revolved surface with bad normal

[pro]

When I create revolved surface, mastercam say that surface have bad normal. For check normal I use Analyse/surfaces/test-norm/All/Surfaces/Done.

Probably problem is in generating curve of this surface, how can i get more complex error description?

Dynamic analyze not enough.

[Camdude®]

pro,

i have never seen this error before so i do not know what would be causing it but i would check to see if the underlying geometry is good. if possible recreate the revolved profile and recreate the surface.

[Eeyore-nonhuman forum member]

Pro!

 

A quote from help :

quote:

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This function checks selected surfaces and reverses the normal direction on any surface whose outward, or positive, normal direction points downward relative to the current Cplane.

 

1. Choose Main Menu, Modify, Normal, Set.

 

2. Select one or more surfaces, then choose Done. In the prompt area, Mastercam reports the number of reversals.

 

3. Press [Esc] to exit the function.

---

quote:

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A surface normal is a vector (direction) that is perpendicular to the tangent plane of a surface at the point of tangency. Each surface has two normal vectors, which point in opposite directions. One is referred to as the positive (front, outward) direction; the other is referred to as the negative (back, inward) direction. When a surface is created, the default positive normal direction is based on the relative directions of the curves defining the surface.

In the following graphics, the arrow shows the normal vector directions of a surface at the position of the base of the arrow.

 

 

 

Notes:

 

¨ Like surfaces, solid faces have two normal vectors. The positive normal direction always points outward, or away from the solid volume.

 

¨ Curves have one normal vector that is perpendicular to the tangent line of the curve at the point of tangency.

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quote:

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There are several ways to identify the positive normal direction of a surface:

 

¨ The Show Back function, when active, applies a defined color to the back (negative) side of the wireframe display of a surface, which distinguishes it from the front (positive) side. For information about the Show Back function, see Showing and setting the back color for surface displays.

 

¨ You can verify the positive normal direction at any position on a surface. For more information, see Checking and optionally reversing the surface normal direction and Analyzing a curve, surface, or solid face at any position.

 

¨ A check normals option is built into functions where the normal direction affects the resulting geometry so that you can check the normal direction without leaving the function. For more information, see Checking surface normals.

 

Note: For solids, the positive normal direction always points away from the solid volume, and the negative normal direction points into the solid volume.

---

Actually change normals you can do through

Alnalize ->sutfaces->set normals .

If your curves are not one spline and this contour is self-overcrossing you can have this problem.

You better convert your geo to one spline

And if your geometry is mirorred .

And beware you can scrap your part in actual milling

 

HTH

ETHH

[pro]

Eeyore,

The problem is not in reverse normal direction.

The Test Normals function analyzes the normal vector of selected surfaces and reports the number of bad surfaces whose normal vector reverses direction abruptly in one or more locations.

Your are right about converting this surface to NURBS, NURBS surface have good normal.

 

But I want get more complex information about reason of this error in revolved surface.

Pro.

[Eeyore-nonhuman forum member]

You may have nonconsistant countour (nonclosed ,overcrossing ,overlapping and so on )

Say you select it using rough countour tolerance

When you dont have constant tangency you `ll have reverced normals .

I do not want to enter deeper ,I may be wrong too ,anyway it is just a guess ,throw your file on ftp to have a look ,if possible .

In two words -go with spline as a tool contour and you`ll never have such a problem .

HTH

ETHH

[pro]

Eeyore,

This error happen also on surface without border.

Now I can't put this file on ftp, maybe tomorrow.

Pro

[Eeyore-nonhuman forum member]

Pro ,What do you mean surface w/o border .

Surface was built with some geometry ,right ?

OK ,waiting for a file and curious.

Regards

[cadcam]

Pro can you email it to me and i will put on the FTP?

I want to see this to.

[cadcam]

Teh file is now on the FTP called Revovled srf.zip

[crazy^millman]

Well I just recreated your surface using new 3 point circles for the 4 sides in 3d then trimmed everything together and swept your surface at it was perfect. I did not see any construction chains as to where your surface was created but did put curves on the edges and only 3 came out as arcs and 1 was a spilne. When I used acrs for all 4 sides it did not give me a problem. What c-plane are you in when try to do what ever you are trying to do with this surface?

[Eeyore-nonhuman forum member]

I can recreate a problem ,IMHO .

At least ,I think so ,checking in haste (very busy )

Yes ,I see a prob. and can build it with or without ,I hope .

I will try to send a file in couple of hours on ftp .

 

Regards ,

ITHH,WTHH and ETHH (specially for Millman )

[cadcam]

Ron his construction lines and acrs were blanked but there.

Pro what is it you are trying to do with this surface that is giving you trouble?

[Eeyore-nonhuman forum member]

HI ,folks !

 

I succesfully recreated and solved a problem .

Teh problem recreated producing spline from two arcs ,one of them overlaps another ,IOW contour changes it`s direction to the opposite .

Trimmed revolved surface comes completly the same - check surface -no problems ,test normals -1 bad surface found

When geometry clean - 1 arc ,15 arcs or one spline ,only direction of the contour not changed to the opposite I had not managed to get the problem .Still had not checked noncontineous and nonconstant tangency contour .

It is so easy thing to get that I think no need to trash the FTP .

If youu still think you want the file I can put it later .

Regards ,

ETHH

[crazy^millman]

Yeah I always forget about blank I never use it so forget to see if something is blanked or not. Good eyes Jay. The owl seems ot have given you a good reason for the problem so see if that gives you the needed information or would something esle be needed and do we need to go futher?

[Eeyore-nonhuman forum member]

Using this method I successfully created bad ruled surface (WITH bad normals ,check model result -OK )!!!!

HTH

ETHH

[Eeyore-nonhuman forum member]

Pro .

Before building surface geometry run delete->duplicate entities command and findovl.dll c-hook (find overlapped entities ) .

DoWnload from Bryan 314 site c-hooks and use colrent.dll to color entities different colors for better analisis and work .

Don`t forget to say thanks to Bryan !

 

HTH

ETHH

[pro]

Thanks for all,

This surfaces was translated from another cad system. I try to find way to check surface like that and repair it.

Eeyore,

Sorry, my English is not quite good.

As I can see generating curve does not have self intersection, but revolved surface probably have overlap. What wrong with generating curve?

Maybe I need change direction of generating curve or axis of revolution.

What is "IOW"?

Pro

[Teh Bear without Brains kinda idiot]

Pro !.

__________

Sorry, my English is not quite good.

________

Mine is not good too ,never mind .

Net problem ,my mojem pereity na russkiy yazyk,esli hochesh

We can talk in Russian ,but this will offend others ,this is English language board .

But if you can not express something ,write in Russian ,you are welcome !

IOW stands for in other words .

Overlapping entities are bad ,especially when you making splines ,if spline will change direction to the opposite ,you will get your problem .

Simple thing :

build arc ,copy it one time and trim one of them in the middle ,you `ve got overlapping geometry.

Now make from them 1 spline selecting both arcs and make revolved surface and you will get the same problem .

Regards ,

WTHH

 

Udachi i horoshego nastroyeniya !

[Teh Bear without Brains kinda idiot]

Pro -EEyore ,Winnie teh Pooh and Iskander teh OWl

eto 3 raznyh uzera menya ,soshedshego s uma okonchatelno

 

Winnie teh Pooh spoke for Eeyore .

Sorry for unconvinience .

[pro]

Why your decide that generating curve have overlapping?

Pro

[Teh Bear without Brains kinda idiot]

It is hard to tell now ,when you have spline.

But it looks like when you look on the surface without shading it`s U and V curves change colors in the corner (it means surface change normals ad the meaning of up and down ) .

I can build it and without oferlapping entities too (without tangency )

It is mainly philosophical question ,when you get such message ,recreate your surface ,otherwice you can scrap a part ,especially in the toolpathes where up and down have meaning (like flowline ).

I make molds ,get models from various cad/cam and also build myself .

My geo is always clean.

When imported surfaces or solid have critical errors I prefer to correct them .

I like to dig deep into the matter of things but at my work I prefer safe ,effective and simple things and I hate risk .

Ps .I succesfully created now bad revolved surface with overcrossing contour and nontangent .

Who needs to dig deeper ?

This thing is dangerous and you have tools to find it .

 

Regards

[pro]

Thanks for help. Spasibo Winnie.

I'll try to find some function on c-hook to diagnose such problems.

Pro.

[Teh Bear without Brains kinda idiot]

Pojaluysta ,Pro !

___________

I'll try to find some function on c-hook to diagnose such problems.

________________

 

This is an interesting topic -dirty geometry analisis and cleaning and Mastercam do has tools for it .

Let`s return to this a bit later .

 

Regards ,