Up till now, I've tended to scale my first layer according to the print quality, so a 0.12 mm first layer for a 0.08 mm print, and 0.28 mm for a 0.2 mm print.
After changing to a PLA which isn't sticking well, I'm wondering if the first layer is best determined by the printer/tolerance/material, rather than the overall print quality settings. Am I going to get more predictable results if I stick to a 0.12 mm first layer regardless? This is with a 0.4 mm nozzle on an Anet-A8.
Default settings for first layer height in Slic3r Prusa Edition print profiles regardless layer height is 0.2 mm.
If you need to improve bed adhesion then try tips from this video 3D Prints not sticking anymore? Watch this! 3DP101 by Maker's Muse. It's about using glue stick and spreading it using paper towel and isopropyl alcohol.
There are other possibilities how to improve bed adhesion, e.g. Ultem sheet or other printing surface like BuildTak.
The first layer height can be the same as the whole printing model however you can set different sizes and speeds; it is recommended that layer height should be 75 % or less than nozzle diameter, this means that for a nozzle of 0.4 mm the max height is 0.3 mm (if you are a master you can use higher dimensions)
The first layer with a height of 0.3 mm with a speed of 70 mm/s will have less adhesion than printing at 50 mm/s. Also the same height and speed of 70 mm/s at 210 °C will have more adhesion than at 195 °C. So printing at 195 °C with speed of 50 mm/s could have the same adhesion than 70 mm/s at 210 °C. This depends on the quality of your PLA
On my prints I have set the prints at 195 °C and 55 mm/s with a height of 0.20 mm, then the whole print uses the same temperature at 85 mm/s with 0.25 mm of layer height. With other PLA quality I have to set 210 °C first layer at 50 mm/s, and other layers at 200 °C with 70 mm/s. So adjustments are based temperature and speed once you have determined the smoothness of your prints.
I made more negative experience for 0.4 mm nozzle and 0.2 mm layer but 0.28 mm initial layer. Change it back to 0.2 mm solves all adhesion problems for me. (Tested on Anet A8 and Ultimaker3)
Layer height in my cura settings means that head of extruder will be going up at 0.3mmm, and how i know that? Because i measure few different settings with height of bed. When I set bed to -0.2mm, ike everybody is proposing on internet, and i started printing first layer, I did stop it and measure with precise caliper thickness, it was 4.2mm, (human precision with leveling bed :P ) that was for me to much, because extruded material almost was not sticking to the bed,, and walls was not connected each other. I did test also with home position of nozzle and setting bed to touch nozzle, to 0 height. ( YEAH) And again I measure thickness of first layer. It was precise 0.3mm. Exactly as I want. That means that or I have better software witch can take nozzle up with initial layer in cura settings?, or magical printer, but my printer is cheap and is buy'ed almost by everybody. That means that peoples who are teaching others how to set bed in a printer are totally wrong. Maybe no one measure thickens of first layer? Even seller from who I buy printer propose me use paper with thickens of 0.25mm to set level of the bed.
Previously I have problems with first layer, because that was too high from bed, now when I set 0 position of nozzle exactly with bed, I don't have problems with thickens of layer, and printed element looks allot better from bottom.
