Hi Michael,

I was just making a ring design for a customer by mainly using Surfaces & ran into a problem were the two major sections wouldn't Join.
I solved my problem by making the two sections into two Solids & then doing a Boolean Union to create what I needed.
But it's made me curious as to "Why" the Surface version wouldn't work this time around, as I've used the same workflow previously without problems?

I thought I'd read that there was some tweaking of certain parts to the Join mechanism, so was just wondered if this is now because of that??
Hopefully it's not something serious like a bug that's appeared this late in the game.

As I said, I've already solved my own problem, but figured you'd want to see both files anyway.

regards Colin

Hi Colin,

Hope you dont mind my making a reply.

The 2 surface edges appear to be out of tolerance for a join, there is a gap.


I deleted the bottom part of the ring and made a sweep from the edge (highlighted in pic) using the circle as a path, then trimmed that sweep with the horizontal line I added (then removing the top half of the sweep). The 2 parts then joined OK.





- Steve

I was just looking at the solid.

If you look at the joined edge, you will see what appears to be a broken edge:-



If you zoom into that area, you will actually see 2 edges with an extra little face.




What as happened is that when you made those 2 surfaces into solids, even though the edge was not in line, the fact that the solids where touching allowed the union, but that then left that little protruding edge.


- Steve

Hi Steve,

No probs & Thanks for taking a look at it.

...hmmm, it's funny because I did suspected that those curves may have been slightly off so I redid all the Curves & parts several times.
I've got 0,0,0 mapped to my F4 key & I constantly use it if I suspect that a Curve might be slightly off...
...all of these ones didn't move so figured all was well & that they were aligned to each other, looks like I was wrong!!

Glad to hear that's it only User Error on my part & not some bug that's shown up.

regards Colin

Hi Colin, thanks for posting the file and thanks Steve for the analysis.

Yes the edges are just barely out of tolerance from one another to Join.

If you bring it into Rhino, you can use the CrvDeviation command to measure the distance between the edges - on one side it is 0.006 and on the other side 0.008, and they must be within 0.005 to be joined.

If you scale down the model by 1/10 in size (run scale, type 0 <enter> then 0.1 <enter>), then that actually scales down the size of the gaps as well and you can then join it.

On that same file where Join doesn't work, Boolean Union actually doesn't work completely either, it does glue the 2 pieces together but only in one small area and there are a lot of naked edges in there still.


> I thought I'd read that there was some tweaking of
> certain parts to the Join mechanism, so was just
> wondered if this is now because of that??

That most recent change (bug fix) to Join was actually only for curve joining and not surface joining. So I don't think this is from any recent stuff.


Did you use Sweep for these, or Network? I think you may be running into a problem where Network is using a looser tolerance for its internal curve rebuilding, to try and reduce the complexity of the generated surface, but this is leading to sometimes having not quite enough accuracy on the outside edges. I'm going to try and tune that up in v3 to tighten up the tolerance for the outside curves of the network to try and improve that.


But one thing you can try for join problems is to scale down by 1/10 in size, then join, then scale back up again. I probably should figure out some way to have some option for a looser tolerance directly in Join, but since Join doesn't really have any options UI currently and just immediately finishes, it's not so easy to figure out how to make options for it without adding in an extra stage to the command.

Anyway, it seems that Join is ok there, but probably you are running into a tolerance problem in Network.

- Michael

Hi Michael,

Yes, I used Network to create the top half of the ring, then used the Finger size to Trim it & get the required shape.
I then found those arc shaped Edges I needed to form the bottom section from that trimmed Network Surface by using Copy & Paste.
Those newly made Curves would be the Profiles for a Sweep to create the lower section which would be the rings band.

So obviously that difference in the Network tolerance & Sweep tolerance was what helped to throw the Join off.
Not a big problem, at least I know I can work around this by scaling the model, Thanks again for all of that tip.

regards Colin

Hi Michael,

>>I think you may be running into a problem where Network is using a looser tolerance for its internal curve rebuilding, to try and reduce the complexity of the generated surface, but this is leading to sometimes having not quite enough accuracy on the outside edges.<<



Well that explains a number of failures I have seen when attempting solid creation from joining network surfaces.


- Steve

One thing I've been kind of torn between for this situation is whether Network should use a tighter accuracy for its outside edge curves, or whether Join should be allowing a looser tolerance.

The problem with increasing the Network accuracy is that it will produce an even denser result surface.

- Michael

Hi Michael,

In loosening the tolerance, wouldn't that then force the adjoining surfaces to deform slightly to make up the gap, It's just that there have been some past situations where small features have been turned into deformed surfaces because the sloppy operator had set the tolerance too loose so their gaps would join.

-

Hi Danny, well Join in MoI anyway does not really deform surfaces, it only does stuff to the trimming boundaries, and even then all it does is basically throws out one of the 3D edges and keeps the other one as the one for the joined structure.

But if the Join tolerance is too loose the problem can be that things end up getting glued together that should have stayed as distinct individual edges.

If tolerances are set too loose for calculations that involve fitting or iterative refinment, that's when you can get stuff like a sagging result.

- Michael

Hi Michael,

If you decide to add some surface editing/rebuilding tools into V3 beta, then that will probably be the best time to look more at this.

I am not concerned, as I have easily been able to find simple workarounds to the few problems I have had with networks.


- Steve

Hi Steve, I do want to work on some surface edit tools in v3.

- Michael