Ellipse Tips

[Chris Rizzo]

How come there isn't an easy way to create an ellipse as a series of arcs, instead of splines?

 

Actually, let me re-phrase that...

 

Is there an easy way to create an ellipse as a series of arcs?

I manually do it creating points along entity, then a bunch of 3 point arcs. Anyone else?

[Philcott]

Cmr,

 

Do you need specific arc sizes? If not, have you tried creating the elipse then go to modify/break/Spl. to arcs, pick the elipse, done, set the error, do it. This will change the elipse into a series of arcs. The smaller the error the larger the number of arcs.

 

This isn't creating the elipse as arcs but you end up with arcs.

 

Phil

 

[ 09-25-2003, 02:27 PM: Message edited by: PhilCott ]

[Harryman]

Got solids? You could extrude a hole into a flat surface.

[Chris Rizzo]

Thanks Phil,

 

That's what I was looking for. Using the same process day in and day out here, it's easy to forget the basics.

[Müřlıń®]

quote:

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modify/break/Spl. to arcs

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Well I'll be........I was always doin that manually......

 

Got to remember to keep runnin thru the menu's for new stuff

 

Thanks Phil

 

 

Murlin teh stupid

[Philcott]

Murlin,

 

On the modify page there is also a convert to arcs option but I haven't been able to get that to work to convert splines so I use the one under break.

 

Anyone know what convert to arcs on the modify page does?

 

Phil

[TheePres]

PhilCott,

If u raise tolerances under options, will convert some splines to arcs.

[Chris Rizzo]

Phil,

 

I frequently try convert to arcs, and myself only have it work on occasions. Scaling drawings I've had what were once arcs (full circles even), turn into splines. Convert to arcs seems to resurect them as arcs again in that situation.

[Rick Damiani]

quote:

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On the modify page there is also a convert to arcs option but I haven't been able to get that to work to convert splines so I use the one under break.

 

Anyone know what convert to arcs on the modify page does?

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It takes circular splines and turns them into a single arc. If the spline cannot be represented by a single arc (i.e. an elipse) the conversion won't work.

[Philcott]

Rick,

 

When you say "circular spline" I take it you mean basically a circle (Full or Partial) that was drawn as a spline. Is this correct?

 

Thanks,

 

Phil

 

Hey! I got my avatar.

 

[ 09-26-2003, 04:07 PM: Message edited by: PhilCott ]

[mayday]

quote:

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On the modify page there is also a convert to arcs option

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nice avitar,

 

if the convert to arcs fails try opening up the tolerance. somtimes it dont take much and it works

[Rick Damiani]

quote:

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When you say "circular spline" I take it you mean basically a circle (Full or Partial) that was drawn as a spline. Is this correct?

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Exactly. It comes in real handy when working with IGES files, as most of 'em either don't have edge curves (so you have to extract 'em yourself) or have all the edge curves represented as splines. It can be helpful when dealing with imported solids that have circular features in or on faces that are not perpendicular to the feature.

[Müřlıń®]

quote:

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When you say "circular spline" I take it you mean basically a circle (Full or Partial) that was drawn as a spline. Is this correct?

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Well rats......I kinda hoping it would break a complicated spline into a series of arcs....

 

We need a function for breaking complex splines up into arcs and lines using a certain tolerance.

 

If you have ever tried to make a Coons and had it sit there and calculate forever only to fail, all you have to do is break up the spline into arcs and lines and the Coons will calculate immediatly. The end rexxxxing surface isn't half bad either....

 

 

Murlin

[crazy^millman]

Well Murlin what I do is take the model in and erase all splines. arcs, lines, and points. I Then go to another layer and go create/curve/all edges if solid then I go to solid if surfaces then I say all surfaces. I also recommned doing a delete duplicate enties after that you get those little extra you dont need out. I call the layer my wireframe and call me orignal layer Model Information. They still may be spines but they seem to do alot better than the imported splines do. I may sometimes have 10 layes of just wireframes for different thing to usein that manner for toolpaths.

 

Crazy Millman

[Müřlıń®]

Thanks for the tip Crazy I will try that the next time I do a surface model.

Makes sense to me

 

But some of the splines that give me troubles are the ones Mastercam makes.

 

I must do some more R&D on the tolerances on the splines.

 

I think keeping the defaut 30 degree break angle is not tight enough, and the tolerances must tighten up on cordal height.

 

 

Murlin teh always open for suggestions...

[Rick Damiani]

quote:

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We need a function for breaking complex splines up into arcs and lines using a certain tolerance.

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Select Modify|Break|Spl to arcs and your wish shall be granted. If it's a circular spline you want converted to a single arc, Modify|Cnv to arcs will meet your needs. Both commands have a tolerance setting, and they do different things.

[Philcott]

Murlin,

 

As I said earlier,

quote:

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modify/break/Spl. to arcs, pick the elipse, done, set the error, do it.

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Will do what you want. We were saying there is another convert to arc function and that one will only do the spline that can be transformed into a true circle.

 

Sketch up a quick spline and test the modify/break/Spl. to arcs method.

 

Phil

[Müřlıń®]

Phil & Rick,

I tried to use that on some complicated splines and it wouldnt work right.

I fooled around with the tolerances from loose to as tight as .00001 and it wouldn't get as close as I could by just breaking up the spline manually and putting 3-d arcs on top of it.

 

 

Sometimes itwould just completely wig out and output a bunch of scribble.

 

Murlin

 

[ 09-29-2003, 02:13 PM: Message edited by: Murlin ]

[Roger Peterson]

toolpath contour > linearization tolerance at .0001 and filter tolerance set to .0001 > backplot saving as geo. Modify filter tolerance as neccesary.

 

 

HTH