scaling issue, model always to small

Hello,
i have a problem with my prints. Overall, they look very good but the problem is, that they are a way to small.
If i print my parts in slic3r with a scaling of 102%, the dimensions fit very well, if not, everything is to small.
For example, the 20mm box is printed out at 19.60mm in x and y. I have now calibrated everything again and again, my prints are always to small. If go 100mm in printrun, it exactly goes 100mm in x and y, i think there is no problem with that... I have no more ideas to solve this, because i can't print mechanical parts because of non fitting,...

calibration:
I have set the steps for x and y to 80 for t5 pulleys and nema17 1.8° with 1/16 stepping. My esteps are calibrated, if i want to extrude 20mm of filament it meaures 20mm. i have make the perimeter calibration, so my thin wall object has 0.7mm and slicer says, in the gcode, 0.7mm for the perimeter. (0.5mm nozzle and a layer high of 0.3mm)

Can anyone give me some hints what to do to get the right scaling, exept to scale the model with a factor of 1.02?

With standard 8 tooth T5 pulleys and 1/16 stepping 80 steps/mm is the correct setting!

What width/height ratio are you using?
This also needs to be calibrated correctly!

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

I set the layer high to 0.3mm and the width (i think its in the advance settings) is set to default 0, means that slic3r calculate that for me. how can i calibrate the width/height ratio?

See RichRap's blog entries from January 2012:

Slic3r is Nicer - Part 1 - Settings and Extruder Calibration
Slic3r is Nicer - Part 2 - filament and printing
Slic3r is Nicer - Part 3 - How low can you go?

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Hello and thanks for your hints.
I recalibrate my printer with the slic3r tutorial (i have used this befor, too) but i get the same results, my prints are to small.
You can look at my calibration test in the pictures, ( and ) for the width/higth ratio, which should be adressed in the perimeter test. Here i use a 0.5m nozzle and layerhigh of 0.35mm.
I am really wondering that printrun shows the cube way to small ( ). but after printing the cube has exactly the dimensions suggested by printrun. ( )
I have calibrated for days, but i get the same results over and over.