Question about Tapered Extrude.

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 From:  blowlamp
5554.1 
Hi Michael.

I'm still working my way around all the goodies in MoI and eventually got around to reading the Beta v3 release notes where you say this: "The height of the tapered extrusion will generally be limited to be less than whatever amount would cause the different sloped profiles to collide into one another."

I know this is the norm for all the CAD systems that I've used (not that many), but I wondered why this is the case? Is it too complex to compute the resulting intersections, or something like that?

In some CAM systems, V-carving (using cone shaped cutters) can create constantly varying depth toolpaths that cut surfaces of quite similar shape (carved text etc), so it feels as if the ability might be useful for creating otherwise hard to construct surfaces, as well as being able to extract the centred 3d 'ridge lines' that would also be created.


Thanks.

Martin (2).
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 From:  Michael Gibson
5554.2 In reply to 5554.1 
Hi Martin,

> I know this is the norm for all the CAD systems that I've used (not that many), but I
> wondered why this is the case? Is it too complex to compute the resulting intersections,
> or something like that?

It's because the most straightforward way to do the calculation is not by doing intersections at all but rather by generating an offset curve from the base profile and then moving that offset curve upwards and doing a loft between those curves.

That approach works well for regular areas of the tapering but the overall approach does not work well when the side walls intersect with one another, in order to handle that a much different approach would be needed, probably one that involved doing intersections instead. But also intersections are quite complex when they're between surfaces that are also self-intersecting too.

In order to get ridge lines I'd think that it would need quite a lot of areas of special treatment in the algorithm, it would probably need to detect areas that would result in a surface being self intersecting and break things apart at those spots, then intersect all the generated pieces and determine how to trim the side walls. None of that stuff needs to be done in the "standard case".

So basically there would be a substantial amount of special work involved in order to make an implementation of that, it's a much more complex case to try to handle.

- Michael
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 From:  blowlamp
5554.3 In reply to 5554.2 
Michael.

Thanks for taking the time to answer this question - I can see it's not an easy thing to automate.
However, with a few sweeps, followed by use of the Trim tool and then a little deleting of unneeded surfaces, I've managed to get a very acceptable result from MoI :-) So I'm happy it can be done.


Thanks again.
Martin (2).



EDITED: 18 Nov 2012 by BLOWLAMP


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