Hi Andrei,

> What other things are depend on size? I remember something about fillet and size.

Some operations used a fixed tolerance of 0.001 but I'm generally in the process of switching things over to the relative scale method. There is kind of a mix of things currently, but a lot of things do use the relative tolerance method such as booleans, sweeps, lofting, offsets, ...


> In what scale is better to work in MOI?

It tends to be best to work with things around 50 to 0.1 units in size, that way things that still target only a fixed 0.001 tolerance won't be either too accurate or not accurate enough.

- Michael

Got it, thanx)

>It tends to be best to work with things around 50 to 0.1 units in size, that way things that still target only a fixed 0.001 tolerance won't be either too accurate or not accurate enough.

Very handy tip, I always thought it was between 1 and 1000. I'll have to work smaller in future to minimise errors in joining things together.

Hello,

You can see your naked edges here. I see that you have a draft to that part( 2°? ), so it might be good to extrude out your cylinder with that taper and then start building out a tapered helical cutting curve or surfaces. Building out then carving away from your part should leave you with some good surfaces.

Hi Kevin,

> Very handy tip, I always thought it was between 1 and 1000.

That's generally close enough that it should be fine. There isn't any exact cutoff point, it's just that if your objects are too large in relation to the fitting tolerance the results can be too heavy and take too long to calculate (because they're trying to reach some very tight accuracy level in relation to your object), and if your object size is too small and approaches too closely to the fitting tolerance then fitted geometry is not accurate enough.

Usually it is worse for your object to be too small in relation to the tolerance though.

But the reason why I'm generally moving to a relative tolerance system that is based on some fraction of the object size is so that you won't have to worry about this as much.

- Michael

Thanks for all your input guys. The scale method worked perfectly.

As to my design approach, unfortunately this was the only way to do it. The bottom (contoured edge is a split-line for a cavity while the top edge (dia 20.5mm) is prescribed by the client. I had to work within those limitations. Cannot reveal more due to NDA.

Thanks again :)

Some thoughts about subject:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6499.12

Hello Andrei,

I guess that set of recommendations are fine for some situations but the original part that was posted looks like it's being used in a molding operation. Finding the simplest way to model something doesn't always leave you with an optimized or usable model for a particular application. Having a plan is a good idea, but you have to work within the limitations of what the model is being used for.

>>Some thoughts about subject:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6499.12<<

I really don't know how this is supposed to help...

OSTexo, bigseb,
Becouse your base shape is simple but made in complex way. It have complex geometry and you could not even join it... So even if client give you sourses in that bad state, you could rebuilt them to get clear geometry. It is not so hard to do.
I can see only one justification for this muddy geometry it is if clien need all that muddy edges and stuff... But I really can not see any reason for client to ask for this? May be I do not know something, tell me :)

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What you don't is how this all fits together. I can't reveal the rest of the project due to NDA. The geometry of the part I uploaded is not open change. It is not always an option to do things the simple way.

bigseb,
One thing I can say for sure - everything can be fitted or connected much more easer to a good geometry than to a maddy one. Peace :-)))!
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Hello Andrei,

That file is not simple, you're misinterpreting the model and it's intended use. It's pretty obvious from his sig that the person who posted the file is in the mold design business. It also stands to reason that someone who is adding draft to parts and naming files thermoform in another thread is using the file for some sort of mold operation as well. Formulate a plan based upon the intended use of the model, trying to do simple all of the time is not possible and in some cases will end up causing more problems later in the process.

Hello OSTexo,

Look pleas what I made, I rebuild its model from his edges, and you say that there is no way to make it geometry clear like this? Some molding process not allow it? You can trim it any time you like to get those pices but still keep clear geometry.

I made it more clear not only in geometry but also in surfaces, look I mark it in red. He made it with mistakes and got those jagged faces. And it is not becouse some molding process or client wish it is just becouse of absence of modelling skills.









He got all that troubles and horrible geometry becouse he do not follow rulles that I wrote in link I gave.

First, he break first rule, START FROM BIG AND GO TO SMALL. He has to be started from Cylinder and then make all other details but he tried to make Cylinder in the END and got all that troubles! Looks like he started from that bottom spiral detail and after that tried to make Cylinder.
And if even that bottom spiral detail was given by client, hi has to make sylinder absolutley another way... May be like I made it.

Then he break second rule:ALWAYS TRY TO FINDE THE SIMPLEST WAY TO MAKE THINGS.
He started to make Cylinder by joining all that sigments and got a lot of problems. It was not the simplest way but also wrong, becouse it produced jagged faces.

So guys all your arguments looks like you are trying to protect BAD GEOMETRY and absence of modelling skills arguing it by some foggy circumstances.
I can not see any arguments to keep that BAD geometry!


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Hello Andrei,

He didn't break any rules, you just don't understand the model requirement and use. I don't understand why you're making such a big deal over the outside surface of this model, for his application it could be just fine, there is one minor issue on the back side of the outer cylinder which is easily closed up. The model gets a bit heavy at a few places spans wise, but if it was a problem for his application it would make sense that he would ask about resurfacing strategies, no? I'd be curious to see how this outside surface should be done, this model is not nearly as simple as you think. Please attach 3DMs.

OSTexo,
I spend about 8 minutes recording video where I repear all his mistakes... Is it normal to make this kind of model?

He asked for help... I made some suggestion for future and you trying to tell me that his model is perfect and he need no suggestions. He had messy geometry with a lot of mistakes his model has 2 artifacts look here:



I really do not understand you, looks like you want to say that all that horrible geometry and mistakes he made are good path to follow..

.3dm - http://we.tl/kym9sjLY1h

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OSTexo, you are correct, this is for an injection mould. The lower contour is for a cavity split AND NOT NEGOTIABLE.

OSTexo,

And Solid .3dm - http://we.tl/6sSYL9ZMPE

In previows post just joined surfaces, and you can say that it is not solid :)
Now with good geometry of this model you can make absolutley clone of his model in terms of edges if needed (I just do not know what is have to be in this model)

Hello Andrei,

Thanks for proving my point. I didn't even need to run the analysis to see right away that you have continuity defects, they are that obvious. It's clear that the red and green profile lines are not identical. If you're wondering where they are I have attached the analysis screenshot that the software spit out. Interestingly the original file has no continuity defects (I did fix the one naked edge in the back, didn't touch anything else). If any modifications need to be made you are going to have a horrendous time trying to acquire required continuity with that surface layout of yours, it's definitely not an improved clone of the original.

It's always a lot more difficult when specific constraints need to be incorporated into things!

If the outside is meant to be one regularly tapered piece, it can be good to build the bottom edge as a wide ribbon surface (sweep with Twist: Flat can be good for that, seems like you may have already been doing that) something like this:




Then that can be used as a cutting object in boolean difference to slice off the bottom of a longer tapered thin walled base object:




The boolean difference between the thin-walled base solid and the cutting surface will yield 2 divided solids, and the bottom one can be deleted to leave this:




This approach may be good if you're focused more on the bottom surface following a particular centerline path rather than focusing on the final boundary edges of the bottom which in this case come from intersections between the side walls and the cutting ribbon.

Anyway that approach would give more regularity in the outer surface since it would come all from one larger piece. It certainly may not apply if you have other things that are more important than that though...

- Michael