Rhino Arc Offsets Arcs as Splines Problem

[PBpaul]

Here is another question/problem I am having with Rhino. I draw an arc in Rhino and then offset it. In Rhino, both are just simple arcs. That is to say, the original is just a simple arc and so too is the offset. Now I open the Rhino in Mastercam and more often than not, the original arc is still just a simple arc (and machines as such) but the offset is a NURBS Spline and if I machine it, it is tons and tons of tiny straight line segments and tiny arcs. I know I can filter the toolpath, but my question is, why isn't my offset just another simple arc? This was not an issue in Ver 9. Hopefully, I just have a setting somewhere out of whack. Any suggestions?

 

Thanks- Paul

[Pete Rimkus from CNC Software Inc.]

PBPaul,

I'll take a look at that. An offset of an arc (in the same plane) should be an arc.

One suggestion in the meanwhile...uou could run X's 'Edit/Simplify" function, (which was "Modify/ConvertToArcs" in V9) and it should find them and turn them back to arcs.

[PBpaul]

Thanks, Pete:

 

I still don't have it clear in my head what is happening but I know it wasn't a problem until X. However, in Ver 9 we were routinely saving our Rhino drawing as IGES and then letting Mastercam convert them to mc9. It may be that because I am now just opening Rhino drawings directly in X rather than converting then from IGES that this arc thing has popped up. The reason I was opening directly in X rather than converting from IGES in X is because of how levels/layers were being lost. We talked about that in another thread and is still an issue.

 

Thanks for looking into this for us.

 

PBPaul

[Pete Rimkus from CNC Software Inc.]

I took a look at Rhino's Offset Curves function and when you offset an arc, you do get a NURBS spline, not an arc. You can use their Curve/Convert/CurvesToArcs function to convert them to arcs, but I don't see any way to have the offset function create an arc.

It seems like their IGES output was somehow smart enough to do that conversion on the fly. Interesting....

[PBpaul]

Pete:

 

Yes, you are correct about their offset being a NURBS spline and I wrote them about it late yesterday afternoon. They said they would put my request (that if you offset an arc then the offset should be an arc too) on the "Wish List." Here is what's crazy, though. If you just open a Rhino drawing in X, the offsets come in as NURB splines. If you save the Rhino drawing as an IGS and then convert it with X, the very same NURB Spline offsets show up in X as arcs.

 

For the time being, it makes the most sense for us to convert these NURB Splines to arcs, as you suggested, in Rhino. That lets us keep opening Rhino drawings directly with X rather than having the IGS save/convert in there, which messes up our levels/layers. That problem, I believe, is probably in X, and I understand that it is being looked into.

 

Thanks for the assistance- PBPaul