Inner dimensions

Hi all:

I hope this is the correct group for this question.

I have my Prusa Mendel set up pretty well with dimensions of print jobs coming out to within 99.5% accuracy but I've hit a weird snag.

When I print something with inner dimensions such as circles and cut outs within a part the dimension of these parts is always smaller than what I've modeled and I can't figure out why.

Has anyone else run into this? Do I need to calculate for this behavior when I design my models?

I'm using a .35mm nozzle, gen6 electronics.

You can see some background here. Short answer is there is no easy fix, you can adjust the STL files based on your machines performance or drill out the holes after printing.

Or turn on stretch [fabmetheus.crsndoo.com]

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FFF Settings Calculator	Gcode post processors	Geometric Object Deposition Tool Blog
Tantillus.org	Mini Printable Lathe	How NOT to install a Pololu driver

I have never tried stretch myself, just read there are other artifacts introduced besides larger circles.

Fascinating article.

I use AutoDesk 123D to do my drawings. On my next model I will use the polygon tool to make my small circles and see what happens.

jv4779 Wrote:
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> You can see some background here. Short answer is
> there is no easy fix, you can adjust the STL
> files based on your machines performance or drill
> out the holes after printing.

I have Stretch turned on, but I can't say that my settings are correct. I've only been successfully printing since last month and I've got a lot of learning to do. Here are my stretch settings:
Cross Limit Distance Over Perimeter Width (ratio): 5.0
Loop Stretch Over Perimeter Width (ratio): 0.11
Path Stretch Over Perimeter Width (ratio): 0.0

- Perimeter -
Perimeter Inside Stretch Over Perimeter Width (ratio): 0.32
Perimeter Outside Stretch Over Perimeter Width (ratio); 0.1
Stretch From Distance Over Perimeter Width (ratio): 2.0

I'm using 1.75mm filament through a 0.35mm nozzle at 180 degrees C. I'm also using skeinforge 4.1.

Sublime Wrote:
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> Or turn on stretch
> [fabmetheus.crsndoo.com]
> forge_Stretch