min and max extrusion width?

The general rule of thumb is to go about 20% over your nozzle diameter.  I myself go over just a bit with my 0.4 mm nozzle to 0.5 instead of 0.48 mm.  That's just cause it bugs me being a weird number to calculate, however easy it is for slicers.

As for how low, really you won't get adhesion for anything under your nozzle diameter.  Of course that is what you want for support is weak material to break off.  I don't like how bad support ends up getting printed up that low, especially since slic3r's support is usually terrible.

I've had my width set to 0.5 for quite a few months now and it seems to be doing me justice so far.

Probably because I have covered it in extreme detail in several other threads.  You might have a search it's amazing what you might find.

I most certainly did not mean to offend.  I was simply in a hurry and thought you'd rather search than wait for me to find a link.
This is one of my favorite topics because so much of it is overlooked or otherwise not experimented with.
When I get some time I will try and find some links but for now if you search "extrusion width" you will get more than you want but dig in about 5 or 6 pages where most of this is covered.

far as slicer settings on this (not firmware flow rates etc) skys the limit. many have had good results all the way from 0.02mm to 0.6mm using either the old 0.35mm or new 0.4mm nozzles respectively. depending what is being printed at those sizes.

cant hurt anything to try and unless using PLA with the 0.35mm nozzle or setting extrusion temps too high or low for material used, this wont cause clogs. so experiment and let us know what you find works best for items printed.

rule of thumb seems to be nozzles 0.4mm and smaller can act like a Nozzle up to plus/minus 0.05mm dia, while Nozzle sizes 0.4mm to 0.6mm etc can have a span of plus/minus 0.1mm dia. thats why the steps in sizes available reflect this.

This is a reassuring post.

i remember jagowilson suggesting the same.
But I tried 0.2 mm thickness for first layer, and it doesn't stick to the bed at all.
Are you maybe squishing it also quite a bit?
This is interesting, any ideas why this improves adhesion? I've been having serious adhesion problems lately (everything I print warps).

I didn't quite get what you mean.

I guess this means it's safe to play around with the numbers.

Okay, so this is what I tried.

Printed rectangles and circular buttons only so far, no overhangs or complex shapes.

Okay, so with 0.2mm layer height, 0.2mm External perimeter width and 0.2mm top solid infill I got a pretty good rectangle. The top is like it wasn't 3d printed. It's not 100% smooth either, there's a tiny bit of texture to it, but I couldn't see the lines

Same with setting the values to 0.1 mm.

Then I went ahead and tried 0.05 mm just out of curiosity. I got some smearing of the plastic in places and in places the plastic had brown spots. I think a sign of over extrusion and plastic burning by contacting the hot nozzle too much or the z motor not moving the bed down enough for each or some layers.
My hotend temp is 215C.

I'll post photos when I find lens for macro photos. These details are really small for my camera.

In general the results are pretty satisfactory so far. Thanks everyone for the input.

One question I have now, is there a point in me getting a 0.2mm nozzle if a 0.4mm nozzle can do 0.2mm already?

I'm going to give it a try, but I really don't get it. Say you have 24 infill lines and then 48 infill lines half the diameter, both covering the same surface and being the same amount of plastic. I don't understand the difference adhesion wise.

The reality is also you don't get 48 infill lines. I've played around with this myself and what you more or less end up with is lines somewhere around the width you asked for but they overlap a bit--the nozzle partially passes over already-extruded plastic. Bear in mind that the shape of the nozzle is no accident. It is designed for more than just extrusion. Nozzles have their shape because it allows them to apply squish to the plastic as it is extruded.

Now I've tried extrusion widths as low as 0.24 for the first layer with a 0.4 nozzle, but I found this trick only worked well for some prints with a 0.4. Sometimes it would stick like glue, other times the plastic would get pushed up off the bed. With a 0.6, I don't have much issue with this trick and it works well. I think I ended up extruding the first layer at 0.36 with good results but I can't remember exactly and I can't check my settings.

I have a theory.... Atmospheric pressure aka suction cup effect.   I've recently gave up on ever getting good adhesion on my printer so before i trashed it.
I did a dramatic thing..i trashed all my slic3r profiles and started with everything hardcoded to .4mm(my nozzle size)and worked my way through about 5-6 independent tuning guides. 

Doing this I learned a couple of things:
1.  Don't use percentages for any value except maybe speed.   Most percentages are based on layer thickness.  Hardcoding values allows you to change layer thickness without screwing up a ton of other stuff.
2.  What most of the numbers ACTUALLY do.

It is a long drawn out process I have to recommend to anyone serious with 3d printing. (thanks again Wardjr for your feedback on that thread)

While printing my hundred or so calibration prints i ran across this effect you mention.  I have always noticed that detachments almost always occur from edges.   When i was printing with the fat .4-.8mm first layer in my journy, i notice the detachments were starting to occur from places not adjacent to an edge.  I reduced the width to .2mm and i got a solid mostly airtight layer. after i made this change my prints started sticking wonderfully. 

Therefore my theory is that not only do you have the mechanical bond for the first layer, but it acts like a suction cup as well ...

If you are interested my final settings were something like:

all extrusion widths .4 except solid infill which is .2
support is .3
3 shells and enough top and bottom layers to give me about .9mm worth of plastic based on layer thickness.
first layer is .15mm

I calibrated my bed to .0608 mm (like third thinnest leaf on my gauge.  make sure they dont stick together,  measure the leaf with a micrometer/caliper to be sure).  that gives a final first layer thickness of about .2108 mm

I think what redbarret is wanting to talk about is the new feature in simplify 3d 4.0 called dynamic extrusion width.

which the main advantage is that you can get higher detail prints. as per their blurb "New functionality in Simplify3D will automatically adjust the amount of plastic that is extruded from the nozzle to create smaller or larger extrusions depending on the shapes you are trying to print. This is extremely helpful for thin or tapering shapes, allowing you to print new features that were not previously possible with a fixed extrusion size."

so for example the tip of a rocket nozzle or a fan blade will be more precise.

this also gets used in the dynamic gap fill.  "Thin walls and gaps can now be filled with a single dynamic extrusion that is automatically adjusted to fill the available space. Even if the thickness of these walls are constantly changing, the software will ensure the gaps are perfectly filled adding strength to your model’s interior. This also provides a significant print speed improvement versus previous gap fill methods"

At least that is what I think he was trying to discuss.