Inaccurate internal dimensions

[Nandox7]

Hi,

(this issue has been reported before: viewtopic.php?f=9&t=1229)

I've created a simple test part with 50 x 50 mm and with 2.5mm of wall, that would give a internal home of 45 x 45mm.

While the external dimensions are ok, 50,04 x 50,07 mm.





The wall gets with 2.9mm and as consequence the internal square hole goes down to ~44.30mm.




So it seems the slicer is for some reason creating a thicker wall, I have tried to play with the extrusion multiplier in case it was over-extruding and went as down as 79% with some improvements but still far from good.
I have not started to try using the horizontal size compensation but again no big change.

Is there any other param that would control this is this a flaw with he slicer itself? as if I can get the external dimension accurate the internal one should be as well.

(STL in attachment in case anyone wants to try it)

[dkightley]

Firstly....your photo site appears to not want you to host photos for displaying on other websites!!! All four are shown as grey "no entry" signs.

Having read your post here and on the linked thread, I wonder if you've tried the same print test on the attached stl file. There are no "internal" edges...but are the dimensional inaccuracies there????

[Nandox7]

Photos links sorted, should be visible now.

I made my own test part to make sure I was measuring against the correct sizes.
Plus the one I made is super simple, no round edges, just straight lines so there is no problem with arc or curve interpretation by the slicer.

[dkightley]

But my question to you is still a valid question. I have taken your shape and cut some off it so its a U shape. There are no "internal" sides....and I'm wondering if the inaccuracies in dimension are there. If they are.....it may not be a simple "internal sizing" issue!

[Nandox7]

What you mean as "There are no "internal" sides.'?

The walls are solid if that is what you mean, is not that I saying there is one singlle thin wall and I'm measuring the extrusion width of that layer.

[zemlin]

Take a look at the "Calibration Cross" part and spreadsheet I posted in this thread:
viewtopic.php?f=9&t=6130

I used these religiously and get great dimensional accuracy, both internal and external. The key is to use a combination of scaling and horizontal offset to home in on a setup that will work with both large and small features.