.stl is "bubbly" after importing for rotary job

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.stl is "bubbly" after importing for rotary job

Postby EmmetS » Fri Aug 30, 2019 1:53 pm

Hi,

I'm trying to create this square pilaster using a 4th axis on my CNC Step and I'm having a problem importing the .stl to make the part.
From my understanding, anytime I am using a 4th axis, I need to create a rotary job setup. When I import the .stl, the whole part becomes "bubbly" (see pictures attached).
Is there anything wrong with my .stl or is there a problem with VCarve Pro? I made the part using Fusion 360 and it looks good everywhere except in a rotary job in VCarve. Is there a different way I can machine this?

I hope to remedy this problem.

Thanks, Emmet S.
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.stl Pilaster.jpg
.stl of 4 sided pilaster in Windows Paint 3D
V-Carve Pro .stl 1.jpg
.stl when importing into VCarve using rotary job setup
V-Carve Pro .stl 2.jpg
"bubbly" .stl after importing
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Re: .stl is "bubbly" after importing for rotary job

Postby garylmast » Fri Aug 30, 2019 3:46 pm

I modeled one in Rhino and got the same results using Aspire. Tried both offset and raster strategy, but had the same results.

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Re: .stl is "bubbly" after importing for rotary job

Postby Bob Jr » Fri Aug 30, 2019 4:01 pm

"Is there a different way I can machine this?"
I would use the moulding toolpath for this, and manually rotate in a pocketed fixture.
This is a rough example:
post.jpg

This would be a great time to have a four sided preview.
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Re: .stl is "bubbly" after importing for rotary job

Postby dealguy11 » Fri Aug 30, 2019 4:04 pm

This appearance is because of the way a rotary project is unwrapped by the software. To get a straight side, you have to actually model curves. In Aspire there is a gadget that sets up the vectors for you, but you need Aspire tools for the 2-rail sweeps. I suppose this could be done outside of the vectric products, but it would take awhile to explain and it's probably not the right strategy anyway.

For something like this I'd set up a model for one side, cut that side, then rotate the part 90 degrees and repeat. Do this for every side. Will probably give you a better result, unless your indexer doesn't have the power to hold the part still when the cutter is off center or your spindle can't go that far off center on a rotary part.
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Re: .stl is "bubbly" after importing for rotary job

Postby TReischl » Fri Aug 30, 2019 8:39 pm

A lot of this depends on how you are using your modeling software.

Here is the best I could do with Rhino:

Capture.JPG


No bubblies, none.

It took a while to figure it out since I am just in the early stages of learning Rhino. Since this is NOT a Rhino forum I am not going to start explaining what I did, just does not seem right to me.

Not sure at all how one would go about getting F360 to output a smooth model.

The stl file needs lots of triangles otherwise it will start creating those bubblies. It is not an issue with Aspire IMHO. If the information being fed into the software does not contain enough data then the software will work with what it gets. In other words, garbage in, garbage out.
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Re: .stl is "bubbly" after importing for rotary job

Postby dealguy11 » Fri Aug 30, 2019 9:31 pm

Ted - I'm curious. Is your example set up as an wrapped rotary job in VCarve Pro or did you bring it in as a 2-sided 3d item?
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Re: .stl is "bubbly" after importing for rotary job

Postby sharkcutup » Sat Aug 31, 2019 2:08 am

Created a similar model .stl file using Atom 3D and imported it into the rotary (4th axis). I have gotten the same similar condition (bubbly effect) on all four sides.

It seems to be the way v-Carve is interpreting the model .stl file in the 4th axis (rotary) because it is fine in Atom 3d and when I import the model .stl file into V-Carve just as a single sided project too.

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Re: .stl is "bubbly" after importing for rotary job

Postby TReischl » Sat Aug 31, 2019 1:29 pm

Steve: That is a wrapped rotary view that I posted, not a 2-sided.

..........
It is NOT the way aspire or vcarve is "interpreting" the stl file.

I got the "bubblies" on my first export from Rhino. So there is nothing special about mine.

Then I paid attention when exporting from Rhino. There were a total of 12 triangles being exported. That would happen no matter what I did as far as trying to increase the number of triangles. Then it dawned on me, Rhino was not going to create a lot of triangles for a flat surface defined by 4 lines. Just was not going to happen. I rebuilt the lines in Rhino to have a lot more points and then did the two rail sweep. That works.

I used F360 over a year ago, I am not sure the same thing can be done in F360.

STL files can be a bit tricky. Normally the problem is seeing faceted faces on flat work because the resolution is not set high enough.

In a 3d solid modeler the software does not look at "triangles" but instead uses math formulae to generate what is seen on screen.

I guess to sum it up: Aspire/VCarve are expecting to read files that already have the resolution determined by the number of triangles.
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Re: .stl is "bubbly" after importing for rotary job

Postby gregk » Mon Sep 02, 2019 5:32 pm

The "bubbly" effect is caused by "unwrapping" of the triangles. It stems from the fact that a flat surface in wrapped rotary project will be actually represented as curved surface in the flat view.
The process of unwrapping an STL is only an approximation. That means that VCarve will measure the error introduced by unwrapping a triangle. If the error is too high, the triangle should be divided into smaller triangles.
Eventually those should be small enough to produce a smooth surface after unwrapping.

It seems that the current tolerance for this part of the importing process is not small enough, allowing visibly bend unwrapped triangles that produce the "bubbly" effect. The workaround is to attempt to produce an STL with more triangles than necessary as per TReischl's suggestion.
There will be a patch for the issue but it needs further testing.

Also, as others pointed out, it may be a better idea to machine your model as a four-sided job. This should allow you to reduce the machining time considerably, compared to the rotary job.

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Re: .stl is "bubbly" after importing for rotary job

Postby adze_cnc » Mon Sep 02, 2019 11:21 pm

I wonder what the result would be importing a Rhino native 3DM file rather than an exported STL file? Will the Vectric unwrap routines properly handle Rhino’s NURBS and unwrapped it properly?
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Re: .stl is "bubbly" after importing for rotary job

Postby dealguy11 » Tue Sep 03, 2019 11:45 am

I doubt it. Any flat facets, regardless of whether they're triangles or any other shape, should be subject to the same issue. Maybe it's smarter than I think, but I don't think so. Someone should try.
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Re: .stl is "bubbly" after importing for rotary job

Postby TReischl » Tue Sep 03, 2019 1:18 pm

adze_cnc wrote:I wonder what the result would be importing a Rhino native 3DM file rather than an exported STL file? Will the Vectric unwrap routines properly handle Rhino’s NURBS and unwrapped it properly?


Gave it a shot. Did not get very far. Aspire pops up message that no model exists in the file. Tried a couple of things, different versions, meshed the model, etc. Just could not get it to read the file.

Want to correct myself from an earlier post where I said "It is NOT the way aspire or vcarve is "interpreting" the stl file." Well, duh, of course it is, sheesh. It was too early, I had not finished my first cup of coffee. I got other great excuses if need be.

Further, did a bit testing. This IS an issue. It is obvious on any flat surface in a rotary job. It is not a big deal for me personally since I do not do a lot of rotary to begin with and secondly I have not had occasion to mill large flat surfaces on the rotary. But I can see for some work that it would be a problem.
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Re: .stl is "bubbly" after importing for rotary job

Postby CharlieP » Tue Sep 03, 2019 2:53 pm

Hi everyone.

Please try doing this with your original models.

Across the part, I would expect your original model to be like the original below where across the width of the model, it is only 1 - 2 polygons for this whole side.

Try to subdivide this model at least across the width to increase the polygon count across the width as seen in my rough example.

This give our software more information to work with when we are unwrapping the model.
We can only add a given amount of this subdivision when unwrapping, so if you are seeing this "bubbling" it mean you have hit the automated limits and the approximation is going as far as it reasonably can.
If you subdivide the model first, then import it, we will have more to work with when unwrapping and can then use this higher polygon count to get a smoother Unwrap result.

I hope this helps
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