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Spiral cup with thick bottom

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Last night I did my first ever "cup" print and using the spiral option in Cura. The design file itself is a solid cylinder. In Cura I did the following:

Layer height: 0.1 mm

Shell thickness: 1 mm

Bottom/Top thickness: 3 mm (I want a solid, heavier bottom)

Fill Density: 0%

Solid infill top: OFF

Solid infill bottom: ON

And in expert settings I turned on the Spiralize outer contour and set to print. It printed, spiralized the walls, great. Except for the bottom. The first two layers were fine, solid. But anything after that up to 3mm thickness, there are gaps between the extrusion lines, almost like the infil was set to something like 70 or 80%. As soon as it hit the 3mm it switched to the spiral and went on till it finished the full cup.

So is there something I need to do to be able to get a thick solid bottom?


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Using the "spiralize" function, the wall of your cup will always be a single layer, because the spiral starts at the bottom and then spirals up on top of itself, like a coil/spring. So you should usually set the shell to the same size as your nozzle (standard is 0.4 mm) when printing spiralized.

You CAN increase the wall thickness by using a higher setting for the shell when using "spiralized". That way there will be more extrusion, so although it is still a single layer, the extra extrusion will be forced out of the nozzle and will be spread out sideways by the "shoulder" of the nozzle (= the flat part of the tip around the hole). This works fine with shell set at 0.5 or 0.6, but 1 mm is way too much to get a good quality print.

HOWEVER: with the shell setting a bit higher than the nozzle size as described here, Cura will increase the distance between the lines of the infill. This is what causes the gaps between the extrusion lines as you mentioned (mainly because you are bound to get some under-extrusion when printing this way, definitely with shell at 1 mm). With shell set to 0.5 or 0.6 the gaps will be smaller (or non-existent), and you can close them up by increasing the flow a bit (try around 105-110%). That way the wall of your cup will be a little bit thicker as well.

OR you can set the shell to the same size as your nozzle, and then use the TweakAtZ plugin to increase the flow at the height where the wall starts, so 3 mm in your case.

Keep in mind that this increased flow will remain in your printer's settings after it has been changed this way, so either switch your printer off-on before the next print or set the flow back to 100 with the controller (but you can only do this AFTER you start the next print, unfortunately, as you need the TUNE menu to do this, which only appears while printing...)

So if you really want your cup to have a wall thickness of 1 mm, there are 2 options: either switch off the spiralize function (watch your print time double or triple...) or use a much bigger nozzle, which is not a very sweet option.

One more thing: the fact that you did not get the gaps between the lines in the first and second layer probably indicates that your nozzle is a bit too close to the platform.

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use the swap at z plugin... I believe you'll have to download it, as I dont think it comes standard with cura.. basically it merges 2 different gcodes together. you can have 1 gcode with settings for a thick bottom, and when you get to, say, 3mm, you can tell it to switch to the second gcode (the specialized one)


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There is no need for this, spiralize respects your top/bottom thickness setting, and uses it for the bottom...

spiral bottom1mm

spiralBottom 4mm

@eriksw; your explanation is very clear, just don't understand why you think a bigger nozzle is not a sweet option? I love 1mm walls (or even much more) from a 0.8 nozzle, makes vases really nice. I usually set flow to at least 120% to make sure the bottom gets watertight.

So if I want a 1.2 mm wall, set the nozzle to 1mm (even though the hardware is 0.8) and the flow to 120%. The actual wall will be a bit less than 1.2mm.

Since I have the exchangeable nozzle on my UM2 it got really easy...



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@UltiArjan: Nothing wrong with a big nozzle, but I assume the majority of UM users don't want to be bothered with changing nozzles (and releveling the bed) for each print...

@Kirash4: please read my reply again: you can have the bottom as thick as you like (up to 20 cm ;) ) but when you set the shell to 1 mm (using "spiralized") while using a 0.4 nozzle this means that your infill lines will be 1 mm apart, and there is no way you can extrude enough PLA through that 0.4 mm nozzle to get that bottom watertight, no matter how thick it is.

Apparently you can file down the nozzle to create a larger "shoulder" so the above MIGHT become possible, but I haven't tried that yet as it seems a bit crude.

Cups/vases with only 0.4 - 0.5 mm shell will be pretty strong already, by the way. But if you don't mind changing nozzles then UltiArjan is right, go for a bigger nozzle.

And of course you could print without "spiralized". Then you can print your wall any thickness you like, because it does not have to be a "single line wall" anymore - but you will get a small vertical seam at the spot where the platform moves down.... however if there is some 3D pattern in the wall (as opposed to a smooth cone or cylinder) this seam is often hardly noticeable, so perhaps that's a better way to go for your print.

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@UltiArjan: nice thread about that exchangable nozzle. Very interesting, but not very accesible to most users yet, I guess...A good one for the "what do you want on the UM3" request ?

And yes, 120% flow can be good for watertightness. However I have noticed that when the flow gets too high this actually makes the bottom leaky again, as the upward ridges between the print lines become too high, creating more pores again.

Also, very high flow can make the outer edge of the bottom layer look ugly, so I often set the TweakAtZ plugin to increase the flow gradually during the first few layers.

Another thing that has not been mentioned yet: print temperature should be quite high to get stuff waterproof. You need nice "runny" PLA to "seal" the bottom, for good layer adhesion in the wall, and it also helps to make increased flow happen more easily.


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