How to sweep a shank - handrail??

[Arnie]

Hi guys . I was wondering if anyone would be able to help me out with this wreath ( shank ) handrail. I have tried with extrude, sweep and loft but just can't make it to work .

Thanks

[SEANT]

That would be a tough modeling assignment for AutoCAD, though it may be more feasible with 2010. Part of the problem is AutoCAD’s inability to trim surfaces prior to conversion to solids.

 

In any event, I tackled it with a more surface oriented application (Rhino) and posted the construction curves (layer 0). The resultant surfaces and made too large a file size so I included a resulting mesh (layer Mesh).

Scroll.zip

[Arnie]

Seant , thanks for your reply.

I see what you've done . I tried something similar with loft and CAD just didn~t accepted. This a real job. We've just got a 5 axis machine and now i need to find a way to get that drawn!!! Would you suggest start learning Rhino ? Is it that difficult to get the hand of it coming from CAD 3d?

Thanks again for your input.

[SEANT]

The Rhino interface is very similar to pre-ribbon AutoCAD’s so the learning curve isn’t too daunting. But, as I alluded to earlier, the focus is more on surfacing with an ability to join “watertight” surface groups to closed solids.

 

A benefit to the Surface centric modeling is the ability to explode and re-“solid”ify at will. As a matter of fact, Boolean operations (Union, Subtract, Intersect) don’t even need a completely closed solid.

 

There are a lot of features that work well with downstream CNC processing. All geometry is NURBS based, though, so initial prep will be a bit more difficult if you are using non spline compatible CNC control software.

[Arnie]

Seant

Thanks again

You wouldn't mind telling me what comands did you you to get the scroll done in Rhino , would you ? Just a rought guide would do , please !

Thanks

[CarlB]

That shape reminds me of a "logarithmic spiral". http://mathworld.wolfram.com/LogarithmicSpiral.html

Spiral transitions to a straight section. My clumsy attempt would be to have 3 curves to define the edges & center of the fairly constant width part; then a disc for the center. Extrude a rectangle for the arm, join it to the disc for the basic shape, like a lump of clay. Then create shape that will be extruded along the edge curves, to be used to "subtract" to round the edges.

[SEANT]

That would be a tough modeling assignment for AutoCAD . . . .

 

I suppose I should clarify that statement: It is not impossible to do, necessarily, it is just that AutoCAD lacks some of the features that assist the workflow.

 

I did make a token effort with AutoCAD but ran into some early “Inconsistent edge face relationship”, or some such. I don't consider it an exhaustive search for a workable AutoCAD solution, however.

 

 

 

 

Seant

Thanks again

You wouldn't mind telling me what comands did you you to get the scroll done in Rhino , would you ? Just a rought guide would do , please !

Thanks

 

That shape reminds me of a "logarithmic spiral". http://mathworld.wolfram.com/LogarithmicSpiral.html

Spiral transitions to a straight section. . . . .

 

In Rhino, I first created a couple of parallel spirals (_Spiral); you have to play with the command a bit to see the best options. As the command stands, the only spiral available modifies the radius arithmetically, not geometrically as in the logarithmic spiral (though there are free plugins available for that).

 

I then rebuilt (_Rebuild) them to a more manageable number of control points.

 

The control points towards the open end can be dragged to the appropriate elevations.

 

Setting up the handrail side profiles should be pretty self explanatory.

 

Each profile set can follow the spiral rail with a Sweep 1 Rail operation (_Sweep1).

 

The outer most edges of those surfaces can be used as rails for the next swept surface feature.

 

Surfaces that intersect can act as cutting elements for each other (_Split).

 

The top and bottom were done as rail revolves (_RailRevolve).

 

All separate surfaces can be joined (_Join) and end can be capped (_Cap).

[SEANT]

I brought some of the construction geometry back to AutoCAD and made these as solids. It is still a little ragged, but I guess it proves it can be done.

Scroll1.dwg

Scroll2.dwg

[Arnie]

Thanks guys.

Will have a go at it again tomorrow in both Rhino and CAd ... The only thing with cad is that can't quite get the extrusion to run its path and keep the bottom part from twisting ... any ideas? Obviously I played with the angles which makes it a little better , however its not quite right is it ? how can I prevent it from happening ?

[iskalipsi]

try using the sweep command then from the sweep path, pick base point.or i might be wrong. can you post a picture so we can see whats wrong? thanks

[Arnie]

Hi guys.

That's how far i got .I found that if I extrude the whole lenght of this scroll from the start point ( curly center ) I just can't get the bottom of the handrail to stay parallel to its base ( prevent it from twisting along the path ) . Is there a way to get over it ?

Thanks for you all again.

 

One more thing . how can I measure the angle between the center of the scroll and end of it ?

 

[Arnie]

Hi people .

 

What about doing it in Inventor . would that be any easier ??? Never used it though.

[Arnie]

Hey guys

Would you think it would be easier to do it in soliworks ?