Are you printing undersized holes ?


There are endless debates on the internet about the possible accuracy of printed parts with consumer 3D printers. Almost everybody thinks that only expensive commercial machines are capable of producing parts with great accuracy:

… I think you have by far too big ambitions about accuracy with 3d printers. Think about again.
You have a nozzle that can make a line that is 0,40 wide or larger, never smaller. in layer height direction you can select a layer height smaller than nozzle width and by that get better resolution, but in x,y plane, accuracy is never better than extrusion width or at least half of it…

But some people say it is possible and you CAN get parts printed the exact size:

I must say this is one of the problems in RepRap. It is believed they can not be that accurate so people except less than they should. I was guilty of this at the beginning too and it was only after seeing some prints in person that were better then my repstrap was doing that I started trying to get perfect prints. Now my prints are always within 0.05mm of the target size and I now model all holes exactly the size I want them.

Here are some videos proving that it is at least possible:

Let’s test that

I printed some test objects to see if I can get that kind of accuracy with my cheap printer with bowden extruder and clone J-Head nozzle.

First try :

  • nozzle 0.4 mm
  • extrusion width 0.4 mm
  • 0.18 mm layer height
  • Cura slicer
  • holes to small

I read some more and also printed some more (I like “trial and error” approach):

As I discovered, the most common problems are:

polygonal-hole

polygonal-hole

  • filaments tends to cut corners when path turns
  • “Z wobble”also causes holes shrinkage
z-wobble

z-wobble

  • low-quality filament with irregular cross-section
irregular-filament

irregular-filament

So what can you do to get good prints ?

  • adjust plastic using the Extrusion Multiplier
  • use good filament
  • reduce perimeters speed
  • use Flow_tweak-post-processor and decrease perimeter flow rate as described above in case of holes coming out too small.
    https://github.com/Intrinsically-Sublime/Flow_tweak-post-processor
  • set the layer height to no greater than 0.2mm
  • use Tantillus Calculator to determine the extrusion width(use the intermediate or higher calculator and enter at least both your steps per mm’s, nozzle and filament sizes)
  • use Cura for slicing and enter a “shell thickness” that is exactly divisible by that width
  • use Sublime’s version of Cura to calibrate the flow to achieve perfectly solid parts and then use the inset feature to inset the perimeters to get the part exactly the correct size
  • https://github.com/Intrinsically-Sublime/Cura
    http://forums.reprap.org/read.php?156,311834

End result 1 :

  • nozzle 0.4 mm
  • extrusion width 0.4 mm
  • 0.09 mm layer height
  • shell thickness 0.80 mm
  • bottom/top thickness 0.36 mm
  • Cura slicer
  • 10cm strong fan blowing across the bed
  • holes perfect, outside dimensions perfect

End result 2 :

  • nozzle 0.4 mm
  • extrusion width 0.4 mm
  • 0.09 mm layer height
  • skin thickness(also top/bottom) 0.80 mm
  • number of loops(around the perimeter) 2
  • KISS slicer (Inset Surface=0 , LoopsGoFromInsideToPerimeter=unchecked)
  • 10cm strong fan blowing across the bed
  • holes perfect, outside dimensions perfect

Now my prints are also within 0.05mm of the target size and am finally comfortable printing stuff for other people without worry. And must say that I have the same results now with higher layer heights, not just 0.09 mm (but I stay bellow 0.20 mm and adjust settings like bottom/top thickness and temperature accordingly).
I didn’t have to use Sublime’s version of Cura or his Flow_tweak-post-processor but instead leveled the bed very precisely, made small changes in temperature, filament diameter and flow settings,shell thickness and infill. Those very small changes made all the difference and I ecourage you to experiment with the settings yourself. Your printer may have different problems than mine but if I figured it out you can do it too. You can spot a lot just by observing what is happening while printing(I use a magnifying glass).

Download redhatman’s and mine Test objects here, also all the pictures of this experiment are on Flickr.