decide between shell and solid? Wouldn't it be ok to use 15% infill (with 2mm wall thickness)? I'm just curious?

What is the problem with the 2mm wall thickness. That should only be a setting in your slicer. The Hight is a property of your model,..

@darthpixel Because if we go with 100% infill then I don't have to worry about having to model the 2mm wall thickness, which is hard because it wasn't originally designed with 2mm walls...

@Matthew ok - you have your reasons :) but you wrote "at last 2mm" so i understand there is a room for some... "flexibility"

Yes, you can just print it solid. However, it might be significantly more expensive to print your object entirely solid. For instance, Shapeways charges \$0.75 per cm³ of material for their full-color sandstone. A solid cube of 5x5x5 cm would cost \$96 to print, whereas it would only cost around \$6 if you printed it hollow with 2mm walls.

a side note: with a hollow stone filled with an infill material you'd also get insulating air pockets in the print, giving a lower need for extra thermal insulation.

To add to the selected answer, again, yes you can, however making all of the walls AT LEAST 2mm thick shouldn't be too hard, depending on your model and modelling app.
If your modelling app doesn't have a good shell function (or if it's too finicky on your model) you could easily define SOME negative space within the larger volumes of your model in order to save costs without having to actually make perfectly consistent wall thicknesses. Just make sure you leave a hole through which the excess material can escape from the interior void.
Shapeways has a good set of guidelines for their full color sandstone prints, which work about the same as any: http://www.shapeways.com/materials/full-color-sandstone
However, you'll want to double check exact measurements with your printing service.


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How can I scan a thing and modify it or scan two things and compare them?
I've been asking people about this, not no clue yet.
I want to scan a thing and modify it a little.
For example I have an object with 3 parts and
I want to change the position of the third part relative to the other 2 parts.
For example I have a certain object and I want to modify it a little to see
how the air flow around them would change.
Or I want to scan two similar things and see what's the difference between them
PRECISELY... is there any way to do this?

We need more detail or clarity here. The "scan and edit" thing is fairly easy, you just do a good-quality 3d scan and then edit the mesh in a 3d modeling program like you'd edit any mesh. For the second request, you can scan two things and just sit one model over the other in a modeling program to get a sense of differences. But scanning two things to QUANTITATIVELY identify differences is probably not going to happen outside a heavy-duty metrology lab or manufacturing QA/QC center. You need precision touch-probes for the level of accuracy I think you're wanting. Scans aren't all that accurate

Actually I am all new in 3D modeling and what I got from people in this area is that first of all, converting 3D scanned data to something model-able is not so easy and cutting a part of an object and replace it needs some extra work because I have to fill in the empty part caused by moving...

@RyanCarlyle it depends on what level of 3D scanner you're using, to the accuracy. I have a vision system with a touch probe and laser module at work that we've repeatedly gotten 0.0002" repeatability/accuracy with the optical measurements. KHKim 3D scanning is definitely not easy and turning the scan into a solid model can be even harder. It might help if you explain what you want to scan and how you want to scan it/them.

While I'm not sure what you mean by I want to scan a thing and modify it a little to see its effect. In general, a 3D scan typically results in a series of raw points. You'll need to convert the 3D point cloud into a Mesh before you can really do any solid modeling with it. Here are a few OpenSource programs that you could potentially use:

MeshLab
Blender
CloudCompare

To compare two scans, you could use the raw data in CloudCompare as well.
However, without knowing what your intended use is, it's difficult to tell how to help you. Please consider updating your response with a bit more of your own research so that we may definitively answer your question.

I modified the question, it might be a little better now. Thank you for the answer


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Seamless prints?
Is there a way to make all your prints seamless?? I know there was this program that printed a vase constantly changing the z axis making it seamless. Why cant this be done with regular prints?

If you ever seen 3d printouts on your own and you did keep it in hand then you probably felt layers. Most printouts contains 3 main "components"

bottom and top component (floor and ceiling)
outline (perimeters)
infill (inside supporting structure)

It is almost imposible (and for sure sensless) to create all these components with one continues line as it would be very complex and sophisticated line.
Second reason. It would be very often that printer would cross outlines (perimeters) so it would destroy good looking external surface.
And third reason. Objects can have "islands". Imagine printed elephant which is standing on 4 legs. How to draw leg leyers with one line if these legs are separated (at the floor level).
That's why "round vase" is the only option to print seamless. :)

With Cura (a 3d printing software) you can go to the Expert tab and click Open Settings and you will see under an area called Black Magic, an option to Spiralize the outer contour.

Look into post processing your model with an Acetone vapor Bath..  ABS plastic disolves in acetone.   if you put your print in a chamber full of acetone vapor, the outer skin will sort of melt, and give you the effect you are looking for. The goal is to leave it in long enough that the outer skin melts a bit.  Too short a time, and you don't get enough melting.  Too long a time and more than the skin melts, and the print may deform.

Thanks, I might just get use to the look, I know there was this guy in youtube who got this stuff that gave it a glazed/glossy look and gave it a smooth surface.

@ChrisManning It's a bit strange you've changed "accepted answer" because you did ask "Why cant this be done with regular prints?" Acetone vapor bath is definitely not regular print.

I was trying to like the comment/answer. I just now realized it was changing the answer.

I use Simplify3d as my slicer, and this has a 'vase' mode.  You end up with a single wall thickness and it only works on simple shapes without supports.
You get no infill or top surface, so it only works for certain shapes; vases for example!!


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Best cheap 3D printer, using FDM, with large print volume?
What are people's opinions on the most affordable 3D printer with a large print volume, of 200mm x 200mm x 180mm minimum, with a good quality over 100 microns?

Hi, welcome to the site. We need to make this question more specific for it to be a good fit for the StackExchange format. General opinion or survey questions are discouraged. For example, you could ask "what is the lowest-cost FDM printer with build volume of 300mm cube?" And that would be a better question. (Or whatever details are pertinent to your needs.)

@RyanCarlyle is it ok now?

I think that we should just avoid "recommend me a printer" questions altogether. The answers will always be highly subjective (no matter how specific you state your requirements) and inevitably go out of date (the printer market is rapidly changing). A better question would be "Does printer model X fit my requirements Y?".

@TomvanderZanden I'm not saying recommend me a printer I'm trying to see what your opinions are on the best reasonable sized printer

"Most affordable" is also too vague. A college student will have a lower reference for affordable, while a professional engineer could have a budget in thousands of dollars. Provide a price range to your question for better results.

It's all of your opinion, I just wanted to see what you guys thought was the best affordable one in your eyes

Better ask "Which printers can do 200x200x200 mm at 100 microns" You can then select the cheapest from that list.

@LarsPötter I wouldn't consider that a good question either. The answer would be unreasonably broad (basically, almost all printers except some very small ones) and go out of date (printers entering and leaving the market).


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Printer randomly moves to home during printing, then resumes as normal
During printing, my printer occasionally makes some mystery moves: it will very slowly move either the X or Y axis all the way to the left/front, before very slowly moving back to its original position and resuming the print as normal. I've checked my G-code files, and the moves are definitely not part of the G-code. What could be causing this?
I'm printing from an SD card on a Cartesian printer.

Which Firmware(Marlin,..)? Which printer(Cartesian, delta,..)? Extensions(Out of Filament sensor,..) ? Source of G-Codes (Printing from SD Card or from Serial interface)? Sounds like the printer is pausing the print. Causes might be no G-Codes (Slow serial connection) or some other signal(Out of filament sensor triggering)

The question is tagged marlin. I've edited the question to include where I'm printing from. I don't have a filament sensor.

Just had the same issue. I could print fine from the computer but load the same file to disk and get the random traveling to the 0 points on x and y at completely at random.

The issue was due to a corrupt SD-card, which was occasionally having some garbage read from it. It turns out that Marlin will try interpret a corrupt move command like G0 X1q3.54 and still read as many numbers as it can. In this example, it would be interpreted as G0 X1 rather than (as might have been intended) G0 X103.54.
This explains my symptoms perfectly:

X and Y always moved to (approximately) their home positions, but it was always only one of them (it's quite unlikely that both moves are corrupted).
Z was not affected because Z moves are much rarer in the G-code (only on layer change) and thus it was very unlikely that a Z move would be affected.
E was not affected since a request to move E to near 0 would be prevented by Marlin's long extrusion prevention.

Eurgh! I don't like that Marlin does that. Interesting find, though. Would love to know how you figured that out.

What is corrupt in G0 X1y3.54?

@Wirewrap My intention was that the "uncorrupted" G-code would have been something like G0 X103.54 and I replaced the 0 by a random character. Unfortunately I picked a really confusing random character. Thank you for pointing that out.

Beides a corrupt SD card that stores worng bits, leading to absurd commands, it's also possible that ithers parts in the Creatin of the file are compromised:
This can for example happen if the card is removed during writing - but in this case it should be mostly an incomplete file on importing into an interpreter.
More a random distribution of bad commands would appear if the writing process in itself is faulty, for example if the SD Port is defect or the adapter hast a error. Another way that writing can fail is if the drivers for the SD card adapter/port are corrupted.
To detect a bad file or corrupted card is possible by re-importing the G-Code into a slicer (for example CURA allows this) and look at the tool paths. If any port does this with any card, software is to blame: See if it persists after a driver update (rare!) and a reinstall of the slicer. If it fails in one port but works in a different the port or adapter might bei at fault and might need replacement. If it is endemic to one card, this one is corrupt and to be thrown out. If it is endemic to a single file, overwrite it with a new one - sometimes writing fails for reasons that are almost impossible to understand.
If the file&card are fine but read wrongly at the printer, then the card reader in the printer or the board are to blame.


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How does Carbon3D's CLIP technology handle bridges and support material?
All of Carbon3D's marketing and demonstrations show their CLIP technology producing contiguous and bridge-free parts. Has anyone seen examples of their M1 printing something like a buckyball within a buckyball or a figurine or some other shape that requires support material to print?
For example, how would the Carbon3D print a shape like this:
 vvvvvBUILDPLATEvvvvv
 ====================
  XXX
  XXX            BBB <----- columns A and B require support material
  XXX    AAA     BBB        in order to connect them to the build
  XXX    AAA     BBB        plate.
  XXXXXXXXXXXXXXXXXX

|~~~~~~~~~~~~~~~~~~~~|
|~~~~~~~~RESIN~~~~~~~|
|~~~~~~~~~~~~~~~~~~~~|

In a similar vein, how do they handles enclosed volumes? I doubt anyone wants a sphere filled with still-liquid resin...
Again, I've looked around, I can find no material addressing these questions, so if anyone can shed some light, I'd be glad.

I believe this could be extended to any DLP/SLA Printer

@Eric Johnson - Well, I understand reasonably well how, say, the Form1 series handle this situation, and I'd imagine that the Carbon3d's M1 handles it in a similar fashion, I was hoping someone might be able to point me towards the M1's implementation—or wven a mention of it—specifically, as the printer operates with very slightly different mechanics than most SLA and DLP models.

@PostEpoch it might make sense to answer your own question with what you know about how this is handled by the Form1. This might make it clearer which detail of the process is interesting for you. It also would make this knowledge of yours available for others. It might also help answering your question.

On Carbon3D's homepage they show a part that appears to have supports in it.

Per a conversation with Carbon3D's support they confirm that their slicing software will generate supports based on the overhang angle geometry, and in the case of a buckyball within a buckyball, there would be supports generated to create the buckyball, and to support the interior buckyball joining the two together that would have to be removed in post processing.
Enclosed volumes need to have a drain hole, and you would have to avoid vacuum forming shapes such as an upside down cup in which atmospheric pressure would keep the interior of the cup filled with resin until the reservoir runs out or the vacuum is able to be broken releasing the excess resin. In the case of a cup you would change the orientation. I am not sure how one would handle trying to print a solid sphere with no holes to avoid this condition.


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Determining the temps and speeds for DIY printers?
I've been going down the learning road with two broken printers that I'm rebuilding with better parts and electronics.
One thing that I've recognized is that there is a pretty low likelihood that any hotend or heatbed that has had the thermistor/thermocouple and/or the printer board swapped with a non-OEM part can be trusted to accurately report it's own temperature.
Sure, there are lots of things I can (and do) do to try to make it as accurate as reasonable like calibrating with thermistors from multimeters, IR thermometers, etc., but each method has limitations.  You never know if the 2nd thermistor is mounted both correctly, or if it is reading the same local temp as the printer thermistor.  IR thermometers have issues with reflective surfaces (like aluminum hot ends and build plates)  Calibrating the thermistor constants from experimental data isn't perfect.
IMHO, any hotend/heatbed temp on a DIY setup might be off by a constant ± 5 °C or so, more if it is poorly calibrated.
Printers use PID controlled heaters to keep oscillations down to a degree or two Celsius, because people say it impacts print quality.
Is there a good visual or experimental way to know whether your temperatures are "correct" for your printer/filament?  IOW, if my filament was supposed to be heated to 220 °C, how would I know if my printer was having issues because the "true" temperature is only 215 °C (or 225 °C) when it is reporting 220 °C?
One common problem I've experienced is the nozzle clogging after the transistion from layer 1 to layer 2.  (Layer 1 = higher heat and slower speeds, Layers 2+ = lower heat and faster speeds.)  It's been a struggle to know which factor (lower heat or faster speeds) are to blame for the clogs after the transition.

The short answer is, you use the temps and speeds that give you good results. It's trial and error.
The temperature number your printer reports really doesn't matter. That's just a process control variable: it needs to be consistent and repeatable, but it doesn't need to be accurate against an independent reference. What you should care about is your print results.
Some signs your printing temp is too cold:

PLA printed parts have a dull, matte surface
Poor layer adhesion
Extruder stalls or strips the filament at fairly low printing speeds for your extruder and nozzle size

Some signs your printing temp is too hot:

PLA printed parts have a very shiny surface
PLA has a very strong sugary/waffle smell, or any material smells burnt
Stringiness during travel moves that you can't eliminate by tuning retraction
Excessive oozing while the nozzle is stationary off the print
Bubbles or cloudiness in extruded strands in extruded strands even with dry filament

You will also calibrate speeds via trial and error. There are two main speed limits for a printer: how fast the motion mechanism can move the nozzle without running into issues or unacceptable print quality degradation (which is also a function of acceleration settings), and how fast the hot end can heat up and melt filament.
The mechanism speed limits you have to find via trial and error. Pick a test print you like (such as Benchy) and repeat it with different tuning until you find your preferred limits.
Melt flow restrictions are slightly more complex, because they are a function of VOLUME flow rate, not commanded speeds. Make a large boxy test print (with long straight lines) and multiply extrusion width times layer height times feedrate. That will give you your approximate flow rate in mm3/sec. Generally speaking, every extruder + hot end + material combo will have a maximum feasible flow rate. For example, most "average" hobbyist printers with 0.4 mm nozzles and good extruders can extrude about 4-8 mm3/sec with PLA. PTFE-lined hot ends are at the lower end, all-metal hot ends are at the higher end. The value will depend on your hardware. But you can do a few quick benchmarking tests to find the limit, and then use that to determine peak feedrates to avoid exceeding the melt capacity of your system.

thanx for precise description of "too hot". I vote up.

Could it be right that the volumetric speed [mm^3/sec] is something like layer_height * nozzle_diameter * print_speed? So a layer height of 0.2mm with a nozzle of 0.4mm and a print speed of 50mm/s would give a volumetric speed of 4 mm^3/sec. This can, for instance, be used for advanced speed control in Slic3r.

@TormodHaugene You want to use extrusion width because many/most people extrude strands much wider than the nozzle, and that's more volume flowing through the orifice. Unfortunately, it does depend on the slicer. They all do volume calculations a little differently. Slic3r's volume calculations in particular are screwy because it requires an oval strand cross-section, which is only physically accurate for [extrusion width > nozzle diameter + layer height]. See micrograph pics here: https://groups.google.com/d/msg/3dp-ideas/2FG_gUxa_fE/tGPx-yPu8lcJ

@RyanCarlyle, Thanks for sharing, I see you have explored the topic quite a bit!

@TormodHaugene A while back, I realized that different communities have different "best practices" for extrusion width vs nozzle size, and I spent a while trying to figure out why. Eventually traced it down to differences in 1) slicer algorithms and 2) nozzle tip geometry. For example, somebody running an E3Dv6 with Slic3r will have different optimal settings than someone running a Replicator 2 with Makerware. Not a lot of people realize that.

@RyanCarlyle, you are right indeed. I have tried to understand how handle random events of massive over extrusion in Slic3r for some time. Setting extrusion with == nozzle diameter appears to "fix" it for individual prints, but at the cost of reduced print strength, increased time to print, and so on. On the other hand, I think your point about nozzle geometry is a very good one, one that I have not thought of until now!

As per the detailed answer given by Ryan Carlyle, it can be a trial and error process to determine the optimal settings for your printer.  This certainly does not require absolute accuracy of the temperature sensors1 or the use of ideal filament to achieve.  In your slicing program it should be possible to increment or alter the parameters - like 'flow rate' or 'printing temperature' during a print of a simple shape - in such a way that is is possible to make subjective comparisons.
Some enthusiast videos detail a method of using a slicer program to print a simple hollow column and to increment a particular parameter from say 90 % to 110 % of the "ideal" values in fixed steps every 5 mm in the Z direction.  One can then observe the output and make a subjective determination of the print quality along the length of the column, and adopt the parameter value associated with the position in Z that produced the "best" outcome in terms of finish, strength and layer adhesion.
A standard plugin for the free slicer program "Ultimaker Cura" called "TweakAtZ" allows one to generate such a script, and could be a good option even if you normally would use a different slicer.  A user on the youtube site (with which I have no association) detailed this approach in a video titled How to Find the Perfect Print Settings For Your 3D Printer.  They went on to recommend this process be undertaken each time a new roll of filament is loaded in the printer.
I consider the method to be a good suggestion, as I find the suggestion "Pick a test print you like (such as Benchy) and repeat it with different tuning until you find your preferred limits." to be a potentially very wasteful and nonproductive proposition to an inexperienced user.

Footnote
1 Directly calibrating the accuracy of the indicator for the temperature sensor inside the extruder would be no small feat, and as has been mentioned above would likely be of little value.  If absolutely necessary it would probably best be done with a small gauge wire twisted Type "T" thermocouple wire tip inserted directly into the extruder nozzle if possible.  Using an IR thermometer not would be appropriate due to the size of the target vs the IR thermometer's field of view and the emissivity of the nozzle as you have already observed.

It looks like you have to calibrate your thermometer first. The easiest way is to use well known thermistor (preferably in well working printer) and then measure temperatures with your thermometer. This way will give you proper calibration of it. Then you can measure other thermistors with this thermometer.
Of course it requires to keep conditions constant as far as possible.
But to be honest... I don't really feel (or see) if there is a big difference with temperature ± 10 °C.
Let's say my filament has temperatures from 185 °C to 225 °C and I tell you there is no difference (at least I don't see it) if it's 190 °C or 210 °C.
Of course this difference is crucial when you reach min/max temperature but in the middle...


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Which belt tension gauge do I need?
I have a 3D printer that is going crazy with x-axis shift, and I need a tension gauge belt to measure the tension.
I've never used one before, and looking online, I can't tell which one would be the right fit.
Any ideas? What things should I look for?

What kind of printer is it? Most Cartesian printers that experience X-axis shift are having problems with fatigued electrical wiring to the X stepper or X endstop.

@RyanCarlyle It's Cubicon. Not popular brand in West. Korean made. Supposed to be good. But soon after getting it, this started happening. Part of their troubleshooting suggested checking the belt

Looks like a cartesian XY gantry printer, from a quick googling. If you can pluck the belt like Tom mentioned and get a low note, but still get X axis shifting, my next guess would be bad X motor or X endstop wiring.

It's extremely unlikely that belt tension is actually your problem. I've never heard of anyone using a gauge to measure their belt tension. Typically you just pull your belt tight by hand so that it produces a low note when plucked. It's far more likely that you're experiencing shifts due to too high or too low stepper current.
Unless your belt is so loose that it easily skips over the pulley (which should be obvious without using a gauge) or so tight that it completely binds up (it would be impossible to get it that tight without some kind of superhuman force) it's definitely not the problem.

I've read of people using smartphone apps that calculate the belt tension by measuring the frequency of the plucked belt. If you (the TO) are completely lost and need any kind of confirmation this might  be a way to get it easily.

I used a spring scale (meant for fishing). But it's really not critical. Just make sure it's not skipping teeth on the pulley and you should be fine.

I tensioned the belts of my delta printer equally tight solely based on their note when plucked. If you have an ear for music, that should be fairly straightfoward.

@kamuro thanks, will do if needed. Although now it seems not the issue.

@TormodHaugene alright. Although now it seems unlikely this is the issue.

@Tom van der Zanden Any tips how to know if this is stepper current problem?
I'll most likely end up opening separate thread for that. But it would be good to have more info.

@BasharAbdullah your issue is one of possible signs of current problem :)
#1. Check resistor on your SS (right next to black central chip.
#2. There should be R200 or R100 so R=0.2 or 0.1
#3. Read current (I) value from motor label
#4. V = I * R * 8
#5. this is max voltage which should be set on SS
#6. set it and check if your printer works ok
#7. if not - reduce it 10..15% and chceck if this helps. you can repeat #7.

@darthpixel thanks. I'm new to 3D printing really, so will try to tinker and see where I get :)

Loose belt doesn't need to skip to cause print problems - it's one of most common causes of a very common problem with small layer shifts, resulting in awful surface of vertical walls.

Also, the phone app is a great way to learn what sound is the "good tension". Once you learn it, forget the app and do it by ear. There's plenty of slack between "too tight" and "too loose" so don't sweat it about getting it perfect.

You may not need to adjust the tension, but you may nevertheless want to measure the belt tension, at least to ensure it's not too tight: the shaft on stepper motor has limitations. For example, NEMA 17 may have 30 N maximum tension then the belt is located at 17 mm from the motor face.
In that case, no need to buy a tool, you can use an audio app showing the frequency spectrum and then you pluck the belt. The lowest frequency peak can be related to the tension as explained here:
https://benchtopmachineshop.blogspot.com/2019/04/printer-belt-tension.html
For GT2 belts and 27 N tension, assuming the distance between belt and motor face is 10 mm, the relation is
$$f [\text{Hz}] = \frac{28531 \frac{ \text mm}{\text s}}{length [\text{mm}]}$$
Be aware that by plucking the belt you will excite the higher harmonics more than the base harmonic, therefore identifying the lowest frequency may take some time and multiple tries. You should display the frequency spectrum as "waterfall". The app "Spectroid" for Android has it.
If the distance between middle of the belt width and motor face is twice the value assumed (for example, 20 mm instead of 10 mm), the belt tension should be halved (based on an inverse relationship).
For those interested in alternative approaches, this page calculates the belt tension based on the datasheet of the belts, but it completely ignores the maximum load tolerated by the motors. So you can follow their directions but do not exceed the values recommended by the motors. The calculations mentioned there are discussed also on the following video:

heh, tuning your belts by sound? I always was going for a nice sound, not a specific frequency, but this is gold!

People are using this

to tighten the belt but I would totally agree with @Tom - there is no need to use such devices or gauges and your problem lies in stepsticks current.
It would be also problem with endstops so PCB doesn't know it's time to stop :)

Can you explain how this belt tensioner (if that is a correct name for it) works?

@kamuro it's just a spring that you put on the belt. It isn't really a tensioner (you still have to pull the belt tight somehow) but it helps keep the tension consistent.

In the meantime I found the idea by image searching 'belt tensioner', too: http://www.iheartrobotics.com/2009/11/timing-belt-tensioner.html The search also turned up lots of other interesting tensioning designs used in various other (industrial) sectors, too. Sweet inspiration ;)

On another note, I would assume that the current of the stepsticks also is a less important effect. I would take a look at the axis motion friction first. Parallelity of rods first, if the strength of the effect is varying depending on the position.

Well - depending on drive train design - this effect can also apear because of low wrap angle. Which means that timing belt surrounds a pulley not enough.

@kamuro as TvdZ said - it's not real tensioner it's more like laundry clip but it works fine so why not to give it a try :) But be careful it cost even $2 (as a "tensioner") but if you buy 10 laundry clips you will get 10 "tensioners" for half od dollar.

I didn't want to diminish the idea of using a belt tensioner at all, sorry if it came across like that.

@kamuro not at all :)

I would advise AGAINST using that kind of belt tensioner. Springs anywhere in your drivetrain add ringing at corners. The last thing you want in a precision motion control device is stretchy belts.

@RyanCarlyle Are you sure about that? It seems these spring-type tensioners are used in "professional" printers (Ultimaker comes to mind) and even some mass-market 2D printers. In any case, this problem is likely not about belt tension.

@RyanCarlyle don't you think these tensioners are just compensate sudden de/acceleration. Belt itself is not stretchy, its dimension change during acceleration only then it gets back to normal so counting whole amount of the movement dimension doesn't change a bit. Timing belt itself is doing the same by its nature isn't it?

Yes, I'm sure. A spring-tensioner is better than a loose belt, which is why some Ultimakers have them (particularly since getting even belt tension on a UM gantry is hard) but a rigid tensioner (adjust and lock) is superior to a spring tensioner. We use fiberglass-core and aramid-core timing belts in 3D printers for a reason, because they're as stiff as possible in tension. Spring tensioners makes the belt more stretchy. Specifically, when you turn a corner at positive velocity (jerk>0) any springiness in the drivetrain causes increased overshoot and therefore ringing.

Should add here that if the clothes-pin spring tensioner is nearly fully extended, it will be fairly stiff, because the geometry creates a force multiplier to make the spring apply a lot more tension. (EG see http://physicsbuzz.physicscentral.com/2015/04/physics-life-hack-number-3-getting-your.html) But if the spring tensioner is taking up a lot of slack and is not extended, it will add springiness to the belt.

Added for reference. To my understanding, especially if you run multiple identical printers, having the same belt tension on all of them is essential to getting accurate and consistent results. The effects of overly loose or overly tight belts have been demonstrated in a YouTube video by CHEP.
As mentioned in the comments above, a frequency analyser on a smartphone can be used, a web-based analyser is available at belt.connect.prusa3d.com. Additionally, the article Adjusting belt tension (MK3/MK3S/MK3S+/MK4) explains the concepts and steps that can be taken for belt tensioning.

Also, a simple belt tension measurement tool called Tension Meter for the GT2 belts of i3 MK3S+ or Prusa MINI+ that can easily be printed has been published by Prusament.

There is a similar printable model called True Open source tension meter for GT2 belts by ChipCE.


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Which properties of real organs do 3D printed organs have?
I've heard of 3D printed ears, limbs, and muscles. I assume if you were to attach one of these ears to a person, it wouldn't have a sense of touch and other properties that a real ear would have. So which properties of real human parts does 3D printing allow and which properties is 3D printing not capable of reproducing using current technology. And how do you predict those technologies will change in the future to further improve 3D printing?
Also can someone explain how human cells can be printed? Would this involve some kind of cell-plastic filament? How would the cells survive, etc. Where would you get these cells from and how would you be able to go from using a 3D printer to layer these cells together to then forming an organ out of that?

Your question covers a lot of territory. I'm not sure if this site is equipped to get into the biotechnology of synthesizing organic tissue, but if you have a much more specific applied question about where you're having a problem with 3D printing specifically, perhaps someone can answer a bit more comprehensively than they can here.

@RobertCartaino I'd like to discuss this question here


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Looking for information on modifying Boots Industries 3D printers
About two years ago I purchased a Boots Industries v.2.5 3D printer in a delta configuration. The wiki is still up at this location where you can see what the printer looked like.
The printer is prone to break and slip because the design uses thin wire to move the carriages up and down. I'd like to convert my printer over to using a belt like the one on this page, but the conversion kit is no longer available. I believe I can 3D print the carriages, but would anyone be able to point me toward the resources to convert my printer over to using a toothed belt?

Did you already modify your printer? If so, could you share how you did it in an answer? If not, I'd try to write an answer to your question. In any case, the last two links are dead, please update them!

Yeah, in the time since I wrote my question the company has taken down their wiki. I don't know that they moved it anywhere though there's still a forum at http://forum.bootsindustries.com/

Contact Brian or Lykle.  We all have Boots Industries printers and have heavily modified it to belt drive and magnetic effectors.  The print quality has improved drastically.  The old Boots support group has since moved on to Slack and we are in constant contact everyday.
https://biv25.slack.com/messages/@slackbot/
https://www.thingiverse.com/thing:1843195

This isn't a very good answer, because it consists of solely external references. On StackExchange, answers are expected to stand on their own. While including external reference material is great, it can change or become unavailable rendering a link-only answer helpful. Please make sure your answer can be read independently of outside sources. Perhaps you could explain how the conversion is done, what parts are needed, how you need to change the firmware, etc...


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Do the TW, THW and THHN or THWN wire insulation types matter in terms of powering RAMPS 1.4 or the MK2a Heat Bed?
I'm still looking at wires for my Prusa i3, to go between the power supply and RAMPS 1.4, and the power supply and the MK2a Heatbed.
I also recently found a 400 ft. Wire Storehouse that I bought from Harbor Freight which has wire sizes in it from AWG 10 through AWG 22 (and additionally speaker wire, Zip Cord and Bell).
I also bought some reading material, I picked up Wiring Simplified 44th edition, and in it on page 28, Table 4-1, there is a table with information about the Ampacity of copper wires including their maximum temp (C), and maximum carrying current (Amps) based on their insulation types.
Unfortunately, the 400 ft. Wire Storehouse does not provide any information in regards to the insulation type or quality and this makes it difficult for one to choose the correct wire based on the specification in the table.
Given that the thing only cost $30 for 400 Ft. of wire, it would lead me to believe that the cheapest grade of insulation was used; as I understand it, the TW type wire.
I also read a forum somewhere in which people were complaining about the cheapness of the wire in this kit, stating that one ought to wear gloves when working with it as there is probably lead in the insulation as well as the wire.
The largest copper wire I have found in the table that I have (AWG 10) says that it is rated at 30 AMP regardless of which type of insulation it has, should I be using the speakerwire instead?  That isn't listed in the table.  Also it should be noted that though the ratings for the Ampacity are 30 AMPs, the max temperatures are different; with the TW being at 60 C.
As far as I can tell if I use the AWG 10 (TW?) to connect everything it won't matter, but I just thought I'd check here to be sure first since my power supply is rated at 30 AMPs and that's probably the same as the wire....

If nobody knows how to answer this, can it please be moved to the electrical engineering stackexchange; I'll probably be laughed off the face of the earth there, but at least I'll have an answer.

There's a warning on the side of the 400 ft. Wire Storehouse that reads "Risk of electric shock!  Do not use on wiring that carries more than 300 volts" that doesn't really narrow things down much about which of the wires it's talking about, but at least that means the 12 Volts from the power supply will be okay.

Those few abbreviations you have there are not even nearly all of them. This here is a nearly complete list: http://www.multicable.com/Content/Wire_Abbreviations_and_Descriptions.asp And the rule is: No label or specification: Assume the worst. For all possible properties. Heat resistance, insulation quality, amperacity, etc. Which in the case of Amperacity means: Take the worst value you do have a specification for and multiply it by 0.8. Or the worst resistance per meter and multiply by 1.2 - I may edit this into an answer at some point. Don't hold your breath though

Is the worst TW?  Or something else?

This appears relevant: http://diy.stackexchange.com/questions/51966/does-voltage-play-any-role-in-choosing-the-appropriate-wire-gauge

THHN wire is thermoplastic high heat-resistant nylon coated wire.
THWN is thermoplastic heat- and moisture-resistant nylon coated wire.
"T" stands for thermoplastic insulation covering the wire itself.
"H" stands for a heat resistance of the insulation max 167°F.
"HH" stands for a heat resistance, but increased max 194°F.
"W" is for moisture resistant.
"N" is for a nylon coating make the insulation oil and gas resistant.
In my opinion the Wire Storehouse is good for simple stuff, but I would not use it for something I consider important.   It's quality is poor on the insulation rating and the number of strands is low.  Higher strands number allows for more flexible wire.
If you get high end audiophile type speaker wire it could be considered as you can find high strand number with good quality insulation properties in heavier gauges.
Or your local auto parts store will carry 8 and 6 gauge wire with better insulation properties.

Old AC adapters are a convenient supply of unusually fine stranded wire, and will usually have the wire info printed on it: gauge, volts, amps, max temperature.

No "mystery meat" wire in AC electrical
That kit is random Chinese "no-name" hookup wire and cannot be used for AC power. It's fine for low voltage hobbyist tinkering, which is what it's sold for.  If it was better than that, they'd say.
But who knows? Maybe the boat didn't arrive and they needed some 12 AWG to finish some kits, so they ran to the electrical supply and bought bona-fide Southwire THHN.  If so, the wire would be labeled "UL Listed" and "THHN/THWN-2". Then you can use it for AC power.
Without "UL Listed" or "UR Recognized" or other mark from a credible NRTL, any other labeling is lies.  CE is not an NRTL.
Proper THHN/THWN-2 is available locally, dirt cheap.
Competent hardware stores and lumberyards will cheerfully sell it by the foot. So like 6 feet for a dollar-ish.
(However they are often not located in strip malls, so some may need to rethink their shopping mindset if they want value).
Any good tinkerer/hacker ought to know the location of every good family-owned hardware store, real lumberyard, and electrical supply houses, bonus points for HVAC supply.
TW, THW and THWN-2 are NOT "good, better, best".
More like the Ford Edsel, Thunderbird and Escape: "obsolete, obsolete, and currently sold product".
Why not keep making TW, THW and THWN? No money savings there. It would cost more to keep 4 separate production lines than to just make everything dual-rated THHN/THWN-2.  So that's what they do.

it would lead me to believe that the cheapest grade of insulation was used; as I understand it, the TW type wire.

No, wiring doesn't work that way. You can't even assume it's a "T" family - there are also XHHW and RHH/RHW and the "S" family cordage, just in NEC Chapter 3 wiring methods.  And many other families not approved for AC power.

Unfortunately, the 400 ft. Wire Storehouse does not provide any information in regards to the insulation type or quality and this makes it difficult for one to choose the correct wire based on the specification in the table.

Doesn't matter what the ad copy says, it matters what the markings on the wire say. Wire that is unmarked is literally nothing.
Wire manufacturers know this.  Chinese wire manufacturers don't care.  But that Harbor Freight pack never claimed to be anything else, did it?

All I had to do was read the first bolded headline (didn't even see the rest of the answer) and I knew this was a Harper answer! You have a distinctive writing style. (Distinctive as in good, clear, simple, somewhat sarcastic. ;)


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Can a heatbed PCB (Prusa Mk2) be straightened out?
I have a really bent heatbed PCB, the middle is elevated about 3 mm with respect to all edges.
I have found this thread Warped PCBs, where a heating method is applied by baking a PCB in the oven, as described here: 3.2 Bow and Twist Repair.
Can this help straightening out a Prusa heatbed PCB? If so, can I apply the heat by the heatbed itself, or do I need to utilize an oven? Will the pressure from the strongly clamped glass plate be enough or will the glass break at these temperatures (given that the heatbed can reach them).

Baking PCB in an oven is not a good idea, I would say. I know PCBs are resistive to the heat (especially heatbeds) but, still, it sounds odd. But the real question is how baking would help. Let's leave it.
If your heatbed is such bent you can do few things depending on your situation/environment.
You can:

Add two glass plates (at the bottom and at the top) and clip them all together;
Support your HB with flat aluminium or even wood;
Add an aluminium frame, or;
If you use glass plate, clip the HB to the glass using stronger (wider) clips.

Ad#1 the thermistor can even stay sandwiched between the PCB and the bottom glass plate.
Ad#2 If your HB is bent up in the middle, you can use the middle thermistor hole. Drill it a bit with fi8mm drill (but not too much, I would say halfway through) and use a cone head screw to screw it flat on to the aluminium/wood support. Of course you will have to install a thermistor into the new place.
The simplest, and less destructive, solution is #1 and I would recommend that.

Some feedback after some time, without using the heatbed too much. The bend didn't go away so far, but with the bulldog clips I use now (it was a weird temporary solution before), the bed straightens out enough under the glass sheet. This solution is good enough for me. I will report if the glass suffers a total loss at some point.

While the suggestions in the answer are OK, the premise (that "Backing PCB in an oven is not a good idea") is factually wrong, given that is exactly as PCB are manufactured, and how they are fixed when surface mounted components become loose.  In fact you can most definitively use heat to straighten up a PCB, see this other answer: https://3dprinting.stackexchange.com/a/5682/9134

Agree with Mac on this. PCB heat beds are essentially PCBs and they can be put in ovens, baked at lower temps (say around 100 deg C) and can withstand temperatures up to 240 deg C (for less than 30s). That’s is how components are soldered to the PCB. This of course requires a reflow oven or a temperature controlled skillet.

AFAIK the question was - "could HB be straightened out ?" I did answer how it can be straightened out and in the first sentence I did mention that PCBs are heat resistive. I also asked how baking could help to straighten it out if his HB did bend after making it hot so how it could go the opposite with the same action? I don't see ANY reason to downvote.

Electrical engineer here.  There is nothing odd about putting a PCB in an oven.  Any surface mount PCB is assembled using a reflow oven which heats all the components, as well as the PCB itself, several degrees for quite some time up to the 'soak' temperature, which is 150 °C.
After that, the PCB (and components, still not soldered but held down with solder paste) are heated up to the reflow temperature, which for lead-free processes (i.e., all of them) is 245 °C.  After this point, they are held at that temperature for 60-90 seconds to allow the solder to completely reflow.  Note, this is not time spent with the oven temperature that hot - this is time the entire PCB, which edge to edge has reached 245 °C, spends at that temperature.
There is absolutely nothing wrong with, nor anything odd about putting a PCB in an oven or otherwise getting it hotter than it's glass transition temperature.  Doing so is a key part of their commercial assembly into electronics and has already been done to every PCB you own.
Please ignore the 'accepted' answer - it's incorrect.
PCBs are usually made out of glass epoxy composite (FR4) with a glass transition temperature of 140°C.  There are high heat varieties with a glass transition temperature of 170°C.  I do not know which variety the Prusa MK2/MK2S uses specifically, but FR4 doesn't have a 'sharp' glass transition anyway, so you want to err on the side of hot regardless of the specific type.  Get it nice and cozy at at 190-200 °C, and increase the temperature until it unwarps.   The solder's liquidus is about 220°C, so you should try to keep 20 °C shy of this just because kitchen oven thermostats are not to be trusted.
I own a MK2S, and have personally heated my heat bed up to above the glass transition temperature of PEI (don't ask) which is 217°C, and this was not a problem (well, except for the PEI but again, don't ask).  It didn't suffer any ill effects, nor did I expect it too.  I'm printing on it right now, as I type this.  It's perfectly fine to heat it up that hot.  That was the entire reason FR laminate was even made - to be rigid and to tolerate being hot.  Solder ain't gonna melt itself.
Note, however, you will need to remove the PEI/Ultem sheet as well as the adhesive before you do this.  Prusa has instructions on how, look under replacing the PEI print surface.
Now, as for the actual procedure, the pcb isn't going to magically just become flat.  You have to force it to flatness. Flatten it into submission. It will only be as flat as the hopefully flat surface it is resting on.  And, given the gradual transition of the material, it isn't going to exactly become super pliable even when a good deal past its glass transition temperature.
What you ideally want is two plates of aluminum large enough to sandwich it between. Or steel, or any metal.  They need to be thick enough to not flex so they are very flat.  A pizza stone, if you can find one that is flat, or a slab of granite also works.  I know none of these are exactly 'just laying around the house' type objects, but really any flat surface that will tolerate the heat that you can rest the pcb on is acceptable.  (Kids - ask your parents first)
The only problem is it will likely not unwarp itself under its own weight.  You'll need to put a large flat thing on top of it too, and either have it be heavy, or add heavy things on top of your large flat thing.  You want to make a heat bed sandwich.  Also, it needs to be shielded from the oven heating elements (be they electric or gas), as these will radiate heat a lot hotter than the oven temperature when they turn on.  Don't worry - aluminum foil is enough to shield anything from the heat, but again, you should have something very flat and substantial on top.
Oh, and remove the screw hole sockets from the PCB.  They just need a hex key and some pliers to unscrew.  Don't lose the lock washers.
Anyway, the above procedure, while definitely a pain, will restore (or if it was always warped, imbue for the first time) flatness as good as the flat things it is sandwiched between.
The flatness of kings.
This isn't exactly unknown either.  People do it.  It works.

YT shows that you can heat up composite material and bend it (in this case make it flat). But on the YT movie we can see a brand new HB. There is no info about it after using it for some time. If there is internal tension - it's possible the HB will bend itself again when heated up without pressure.

Since aluminium has a melting point at 600°C, you're unlikely to get it to a state where it flexes much by heating. I would doubt you even manage to aneal it (release the internal stresses).
Your best option is to construct a jig which allows you to press the distortion out (or pull, using a screw in the existing holes), whilst also taking care not to apply pressure (at least with a sharp edge) to the tracks or coatings.
This will only be a partial fix, but might be worth trying with a glass sheet in addition.
Edit: This might be relevant for a Mk3 heatbed, but not the Mk2 as asked in the question.

I am not completely sure why you bring up the melting point of aluminium, can you elaborate on that?

You have a bent metal plate, which you're trying to make less bent. In the case of a warped PCB, heating will soften the resin. The same is not really true in your case, I think - or maybe I mis-understood the question, and it is just a bare PCB you have?

Yes, - sorry, I could have a) understood what you meant (MK3 type PCB heatbed) or mentioned that I only use a MK2 type heatbed PCB as portrayed in http://reprap.org/wiki/PCB_Heatbed

Easiest way would be to place a glass sheet on top of the bed and run a calibration... Although, that way you may lose a few millimeters of print height.


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Micro 3D filament food safe
Before you put duplicate from this Which are the food-safe materials and how do I recognize them? please read
I need to know if this 3D Ink™ (PLA Filament) is food safe

In general, PLA is known as a "food safe" filament, especially Natural PLA. However, filament suppliers have different processes that may detriment the food safe quality.
Doing a little digging, I found an article on the M3D site which mentions the following about their filament

All of our products, including our filaments are made from 100% non-toxic components and considered generally safe under normal use. They are not considered a chemical, or a hazardous material by OSHA standards. Therefore, OSHA defines it as an "article" and does not require MSDS sheets. You can see more information about that here: http://www.ilpi.com/msds/faq/partb.html#article

So, without contacting M3D directly to acquire an MSDS (or asking if its food safe), you will not find one online.
Here is an article on a few tips for printing food safe objects as well. In a nut shell, don't 3D print food handling objects with crevasses, using uranium, or intend to put in the oven (a.k.a common sense).

What about the potential contamination from going through the hotend and everything before it or even from the substrate being printed on?  Without some type of coating, no plastic is really safe coming off the printers.
You could have coolant, oil, metal particles and other contaminants just from the hotend manufacturing process.

Those are all good points and I would really only be concerned about potentially flushing the hotend and wiping the build surface of debris. In all reality, you could probably just wash the part in the dishwasher on the top rack and call it good if the material is food-safe. However, I suppose it depends on the intended use of the part; personal use or consumer.

Stuff like lead in brass nozzles seems alarming at first sight, but the same metals and fabrication techniques are used to make household water plumbing components.

Is it inappropriate to use the "What doesn't kill you..." line?

In general no filament is safe as the printing process leaves "nooks and cranies" between the layers where germs can gain a foothold.
For food safe, I would advise:

print with white filament
use an acetone vapor bath to smooth and melt many of the "nooks and cranies" away.
Use a spray polyurathane and coat with 3-4 layers to reduce the evil "nooks and cranies" even more.

At that point it it should be dishwasher safe and food safe.


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Printer randomly stops, Is the power supply bad?
I have a prusa i3 with Mendel firmware and a RAMPS board.  Recently it has been randomly stopping during prints.  The LCD screen will lock up, the print will stop, and the heating elements will turn off.  Pressing the reset button on the RAMPS restarts the system and it works fine.
In addition to stopping during prints, it has also frozen up while just sitting while on.
My first thought is the power supply (12V 30A) is going bad, but is there anything else I should check before I buy a new one and replace it?
Update:
I replaced the power supply with a new one, and the printer did not stop and completed a print.  I am voting to close the question.

Do you have a multimeter to check what the supply voltage is doing?

I have measured the voltage on the supply and it is 12V.  I am guessing it drops for <1 second which would cause the problem.  I am planning on getting a scope and and putting a trigger on the voltage and also measuring current out of the supply.

Are you confident that your mains power is stable? If you have a spare UPS unit or one you can temporarily assign to the printer, using it will eliminate or confirm problems with commercial power, as opposed to on-board power supply trouble.

I'm a little suspicious about the PSU being the issue here, because locking up implies the processor froze, and the processor is on a 5v regulator circuit that should be pretty resistant to input voltage variation.

As an add-up to Ryans comment: If the voltage drops below operation level (as in the case of complete loss of power for a short time), the board should not freeze but simply restart as soon as power is back (not 100% sure, correct me if any of you have experience with too low voltage)

It could be several things.
Your ramps board is overheating or has to much load on it. If you're not cooling the ramps board adding a fan may help the issue.
I know Robo3D had this issue and started shipping with a fan to cool the ramps board.
The ramps/arduino board could be faulty, the firmware may have gotten corrupted or the current version has a bug in the code.
If you are not printing from the sdcard on the lcd controller and using software through a usb connection, that computer may be causing the issue as well.

for anyone who could be interested in cooling ramps

I had the same thing, the printer was not heating the nozzle anymore after starting the print.  I fixed this by reinstalling the firmware.
It could also be that your stepper drivers are overheating. you can add a fan to cool them.
The SD card could be bad, maybe try an other card or another .gcode file.
It is probably not your power supply, a 30A power supply is more than enough, but you can measure the volts on the power supply while the printer is running, if it is around 12V it is probably alright.


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How to create a very accurate STL file as well as the slices for a 3D printer?
I have been using Solidworks and AutoCAD to create STL file of a 3D model I want to print. I slice the STL file using Freesteel Z level slicer (http://www.freesteel.co.uk/wpblog/slicer/) and save the slices in a bmp format.
My 3d print has an array of circular channels, all of one radius. I expected the bmp slice to contain the circular shapes looking exactly identical to each other. However, I don't obtain the exact same replicas. Looks like the pixel-wise mapping has not been done uniformly. (View http://s24.postimg.org/p7w09zvkl/snippet.png for the image).
I want each and every circle to be represented by exactly the same set of pixels in the bmp image, so that all of the circular contours are identical. (I do not prefer changing the pixel resolution.)
How can I overcome this problem? Are there any better tools which would lead to a perfectly uniform pixel-wise mapping?
Thanks!
PJ

One approach is to crank up the fidelity of the STL mesh, and then perhaps first sample at a higher resolution before passing through a more intelligent (potentially custom) decimator to your target resolution.  Another, if the complexity of your design is not beyond what you can describe mathematically / programmatically, would be to skip the cad pacakge and slicer and instead try to write a program which directly generates the output bitmap.

I think this link can help you a lot!
https://www.mathworks.com/matlabcentral/fileexchange/68794-make-stl-of-3d-array-optimal-for-3d-printing

Your objective has a serious constraint regarding the pixel resolution. Within that limitation, the software (slicer) you are using will generate "best guess" images, particularly dependent on floating point math. There may be a single combination of circular shapes (radius) and spacing for these shapes that provides your objective, but that's likely not a practical exercise.
You have not indicated if you've tried other slicers, which would be the primary direction. A list of choices can be found here:
Free Slicing Program List
Another option that you can consider, not included in this list, is to use OpenSCAD, import the STL file, then use the projection() command to manually slice and export the image file. I use the term "manually" but the program can be coded to perform this task automatically, and there is a command line feature to OpenSCAD that may be useful.
Note also that the output of these slicers and/or OpenSCAD may exceed the resolution you desire. Manipulation of the image with a graphics editor could result in the same floating point disarray as you perform the changes.

I'm not sure I'd blame floating point math, as much as the fact that the design if first being approximated by a triangular mesh, and then sampled at the resolution of the destination bitmap.

You seem to have a pretty good understanding of how STL, so in case it helps anyone else, there is a file format (currently) in design called 3MF which should help with more accurate 3D Printing. While its focus is to ensure solidarity in a model (or manifold), the XML-based format should leave itself open to allow the machine/slicing software to be the only limiting factor in design geometry.
Since STL relies on triangulation to define its shapes, it is common to see the discrepancy, especially on a circular feature.