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Variable layer height settings

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Just tried out the variable layer height and the settings you can adjust don’t quite make sense for what I think it should do. 

 

For example if if I have print with a non variable layer height of 0.2mm and I want the variable range to be from 0.1 to 0.2, I don’t want bigger layers than I have as the default just smaller ones. How do I do that ?. The release notes say you can set a range of layer heights it will work with but it always seems to increase the layer height. For example you can adjust the offset around the default layer height so if you set the offset to 0.02 with a height of 0.20, you will get layers from 0.18 to 0.22 ?. 

 

Is doesn’t look like I can set a max layer height ?

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I'm not sure but I think "layer height" is what you are calling (rightly so) the "max layer height".  disclaimer: I haven't played with this feature yet.  But I did look over the code.

 

[edit - as shown below - layer height is the middle value and then you can set the "variation" which varies equally above and below the "layer height"]

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Wondering how do I set it so the variable layer height never goes above 0.2 and only below, I need to set my default layer height to 0.18 then the offset to 0.02, the I will get a max of 0.2 and a min of 0.16 ?. It’s not straight forward to understand how to set the layer height ‘range’ ;)

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I hear you but just play with it in cura and in layer height go to the color window and set the colors to show layer height and you can see instantly the range of resulting layer heights.  So in other words instead of asking us, try asking cura directly and let us know what you learn.  (please let us know).

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Ok, didn’t realise I could change the colours to see exact layer heights, as it stands you can’t tell exactly what has been set, just a rough estimate based on colour along the transition line all the way to 0.27 (yellow)

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Ok, yes it appears to work like that. 

 

If you want to have your variable layers range from 0.16 to 0.2 for example, you have to set your layer height to 0.18 and your ‘adaptive layers max variation’ to 0.02. 

 

It seems a bit of a strange way of doing it, it essentially offsets your default layer height plus and minus by the adaptive layers max variation value. So by default it will always make the layers greater (and smaller) than your nominal layer height by the same value. So to restrict your true max layer height you need to drop your default layer height to compensate. 

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The reason for that is that changing layer height affects flow rate, thus line width, extrusion speed/volume, and so on. To limit the amount of change from all the other parameters, we use the profile as the middle of the variation instead of one of the edges. This gives far better print results.

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3 minutes ago, ctbeke said:

The reason for that is that changing layer height affects flow rate, thus line width, extrusion speed/volume, and so on. To limit the amount of change from all the other parameters, we use the profile as the middle of the variation instead of one of the edges. This gives far better print results.

 

 what speeds are set on the variable layers ?, are they varied by some factor based from the profile setting, or is the profile setting used for all layer heights ?

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The most important one is extrusion speed, which affects the amount of material extruded per distance. The amount needs to lower when using a lower layer height (e.g. ~50% when using 100mu instead of 200mu). We we can't change extrusion speed to quickly as that would result in poor print quality due to changing nozzle pressures. That's why the max. difference per step parameter is there (to tweak these changes).

 

The print speed itself also changes when the engine detects the material volume is lower than a certain amount, but I'm not familiar with all these details of the engine.

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