Voids of unknown origin

tom_seibold

Considering what a friendly welcome I was given the first time I posed a question about modeling a part, I thought I'd throw out another challenge to the skilled and helpful individuals who monitor this community.

I completed my model (which those who helped may with my extruded logo path may remember), which is part that goes into a Bluetooth speaker housing and holds a power switch and some small circuit boards. I exported it to STL, examined the file in two different STL viewers, and saw no problems. Then I uploaded it to Shapeways for printing.

Unfortunately, when I got the model back, there was a strange void that sliced across the tubular flange and crossed into two of the holes on the mounting flange. I hadn't seen such voids in my STL viewer, but when I looked at the file I'd uploaded in SW's online viewer, there it was. (Text continues below images.)



I contacted Shapeways, and their tech support said "This looks like there was an issue with the geometry, some faces may have been inverted. When you uploaded your model, our system tried to automatically fix these issues, which unfortunately caused the holes." The seemingly random angle of this void doesn't help me with troubleshooting, and I'm not sure how faces got inverted, if that's actually the cause. All I know is that the part looks fine in both my STL viewers, as shown below. (Text continues below images.)

 

If you'd like to examine my model and see if you can track down the problem, here's a link generated by the "Share" function (which appears to be the same as the actual URL). Note that I am working in the "Rev Dim 1" branch/workspace.
https://cad.onshape.com/documents/699a9674479007024e599743/w/d970435e2789ad48186baaba/e/4fb5d462993aa511cef60aee

lana

@tom_seibold We see such issues from time to time when cached data gets out of sync. I've cleared the caches for your document. Please try opening again. If you continue to see the issue please contact the support via "?" menu.

tom_seibold

@lana : Unfortunately, cache clearing must not be the problem. I closed and reopened the file. The model still looks fine in OnShape and the exported STL looks fine in my viewer. But when I upload the STL to Shapeways, their viewer clearly shows the same voids as before, and that's how they're going to print it.

Jake_Rosenfeld

@tom_seibold

Does it look ok in other third part viewers?  For example: https://www.viewstl.com/

If it looks ok in Onshape, and it looks ok in your STL viewer, and looks ok on that site, it seems like Shapeways probably has a bug in their import.

tim_hess427

@tom_seibold - you could also try comparing to other printing sites like xometry.com or protolabs.com.

tom_seibold

In fact, viewstl.com was one of the two viewers I referred to in my original question, along with the OS X app, Preview. It looks fine in both of them. I just tried another online viewer and it shows the part perfectly, too. I can try a different printing site such as those you mentioned, but wanted to avoid the hassle of setting up a new account with someone else.

tom_seibold

Shapeways did an analysis and came up with this:


So I think this issue might be based on how I constructed the model. In this section view, it's clear that the things I added "below" the main plate are "merged" into the model, as if in one piece. But in the area "above" the main plate, the mounting flange actually is just edge to edge with the tubular ring below it, and there's only the filleted rounded ring (not visible on the yellow-line analysis above) that joins the two together--And, at that, they don't appear to be joined, just adjacent, based on those black lines I'm seeing. Time to do some model dissection and see if I can do better . . .

tom_seibold

Sorry, here's the section view I meant to embed:

tim_hess427

@tom_seibold - based on that cross section, it does look like you just have multiple overlapping parts. 

You can either select all of the parts and do a "boolean" operation to add them together. Or, you can go through the operations the created the parts (such as extrude and revolve) and make those operations are set to "add" to any existing parts. Check out the help page for the Extrude function and look for the heading "Extrude: New/Add (new material)":  https://cad.onshape.com/help/Content/extrude.htm?tocpath=Part%20Studios%7CFeature%20Tools%7C_____1

owen_sparks

tim_hess427 said:

@tom_seibold - based on that cross section, it does look like you just have multiple overlapping parts.

They also seem to be three different colors...

Owen S.

tom_seibold

@tim_hess427 - Thanks for that tip on Boolean part merging. I now know a new technique for what I was trying to do earlier. However, I wanted to make my model in one piece, rather than from three pieces, and figured out how to create a new version of the file (well, technically a "workspace") and rebuilt the mounting flange in a way that properly added it to the existing body of the part. So now it's in one piece and the earlier issue with that random void is gone. What a cool program!

@owen_sparks - You're right--I'm not even sure how I got three different colors, but it appears to be just a setting under "Edit appearance."

tim_hess427

@tom_seibold - Glad things worked out! 

When you create more than one part, Onshape automatically assigns different colors to each part so that its easier to tell them apart.