Spline - Sweep

[woodworks]

Getting started on a curved stair drawing and having trouble with sweeping and a spline. I've used a rectangle instead of handrail profile because it shows the problem better. Swept object starts out in correct position then twists. Used align perpindicular with different ucs but still doesn't stay in vertical position along the entire path. The pdf is stairs with spline path. The drawing is how it looks after sweep.curved stairs.pdf

spline sweep 1.dwg

[Greendamo]

Hi woodworks. im looking for that same answer aswell. The company i work for produce very complicated curly handrail with scrolls, volutes etc and ive been trying to model the handrail with autocad for ages now but get the same problem when i try to use the sweep along a spline. A guy at work makes it using alphacam alone by creating a flat surface and offseting that surface up to give it a thickness (Autocad wont offset a surface!!!) but im not good at alphacam and it seems a very complicated procedure which could be so simple if that bloody sweep command was to keep the profile nice and level all the way along the path.

Any help on this please!!!!!

[ReMark]

Is this kind of what you are trying to achieve?

 

[ReMark]

By the way, if you upgrade to AutoCAD 2011 you can offset a surface with the newly added SURFOFFSET command.

[Greendamo]

That is wat im looking for.. every time i try to sweep a handrail profile along a spline it always comes out twisted and hasent maintained its orientation.

 

So dose autocad 2011 have a new option to offset a surface?

 

creating one single sweep along a spline path in solid would be brill.. that way i can explode it in to wire frame inport it in to alphacam and use the geometry to run tool paths down.

[ReMark]

Confirmed. ACAD 2011 does indeed have the ability to offset a surface. This new feature was covered in Lynn Allen's "Tips and Tricks for Using AutoCAD 2011" that I downloaded and printed out just last week. It appears in the section entitled "Surface Modeling" that starts on page 31.

 

In regards to the image I posted. I did not use the Sweep command. I used the Loft command and your spline as a path. I took the profile of the rectangle and placed it at the lower end of the spline in the orientation you have it. I took a copy of this profile and placed it at the upper end of the spline. However, I rotated the profile (did this via a top view) such that it appeared to be perpendicular to the curve of the spline (I "eyeballed" it). Then I used the Loft command and the Path option to obtain the result pictured above.

 

I tried working with your drawing last night but kept getting the same results as you did. So I gave up. After sleeping on it I came to the realization that what was happening (the "twist") reminded me of a plane taking off on a curve. The plane, in make the arcing and upward ascent into the sky, would have to tip its wings (the left goes up and the right goes down) thus simulating the twist you and I were both encountering. That's why I switched from using Sweep to Loft. Repositioning the upper copy of the profile kept the railing from twisting. I hope all this makes sense. All I know is there appears to be little or no twist in the railing I constructed. Give it a try and see what you think.

[woodworks]

Loft, why didn't I think of that? I understand the twist when sweeping because when you physically bend a wooden handrail it tries to do the same thing. You have clamps and a little muscle to keep it straight. Remark comes through again, Thanks

[ReMark]

You're entirely welcomed. But let's not be too hasty. I suggest you give it a try and check the results for yourself. I may have overlooked some critical detail.