Why does my domed print have a thin shell?

7

1

I am making a "fun button", with a dome-shaped top. The vertical sides, top center, and raised lettering seem fine, but the more sloped outer parts of the dome are very thin, with some gaps and the infill pattern is quite visible. It's almost like the slicer isn't recognizing the sloped part as an exterior shell.

What is causing this, and how can I fix it?

My Fun Button

The model was made in Fusion 360, sliced in Repetier with Slic3r, and printed on a Monoprice Maker Select Mini.

Edit: More information after checking values used and taking more photos.

This was my second attempt, after increasing the shell count already.

On my first print, I clearly had a low value for horizontal shells, top and bottom were both at the default of 3. I upped these both to 8. (Layer height is 0.13125.) The bottom of the button is now good. The "good" center area extends a little further out, so I think it's probably thicker up at the top of the dome. But the sloped sides are pretty much the same - this is why I'm thinking it's not being considered as a "horizontal shell".

Comparison:

bottom of buttons

top of buttons

There are some design iterations, but the top surface is the same shape.

Update:

I did a print using Cura, with 0.8 mm shells, and it looks great!

Printed with Cura

I cut the two bad prints with a hacksaw to see a cross-section. The bottom is clearly thicker. The top on the outer infill void is pretty much the same. The top on the other void is thicker most of the way across, but suddenly changes to thin.

Cross section

mbmcavoy

Posted 2017-01-24T23:27:06.750

Reputation: 758

1Looks like theres just one top layer? You should use at least 3 top layers. If i'm not seeing it right, and it's more than one top layer, than I think its under extrusion... put the printing speed for top layers down... – MrOnkelChiller – 2017-01-25T08:33:00.423

1I'm thinking I might try with Cura to see what the result is... – mbmcavoy – 2017-01-25T14:33:22.033

Well thats worth a try... isn't there the opportunity in slic3r to change 'solit top layers' maybe you just changed 'shells' and 'solid bottom layers' – MrOnkelChiller – 2017-01-25T14:37:42.353

1The settings in Slic3r are in a box labeled "Horizontal shells", then Solid Layers, with a setting for Top and Bottom. With my first print, they were at the default of "3", for the second, they were changed to "8". – mbmcavoy – 2017-01-26T06:22:56.743

1Well its curious that it prints just one top layer when slicing with slic3r... I cant explain why... But good that it's working with cura. I dont lice Slic3r very much. Symplify 3D is the best slicer from my point of view, but it'sa bit expensive... – MrOnkelChiller – 2017-01-26T10:22:29.487

1Re the cross section images added: It may be an issue with the slicer determining to use your values for perimeters versus top solid layers when deciding how many layers to use for the slope; at some point, it may switch from perimeters to top layers when the angle passes a threshold. – Davo – 2017-01-26T12:21:13.217

Just for grins, I set Slicer to use high values for Solid Top Layers, varying from 15-30, and inspected the print preview. I could see that it was definitely making the center of the dome and areas under the text thicker, but even at 30, the outer edges still looked like only one layer would be printed! This looks like a Slic3r bug to me. Also I didn't mention it, but the print with Cura seemed much higher quality overall. – mbmcavoy – 2017-01-27T05:18:22.497

Answers

3

Slice with more solid top layers. I always use five with low-density infill.

Davo

Posted 2017-01-24T23:27:06.750

Reputation: 2 113

1Even with two layers, a sloped top shell may show gaps. – fred_dot_u – 2017-01-25T14:24:12.527

1I realize the original question didn't have this information. My second attempt that prompted the question was printed with 8 solid top layers, and the print quality was nearly the same as with the first, using the default of 3 solid layers. – mbmcavoy – 2017-01-27T05:05:03.863

1

You can either increase the shells, or you can increase the infill density. In addition different fill patterns will help. I would do 4 minimum for such a print.

StarWind0

Posted 2017-01-24T23:27:06.750

Reputation: 2 913