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Reywas

Nozzle height vs "Initial Layer Height"

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Posted · Nozzle height vs "Initial Layer Height"

Hi,

 

I'm just getting started in 3D printing and I'm having trouble understanding the relationship between the  nozzle height at Z = 0 (against the Z end-stop) and the CURA setting "Initial Layer Height".  The setup instructions for my Ender 3 printer tell me to home the printer (against the Z end-stop) and use the paper-drag method to tram the bed.  So, hypothetically, if using that method I end up with a 0.25mm gap between the nozzle and the bed at Z = 0 and the "Initial Layer Height" is set at 0.3mm, how high is the nozzle above the bed?  Intuitively I would say the answer is 0.55mm but it seems to me that, if that is correct, I would need to set my "Initial Layer Height" to 0.05mm to actually get the desired 0.3mm height.  

 

Thanks for your help,

Paul 

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Posted (edited) · Nozzle height vs "Initial Layer Height"

I can see where this could be confusing at first.

 

The zero position for Z is with the nozzle above the build surface by some distance, often a thickness of paper.  The Initial layer height is referring to the actual thickness that the printer is trying to print in the first layer - not the Z position.  A good practice for strong adhesion to the build surface is to print a little more material than the actual gap from the nozzle to the bed.  In your numbers above, your printer should extrude enough material in the first layer to a achieve a .3mm layer, however there is only .25mm of space.  This will result in the material being slightly smashed into the printer bed promoting good adhesion.

 

On materials that resist sticking to the build plate, it can be helpful to over extrude even more than in your example numbers.  On lots of printers, you can manually adjust the Z position at early moments of the first layer to get the distance just right.  Not sure about your printer, but I don't hesitate to give the Z screw a twist (by hand, over-driving the stepper by a few poles) at the very beginning of a print to get the distance just right.

Edited by mastory

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Posted (edited) · Nozzle height vs "Initial Layer Height"

Thanks for your help mastory. So if I'm understanding you correctly, the first layer is printed with the nozzle at Z=0 (which is actually about a paper's thickness above the bed) ? 

 

And while I've got you on the line:  Is it normal for the first layer to form a narrow brim around the object or would that be considered an "elephants foot"?

Edited by Reywas

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Posted · Nozzle height vs "Initial Layer Height"

Nominally, Z=0 is supposed to be when the nozzle touches the glass.

 

When you calibrate with the calibration card, the printer knows the thickness of the card.  For example if the card is 0.1mm thick then it can set the height to 0.1 when you calibrate such that when the nozzle touches the glass Z=0.

 

But that's not exactly what it does - it sets Z somewhere inbetween 0 and 1 such that the first layer gets squished slightly.

 

If the first layer is 0.3mm thick Cura will absolutely, definitely set the Z to 0.3mm when printing that initial layer.  But because the calibration cheats slightly it will hopefully be closer to 0.2mm above the glass.

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Posted (edited) · Nozzle height vs "Initial Layer Height"

@Reywas,

 

I'm not prone to strike an argument with gr5.  There's likely more to the issue that I don't see and George is vastly more informed.  I defer to him.  That said, I checked my start gcode and initial layer gcode to see what is happening.  On my machine, the start code zeros the X & Y, then Z, and other unrelated stuff.  In the lines that begin the first layer, my build platform positions the bed at 0.2mm (my 'initial layer height') down from the start position, further, not closer to the nozzle.

 

@gr5, During a homing routine, does the firmware jog the bed downward X distance after seeing the Z switch, attempting to offset from the switch position so the nozzle approximately touches the glass - supporting your explanation.

 

From my maybe related and maybe irrelevant experience with production machinery, it is common to 'zero' mechanisms to a switch or prox.  That precise position is then referred to as zero.

 

Sorry to confuse Reywas

Edited by mastory

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Posted · Nozzle height vs "Initial Layer Height"

Did you see there’s a plugin called Z Offset Setting in the Marketplace? It allows you to shift the entire print up or down a little, for this purpose.

 

After installing the plugin (and restarting Cura), a new setting is added named Z Offset (use the Search on top of the custom settings to find it)

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Posted · Nozzle height vs "Initial Layer Height"

Thanks for your responses gents.  Keep in mind that I have a no-frills Ender 3 which knows nothing about calibration card thicknesses or the location of the print bed.  It only knows where the Z-stop is.  I could manually tram the bed using the paper-drag method and then adjust the Z stop so that the nozzle is just touching the bed.  Would it then be OK to adjust the "Initial Layer Height" to get the proper amount of squish?

 

ahoeben-  I will have a look at that.  Thanks.

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Posted · Nozzle height vs "Initial Layer Height"

"Initial Layer Height" does not affect squish.  The "Initial Layer Height" setting is meant as a workaround for not-quite-flat buildplates. If you lower the initial layer height, Cura will tell the printer to extrude less material so you effectively get the same amount of squish. It is recommended to keep the initial layer height higher than the normal layer height.

 

The "Z Offset" setting will let you move the entire print closer to the buildplate with the same amount of material extruded, thus squishing the print into the buildplate.

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Posted (edited) · Nozzle height vs "Initial Layer Height"

Ok, thanks.  I think I'm starting to understand the relationships among the various factors now.

 

Is there a relationship between the "Layer Height" and the "Initial Layer Height" in Cura?  A guy on  YouTube recommended the "Initial Layer Height" be set at 150% of the "Layer Height", but he didn't offer any explanation for that.

Edited by Reywas
added question

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