Need some remedial nozzle height assistance

[LuckyImperial]

So, my basic questions assumptions are:

- When properly zeroed the nozzle should be just touching the surface
-- When printing, if the LCD screen indicates a specific height, that nozzle should be that height above the bed (so for .35 first layer height, g-code sets the z height to .35 and that should be the distance between the nozzle and the bed)
-- For a layer height of x the nozzle should be x height above the last layer (or alternatively the bed)


Are these assumptions correct?

Since I'm struggling so much I'm leaning towards I have a misunderstanding somewhere of what is supposed to be happening.

Thanks for any feedback.

Thanks,
Bill

Your assumptions are essentially correct, however this is ignoring the paper thickness.

1) When properly zeroed the tip of the hotend (nozzle) should be at the shimmed paper height, which is not touching the surface but very close. The gap is usually around .1mm, or whatever paper thickness you are using is. Your LCD should read 0.00 at this point.

2) When printing, the tip of the hotend (nozzle) should be at the LCD height PLUS paper shim height. If LCD reads .35mm then your nozzle height should be ~.45mm.

3) This assumption is correct. Deltas between layers should be exactly what the layer height is set too. In practice, the first layer height on the bed is hard to pin down to an exact number...it's more important that you just achieve good adhesion.

I've been suffering from issues similar to these lately too. My Kossel is running RC Marlin and it's G30 A Dnnn auto-cal didn't build a very good map of my bed heights. There could be a lot of reasons for it (which I'm slowly eliminating) but when it comes down to it, my first layer print is usually only .1mm-.2mm thick despite my kossel reading .35mm on the display. I've calibrated it to this point by adjusting my Z Max Height (seen as Z-Height in RC Marlin) to be larger than it was, which offsets the head a lower from the Endstops. Essentially your just tuning your machines build height (which auto-cal doesn't always figure out well).

If subsequent layers are the correct height then I would recommend you increase your Z Max Height. Adjusting the Z Probe Offset will not work if your machine/firmware has Z negative protection enabled. Theirs a G code command to disable it, but I don't have it handy right now. Anyway if I were you I would just increase Z Max Height, or Z-Height or whatever it's called in your machine, and give it a try.

In the couple days that I've had my printer I've come to find that auto-cal is not a magic bullet that works perfectly. Manual calibrations are necessary for most machines.