Model Z dimensions - Clarification Please

Hope someone can clarify these noob questions please.

If I set my nozzle to be .1mm or .08 or whatever value I choose from the print bed, this value will actually add to the resulting print height? A 20mm cube would end up at 20.1mm high?
I would set my nozzle touching the bed if I could (but don't dare until I replace my mechanical z-endstop with a hall sensor). Does anyone do this or does everyone stick to a piece of paper feeler gauge?

Thanks

Mick

I home my z .1mm from glass to tip.

I use a feeler gauge and home mine to 0.02mm. There's certainly some error, but I also set my first layer height to 90% and things have worked very well for me for a few years now.

You realize of course that if you print a 20mm cube, and 20mm is not a multiple of your layer height, you are not going to get a 20mm cube - you will get the closest multiple of your layer height. I have my layer height set to 0.2, but because of the 90% first layer multiple my first layer is 0.18mm. If I print to 1mm of height, I only get 0.98mm - close enough for me.

I use paper and if I print a cube 20mm high it is 20mm high +/- .05mm The first layer (nozzle height) is correctly accounted for.

A 20 millimeter cube is a bad example. Print a model with various height horizontal surfaces. It can't adapt for them all, especially if you have two surfaces that are less than a layer height apart. You will simply get integer multiples of your layer height adjusted for whatever modifications you make to layer 1.

If I open up the g code for a 20 millimeter cube, the z value for the top layer will be 19.98 millimeters, guaranteed. I get 20 millimeters because I use the .0.2mm feeler. However if I tried to print a 20.5 mm cube, it might be 20.5 in the x and y direction, but it won't be 20.5 mm high. I'll either get 20.4 or 20.6

Thanks for the feedback guys. I hadn't actually thought about how the layer height affected the outcome of possible end heights but it is obvious now.
I will try .02 as my nozzle gap and adjust 1st layer to 90% for .2mm layers or 83/84% for .12mm layers. That sound about right? I'm sticking to multiples of 40microns as I'm using 5mm threaded rod for my z axis drive.

Mick