Hi All. I'm trying to modify a model done someone else using Rhino and modify it for my needs and of course trying to learn at the same time.

Here's the part I'm working with which as a number of problems:



There's a couple issues with the part. One is that it's missing the top. My methodology for that is that once I fixed the other issues, I can select/create a closed curve along the top and then run "planar" on it.

?is this a good strategy?

Before I can do that I need to fix two other issues. One is that on one of the faces, this one:



It extends out past the edge of the part, making patching the hole a problem:



?What the best way to address it? Is it to trim it (not sure how) that or create a new face that doesn't exhibit the problem?

Finally, I have the hole (actually two) to fill. I have to two strategies for that. One is to (once I've created the top), use "N-Sided" to create a patch. The other would be to create a grid and then use "Network" to create it.



?Is there a better, more MOI way to do this?

Thanks in advance.
Scott

Hello Scott,

The model looks to be out of square, is this intentional? If not my strategy would be to recreate the part from scratch, it may be faster to do that than to get all the surfaces matching up fro ma model that's a bit out of alignment. If you like I could hammer out a quick video showing this.

Hi, thanks for the response. I don't believe that it's intentionally out of square (I can't confirm currently).
I would love to see a video of how you would reproduce the part in that I'd learn a great deal from it so I do greatly appreciate the offer.

I also still would like to learn how to address issues in an existing model so I look forward to more responses.

(A meta question, is anyone interested in providing for a modest fee some 1:1 MOI tutoring perhaps via screen share?--I love the simplicity of the UI of MOI but just still having a problem getting to the aha! moment with NURBS modeling)

Scott

Hi scott, it kind of looks like you're currently constructing this by going around and building individual pieces of it surface-by-surface. It's possible to do things that way but it usually tends to be easier to try and build a base solid block to start with and then do booleans to carve off chunks of it. So you'd want to have some base extrusion with the top capped off right from early on rather than leaving that as something to do at the end.

I guess the difficulty you had in this case is you have some kind of scooped out areas that you were focused on building first maybe?

You might want to build scooped out areas by having an extended cutting surface that does shoot out a ways past the base solid, and then do a boolean difference to cut it out, something more like this:








So note that with this example above here I'm working with a larger solid block that I created initially and the scoop out part is a larger extended surface that intentionally extends a fair distance punching all the way through the solid. Then the final edges of the scoop are not something I tried to draw in directly myself, rather they are calculated during the boolean operation that intersects the scoop piece with the base solid.

This method of building extended pieces and then letting some of the final edges be calculated by intersections between parts during boolean operations rather than trying to draw them in directly yourself is probably the key difference from your current "patch by patch" type modeling strategy.

Does that help make sense on a better approach maybe?

If you are not using booleans to form many of your final edges it probably means you are not using the best NURBS workflow, it's easy especially for people coming from a polygon modeling background to want to manually draw in every single edge and be very hesitant about using booleans but in NURBS modeling it's usually optimal to be using booleans as much as you possibly can and having some of your final 3D edge curves come as the result of boolean calculations rather than directly drawing them in 3D yourself.

If you try to keep your model as a solid from the beginning and then try to cut pieces away from that solid it's usually a better approach than going around patch-by-patch and focusing so much on individual hole filling.

- Michael

As far as tweaking your existing model, if you draw in a couple of line segements on the top you can use Construct > Planar to build a top cap, I'd probably do that to start with, then the area where a "scoop out" is not behaving well seems to be here:





That surface kind of swoops outwards a way making a little slivery extension - this is the type of thing that can easily happen if you are trying to construct every single piece individually rather than using boolean or cutting operations to slice pieces off to some common outer boundary shape from the start.

To fix that up, you'll need to trim off the sticking out area, you can do that by selecting these 2 faces here and then running Edit > Separate to break them out from the main body so they are their own separate object for the moment:



Now with that separate piece (made up of 2 faces) selected, run Edit > Trim and at the first prompt to select cutting objects, select these edges on the top of your main body piece:


You can select planar curves as the cutting objects in Trim and it will automatically extrude them out internally. Then right-click or push "Done" to signal you are done picking cutting pieces and the Trim command will slice up the objects and the next prompt is to pick which fragments to discard. Pick this little excess piece here:




Then right-click or push "Done" to signal you are done picking pieces to discard and that will leave you with a better formed piece with the excess removed. Select the objects and run Edit > Join to glue them back together and then you can form a new planar surface to fill in the hole. I've attached a 3DM model file with this done to it and so there's only one hole area remaining to fill in.

But I hope it makes sense what I wrote about earlier, where you want to have more of the "outer block" of the object constructed as a solid to start with and then try to cut pieces off of that, that tends to be easier and especially with making pieces align with one another when they are all cut by one single common surface rather than all constructed by individual surfacing operations without any cutting happening.

Basically you don't want to avoid pieces sticking through each other - in fact in many cases you want to intentionally make things push through each other with plenty of extension on them and then slice those off using booleans. Or using trim - you can use booleans if you are working with solids, and trim if you are working with surfaces. The difference between them is basically booleans automatically decide which pieces to discard based on which volume they are contained inside of and automatically join the results together, that tends to make it convenient. With Trim you will have to manually pick which pieces to discard and do joining yourself, it involves more steps but allows you more level control as well. But if you are doing lots of trimming it tends to mean you are using a "patch by patch" type modeling strategy instead of a "solids and cutting" strategy which is where NURBS modeling tends to shine.

- Michael

Thanks everyone for the input. I did rebuild it from scratch and it looks great (tho I'll go back to the other one for some practice). One question, does it matter if you take a solid and cut everything from it vs drawing a closed curve outline and extruding it to a solid and then cutting from it?

Also with Trim, how does it know what direction to take the cutting plane from?

Thanks,
Scott

Hi Scott,

> One question, does it matter if you take a solid and cut everything from it vs drawing
> a closed curve outline and extruding it to a solid and then cutting from it?

It doesn't really matter how you make the base solid, a solid extruded from a closed curve is just as much a solid as any other way... I'm not exactly sure what other method of creating the solid you are asking about for comparison with extrude though...


> Also with Trim, how does it know what direction to take the cutting plane from?

If the cutting object in Trim is a planar curve, it uses the normal of that curve's plane as the projection direction.

Hope this helps!

- Michael

Hello,

I've uploaded one method to make the part from the reference. Comments and critiques are welcome.

Part Creation From Reference

https://vimeo.com/125976976

Cool re-engeneering!

Thanks so much for producing that. It's great to watch over someones's shoulder as you did. I learned a lot.

Scott

Hello,

I finished off the back part of the model since there were a few more commands in MoI that could be useful in the part creation process.

https://vimeo.com/126180724

Very clear explanation!

Hello Pilou,

Thank you for the compliments, now if only I could distill it down to a few minutes.