printing small radii problem

[alexanderswo 1]

Hi together,

I made this model with small radii (r=0,25mm / d=0,5mm) for a locking mechanism:

I sliced it with cura engine in Repetier and used a DeltaTower with 0.4mm nozzle:

The preview of slicing looks fine, but when the outer contour is actually printed, it makes moves with unregular speeds (I looks like it hangs on some radii, and then more filament is coming out on that spot)

Any suggestions on how to improve this?

Thanks!

 

[Dim3nsioneer 557]

What if you change the nozzle to 0.25mm and slice it with this size? Cura has a problem with dimensions that do not allow a doubled wall...

 

[eriksw 0]

Never seen anything like that on Ultimaker with Cura, so I doubt this is bad slicing.

Good to know, and PERHAPS this might be causing it: a model of a thin walled cylinder is never 100 % round. The cylinder has sides and although it might seem round when there are many sides (120 or more for instance), it actually isn't. Curves don't really exist in a digital system, they are always "steps".... As a result, the thickness of the wall is never exactly the same all over. This is always the case in all curved walls.

So if you have a straight wall that is exactly 0.4 mm thick, when you put a curve in it there will be areas where the wall thickness will be less than 0.4 mm, which usually results in Cura "skipping" these areas.

When this happens, an easy way to solve it is to scale up the model just a tiny bit. 0.5-1% is usually enough. Or you can change the setting for the nozzle size a bit, that also works.

In your case it might be the other way around (so that some bits are just OVER a certain wall thickness) in which case it might help to scale the model DOWN just a bit.

And you only need to scale in x and y direction, no need to scale the height as well.

Again, I doubt whether this is the cause, never seen defects like that, but it can't hurt to try scaling to see if it helps.

[IRobertI 520]

This is just me talking out of my ass so I could be completely wrong. But, could it be something caused by cura trying to "optimize" the path by getting rid of moves that it thinks are too small? Simplifying the path so to speak?

 

[eriksw 0]

If these bits are caused by the slicer then you would definitely see it in Cura's layer view. If you don't see anything like that there, it is not caused by Cura or a "faulty" model. In that case the problem is in the printer, mechanical or firmware.

Or perhaps it is caused by cheapo Chinese PLA, but then I would expect to see a lot of other shit in other parts of the model as well. Still, don't use that stuff. Always get good quality PLA if you want good quality prints.

Another tip for delta printers: accuracy of those is worse in the centre of the platform, and better towards the edges...

 

[anon4321 16]

To be honest, the rest of the print doesn't look that good.

What is the layer height and material?

The layers are very obvious. Even the other larger radius towards the right doesn't look very good.

Could be a material or temp or flow problem.

 

[deepshots 2]

Just out of interest.. what version of cura is being used here? 13.something had these issues when doing small cylindrical shapes. I used to struggle with this but suddenly these issues disappeared with later versions.

 

[alexanderswo 1]

Hey guys, thanks for your replies.

I used Repetier Host V1.0.6, what version the Curaengine is, I couldn't find (Anyone knows where too look? In the slicer manager there is nothing said). The PLA is coloufabb and layerheights was 0.3mm which is often good enough for me. I tried other heights for this model, but it didn't make any difference regarding the problem.

I took a closer look to the layer-preview and made out some irregularities at the radii:

 

could this be the cause?

 

I used a stl with a higher resolution but got the same irregularities:

Any guesses?

 

[eriksw 0]

That looks weird. Something is going wrong with the slicing here, so you can rule out printer problems for now. Never seen this happen in Cura (nor in Repetier, but I don't use that a lot). You could download Cura from the Ultimaker site (it's free), and see if the same thing happens when you load the model in Cura.

 

[bagel-orb 61]

What's going wrong then? The toolpath seems to comply with your model.

 

There does occur a problem which you didn't mention: the second perimeters are overlapping, which causes an overflow of material, causing the surface to be ugly.

This bug has been fixed in a new version of Cura.

 

[izzy 33]

What resolution or step size did you use, zooming in you have definate layers showing and the other radi seem poor, did you try printing at higher resolutions ie 0.1mm or 0.06mm?