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Improve bottom surface printing on glass

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Hi all,


I am printing with PLA and am trying to improve the surface quality of the first layer laid down on glass.

My printer is a UMO with the glass bed upgrade; I slice using Cura 15.4.3.


I found 196 degrees / 55 degrees at about 50 cm/sec giving good results. 

I had to increase the feedrate to 140% with the PLA filament I currently use to assure solid parts. At 100% the lines tended to seperate.

For adhesion I use a very fine layer of diluted wood glue - works great.

To improve first layer quality I increased the bottom layer line width to 130% and slowed down the bottom layer speed to 25 mm/sec.  

Bed is levelled to give a nicely squished first layer.

I increased the infill overlap somewhat - I believe 30% (am not at my printer right now).


The photo shows the bottom of a part I just printed.

(I am not concerned about the diagonal travel tracks - I might try to do something about them later.)

The surface is generally ok, but some areas are not - i.e. at the lower left or to the bottom right of the center hole.

It looks to me like it is printing well going towards the edge but underextrudes as it moves away from the edge.

The areas immediately surrounding the small holes left and bottom look real nice.


Any tips on what I can do to get a more uniform, solid bottom surface?


Thanks - Thomas  



Edited by aggertroll

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I don't have an UMO, and I don't know its mechanics, so it is difficult to draw conclusions.


However, if this would be done on an UM2, then I would first look into possible causes for underextrusion. For example a deformed teflon coupler in the nozzle (don't know if the UMO has one?), a feeder or feeder drive-wheel slipping or dirty, bad temperature control (e.g. loose sensor), partially blocked nozzle, low-quality filament with variable diameter, filament stuck on the spool or wound too tightly near the end, and similar things that might cause irregular extrusion.


And only then I would look into bed leveling, for fine-tuning the result. But I don't think this is the main problem here.


Normally you should be able to get shiny, almost totally flat undersides, with hardly visible layer lines. Like in the best parts of your photo, but then everywhere. Or like this photo below. See the long name plate with copyright info (center-right): the text is hollowed-out inside the material and shines through the flat bottom, which is almost as glossy as a mirror. You can see the window reflecting in it. This material is tranparent PETG, but for PLA is should be equally smooth.



Edited by geert_2
corrected typo in UM2

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My first suspicion would be the teflon part like Geert said, because printing at 140% is not normal. Did you ever look at it? If it is dark and burned the shape could be deformed and become an obstruction for the filament.

For the first layer you could also print a bit hotter and then dial it back to your preferred temperature.

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Thank you geert and peggy for your feedback. OK, I will check the teflon coupler first (hoping I will not damage anything in the process).

The 140% feedrate has me baffled, too. I checked the extruder steps and did a few atomic pulls - everything looks good.

Temperatures are steady - I am using the Pronterface plugin that graphs the temperatures.

(Btw: UMO refers to the Ulitmaker Original - really happy with it.)


I remember seeing different couplers offered.

Any advice on which to get? - I'm in Europe.


Happy printing.


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