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uneven bottom surface quality

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I have seen a few posts about surface quality when using PVA materials.


Recently, @SandervG held one of my prints and immediately noticed that the underside of one side was a bit rougher than the other side. I was curious to see if he could elaborate on it as, if I remember correctly, he stated that it could have been due to uneven heating from the buildplate.


I thought a bit of info for everybody on what caused this and how to remedy it would be a nice refresher for me, but also good info for all the other people dealing with this.

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Ok, this will vary from printer to printer but the concept is the same.

1. The heater on my printer is located in the centre of the print bed

2. The temp. sensor senses the temp. of the bed - not the glass plate siting on top of the bed.



3. When  your temp. reads say 65 the glass plate will not be 65, probably a minimum of 10-15 degrees cooler

4. When your glass plate reaches 65 it is only the centre that is 65, not the perimeter areas of the glass plate. Again they will probably be a minimum of 10-15 degrees cooler. Of course if you are printing a small part in the centre of the build plate this is not of concern.


The only way to manage this properly is to get an IR thermometer or whatever they are and measure the temps. until satisfactory. You probably need another 10 mins for the glass plate to reach temp. and probably another 10--15 mins for the entire plate to reach temp. if you are printing something with a v. large surface area.



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I have measured the glass temp with an infrared thermometer (they are not too expensive: ca. 30 euro), on both of my UM2. If the glass is warmed up well (without printing, without model), the temp was reasonably uniform. Except on the edges, where the last few centimeters (an inch) would be 5°C cooler on a 60°C bed, and 10°C cooler on a 90°C bed. Aluminum is very conductive, so the aluminum plate should provide a good temperature distribution. But the upwards air flow around the bed will cool the edges much more than the center: I think that is the main reason.


However, as soon as I started printing, and the fans came on (PLA), there was a huge drop in temperature in the area where the head wais printing. At first I was surprised. But then, yeah, it seems logical: the purpose of the fans is to cool, so that is what they do...


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