How to improve first layer quality

Hi,
Im slightly improving my prints but I cannot get the first layer to print nice and smooth... I'm using 3DLAC and with 4mm brim it really helps the print to stick but the quality of the first layer is sh***, top layer however is very nice
How can I improve this ?

I'm using shell thickness: 1.2
Top/bottom thickness: 1
infill overlap: 15%
Layer height: .015
First Layer height: 0.15
First Layer extrusion widht: 100%
Brim: 4mm (just to prevent warping and lifting corners and it does the job!)

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In my experience, first layer print quality requires two things:

1. Using a low enough print speed, especially for small perimeters.

2. Getting an accurate Z=0 height when the print starts, over the whole part of the bed that will be occupied by the print. This may involve auto bed compensation, or accurate delta calibration if you have a delta printer.

Some people recommend using a higher first layer thickness in the slicer settings, although I don't do that.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

But in terms of best settings for getting good first layer quality, are mine good or i should increase/decrease first layer thickness and height ?

Hard to tell because you haven't said what speeds and nozzle size you are using. I presume your layer height is 0.15mm not 0.015mm. A first layer height of 0.15mm is very low; you will a very level bed and accurate Z=0 setting to make it work.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

I agree with dc42. Remember the first layer thickness must be under 80% of the nozzle diameter. Otherhand, the first layer depends a lot ot the flatness of your print bed, and its leveling. A good calibration of your extruder is crucial too. I mean above and below the extruder, because melt filament often expands a bit. You need to do some fine adjusting of your steps per millimeter first, then adjust the flow to get the expected output volume.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

I spent some time leveling the bed and got better results.
There's some contamination, like burnt marks on the first layers , guess they were due to too high temperature (using 215ºC for PLA) :/

215°C is high for PLA. Print a temperature column (folow instructions on the link) to know what temperature to use with that spool of PLA. I print a column with each new roll. Sometimes, same brand, same colour; but you need to print 5°C warmer or cooler... Dunno why. Some people raise temperature for the first layer. IMHO you don't need that. The adhesion will be perfect at the good fusion temperature for your filament. No need to go warmer. Same for bed temperature. Find the good temperature and stick to it from start to end.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

I would increase the extrusion width.

Also calibrate your steps pr mm for the extruder you can find a guide on youtube.

After that you need to calibrate the multiplier for the filament you want to use..

You need to see the difference for yourself my first layer quality increased ALOT

I've got a pretty damn good first layer..It looks almost like a mirror, the only thing that bothers me now is the inaccuracies on part dimensions.
I believe I should stick with default 80 value for steps per mm for X and Y and only adjust the value for extruder.

Damn right !

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

Quote
Zavashier
Damn right !

I've now calibrated the extruder steps per mm. It was set to 100.47 (default value on Hephestos) and I measured 100mm of extruded filament got 100.38 so I adjusted the value to this new one.
however i still cannot get parts to print with +- 0.1 precision on X and Y :/
Tested lowering the value of extruder to 85 and got the 20x20 cube with 19.96x19.99 , but this way it'll be under extruding right ? since from the measurement the steps per mm value of extruder should be 100.38 not 85.

You're not under extruding. Try to print a thin wall cube, with wall thickness equals to your nozzle diameter. Measure the wall thickness. If your over your nozzle diameter, you over extrude. If you're under you under extrude. Adjust in your slicing program the % of flow to get the closest thickness possible with a rule of the three. When you're done, you're as precise as your printer can do. Appreciate a bit of wooble in your components or a bit of missalignment in your printer assembly can introduce errors in your parts geometry too. A 0.1mm gap in XYZ axis is a very good precision for a $500 printer.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

I think you are experiencing what slic3r and curb sometimes do with calibration parts and that is line width. for a 0.4mm nozzle slicer will default the line width to 0.67mm. In slic3r you should print a single walled object the same thickness as your nozzle and set the extrusion width to your nozzle width. I realised the other day that I had overlooked this and decreased my extrusion multiplier so low to get a wall thickness of 0.4mm and then set the extrusion width to 0.4 and it didn't print any filament. Give that a go and I'm sure you will be set