Half pipe

don3sch

Hello, I was able to make a multi-plane pipe route like: https://cad.onshape.com/documents/87f2e2e15b2746ffa4a2fd9a/w/23826dee1d95463390d39d58 but all attempts to make it a half pipe, such as for a marble track, the bottom half twists around so that the marble would fall out of the track.  Is there a way to make a half-pipe like my example pipe so the bottom stays horizontal and level?

andrew_troup

In theory, if you sweep a sketch containing a horizontal line along a curve representing the centreline of your pipe, you should end up with a surface you can use to split the pipe in the way you seek.
However twist controls for sweeps are currently not implemented, nor are 3D curves, so a satisfactory result is not guaranteed by this method at the present state of the art.

andrew_troup

@don_schaefer697
One possible but rather laborious workaround would be to distribute planes at regular intervals along the edge you are using as a path, for the portion which is currently problematic (the "downhill" part)
Those planes would lie normal through the edge at a point on that edge.
You could then sketch loft profiles, similar to your sweep profile, and the horizontal constraints would be correctly respected in that context.
So, basically, substitute a lofted cut for a swept one (a sweep is really a way of automating a loft, so really you're just doing some hand-holding, to help the application see things your way)

andrew_troup

If I was doing this I would probably leave the locations of the points defining the planes parametrically defined. I would start with relatively few planes for the downhill portion, and relocate them once the loft was working. so that inspection revealed them to be optimally situated with respect to the "trouble spots". The fewer planes the better, for smooth results, so possibly worth trying only three to start with
 

viru

@don_schaefer697 , I triad on your part and achieved below profile as shown in below image.Kindly refer below link for half pipe
https://cad.onshape.com/documents/05b3eeb2618a41df9326a3c0/w/74dacb73e3bb413a92809550/e/517eac09d9a14edf955a8773 link.

Narayan_K

@ don_schaefer697, As per your requirement i tried to get half pipe at bottom horizontal as below,







You can find the model from below link
https://cad.onshape.com/documents/f0c398965b90493a98544a2f/w/fbe0c93e85944ab78cd3685f/e/90fc8061d724443f98848eef

don3sch

Thanks for all the responses and examples.  It looks like I'll be losing my marbles for now.  One example looks really close though, but the high speed bend in the second corner will still let the marble out of the track.  I suppose I can leave that bend a closed tube to insure the marble doesn't jump out of the track.   I just now thought of that.  The real track will have tighter curves in it.

andrew_troup

@don_schaefer697 

It just occurred to me that a variation on a method I posted in a model for a barrel cam could be used to provide a horizontal parting surface for a ball track

refer the current thread entitled "Powerful workarounds"

don3sch

Thanks, I'll study these pro tips to see if I can make one of them do what I'm trying.  Either way, there are at least two other routes I can go to skip over not being able to make a horizontally level half pipe on a multi-plane slope.

andrew_troup

@don_schaefer697
The method is perhaps illustrated most simply in this model:
https://cad.onshape.com/documents/73ba229cd7204ed4a803e0c3/w/652f1d601aa54b39b177c521/e/8a9e9ff8fbf6492686d07050

in Part Studio 2 -- Don't pay any attention to the derived part which begins it: the subsequent model does not rely on it, it was just a convenient armature. The point is that the surface is lofted through lines which are
a) Horizontal, and
b) Normal to the local path (which in your less regular case, is easily arranged by choosing a point at the beginning or end of an arc, and the arc, and asking for a "Curve Point" plane)