Very thin first layer

Not sure this is a Slic3r problem but its my best guess after trying everything else.

I am an experienced 3d printer user and my homemade machine has been prodicing beatiful prints up until a few days ago, indeed it still is but the first layer seems to be under extruding.a lot.

First off have tried all the obvious things
Bed gap
Temp
Extruder power adjustment.

Slic3r is 1.1.7
Rep host 1.0.5

Have tried various values inder - print settings - advanced - extrusion width - first layer %. (higher % seems to make it worse)

Previously the first layer was solid and shiny but now can see the extrusion and its rough when nail dragged across.
To help i am doing the first layer at 150% under manual control - it helps but still not enough.

Just the confirm, the rest of the print is perfect.

any suggestions welcome.
Thanks
Vince

You are describing exactly the symptoms of the Z zero height being too high (extruder too far from bed for first layer). In that case increasing the extrusion width will indeed make it appear worse - the increase in height effectively causes the extrusion width to become narrower by the same percentage as the height error. The thicker the extrusion width the greater the absolute value of the decrease in width, and so the wider the gaps. The effect is however diminished if you increase the first layer height because the percentage error then decreases. The thinner the first layer height therefore, the more critical the Z zero (homing) is.

While you say that you checked the bed gap, it is likely that it is in fact too high. An increase of just 0.05mm is very noticeable with first layer height of 0.25mm or less. Perhaps something has changed that affects the Z home (zero) position?

Dave

Thanks Dave but its not bed gap. Over last few days have gone from hi to low and back again many times.
I adjust my first layer 'in the fly' during the brim print so its pretty much spot on every time.

Problem just started a few days ago. Have reversed my steps (not sure i did anything) but cant get it back right. Even the same after loading old settings.
Thinking something in the firmware has got screwed up perhaps.

Example of 30 mm test disk, removed from bed after first layer

Assuming that the distortion in the shape happened after you removed the layer from the bed, I still believe the problem is the first layer height. I'm not sure what you meant when you said "I have gone from hi to low and back again many times". I am not talking about the first layer height setting in Slic3r, I am referring to the Z height on the actual printer, which is determined by the Z homing sequence prior to starting the print. Changing the physical Z height of the first layer using the same G-code must affect the gaps between the extruded lines on the first layer no matter what settings you used. There will always be a height where there are no gaps. Halving the first layer Z height will double the extrusion width for the same G-code.

(If it was printing that distorted shape when it should have been a circle, then you have a far more serious problem).

How does your printer set its Z height? (e.g. microswitch, I.R. sensor, ultrasonic sensor, manually etc.)

Dave