PWOT Calibration oddity

Hi,

I was setting my PWOT (Perimeter Width Over Thickness) setting (Carve Tab) last night. I observed some odd behaviour (I think)

I printed a 20mm square cube with 0 solid layers and 0 infill, to give me a nice single walled cube. I printed it and measured the wall thickness. I did this for several different PWOT settings the idea being that I'd get 'the right one' and know that was the correct setting.

I was using a layer thickness of 0.4

- PWOT setting = 1.0, measured thickness 0.53. Therefore measured PWOT = 0.53/0.4 =1.325
- PWOT setting = 1.2, measured thickness 0.6. Therefore measured PWOT = 0.6/0.4 = 1.5
- PWOT setting = 2.0, measured thickness 0.93. Therefore measured PWOT = 0.93/0.53 = 2.325

So, it seems whatever I set the PWOT to in skeinforge, my actual (measured) PWOT is greater (approx 0.3 on that limited data).

Is this odd?
Am I doing something wrong?

An effect of this is that solid layers (100% infill) are always wrong (I set my Infill WOT the same as my Perimeter WOT).

My solution (such that it is) was to modify the Filament Packing Density (Dimension tab) to 1.25 (1.5/1.2=1.25 for a PWOT setting of 1.2). This did the trick - the wall thickness was approx 0.44 giving a measured PWOT of 1.2). However, that feels like a nasty solution. I'm not sure if there are other effects I'm not aware of.

I just wondered what peoples thoughts are

Thanks

Pete

PWOT is just stupid. It's old, it's backwards, and as far as I understand it comes from a time when there where no step extruders. And you just had a constant rate of extrusion.

I'm using my own version of Skeinforge, which got rid of the PWOT value, and just uses a line width. My version can be found at: [github.com] (use Alpha4, the beta is an experimental new UI which still has a few bugs)

But you could have other problems then W/T issues. Maybe your filament is slipping depending on the extrusion speed?