GreetB,

I don't use much of Skienforge. I just use slice.py and fill.py from a version over a year ago. That means the only things I ever change in Skeinforge are extrusion diameter, infill density and extra shells. I only extract the paths from Skeinforge g-code, nothing else.

I set the speed, nozzle size and temperatures in my Python script. I also specify the feedstock diameter. Everything else is worked out algorithmically.

I set the extrusion diameter to the nozzle aperture, or less. The layer height is always 0.8 times the extrusion diameter, which makes the widt
h 1.2 times the diameter. I program the extruder feed speed to give the specified extrusion diameter at the head feed rate. In practice that stretches the plastic because it would naturally swell bigger than the nozzle aperture.

It is critical to get the feed rate spot on the get a good top surface
. Too little and you get gaps or valleys between filaments, too much and it rucks up into ridges and blobs. That is why I have always used a shaft encoder or a stepper. It is closed loop and there is not trial and error, my software simply calculates the extruder motor speed from the parameters men
tioned above.

You also need at least 3 solid layers to get a flat top surface. it takes that many to recover from being bumpy from laying over sparse infill.

I'm surprised that the spanning works so well for you. When I started out with my MakerBot, I used the default layer height of 0.375mm. I probably had bumped up the feedrate a little, before I understood Skeinforge well enough, so my objects didn't have quite enough plastic in them, and especially horizontal planes were too open. So, I lowered the layer height to 0.35mm with great results. Now, as experiment before printing this, I changed my layer height to 0.35 mm, while adjusting the speed to my original speed (30mm/s) multiplied by (0.35/0.32)^2 to get 36mm/sec. Printing a little minimug, I seem to have a bit too much material, so I increased the feedrate to 38mm/sec. For the bridge speed I've set 1.25 times the regular speed, and 0.9 times layer thickness and infill width, IIUC.

Could you sometimes blog a bit about how you use the various skeinforge settings? This really seems key to good print quality, but the number of knobs to fiddle with is truly staggering...
Recently I reduced that to 0.35mm, with a slight bump in feedrate

If you take a look at the STL it becomes clear why the support is needed, take a look at it sliced in half.