Undersized circles - Has this been solved yet? Hi everyone! I've managed to get my Prusa i2 printing pretty smoothly, however one issue still exists. I cannot get circles to print out to be the correct size. I created a circle test plate with holes ranging from 12mm to 3mm, and all holes are coming out small by a pretty fairly consistent measurement of 0.7mm under. i.e. (12mm = 11.3mm actual ID, 11mm = 10.3mm actual ID...etc) [b]My current setup is:[/b] -Prusa i2 -Slic3r -Repetier -MK2 Heatbed -Sanguinololu Board (I believe 1.2 or 1.3) -Marlin Firmware -Geared Extruder -Prusa Nozzle Hotend, 0.4mm -3mm PLA Filament The issue only seems to happen when drawing a circle on the X-Y plane. Outer diameter dimensions of circles and parts seem to be pretty well spot on. I have come across the issue in searches, however most people seem to just say "drill it out" to whoever asked.... I would like to know if there's a way I can just make the part print the way it was designed? [b]Attempted Solutions/What I've tried[/b] -Recalibrating the steppers by measurement, also by the online calculator -Tightened down hardware, gears, etc -Played with Slic3r's extrusion width values for perimeters (I tried 70%, 50%, and 30%). -Designed a part with a 15.8mm hole, and it indeed printed out to just about 15mm actual I.D. My thought is that simply there is too much filament being dumped on the outer perimeter, which is causing the circle to "cave in" on itself. I think this is going on because of the consistency of the error when measuring. All other aspects of the print seem to be working great. Has anyone else had this issue? How has it been solved? All input is appreciated, thank you! -Pat https://reprap.org/forum/read.php?262,407139,407139#msg-407139 Fri, 07 Aug 2026 21:45:24 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?262,407139,744743#msg-744743 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,744743#msg-744743 G2/G3 only makes sense based on the .amf format]]> nokian Printing Thu, 02 Feb 2017 15:03:59 -0500 https://reprap.org/forum/read.php?262,407139,744620#msg-744620 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,744620#msg-744620 So the main problem remains: In the 3D models there are circles. This information needs to reach the 3D printer, but this will not work with STL files.]]> Inhumierer Printing Thu, 02 Feb 2017 08:49:19 -0500 https://reprap.org/forum/read.php?262,407139,744472#msg-744472 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,744472#msg-744472
Most 3D printer firmware already supports the G2 & G3 arc drawing commands. I'm not sure how well they do this -- IIRC some software just turns these into G1 commands of about a mm each, rather than into steps or microsteps.

However, slicers (mostly) don't generate G2/G3 commands, because they (mostly) work from .STL files which represent meshes of straight lines. A slicer would have to somehow figure out whether a series of straight lines represent a curve or not, and what that curve ought to be. The information about the curve has already been lost. So a different file format is needed which represents arcs as well as straight lines.]]> frankvdh Printing Wed, 01 Feb 2017 21:49:06 -0500 https://reprap.org/forum/read.php?262,407139,744051#msg-744051 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,744051#msg-744051
If the printer firmware has to do this, the GCode will be way smaller, but the firmware has to do lots of trigonometric calculations. And those typically used processors like ATMega something are no really good choice for doing maths. I haven't checked this out completely, but for a quick glance, if the printer sets a point to print in an arc, there has to be done at least one sinus and one cosinus calculation, and I know these are heavy duty crunching numbers operations. It would be interesting how many sin/cos calculations per second an ATMega can do at 16 or 20 MHz.

On the other side, if the slicer does the work and approximates "perfect" circles by increasing the line count, this massively increases GCode size. The data transfer rate from the SD card will probably be high enough, and (I assume) the high BAUD rate of the USB connection is still high enough to compensate this. But anyway some more numbers and tests would be interesting. If my time allows me to do, I'll do some trigonometric performace testing with Arduino Mega boards.

Circles don't live in STL files, that's a fact (as far as I know). In a resume I do see two problems: If there is a circle or cylinder in a 3D object, the 3D designing software needs a way to tell the slicer "Hey, this is a circle, so treat it as a circle!"

If the slicer recognises a circle, it has to decide to either approximate the circle by linear movement on it's own, or let the printer firmare do the job. In this case I'd rely on the slicer more than on the printer firmware, but we have to make the slicers know about arcs.]]> Inhumierer Printing Tue, 31 Jan 2017 13:25:22 -0500 https://reprap.org/forum/read.php?262,407139,744036#msg-744036 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,744036#msg-744036 I'm curious how it can increase the dimensional accuracy of holes.

[www.reddit.com]]]> nokian Printing Tue, 31 Jan 2017 12:00:17 -0500 https://reprap.org/forum/read.php?262,407139,737519#msg-737519 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,737519#msg-737519 en.wikipedia.org] which allows curved triangles to be supported by CAD design software and by slicers. Current slicers work with mesh files (e.g. .STL) which describe objects as flat surfaces, so any curve must be represented as a series of straight lines. Some slicers (e.g. Slic3r) can convert straight lines (back) to arcs, and there is a post-processor that can do that too [github.com]. However, the quality of the resultant arc will depend on the fineness of the mesh and the errors allowed by the slicer software in deciding whether a point is on an arc or not. Only some firmware can print arcs directly using the G2/G3 codes [reprap.org].]]> frankvdh Printing Tue, 10 Jan 2017 17:51:59 -0500 https://reprap.org/forum/read.php?262,407139,737502#msg-737502 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,737502#msg-737502
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Farnomat
I don't know if somebody already suggested this, but if the holes are constantly too small (for example always .5mm), there's a setting called "Dimensional Accuracy" or "horizontal size compensation" or smth. like that in most of the slicers. If your holes are always .5mm too small, try typing in -0.25mm (so just half of the amount that they are too small) If your holes are too big then do the same but with positive values.

You have to be careful with that setting as it affects the entire part and not just the holes.]]> PDBeal Printing Tue, 10 Jan 2017 16:24:54 -0500 https://reprap.org/forum/read.php?262,407139,737452#msg-737452 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,737452#msg-737452 Farnomat Printing Tue, 10 Jan 2017 13:43:16 -0500 https://reprap.org/forum/read.php?262,407139,737404#msg-737404 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,737404#msg-737404
No not polygons. I was printing some gears to fit on special axles. The axles are basically circular but have three flats on them to prevent the gears rotating on the axle.]]> Supermec Printing Tue, 10 Jan 2017 11:59:42 -0500 https://reprap.org/forum/read.php?262,407139,737371#msg-737371 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,737371#msg-737371 @Supermec: Thanks for the formulas. Do you mean polygons by non-circular holes?]]> nokian Printing Tue, 10 Jan 2017 10:32:11 -0500 https://reprap.org/forum/read.php?262,407139,736768#msg-736768 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,736768#msg-736768
They suggested that where X mm was the required diameter of the hole then Y mm was the dimension needed to achieve it and that:

a) for vertical holes Y = 1.0155X + 0.2795 mm

b) for horizontal holes Y = 0.9927X + 0.3602 mm

These figures were for PLA, and as I understand it, they take into account various factors including the fact that the inside of the hole is unrestrained against shrinkage.

Have a look and see how they compare with what you have found. I have had success with these in sizing non-circular holes to accept metal rods as a tight fit.]]> Supermec Printing Sun, 08 Jan 2017 15:49:49 -0500 https://reprap.org/forum/read.php?262,407139,736735#msg-736735 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,736735#msg-736735
On a side note, I have noticed my holes are more accurate on the machines with a direct drive than they are with the bowden tube setup. I'm assuming this is probably due to the flex of the filament inside the bowden tube.]]> PDBeal Printing Sun, 08 Jan 2017 13:31:07 -0500 https://reprap.org/forum/read.php?262,407139,736730#msg-736730 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,736730#msg-736730 nokian Printing Sun, 08 Jan 2017 13:23:27 -0500 https://reprap.org/forum/read.php?262,407139,692610#msg-692610 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,692610#msg-692610
At work we have a Stratasys uPrint SE Plus, and it does exact dimensions so it is possible for the FDM machine to be capable of printing exact dimensions on holes and parts, but I have not been able to figure out without disassembly of what nozzle size this machine is using.]]> PDBeal Printing Fri, 29 Jul 2016 10:44:06 -0400 https://reprap.org/forum/read.php?262,407139,684493#msg-684493 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,684493#msg-684493
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PDBeal
Wouldn't the width be different depending on how much filament is hanging from your hotend, as it gets longer, I'd imagine gravity will pull it down more so than if it was fresh out of the nozzle. I've also seen right as it starts to extruder in mid air it begins to overlap itself at first and then finally begin to fall slowly which in turn would also affect the width of the extruded filament.

I wonder if it wouldn't be better to have a given gcode string to extrude a known line on the bed and measure that rather than extruding in mid air.


Honestly just try it, extrude 300mm to 500mm (extruded length) and measure a few spots, it will be remarkable consistent. This is the die swell factor.

Rather than a single line on the bed you would be better to print a single wall cube and measure the wall thickness for each layer thickness you commonly use, this factors in the "squish" spread. This doesn't take into account path overlap that slicers will have when doing multiple perimeters.

I only suggested checking the free air die swell as this has been remarkable consistent in determining how much smaller the inside diameter will be (for me).... the whole polygonal hole is also a factor.]]> aussiephil Printing Wed, 06 Jul 2016 03:07:11 -0400 https://reprap.org/forum/read.php?262,407139,684451#msg-684451 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,684451#msg-684451
I wonder if it wouldn't be better to have a given gcode string to extrude a known line on the bed and measure that rather than extruding in mid air.]]> PDBeal Printing Tue, 05 Jul 2016 22:03:52 -0400 https://reprap.org/forum/read.php?262,407139,684152#msg-684152 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,684152#msg-684152 To even get a handle on hole size issues once you have the rest of the machine calibrated you need to measure the diameter of the filament extruded into free air.
I have found for ABS on a range of nominally 0.4mm nozzles that I constantly get 0.58-0.60mm. This is 0. to 0.12 larger than the slicer set width.
As slicers set their paths based on the set extrusion width any actual width will be reflected in the internal sizing of things like holes.

Other people may get different results from their nozzles and this is why you should measure.]]> aussiephil Printing Mon, 04 Jul 2016 21:03:58 -0400 https://reprap.org/forum/read.php?262,407139,683949#msg-683949 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,683949#msg-683949 Blisk Printing Mon, 04 Jul 2016 07:45:47 -0400 https://reprap.org/forum/read.php?262,407139,607911#msg-607911 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,607911#msg-607911 RRuser Printing Mon, 11 Jan 2016 02:28:00 -0500 https://reprap.org/forum/read.php?262,407139,607905#msg-607905 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,607905#msg-607905 henryx7 Printing Mon, 11 Jan 2016 02:09:21 -0500 https://reprap.org/forum/read.php?262,407139,474875#msg-474875 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,474875#msg-474875
You might get better results if you start with a higher resolution STL file. If you're going to calibrate yourself for adjusting designed hole sizes to compensate for the printer's errors, you should probably standardize on one STL file resolution,otherwise you're going to be getting different results from different CAD files.

This is one of the reasons why 3D printers are not consumer products yet. It takes a lot of arcane knowledge to get a printer to produce quality prints.]]> the_digital_dentist Printing Mon, 23 Feb 2015 21:15:48 -0500 https://reprap.org/forum/read.php?262,407139,474283#msg-474283 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,474283#msg-474283 www.thingiverse.com]]]> tmorris9 Printing Sun, 22 Feb 2015 17:43:10 -0500 https://reprap.org/forum/read.php?262,407139,474282#msg-474282 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,474282#msg-474282
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pistolero
Quote
DinoK
I wrote more detailed article about it on the blog.
...
To sum it up, everybody can do it, you just have to fine tune the printer :)


I've read your post dozens of times, but still don't understand what to do to make my Kossel print holes with exact internal diameters.

I'm printing with PLA now, 200C, 60mm/s. Shell thickness is a double of nozzle diameter (2*0.4mm=0.8mm) and layer height is 0.2mm.

I've tried bigger shell thickness and 0.1mm layers and other temperatures, but regardless of the settings my holes (either round or square) are printed smaller than needed by ~0.5mm.


This is blocker for me. I'm trying to print engineering parts and precise dimensions are required for assembly.

Any help how to teach my Kossel mini to print holes with exact diameters would be appreciated .


With an FDM machine it's just not going to happen. At least not yet. It's not your machines fault but the nature of the plastic and how it expands and shrinks. The best we can hope for is a slic3r that figures out how to compensate for the problem but even then it's going to be different on every printer and every filament type / brand.

So, the best you can currently do is either design the parts with slightly larger holes (print a reference hole chart then measure) or drill out holes after printing. Or, wait until the technology matures quite a bit and a solution is found.]]> tmorris9 Printing Sun, 22 Feb 2015 17:40:56 -0500 https://reprap.org/forum/read.php?262,407139,474109#msg-474109 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,474109#msg-474109
Quote
DinoK
I wrote more detailed article about it on the blog.
...
To sum it up, everybody can do it, you just have to fine tune the printer :)


I've read your post dozens of times, but still don't understand what to do to make my Kossel print holes with exact internal diameters.

I'm printing with PLA now, 200C, 60mm/s. Shell thickness is a double of nozzle diameter (2*0.4mm=0.8mm) and layer height is 0.2mm.

I've tried bigger shell thickness and 0.1mm layers and other temperatures, but regardless of the settings my holes (either round or square) are printed smaller than needed by ~0.5mm.


This is blocker for me. I'm trying to print engineering parts and precise dimensions are required for assembly.

Any help how to teach my Kossel mini to print holes with exact diameters would be appreciated .]]> pistolero Printing Sun, 22 Feb 2015 11:52:32 -0500 https://reprap.org/forum/read.php?262,407139,415930#msg-415930 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,415930#msg-415930 you may have to account for shrinkage.]]> pushthatbolder Printing Sun, 05 Oct 2014 21:11:31 -0400 https://reprap.org/forum/read.php?262,407139,415929#msg-415929 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,415929#msg-415929 I am getting the prints within 0.05mm of the target size which seemed imposible before. I wrote more detailed article about it on the blog.
Redhatman, I used your STL file and published it on Youmagine, hope you don't mind. I also made my own test STL files with squares and circles.
To sum it up, everybody can do it, you just have to fine tune the printer :)




]]> DinoK Printing Sun, 05 Oct 2014 21:06:02 -0400 https://reprap.org/forum/read.php?262,407139,410642#msg-410642 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,410642#msg-410642
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DinoK
@redhatman Can you please give some STL or(and) GCode examples of your failed prints ?
I would like to try and print them myself as I have been researching this issue myself.

Essentially, if a part involves a circle hole, it will come out undersized. I made a circle test plate to use as a calibration/practice part which is used solely for messing around with this stuff.

I have attached the .STL file, the holes should be 12mm down to 2mm, in step sizes of 1mm. Please let me know if you're able to get anywhere with it, the closest I have come to getting the accurate dimensions are 0.4mm undersized.

[attachment 40814 circlestestplate.stl]


[attachment 40815 Circleplate.PNG]]]> redhatman Printing Mon, 22 Sep 2014 18:21:48 -0400 https://reprap.org/forum/read.php?262,407139,410565#msg-410565 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,410565#msg-410565 I would like to try and print them myself as I have been researching this issue myself.]]> DinoK Printing Mon, 22 Sep 2014 15:34:46 -0400 https://reprap.org/forum/read.php?262,407139,410141#msg-410141 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,410141#msg-410141
I have now tried Slic3r, Kisslicer, and Cura all with the same results. I have managed to get better looking parts with all of this messing around, however I still do not have accurate inner dimensions for circles.

I would be interested in helping solve this issue if I knew a little bit more about the way slicing software works. I understand the basics of how flow width, height, etc is calculated, however, I'm referring to how the software actually interprets the .stl file and outputs the g-code.

Again, thank you to everyone chiming in here. This forum has been great and continues to be a great benefit. I appreciate it,

-Pat]]> redhatman Printing Sun, 21 Sep 2014 17:21:19 -0400 https://reprap.org/forum/read.php?262,407139,409002#msg-409002 Re: Undersized circles - Has this been solved yet? https://reprap.org/forum/read.php?262,407139,409002#msg-409002
I would imagine this could be taken care of with slicing software - if they haven't already done it, they may soon. Anyone know if Slic3r has done this yet?]]> Wissing Printing Thu, 18 Sep 2014 12:39:52 -0400