Question about preview

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budi67
Posts: 46
Joined: Sat Oct 15, 2016 5:56 pm

Question about preview

Postby budi67 » Sat Feb 11, 2017 2:23 pm

Hi,

I have a question about preview.
Why at the base, I have 5 shell, but more I have a hole ?
It's a preview bug or it are like that going to print ?

Thanks
Budi67

Image
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Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:00 pm

This the the known fact of most slicers.
Shells take of space to the inside of infill. That said, if too many shells will not fit, then only the number of shells that fits is made and this may leave a gap. Infill comes behind after the shells and will not ever attempt to fill the hole left when a shell did not fit. In other words, to the infill section it only knows that shells claimed that space.

This has been around since I started this hobby in 2009 and most every slicer has this same action. You must be careful whenever you choose more shells to preview your gcode and see if this problem manifests.

Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:03 pm

In other words, right or wrong, this is a common to all 3D printing knowledge point.
Regardless of what brand of printer or slicer, most all have this situation and you must be aware of the impacts of adding extra shells.

You can request this as a fix to Ideamaker, but given other slicers have the problem and it's not been solved in 7-8 years, I would say it's better to just know about it and use the workaround- reduce the number of shells and always preview gcode for problems.

Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:05 pm


Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:12 pm

Makerbot page describing the shells issue as far back as 2011 https://www.makerbot.com/media-center/2 ... rge-shells

The keys words from that so long ago:
However, more shells isn’t always better!

Thin Parts. When you have extra shells on a thin part, a current bug in Skeinforge (an older slicer used with MakerBots and many other early 3D printers) will cause your thin parts to be hollow. Basically what’s happening is (your slicer) looks at the thin section of your object, figures that it cannot fit the required number of extra shells in there, and then skips the shells and the infill. 4 So, if you’ve got a small or thin part or a part that has small or thin features, you will want to turn (extra- specific setting in Skeinforge, in most slicers this is just known as # of shells) shells down to (0- again talking about extra shells in addition to the default 1).
Attachments
shells.png

budi67
Posts: 46
Joined: Sat Oct 15, 2016 5:56 pm

Re: Question about preview

Postby budi67 » Sat Feb 11, 2017 6:26 pm

Thank you for your explanations Jetguy, very instructive.

I ahve test with 1 and 2 shell, it's OK, But how will be the outside aspect ? Unless reducing the speed for the exterior shell ?

Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:47 pm

I'm not sure I understand your question at all and I'm worried you understand slicing.
The STL is a 3D wireframe of coordinates. When you slice it using the slicer, it it the equivalent of taking it on a meat slicer machine and it makes 2D layers. Those layers have an outline shape of the object at the layer. You told the slicer your nozzle size, so think of that like a wide maker or paint brush. The resulting gcode path is INSIDE the physical outline represented by the STL layer slice for that layer.
Again, this has NOTHING to do with speed. It's simply math and distances. The gcode path is a centerline of the nozzle as it moves. Since the nozzle is wider than nothing, then that path is spaced according to what values you gave the slicer. Again, we are at a classic color between the lines on a layer by layer basis.

Jetguy
Posts: 1841
Joined: Tue Mar 22, 2016 1:40 am

Re: Question about preview

Postby Jetguy » Sat Feb 11, 2017 6:52 pm

Again, what worried me here is I have no idea how you came up with this.
"But how will be the outside aspect ?"
"Unless reducing the speed for the exterior shell ?"

Speed of the outside shells is often reduced because the mechanical machine can create defects in positioning error due to inertia of the moving extruder head. It weighs about 3 pounds or more and can flex the hard steel rods at stops and starts of the motion. Printing a perimeter (since that is the outside visible layer of the object is meant to smooth out and prevent these tiny and yet visible positioning errors. But that is already built into every slicing profile. Again, by default, that's something already for you. The inside shells and infill can be done faster to reduce total printing time and normally minor errors in these layers are not visible and do not effect the outside of the part.

budi67
Posts: 46
Joined: Sat Oct 15, 2016 5:56 pm

Re: Question about preview

Postby budi67 » Sat Feb 11, 2017 7:59 pm

I believe that one it is not understood, but it doesn't matter, thank you anyway.
I use a translator, it does not translate can be not correctly!!


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