Newbie question> How do I do this?

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 From:  Rudy
1252.1 
Hello all,
hello Michael. Hope your vacation went well.

I have been working to learn MOI in the past months, then I stopped for a while. I am back again, and even though I made a couple of workable models (I am in the jewelry industry...had the STL files RP printed...came out flawless!), I still get stuck in probably silly points.
Having said so, I would like to create a solid "tear". See attachment. But it seems I do not get the result. The free form shape should have a flat bottom, and eventually to shell it.

Any advice is surely appreciate it, and I thank you all for the immense contributions to this beautiful MOI.

Best,
Rudy
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 From:  Michael Gibson
1252.2 In reply to 1252.1 
Hi Rudy - the immediate problem here is you've got one big outside closed loop, and then one open curve running down the center. Most of the surfacing commands will want to match similar kinds of curves, so instead of one big closed outside curve you could split that into 2 halves (select it and then run Edit/Trim, click the "Add trim points" button and click 2 points to split the closed curve by). Then with 3 open curves running lengthwise you can then select everything and use Construct / Network to build a surface there.

However, even after that the surface is kind of messy with some sharp pieces near the base, and probably the pointy tip part will be messy enough to prevent any shelling.

Instead of trying to draw a blobby rounded thing all in one go with an outline, you will generally be better off starting with a more simple blocky shape and then using some fillets to round things off. The place where you want a dimple can be constructed by cutting the dimple with a boolean and then using fillets to round that off again.

The problem with trying to make blobby outlines directly is that it tends to make messy surfaces with some parts of the surface squished together and kind of wrinkled and overlapping over bits of itself. That will generally cause problems with further operations.

I'll try to create an example of the "simple blocky + fillet" type approach.

- Michael
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 From:  Brian (BWTR)
1252.3 In reply to 1252.2 
Is this anything like the end result you wanted?
I had some fun anyway.

EDITED: 30 Dec 2008 by BWTR

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 From:  Rudy
1252.4 In reply to 1252.3 
Dear Brian,
Thanks for helping me out. It is closed, but it is no the result I would like to see.
Michael, yes, I got your points.

I will come back on this as I am ready to rest my bones.
Thank you very much and have a good night rest,
Best,
Rudy
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 From:  Michael Gibson
1252.5 In reply to 1252.1 
Hi Rudy, here is an idea on a different approach.

I started with this profile and 2 rails:



Then doing a sweep, turning off the "Maintain height" option:



To tweak the shape you can run another curve down the middle like this:



When you are inside of sweep, you can push the "Pick scaling rail" button and then pick that middle rail curve to customize the shape some more:



So at this point note that the shape is pretty blocky and ends in a flat piece - I have not yet made any attempt to make that part rounded, because trying to force that now would cause a rather sudden change in direction right in that area which will tend to create various kinds of surface flaws, like parts bunched up and running over top of themselves.

At this point you will probably want to delete or hide the curves used for sweeping so they won't get in the way.

Now to make the front part rounded, select the upper edge and do a pretty large fillet:



Then I drew a curve in the top view and selected the main shape, and did a boolean difference to cut it with the curve:



Then another fillet to round off that edge, with a smaller radius than the previous fillet:



Now I can select the bottom face and run a Shell with a small distance (in this case 0.05):



I hope this gives you some ideas on a different approach. One problem is that I did not really drop the smaller end to a tiny point - you can do that, but the sheller will probably not like shelling a shape that comes to narrow point like that, it is likely to fail. So if you want to do that instead of using shell you may need to manually construct a smaller inside piece and then use a boolean to cut it away instead of relying on shell to do it automatically.

The good part about this method is that there aren't profiles that have abrupt changes in orientation, like going from a vertical profile to one slammed down flat on the plane in an abrupt 90 degree change of orientation. Those kind of abrupt changes are going to be what will cause bunching and bad quality surfaces.

- Michael

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 From:  Rudy
1252.6 In reply to 1252.5 
Great,
Thank you Michael!
Yes, my designs will involve a lot of frre form from now on and all these tricks are very welcome.
I really appreciate the time you are taking with me.

Best,
Rudy
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