Calling Ron, 5 axis flow question

[jlw™]

Ron, message me your e-mail please.

[BenK]

That could be. It has been known to cause issues in the past. What program do you run?

[Colin Gilchrist]

There are 3 different "methods" of generating surfaces in Mastercam; NURBS, Parametric, and Curve Generated. There is a setting for the "Default" under the CAD Settings. There are fundamental mathematical differences in how the shapes are described.

 

NURBS is the required "input" to the Moduleworks functions, so if that warning comes up, the "convert to NURBS" command is used to convert the surface to a different mathematical definition. Oh, I see Thor's Hammer already covered it. Carry on.

[Colin Gilchrist]

Here is some light reading on the subject:

 

http://web.mit.edu/hyperbook/Patrikalakis-Maekawa-Cho/mathe.html

[BenK]

There are 3 different "methods" of generating surfaces in Mastercam; NURBS, Parametric, and Curve Generated. There is a setting for the "Default" under the CAD Settings. There are fundamental mathematical differences in how the shapes are described.

 

NURBS is the required "input" to the Moduleworks functions, so if that warning comes up, the "convert to NURBS" command is used to convert the surface to a different mathematical definition. Oh, I see Thor's Hammer already covered it. Carry on.

 

That would explain why most of us have never seen this error. The fix should be as easy as switching the default. Thanks for the information, that's good to know.

[Mjölnir]

Here is some light reading on the subject:

 

http://web.mit.edu/hyperbook/Patrikalakis-Maekawa-Cho/mathe.html

 

got any light reading on possible advantages of using one surface type vs others for generating toolpaths? i made the decision to use curve generated surfaces based on assumptions. i'd like to know more on the subject.

[Colin Gilchrist]

I wish I did have more info that is "published". I was being a little bit facetious regarding that being "light" reading. It is some pretty heavy duty math involved when describing a "surface", and much of that traces back to the origins of how the mathematics were developed.

 

In a nutshell, Curve-generated and Parametric surfaces are able to create "simple" shapes much more easily. They are great for describing things like a plane, circle, cylinder, or cone. You can think of these shapes as akin to "primitives", and they are easier to display in the graphics "scene".

 

https://en.wikipedia.org/wiki/Non-uniform_rational_B-spline

 

The origins of much of the math involved comes from two different French Mathematicians; Paul de Casteljau, and Pierre Bezier. The math uses a piece-wise polynomial formula to exactly describe the shape of a curve. These curves could then be manufactured on any piece of equipment by the application of math alone, without needed to have a "physical model" to use for reference.

 

For practical purposes, Parametric Curves and Parametric Surfaces are more "lightweight" in the database, but also have an issue when it comes to the "smoothness" of the transition between surface edges (patches). With Parametric surfaces, you can really only get G0 or G1 continuity. This is known as Positional (G0), where the surfaces can meet at a "sharp" angle, unless they are both completely "parallel" to each other. Think of a Cylinder, with a tapered Cone attached to the top. The meeting of the surfaces forms a sharp edge or corner. With Tangential (G1) continuity, you have the end vectors of the curves or surfaces pointing the same way, which eliminates the "sharp" edges. This is often more than sufficient to machine an object or set of surfaces, but slight imperfections may still exist in the transition between the surfaces.

 

NURBS curves have the ability to achieve G2 continuity, also known as "Curvature continuity". Not only are the edges of the surfaces "tangent", but they share the same "curvature" as well. This is important in fields like Optics and when the highest precision is needed. This is the equivalent of a "perfectly smooth" transition between the surface edges.

 

http://www.rhino3d.com/nurbs/

 

http://www.mactech.com/articles/develop/issue_25/schneider.html

 

http://web.cs.wpi.edu/~matt/courses/cs563/talks/nurbs.html

[crazy^millman]

There are 3 different "methods" of generating surfaces in Mastercam; NURBS, Parametric, and Curve Generated. There is a setting for the "Default" under the CAD Settings. There are fundamental mathematical differences in how the shapes are described.

 

NURBS is the required "input" to the Moduleworks functions, so if that warning comes up, the "convert to NURBS" command is used to convert the surface to a different mathematical definition. Oh, I see Thor's Hammer already covered it. Carry on.

 

Guess that is the difference that has been my default for 15 years.

[jlw™]

I do recall seeing that when I was tinkering and like Mjölnir I set it to curves thinking it would be better. will I still get arc output with nurbs surfaces?

 

I also tried the conversion thing and it didn't work. like Ben said, same file. ben, did you convert it or go straight at it?

[crazy^millman]

I do recall seeing that when I was tinkering and like Mjölnir I set it to curves thinking it would be better. will I still get arc output with nurbs surfaces?

 

I also tried the conversion thing and it didn't work. like Ben said, same file. ben, did you convert it or go straight at it?

 

Most times now I don't get arcs, but I am working with solid most of the time so I make the curves I need from the solid and then use the surfaces from the solids and good to go. People love parametric stuff and it has its place, but I have used Mastercam the way Mastercam was designed and it has served me well. You when you trying to force a Square peg in a round hole it would either need to be smaller than the hole or you need a much bigger hammer. Me I like getting a round peg and trying it that way.

[crazy^millman]

Ron, message me your e-mail please.

 

Okay I had the same results as Ben. It was slow, but I was able to process the toolpath. The surface normal was inside and not outside so I did reverse the surface normal and yes for these toolpaths the drive surface normal is important.

[jlw™]

I did flip the normal several times trying to get it to work. I did as you, imported the step and then created curves from the solid as needed. I still get the same error on the file ben sent me. I may send it on to qc@mcam.

[Müřlıń®]

I have never seen this error either.

 

But Colin hit the nail on the head I think.

 

I think there must be some correlation in files from Inventor.

 

Could this error be cause by opening a STEP file from Inventor instead of having Mastercam running and merging the STEP file?

 

Something would have to change the default from NURBS.

 

Inventor is a parametric modeler so it wouldn't want to use NURBS....right?

 

And when surfaces are created from STEP, which includes far more data than an XT/XB,

 

perhaps that is where the surfaces and output entities are no longer NURBS.

 

Like I said,  I have NEVER seen that error before and I have opened lots of solids before but very few from Inventor that I have used on 5-axis stuff...

 

Interesting thread and will know what to do should this happen to me...thanks...