Prusa i3 calibration problems

Hi Guys,
Im having an issue with my i3 where the external dimensions are pretty good (40mmx40mm cube comes out at 39.81mmx39.83) however holes etc are coming out approx 0.5mm to small. I've tried several different stl's with the same result in each case. I'm using repetier host and the latest version of slic3r, im sure that it must be a setting somewhere as i doubt that every i3 would have the same issue, has anyone else come across this issue? is it mechnical? firmware? slicing?

Regards
Max

Max:
What size nozzle? What is the default extrusion width set to in Slic3R?

Did you do the .5mm thinwall test? What did the wall size measure?

Finally, how many perimeters/shells?

Most likely it is extrusion width related.
The newest Slic3r has a glitch where you need to set the default extrusion width to your nozzle size.
After that look at your extrusion multiplier.

Hi, i have a .35mm nozzle with default extrusion width of 0.35mm and an extrusion multiplier of 1, i run with 2 perimeters, ive just run the 0.5mm wall test and it came out at 0.52mm, hope this info helps

Just to give an update on things i have tried without success, i've tried printing with 1 perimeter, with the default extrusion width set to auto, ive tried slic3r versions 0.9.10b and 1.0.0RC2 and tried to reduce the extrusion multiplier down to 0.9. None of this helped, the internal holes etc still come out approx 0.5mm to small, i'm really confused as to how the holes can be to small when the external dimensions and wall thickness come out spot on

You didn't say what kind of plastic you using but all plastic shrinks ABS and nylon probably the most that is why parts warp and pull up from bed. People who design plastic parts when they make their molds they make them oversize because even in injection molding the part shrinks. Calibrate your extruder it is one of the most important things and depending on what you have for pulleys and belts you might have to also calibrate

Edited 1 time(s). Last edit at 02/05/2014 11:50AM by cnc dick.

Hi CNC, sorry forgot to mention that i'm printing in ABS using gt2 belts and pulleys, i realize that as abs cools it will shrink slightly, however as the outer dimensions and walls are nearly perfectly sized i dont think this is the issue with the holes, i have read that slicing software (especially slic3r) makes all the holes to small, i downloaded a test object with 3mm/5mm and 8mm holes, each one came out nearly 0.5mm to small which points to slic3r not calculating the sizes correctly but can't figure out how to fix it, ive tried repetier host with slic3r and cura which i think uses a different slicer and the results are exactly the same