Relationship between nozzle size, layer/nozzle height, print quality, print speed

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ido
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Location: Rotterdam - The Netherlands

Re: Relationship between nozzle size, layer/nozzle height, print quality, print speed

Post by ido » Sun Jul 23, 2017 10:08 pm

But how does this work?
>>the slicer will take care of adjusting your extrusion width based on your nozzle size and extrusion multiplier (the more material you push through, the wider the line)
>>Wall thickness should be a multiple of your nozzle size

If the slicer can define the line width, why is the multiple of nozzle size still important?

Dont get me wrong, I am not in doubt, there are plenty of posts about wall thickness and nozzle size, but don't understand the relationship

chumm
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Re: Relationship between nozzle size, layer/nozzle height, print quality, print speed

Post by chumm » Mon Jul 24, 2017 3:19 am

The nozzle width will define the minimum width of the line, i.e. there's no way to create a .3mm wide line with a .4mm nozzle. You can create a wider line, though not by much (up to 25% more than the nozzle width generally). Think of it like squeezing out a line of toothpaste, you can squeeze harder and increase the flow and it will push out to the sides. So, the above is true, but only in a really limited range.

If you want to make very thin lines you need a very thin nozzle, and a large nozzle can help you push through a ton of material, which can greatly decrease the time a print takes, at the expense of having to use thicker walls. This is also potentially limited by the hotend's ability to keep the filament hot when extruding at a high rate. .4mm nozzle and .45mm extrusion width is the standard and should serve almost all applications.

You're right that the multiplier point was slightly misspoken, wall thickness should be a multiplier of your extrusion width, not necessarily your nozzle width. This also only applies to thin walls: if your perimeter layers are 3, and you have a .45mm extrusion width, anything larger than (.45 x 6) 2.7mm could be any size you want, since the space between the walls can be any size.

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ido
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Re: Relationship between nozzle size, layer/nozzle height, print quality, print speed

Post by ido » Fri Jul 28, 2017 9:05 pm

Thanks. Things have become clear concerning the Z en X/Y resolution.

Funny how Z resolution is not dependent on X/Y resolution. You'd expect when printing in a 0.20 layer height, you would also want to use the 0.2 nozzle, so height and width are the same. But in practice this doesn't seem to matter and its pretty handy you can vary Z resolution quite easily.

One thing I am still pondering about, say you sliced with 0.20 layer height.
If the printer is busy with layer number 2, does the printer always print this at 0.20 layer height (does the printer even know how high it is?), or does it print on top of layer 1?
With my Prusa mk2s I can adjust my Z value for the first layer while printing. Sometimes the layer height after printing is 0.2 mm, some prints 0.24 (wrong Z value).
Will the second layer print at 0.24 + 0.20 = 0.44, or will all layers be 0.24, so second layer will be 0.24 + 0.24 + 0.48?

chumm
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Re: Relationship between nozzle size, layer/nozzle height, print quality, print speed

Post by chumm » Mon Jul 31, 2017 1:23 am

Each subsequent layer will just be .20 above the prior, so .24, .44, .64 etc. Adjusting Z on the first layer isn't about changing the layer height, it's about correcting for Z = 0 being inaccurate. So ideally if you made that correction appropriately on say a 30mm tall print, it would measure exactly 30mm, not 30.04, because the adjustment was to ensure that the first layer printed at the right level.

Narnash
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Re: Relationship between nozzle size, layer/nozzle height, print quality, print speed

Post by Narnash » Tue Aug 01, 2017 5:52 pm

Just to add something for a new person, there are layer hights that will work better or more consistent on your specific printer due it's mechanical properties. I mean by that that it's possible that your print result could be better with a layer hight of 200 micron instead of 150 micron for example, even though you should normally have better details on the 150 micron you can have gabs, inconsistent lines or bad layer adhesion or over all a bad looking print in the end.
This can happen due the manner how stepper motors and micro stepping (Tom has a video about them) works and which threaded rods you use, more pricise which pitch they have. The pitch size is the travel in (normally) mm that the threaded rod is able to transport with one rotation.

You may know this behavior when you rotate a stepper moter that it's snaps every few degrees (when it's not on) in a specific position so to a specific step. Your electronics normally calculates the needed amount of steps for your desired movement. For the z-axis every X micron setted in layer hight per each layer. But if you set in a layer hight which isn't or isn't nearly matching a multiple of the travel amount per each step of your z-axis mechanic it can only move to the nearest possible. The whole micro stepping is actually a thing to emulate parts of a full step but aren't as accurate and not effective if the motor has to hold it's position. It is also a problem that the slicer calculates the rest of the model with the dialed in layer hight instead of the "right layer hight for your printer", so if the last layer is a few microns less or to tall than expected with the wrong layer hight the next layer has to neglit that which reduces in bad layer adhesion.

But what is the right layer hight for your printer you may ask? Well as I said the effect is caused by the stepper motor and threaded rod, you can increase the amount of "perfect working" hights by a factor of two for example by picking a stepper motor with 400steps/revolution one instead of the common 200step motors or you can pick a threaded rod with a super low pitch size but this way your printer has to step several thousand steps more than necessary for homing (=slower movement, for z-axis only not a big deal) or fast movement which stresses the controller.
Another easy way which also doesn't lead into the need of new parts is to actually know which layer hight are ideal for your printer. The super handy calculator from Prusa (http://www.prusaprinters.org/calculator/) can help you with that, just dial in under Optimal layer hight for Z-axis which pitch your rod has (and layer hight if you look for a specific one) and it will show you if the mechanics of your printer is capable to replicate these accurately.

For this example of a printer with 200step motor and a threaded rod with a 8 mm pitch, are increments of 40 micron when choosing the layer hight ideal.
Image


EDIT: corrected a bit of spelling and the image

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