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Cylinders are thicker on top than at base


canadaduane
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Posted · Cylinders are thicker on top than at base

Hi! I've started printing on a new-to-me UM2E+ and noticed that cylinders (circular "posts") are printing wider at the top than at their base. I would think this is a software configuration issue? I'm using default print settings, but with a layer height of 0.32 on a 0.4 hotend. Everything else is printing beautifully. Any suggestions?

 

Thanks,
Duane

narrow-post-base.jpg

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    Posted · Cylinders are thicker on top than at base

    Short answer - cooler.  More fan, lower temps.  But first double check that cura sliced it the way you wanted in cura slice view.  It might be that it's actually sliced like this for some reason (bad cad, strange cura setting).

     

    Notice how the base of the part also curves inward and then recovers and curves back out.

     

    This is caused because liquid PLA is like a mucus - like snot - when liquid.  It sticks to itself nicely when still liquid (unlike many other materials such as PVA).  So as it comes out of the nozzle it's already (in milliseconds) cooled a bit and shrunk a bit and is like a liquid rubber band and as it is placed on the bottom most layer - glass - it sticks where it is supposed to but the next layer up is pulling inwards so for a few layers it pulls inward - but as you get farther from that hot heated bed it recovers.  

     

    Lowering the temp of the heated bed will improve that lower area but then your part might not stick as well so for a small part like this you could probably just lower the heated bed from 60C (typical default for PLA) to 50C.  That will help the lower area and possibly the upper area.

     

    For the upper area you should be able to lower your nozzle temp another 10C.  Whatever you are printing now try 5C to 10C cooler.  Also it is CRITICAL that the fan be at 100% by the time it gets to the arrowed region in your photo.  That could be related to the problem or the entire problem.

     

    Or it might be sliced this way - I would love to see it in slice view.

     

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    Posted · Cylinders are thicker on top than at base

    In cura among the cooling options there is a spot where you can set what layer or height the fan reaches full power.  Check that - I like that to be around 1mm or about 5 layers.  The point is if the fan comes on too quickly the temperature drops a bit on the head for maybe 20 seconds.  So having it come on slowly helps with that.  You want it off for the bottom layer.

     

    Anyway you can go into the TUNE menu at any point to see what the current fan speed is at any given moment.  Or you can change it in there but it will change again when the next fan speed gcode is read out of the gcode file.

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