What am I doing wrong?

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 From:  Sean (REGULATORJOHNSON)
8208.1 
I have been fighting with this part for several days and I can not get it to do what I need it to. It is difficult to describe the problems I am having so I made a very short video:

https://youtu.be/7R42xNhFX4k

Boolean is simply not working, and extrude also seems broken when used on this part. I have even cut off large portions of the component and rebuilt them and still have issues with Boolean and extrude, but I can at least get rid of the weird problems I am having. Am I doing something wrong? I am at my wits end trying to get this to work.

I hugely appreciate any advice that can be given. I am extremely new to 3d modeling and hope there is something obvious I am missing.


P.S. re-watching the video I say faces several times where I actually mean edges. Sorry for any confusion.
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 From:  Sean (REGULATORJOHNSON)
8208.2 In reply to 8208.1 
Now that I look back at my drawing I am seeing tons of similar strange problems. What the heck is going on? I noticed stuff like this about a week ago and thought I screwed something up so I remade most of my parts. Now they are doing it again, and I KNOW I had them done right. Pretty much any area you zoom in on will be screwed up somehow, granted you sometimes have to zoom in pretty far. Is this a limitation of the program? Will these print properly will all these strange errors?
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 From:  Michael Gibson
8208.3 In reply to 8208.1 
Hi Sean, so a couple of the things you're worried about there are just display artifacts that will happen when under extreme zoom.

Basically if you zoom in a whole lot you'll start to see some evidence of the limited precision of floating point mathematics on the computer. The computer uses a number representation that has to fit in a limited amount of memory and that causes little rounding errors for every bit of arithmetic. But they're very small and so it's just a normal part of how things work on computer CAD.

The deviation that you're worried about in the first part of your video is about 0.0000019 units, which is small enough to just not really worry about. Not that it's bad for things to be exactly aligned but many things like intersection calculations are calculated by a refinement process that adds more detail to the intersection curves until they are within 0.001 units of the ideal answer. That's a different thing than arithmetic precision but it's also another thing that means that very small deviations on the order of what you're worried about are just normal things.

The second thing when you're asking "what's this stuff" is where the shaded surface display is separating off a bit from the curve display - that's also just a display artifact under high zoom, the shaded display part of video cards tends to use a smaller sized floating point number even yet and so tends to be a little more hit by precision issues and also the curve display is done fairly differently than the shaded surface part, curves are broken down dynamically on every draw to within a fraction of a pixel of the true curve so those display very accurately but it's too much work to do this for the shaded surface and so the surfaces have a triangle mesh formed for them just once using world space angle metrics and then that's what is still used to draw even under high zoom. So it's just another normal thing that they will separate under high zoom.

A lot of these things just boil down to shortcuts that have to be taken in order to make things work quickly and without taking up gigantic amounts of memory, if all operations worked to tighter than 0.0000019 and the display tried to draw even extreme zoom at super accuracy everything would run like molasses.

I'll try to take a look at your little line floating out in space, that might be something to actually worry about.

- Michael
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 From:  Michael Gibson
8208.4 In reply to 8208.1 
Also some details on your part are getting pretty small in size, like there are some surfaces around 0.02 units in width. That's probably not quite too small yet but if you get much smaller than that it can cause difficulties because it's getting too close to the intersection tolerance. It probably wouldn't be a bad idea for this object to be modeled at about 10 times it's current size instead. I've actually tried to change most things so that the calculation tolerance is adaptive to the size of the object but there can still be things that target a fixed 0.001 and if you run into one of those that can be a problem. Like I said you're probably ok for what you've got now but it can be problematic to make things at a small numeric size and this is getting towards that.

- Michael
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 From:  Michael Gibson
8208.5 In reply to 8208.1 
Hi Sean, so your little dot is not a totally extra thing hanging out there, it's this edge from the top face:


If you zoom in to the top there you can see that edge is some slight distance to the right of the other ends:


However, again this distance is just 0.0000168 units, so it's like some fraction of a flea's eyebrow hair off, and well within tolerance, so it's totally fine.

If I was able to see exactly how you built that area I might be able to suggest some other way of doing it that would make the accuracy even tighter but the current deviation is so small I'd recommend just not worrying about it. It's normal with any kind of CAD model for edges to be off by orders of magnitude more than that, although often times with planar geometry it can be all exactly aligned like you were looking for. It depends on the particular things you're doing though, and it would probably help if your model was a bit bigger, like probably if your model was 10 times larger in size that particular calculation would have still gotten down to 0.0000168 units but then that's another 10 times tighter.

Hope this helps, as best as I can tell your model is totally fine and should print ok.

- Michael

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 From:  Michael Gibson
8208.6 In reply to 8208.1 
But now I read your message again and you mentioned booleans and extrude not working, can you post an example of those problems? Booleans that have pieces with overlapping surface areas can be sensitive if the overlapping areas are not very tight to each other. It can be a lot easier for a boolean to work if the pieces push through each other a little bit rather than skimming each other.

- Michael
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 From:  Karsten (KMRQUS)
8208.7 In reply to 8208.2 
Hello Sean,

maybe check first the angles and decide what you can use to rebuild and use the construcction lines often as possible. Make your lines longer and use trim.

I tried to rebuild it - have a look - I'm not shure if everything is okay for you.

Have a nice day
Karsten
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 From:  Sean (REGULATORJOHNSON)
8208.8 In reply to 8208.6 
Here is another quick video showing what im talking about using the same file as before. I was having a ton of similar problems a week ago so I rebuilt several parts and I am wondering if something like this was the cause, and if so how can I fix it/prevent it from happening again?

https://www.youtube.com/watch?v=IzfUZ6z_Ig8

I didn't realize the deviations I was stressing over were so small. I have been building with object/straight snap and am concerned that they don't seem to perfectly snap every time, but also realize that at those sizes it doesn't really matter anyway.
I really appreciate all the help. It is awesome that there are people willing to answer questions from people as green as me.

EDITED: 2 Dec 2016 by REGULATORJOHNSON

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Message 8208.9 deleted 3 Dec 2016 by KMRQUS

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 From:  Michael Gibson
8208.10 In reply to 8208.8 
Hi Sean, the best way to get rid of that edge (which again is not really necessary, it should generally be ok to have it such a small distance away it is well within tolerance), would be to do some lower level operations than booleans. I'm not exactly sure why the extrude of that one face doesn't produce any result, but that probably does indeed have something to do with this edge you're worried about - when you extrude a face it is really a batch operation of internally generating a non-attached extrude followed by a boolean union between that extrusion and the main piece. Like I mentioned earlier, booleans between pieces with overlapping surface areas do tend to work better when they are very precise in the overlapping region.

So anyway to remove your pernicious edge ;) try the following process - select the 2 adjoining faces to it, the top and side wall faces and delete them. Now that edge is gone and you can construct a better one to take it's place. You'll do this by using Draw curve > Line, and placing a new line between the 2 corner points, make sure Object Snap is enabled and you see an "End" snap tag show up for each point of the line you place, that way you know the new line is snapped on to ends of those other existing edges.

After your new line is placed, select the new line and the 3 open edges of the top square, and the circle edge in the middle of it. So now you have 5 objects selected, one line curve you just drew, 3 line edges on the main solid, and one circle edge on the main solid. Now run the Construct > Planar command to build a trimmed planar surface through those selected objects. You can now clear the selection and select the line you previously drew and delete it, you don't need it anymore.

Now select the new planar surface you just constructed, and also the main object. Now use Edit > Join to glue those together. Now you need to rebuild the side wall as well, since that's a planar opening bounded on all sides by edges there is a shortcut for doing that, just select the entire object and run Construct > Planar and it will build a surface there and automatically join it. Construct > Planar can be used in 2 different ways, when used with a curve selection it will build an individual planar surface through those curves. When used with a joined surface object that has open edges, it will look for any sequence of unjoined (so-called "naked" edges) in the object and build planar surfaces through those and automatically join it in.

It looks like there may be another couple ones like that around because I'm still seeing that a face extrusion of that vertical side is not behaving well. I tested it by selecting the edges around that face and duplicating them as curves and then going to the Front view and trying to squish it down and seeing "flat" snap engage (see here for a demo of flat snap: http://moi3d.com/forum/index.php?webtag=MOI&msg=3378.4) - the thing is flat snap will only engage if the objects being squished were not already very tightly planar. But if you do want to extrude in that direction it seems to be enough to duplicate the edges, flatten them with flat snap, then extrude those and boolean union that result to the main object.

Hope this helps!

- Michael
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 From:  Michael Gibson
8208.11 In reply to 8208.8 
But again let me stress - your object should be 3D printable exactly as you currently have it, you do not need to worry about tuning up that edge you're worried about before printing it. I guess if you want to do face extrusions it would help to tune it up though.

- Michael
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