I am new to this forum and Rhino CAD and have a couple questions before making an investment in the SW. What I am aiming to primarily use the SW for, is engine and 2-stroke expansion chamber design/modeling, primarily the latter. Doing some research online it does appear some users have used Rhino to model and flatten (patterns for laser cutting, etc.) expansion chambers, but want to see if anyone thinks there would be any issue(s) with trying to flatten something similar to the attached pics. This is a good example of what I would be intending to design and flatten. In other SWs, the flattening part is usually the tricky part due to the multiple curves… Basically, for the curved sections, these will be sliced so the bend can be created in actual sheet metal. Each section will be butted to the adjacent and welded together to form the entire pipe. The picture in this post shows the slices/pieces I am referring to.
If you know what your doing Rhino should be able to get you the result you want.
The important thing is that the individual surfaces need to be developable so that they flatten without distortion. The UnrollSrf command is what you use to flatten the surfaces and CurvatureAnalysis can be used to check if the surfaces are developable.
It looks the surfaces in your image could be made by creating the circular curves with about 10-14 spans and using straight loft to create each surface. The rebuild command can be used to convert a circle to a NURBS curve with the number of spans you want. You should make sure the seams of all the curves and surfaces line up so that the seam can be used to orient all the pieces you want to weld together.
Quick version:
Create centerline curve and circular cross sections to define the shape.
Concept shape using Sweep1 with centerline curve as the rail.
ExtractIsocurve from the concept shape where seams will be located
Loft with straight sections the lofted shape.
UnrollSrf the lofted polysurface.
variation using pipe instead of sweep the cross sections can be then set on the run within the pipe command, then rebuild to get equal isocurves extract iso curve and loft with straight sections.
I initially used Pipe, then switched to Sweep1 with explicit cross sections. The circles were created using Circle with AroundCurve option. The advantage of the explicit cross sections is revisons only require changing the circles of interest without having to remember the diameters and locations of ll the circles.
ExtractIsocurve works anywhere on a surface, not only where isocurves are displayed. Rebuild with uniform spacing will be uniform in paramter space, not physical space.
that is a good point. a change radius for pipe would be interesting though… maybe for next xmas
right, but still worth a shot, it is after all also about approximating (discretizing) the shape somehow, but ok i have no experience how exact the crosssections spacings have to be but i assume it does not matter so much maybe.
This is just an example online, but yes, this is similar to what our chambers look like when complete. Was trying to get something posted quick and was being a little lazy… It is labor intensive as all sections are hand welded, but not as bad as one would think. As soon as a pattern is finalized thereafter the fabrication time is cut dramatically. The design and fitment takes the longest and this is what we are trying to optimize/streamline.
Thank you for all the replies. Definitely looks possible and I think we will be purchasing the SW.
The trickiest part making expansion chambers such as, is keeping the centerline lengths for each section of the chamber exact while bending the pipe around. The angles and cross sections are also very important and need to be maintained. Normally, we calculate all the dimensions based off the engine parameters and make a straight pipe. From there we have all the lengths/diameters/angles required. Then, we apply the constraints (engine compartment, etc) and start to design/fabricate the cones to come up with the final shape. A bit of trial and error…. The idea of using CAD is to optimize this part of the process and not have so much trial and error.
Thanks again for all the replies and effort making a pipe just to see if it were possible! As we start to use the SW I am sure more questions will come up. Thanks again!!
I’m assuming when you mean equally spaced you are referring to the slices or cutouts, correct? If so, this isn’t that important. Depending on how smooth you want the transitions from one diameter to the next will determine how many slices/cutouts are required. You do however try to make each piece equally as wide to the next, but it normally doesn’t work out that way. The design dimensions are more important and even a mitered corner isn’t too detrimental, it is really the angles, diameter, and lengths that weigh the most. As long as those parameters are met it doesn’t really matter if it takes two or ten pieces to make up that section (I.e. header, baffle, belly, etc.).
Does this answer your question or did I still miss it?
Aaaah! Reminds me of the good old days when I raced Yamaha TZs. Good to see 2 strokes are still out there.
All of the above suggestions sound right and you onbviously know what you are doing with respect to maing it fit the frame and engine.
The only thing I would add is to try the devloft command for lofting the sections. This will help to force developability a bit more.
