First layer modifier %

I think I've only done one print since I learned to calibrate bed height with the nozzle and bed heated. Before that my fist few layers were probably a milometer or so high, until the plastic would form a level base after 3 or 4 layers maybe. On that one print though, I had the bed very level and I added a -0.04 modifier in sli3er to compensate for the paper so the nozzle was probably pretty true to where the bed was. I noticed in slic3er the default first layer extrusion is at 200%. Is that necessary or beneficial if the bed is pretty level? I'm thinking theoretically the double extrusion could cause inaccuracies. What setting do you guys like to use? Any experiences? I'm considering trying 100% but maybe you guys have some knowledge with this.

Edited 1 time(s). Last edit at 12/18/2015 08:31AM by Allnight.

Depends on you nozzle size and what layer height you're trying to print at. A 0.4mm nozzle set to print an object at 0.2mm layer height can give you a 200% thicker first layer which should help you to get it to stick. But I usually use 150% as you can't print 200% with a 0.4 nozzle and 0.3mm layer height as 200% of 0.3mm is 0.6mm which is wider than your nozzle.

Your choice of layer height depends on whether you want your object to print slowly and be pretty (use as thin layers as your printer can achieve 0.1mm or even 0.05mm for the brave), or print fast and be strong (use thicker layers such as 80% of your nozzle diameter).

If you have thin first layers ie 100% of 0.2 or 0.1mm, then your nozzle to bed gap and bed level have to be very precise to get an even, well adhered first layer. Your object should come out the same size though as the z axis lifts by the amount specified, so ends up at the correct object height at the end of printing.

Edited 1 time(s). Last edit at 12/18/2015 04:09PM by DjDemonD.

DjDemonD is of course quite correct.

Note that you do not heed to use a percentage for any of the extrusion width values.
Using a percentage there can be confusing - is it 200% of my default extrusion width, or 200% of layer height... Well Sliz3r uses the latter, so when you use a different layer height then the extrusion width will also change.

For several reasons it's a good idea to use an explicit, sane extrusion width for the different extrusion types, and you will always know why it's printing the width that it is.
Sane values for extrusion widths are > 1.05x, < 1.7x nozzle diameter. This is detailed here: Slic3r Flow Math

So for your nozzle you would use extrusion widths of between 0.42 and 0.68, with .5mm or more being a good starting point (others may have different preferences). The wider you make it then the more it will squeeze that bead into the bed. Then micro adjust your first layer height, and speed to find a point where it sticks properly, but is not so mashed in that it causes ridges and blobs to form. A well calibrated extruder is required.

As a rule of thumb max layer heights should be less than nozzle diameter * 0.80, so < 0.32mm, with 0.2mm for regular layers being common.

Hope that helps.

Edited 1 time(s). Last edit at 12/18/2015 09:41PM by Paul Wanamaker.