27 Replies Latest reply on Jan 15, 2018 2:29 PM by Harold Brunt

# conic sketch help

Can anyone help me? I think I know that I can't measure a radius when I have used a conic sketch. I really need to know if there is maybe a equation to figure out the radius of the conic sketch created?

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A conic sketch is multiple radius - like a French Curve....

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I know, but was hoping there would be some kind of equation to calculate a close radius

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You could add a few points and use a 3 point circle and make the circle a construction line, then snap dimension on that circle, then as you change the conic sketch, the circle will move with it..

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Working on a confidential project,I wish I could to make it easier to get help.

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Seems like this requirement would be relatively easy to reproduce in a dummy part that exhibits the behavior needed in the proprietary design.

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It might be, but I am at a loss

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A conic section is exactly that - a planar section through a cone.

The type of section (circle, ellipse, parabola...) is dependent on the size of the cone and the position and angle of the plane.

Are you attempting to reverse-engineer an existing curve, or are you attempting to create a new curve?

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conic curve can be elliptical, parabolic or hyperbolic - how it can be defined for your measurement?

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I was taught this trick by someone:

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I see that I forgot to point out something:

The highlighted number gives you the virtual radius in that area.  It isn't perfect, but can get you close anyway.

It is a good way to measure imported fillets and curves if it comes in as a spline.

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is there any way to get a list of the radius through the curvature?

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Hi Jennifer

I think it's possible to sub divide any conic into two smaller conics

like this

repeating again

Once you have enough its easy enough to approximate with 3 pt arcs

Solidworks isn't bad at keeping up with changes, but its best to not do BIG jumps, or the sketch solver gets lost

and you have to suppress or delete a relation or two so it solves again

2016 attached

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Trying to backwards engineer this part, need to get radius for boss. I will look at how you have your pictures thank you Rob

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There's also this information provided in the conic property manager

good luck!

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Hi Rob,

Use the segment tool and add points, then overlay 3 point construction arcs. That doesn't split the curve and gives you approx. curvature

Elmar

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That's a good idea!

I'm not sure what Jennifer is trying to do...  If she's reverse engineering a conic, you can always use a driven dimension and an end tangent relation

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I will try both options. I am not very familiar with using this command.  Completely new to me, but hopefully with all your help I can figure this out.

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..wait... did someone already mansplain that???

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Maybe...

If you're trying to measure instantaneous radius at a point, you could possibly attach an arc and use equal curvature constraint.

It may not work within the same sketch originating the conic. You might have to do this in a second sketch.

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Yeah I know it’s multiple radii, they want to know out of all the radii the smallest one.

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Hi Jennifer

I'm not 100% on this, but its my best guess

For a random conic

sketch in the tangency

Now in a new sketch (you are allowed to use the tangent relation)

I think you can only look at this value, but easy enough to remember it and add a circle

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Hi Jennifer, Completely unrelated I just stumbled upon this in the API and thought it might help you.

Looking at the code it requires a model edge, so to test it I just made a planar surface with a conic edge.

I then used the output to draw a circle.  Note the coordinates returned are the point on the curve, not the center of the circle so I tested it like this....

looks good to me

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The conic sketch tool in SW uses a different form than typically found in optics which is what I have used with the Formula Driven Sketch Tool. I use the formula driven sketch with this form:

y = (x2/R) / (1 +[1 - (1+K) (x/R)2]),

Where: The axis lies along the y-axis and represents the height as a function of x.

The vertex is at y = 0.

K = Conic constant Rho

You should be able to match your existing curve starting with a Conic constant K = -1 for a parabolic.

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Ok I thought this was for the sketch. I just figures out that it's for the conic fillet. Is there a equation to find that information?

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I'm not exactly sure what you're looking for and since you can't share the proprietary design that makes communication just a little bit harder (my company does consulting so I understand not being able to share a design issue!). If you are looking for the radius of curvature for a conic filet then I'm not sure how you will go about getting it. My understanding of the conic sketch tool interface is limited since it does not serve any purpose for me. The formula driven sketch tool allows the formula I posted is (x2/R) / (1 +[1 - (1+K) (x/R)2]) and can be entered as:

((X^2)/R)/(1+((1-(1+(-1))*((X/R)^2))1/2)

You need to enter a value for R and values for X1 and X2 to create the curve.

The formula I posted is commonly used in optics and simulation software like Zemax or SPEOS. I know you can't post the part or design but fitting a parabola is proprietary so if you feel you create a new parabola sketch similar to the problem you are trying to solve then perhaps you'll get a solution sooner.

Edit - If you already know this a parabolic you can select the construction points for the sketch and multiply by 2.