Skip to main content
ptc-47663301-Visitor
1-Visitor
March 28, 2014
Question

Advanced ISDX questions

  • March 28, 2014
  • 19 replies
  • 9221 views

Hi I am trying to draw some curves with C2 curvature. I am using ISDX. The curve basically forms a corner (one end is on the vertical the other horizontal) so I want it to be symetrical on both end. I create the curve and make the ends curvature. In tangent >length I make sure both ends are the same number so I can be sure it's even. My curve isn't right though. I switch on "edit curve using control points" and 5 degrees. Now when I try and move the control points the two horizontal and 2 vertical points move together. This isn't what I want. If I change the end tangency to "tangent" rather than curvature, then I can move them independantly. Does this mean my curve is not C2, I am confused??


At this point I am also having difficulty making sure the control points are even on both sides. I seem to only be able to input coordinates which is not convenient at all. Is there a way to drag them together?


If I increase the curve to 7 degree, is there a way to align control points or snap them to another point?



As you can see I'm a little confused. Any help most appreciated...



This thread is inactive and closed by the PTC Community Management Team. If you would like to provide a reply and re-open this thread, please notify the moderator and reference the thread. You may also use "Start a topic" button to ask a new question. Please be sure to include what version of the PTC product you are using so another community member knowledgeable about your version may be able to assist.

19 replies

Show previous replies
vmcdaniel1-Visitor
1-Visitor
April 2, 2014

R R,


What you are describing with the control points is how 3 (or is it 5)degree curves controls act when restricted to C2... For the math to work.If you want more ability to have the ends curvature you need either a higher degree curve (in Creo 2 Style) or another point on the curve.


Theoretically you can make a curve C1 or C2 without the end constraint being set as such. You'd just have to get those control points in the exact right place by manually moving them. When you add the constraint Creo automatically sets them in the right place. And when you go to move them, Creo follow the constraint rules you just set.


So, one advantage of the Style curve is the ability to increase the degree of curve, which I believe is unique to the Style tool and not available in sketch or datum curve.


You analysis being blocky is strange, I've never witnessed this behavior. I suspect weirdness in the analysis tool.


Too bad you're not on Creo 2 where you can just create a G2 fillet.



Hope it helps!



-Vaughn McDaniel

Greg_McMurray1-Visitor
1-Visitor
April 2, 2014

"As for your other issue, (someone please correct me if I'm wrong...) I
don't know that Extrude features have ever been able to maintain Curvature.
IMHO...As for your other issue, (someone please correct me if I'm wrong...) I
don't know that Extrude features have ever been able to maintain Curvature.
IMHO... "


Here's what's going on.


After you select "Project" and pick the ISDX curve, you can see the "Use Edge" constraint on the curve.


It looks like a small backwards "S". Toggle until you can select just this constraint, then delete it.


You can see that the curve created in sketcher is not an exact duplicate but really a spline with many control points approximating the original curve. This is why the curvature analysis of your extrude is looking so rough.


If you want more accuracy, you have to build the surface in ISDX or as a boundary blend as Bernie says.


Or if you really have to make it an extrude, then you're going to have tosketch a spline and constrain the polygon.

ptc-47663301-VisitorAuthor
1-Visitor
April 2, 2014
Hi Greg that's a really helpful explanation thanks!

I think I am understanding more. I have one more question. Is there a way
to select and drag 2 control points in ISDX proportionally? (image C in my
screen shot and another point C on the vertical section). I'm spending a
lot of time fiddling with numbers!

Anyone know of any really advanced tutorials on C2 curves/surfaces ISDX?


mpeterson1-Visitor
1-Visitor
April 2, 2014
FWIW: Once I learned about Conic curves and how to use them they are my preference in defining and control complex curves which might have been created with splines or in ISDX in a reference part. Granted I have not been creating critical automotive styling, but for some rather advanced complex shapes on consumer products I think they are fine. When needed I will use the initial designers part as a "template" to define my conics to "match" or very closely simulate and then the curves are easier to change and control later. It does take some getting use to to conics. When I was a Pro/E neophyte I wondered why conics would be used, but after designing some plastic parts for consumer products I saw the light.

Mark A. Peterson
Design Engineer
Varel International
lxandr@sbcgolbal.net



DeanLong1-Visitor
1-Visitor
April 2, 2014

Lots of good nuggets in allthe posts.


RR, keep in mind that adding all the "control" mentioned in other's posts you can run the risk of doing a couple things. 1. the complexity of the math gets intense by increasing curve order (I.E. knots in the curve) and can increase regen time and file size. Not necessarily a bad thing but you will have to watch it over time that your model does not get too heavy. 2. Even though you are gaining knowledge and skill, the next person may not be as versed in your, or the others,techniques and mess things up badly. And they can do it without knowing it. Tweaking, stretching and dragging nodes, as Bernie stated, gets a little messy and is essentially "hidden" and can be really subjective to the Designer's eye. If you are creating a part that will be touched by others in the future...try to keep it simple and as mathematically explicitas you can.


Be wise in the techniques you use. If you aredeveloping Class A surfaces thatare stamped and/or formed metal that will be chromed or painted, then yes, you indeed need to bring out the big guns and use all the control needed to get sweet surfaces.However, molded plastic is another story and is a subjective call. IMHO, 95% of products molded do not need to be Class A....just really pretty.

vmcdaniel1-Visitor
1-Visitor
April 2, 2014

It took me years to learn about how to make a sketched spline curvature in sketch. So, for anyone out there, this image shows how to do so.

JWayman1-Visitor
1-Visitor
April 3, 2014

Vaughn,


Probably a daft question, but how did you create the angular dimension?



John

SteveBirman5-Regular Member
5-Regular Member
April 3, 2014
John,

To create the angle dimension:

1. Select the spline.

2. Select the spline end point.

3. Select the construction line (or the reference that you want the dimension created between) MMB to place.


Vaughn - Sorry to highjack your posting.

Steve Birman
Chief Designer
Stryker Medical
3800 East Centre Ave.
Portage, Michigan 49002
Greg_McMurray1-Visitor
1-Visitor
April 3, 2014

"Anyone know of any really advanced tutorials on C2 curves/surfaces ISDX?"



You have to go over to Design-Engine.


Bart will teach you everything you need to know.


They teach ISDX and also Rhino and Alias, so they know everything about the underlying definitions of curves that you won't find out from any other Creo-specific classes or tutorials

Terms & ConditionsAccessibility statement