@nicholam77 and I were discussing first layers/initial Z height over on his thread, and rather than clutter up his stuff I thought I'd post some more details here.
Nick was mentioning the difficulty of establishing a "proper" Z offset for the first layer. Too high and the extrusions will have space between them and not adhere well to the build plate; too low and they extrusions will squish too much into the build plate causing extrusion width to be too large and a raised blobby effect in the print. To try to better illustrate this, I printed the first layer of one of the puzzle trays I posted recently in this thread since they cover a large surface area on the build plate. I did my best to photograph what it will look like when the nozzle is too high, too low, almost right, and just right. Keep in mind, my build plate is quite flat after my recent nylock mod I posted here earlier, but if it's not flat you will have to find a happy medium.
I paused mid print here to try to capture what I'm talking about. The print starts left and is working right. To begin, the offset is good. I then raised the Z height to a point in which there was space between the extrusions and they were barely if even sticking to the build plate. I then lowered the offset back down to a good height, and kept lowering it as it went. You can see the raised blobby ripples get more pronounced as I lower the Z height more and more.
Here is a close-up shot of the section where Z was too high:
And a close up of the section where it is too low:
Here are some low angle shots taken after the entire first layer is complete. It's hard to tell, but after the section with Z offset too low, I raised it back up for about 3/4" where it was almost good, but actually a little too high. After that I lowered it a bit an established a good initial Z height.
You can more clearly see where I established my final Z height in the lower left hand corner of this image, right at the apex of the corner where the print gets slightly darker.
Here are some shots taken from directly above. Hopefully you can see each transition where the adjustments were made.
And a close up of the problem areas:
Here I'm trying to show the section right after the low area where it's almost right - but just a bit too high. You can see some space in-between the extrusions in the lower center-left of the image. I dropped the Z height about .01mm to establish the optimal height.
I'll continue on the next post...