Part height / thickness question

Hello,

I have a part that I printed that in the model the vertical thickness is 2mm and I measure 1.7mm on the part. Trying to figure out why it's shorter. I know this should be only effected by the z height rather than extrusion. So here are my questions about z height:

I have a starting layer of 0.35 and printing at a 0.2 layer height. So if i take 2 mm(total height) - 0.35 (first layer) = 1.65, now if i take this value and divide it by 0.2 (layer height) I get 8.25 which tells me it will give me at least 8 layers. Which in the end will give me 1.95 mm. This isn't very far off, but is it good practice to make the layer heights so they work out as a whole number of layers? Or isn't this much of a concern?

My next question is about z home height. I feel I'm over squishing the first layer since it puts a ridge around the part. Could this have some effect why my part is shorter? Due to shorter z home? I'm confused on this on what the printer thinks is 0 on the z axis. I know the z home height should be around 0.08 mm (thickness of paper) above the bed, but is that 0 to the printer? So when it prints the first layer would it be 0.35 + 0.08 =0.43 mm , this being the true first layer height?

Sorry for so many questions, I have a feeling my thoughts are correct (or maybe not) and just want some confirmation. Thanks!

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Printer: Makerfarm Prusa I3 6"
Nozzle: 0.5mm Jhead
Filament: 3mm
3D CAD: Creo Elements/Direct Modeling Express
Slicer: Cura
Printer Interface: Pronterface

If your Z height is way too low, you could easily loose 0.3mm on the total height of the print, if the starting layer is 0.35mm, but the bottom of the print would appear very squished.

If you print with a skirt you can measure the height of the skirt, this would give an indication of the actual Z height.

Do you calibrate Z when everything is warmed up, hotend and bed?

Should the first layer height match what I have set in the slicer or will it be shorter in the first layer since it needs to be squished? Or does the extra extrusion on the first layer account for the squishing?

The skirt measure 0.15 mm thick. So what should this first layer be when i have it set to 0.35?

I set my z endstop and level the bed when the bed is warmed, but not the hotend (if this is the same thing as calibrating the z).

In a perfect world the first layer height would match what set in the slicer, the squishing comes from trace width being bigger than the nozzle diameter. Z zero is when the hotend just touches the bed.

So if your skirt measures 0.15mm in height, the hotend is 0.2mm too close on the bed, probably even closer depending on the hotend design.

Normally you should calibrate the Z endstop, when the hotend is also warmed up.

Thanks for the info. I tried measuring the distance when the hot end and bed was warm, and it was a lot tighter to the bed. I'll keep raising my Z endstop until i get a decent measurement of my first layer matching my slicer setting. Hopefully this fixes my height thickness issue. Thanks.