Round to Rectangular Surface

[OldPup]

First Post: Hello to you in the CNC world!

Messing around with Rhino 3D learning how it works etc etc but I have bumped into something that requires someone with some skills so I found the CNC forums in the hope of finding just such a person.

Basically I need a surface to flow from circular to rectangular.

I am attaching two images. First image is of Rhino and a wireframe. The second is of the post I want to emulate. I have tried rail sweeps of various kinds, curve networks, revolves and just cannot get what I want. I can get close but not quite.

I am sure someone can give me a pointer on the direction I should go.

Thanks.

[OldPup]

Did I not offer enough info or is this impossible? My problem is that as the rounded part gets about half way toward the rectangular the edges begin to pinch and it should stay rounded until very near the rectangular end.

Thanks.

[Dan B]

Just define more cross sections to control the shape. Or maybe you want to create the rounded surfaces, then trim off the rectangular bottom after. There are a few ways you could go about this. It might be better to shade your results and post them, because it will be more obvious as to what your issues are.

Hope this helps,

Dan

[flyinchips]

Here is a link to Cadjunkie.: <http://cadjunkie.com/1239/tutorials_rhino-basics-week-04/>

It begins the discussion on NURBS. If this very video doesn't meet your needs, one of the other units in :Rhino 2010 Level 1" will.

[OldPup]

I'll try adding some more cross sections and see how that works out. I'll also watch those videos. I'll get back with you. Thanks!

[BurrMan]

Here's a visual.

[OldPup]

Those videos are very very good. The explanations are simple and easy to understand.

I do have a question on one. The Ipad video - he explains that a fillet between two straight curves does not create a smooth surface. I guess in my mind if I see a fillet created by a circle the two endpoints at the quads are tangent and should create a smooth surface. Why is a blend curve needed to create a smooth surface. I guess I am just confused on that a little.

Burrman - I downloaded your example file and ran the loft command. What I get is rounded corners. I upped the control point numbers but still don't get nice square corners. How did you do this?

[OldPup]

On the right track I think. I used the "refit tolerance" option instead for the loose loft tool. That seemed to do the trick. However, when using the analyze tool I find there is some pinching that happens. I am not too concerned about this as the photo does show some of that taking place.

I ran the same tool on BurrMan's models and saw that they contain the same pinching so I think I have duplicated the process.

Yes?

[BurrMan]

Hi old...
That really isnt "pinching".. Thats the transition from "round to square".. There has to be some type of transition for that op..

Did you look at the "blue or Red ones?? If you seperate out the curved surface part and turn on the surfaces points, you will see the last loft curve.. It's an even larger "rounded corner" shape included in the loft.. Then the end was trimmed off with the square.. The red and the blue are the same method. I did some alignment of the surfaces end points on the blue one to flatten it out a bit... Is there any pinching on those?

These are just methods for you to look at.. Cant really tell exactly what you are looking for from the first screengrab...

[OldPup]

I took at look at the last of the three that you did because it was most like what I wanted to get. I noticed the red and blue ones had an arch to them on the sides which is not what I wanted.

Just went back and looked at the red and blue versions and they both are smooth.

If you seperate out the curved surface part and turn on the surfaces points, you will see the last loft curve.. It's an even larger "rounded corner" shape included in the loft..

Ah yes, Now that you explain it I understand it now. I wondered if maybe you had done something like that but wasn't sure. I should have thought to explode and turn on the points. I see it is much larger.

Thank you for explaining things.

[BurrMan]

Hi oldpup,
So you can make that last loft curve "LARGER" and align the endpoints to be flat, but to cut it with a square, at some point, you will have "arced edges" on those sides (the red and the blue) The larger the last loft curve, the smaller you can get those, but I dont htink you can get them "Flat"...

If you use a "square" as the last loft curve, you will get that transition (Pinching).. You can make the square with "filleted corners" to create a different type of transition (Less abrupt or sharp)....

Anyway, some info for you to play and get the surface you are looking for..

More advanced use could be to make to surfaces, like just a curved revolve and the square block, then have some space between their ends and use some surfacing commands, like blendsrf or others to create the transition in different ways...But I dont know Rhino well enough to walk you throuhg that cleanly...

[OldPup]

If I may piggyback on my previous question. I now need to create a diamond knurl spiral pattern. I watched a video that was working with solidworks so the idea has to be the same but if anyone has some rhino tuts on this I would be very grateful for any help. The other knurl pattern I had didn't spiral like this one so it was much easier.

Thanks for your help.