×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Constraining a Spline

Constraining a Spline

Constraining a Spline

(OP)
I have imported a spline (an airfoil), and want to constrain the entire spline to a point.  The problem arises when I try to constrain the starting point of the spline to a datum or line.  The single defining point moves, but the rest of the spline stays put, and consequently my airfoil is "modified" because the rest of the spline does not follow.

Is there a way to constrain a spline relative to its own defining points?  I really don't want to constrain the splines individual points, as there are about 150 of them.  

Anyone have suggestions?
  

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

RE: Constraining a Spline

What does it gain you to constrain a spline to a point? I've never tried it before so I'm not sure what advantage there would be in it.

RE: Constraining a Spline

(OP)
Well, here is what I am doing:

I import a spline (airfoil) into a sketch, and then draw a line from the trailing edge to the leading edge.  This defines the chord lenght.  I constrain the leading and traling edge of the airfoil spline to the line, so that I can move the line around, and the airfoil moves with it.

From here, I can rotate the line and the airfoil rotates with it, defining the incidence angle of the airfoil.  Then I can fix the line in space, and then define planes (to create additional sketches on) to the line, making all other geometry associative.

Anyway, I think I found the solution.  You have to insert the spline by poles, rather than "through points" to get the spline to constrain to the line.

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

RE: Constraining a Spline

I generally use positional constraints on sketchs with splines, esp. when I don't want the spline to be modified.

-Dave

-Dave
http://www.moslerauto.com

RE: Constraining a Spline

Wittenborn,

You could possibly use an angled Datum Plane through the Stacking Axis as your Sketch Horizontal reference then by modifying the angle of the plane you could constrain the twist angle of the section with the Angle of the Datum.

You could name the planes and give them Parameters that you could easily modify from Expressions. For your chord you can just make the line collinear with the angled sketch reference plane.

Then you can modify the angle and the spline should stay oriented the same relative to the H ref plane for each angle. Give this a try and let me know if it works or not.

Michael
  ~~

RE: Constraining a Spline

(OP)
Michael,

Thank you for your responese to this question, however I think you may have mis-understood my problem.  (But I wouldn't put it past me to misunderstand your solution, either.)  Let me define it a bit more clearly:

I have an Excel spreadsheet, with a list of about 100 coordinates (X,Y,Z) that define an airfoil.  I copy these coordinates into a .dat file so I can import them as a spline through points, either in modeling, or in Sketcher.  

I have no problem getting the spline imported, but now I need to constrain it to something, but I don't want to constrain all 100 points defining the spline.  

For instance, I want to constrain the leading edge of my airfoil to the horizontal and vertical datum axis I have defined.  When I set the constraint on the point, it moves the single point on the spline, but leaves all the rest of the spline where it was, thereby screwing up my spline.

Basically, I want to constrain the ENDPOINT of the spline itself, not the defining coordinate point.

So I guess the question is:  Is there a way to select a spline, without selecting it by its defining points?

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

RE: Constraining a Spline

Use Position.

What version of UG are you using?  in v.18 and lower, this would be the middle button, under "Sketch Options".  I don't have a machine with NX handy, to tell you where it is there.

Basically, Position will locate the sketch in space, and not the entities within the sketch(point, spline, etc.).  You can select your leading edge point, and set it to a distance of 0 from your datum, and the entire sketch will move to this location, leaving the spline in its original shape.

-Dave
http://www.moslerauto.com

RE: Constraining a Spline

(OP)
Dave,

So if I understand you right, you are creating the sketch, and then in modeling, you are positioning the sketch?

Ideally, I want to position the spline in sketch to some datum axis that defines the sketch plane.

Regards,
Grant Wittenborn
Aerospace Engineer
www.darcorp.com

RE: Constraining a Spline

This is still within the sketch dialog, but you don't use the typical dimensional or geometric constraints.  "Position" works just like when you position a feature.  

Actually, if you create the sketch, and then exit the sketcher, and go to Edit->Feature->Positioning (referencing v.18 dialogs, hopefully NX is the same or similar) you can position the sketch this way too.

-Dave
http://www.moslerauto.com

RE: Constraining a Spline

Wittenborn,

I understand what you are asking so Using My suggestions and Dave's you should be able to get what you want.

I tried this out and can send you a sample file with a sweep feature. The second section I made, in no way resebles a correct airfoil but you would be able to see how using offset datums and the Sketch positioning, you can control your section orientations.

If you have a feature for your stacking axis and a plane for the 0 degreee horizontal plane you can create offset datums for each section to constrain position along the axis. for each section create a plane through the axis at an angle from the 0 degree plane start with value of zero. then choose the sketch plane as an offset plane normal to stack axis.
Move your WCS Origin to the sketch csys location and do the spline import and create your sketch spline through the points.

Then use the sketch positioning to place your section point from Stacking Axis. Not if you name the Dimension for the angle plane something like SEC_AA_ANG and positioning dims SEC_AA_X&Y it will be easy to make changes to the section orientation and still have your spline points in the same locations relative to one another.

Send me an email at mikecolecole@excite.com and I can email you back a V18 sample file.

Michael

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

Solutions Brief - Protecting and Rescuing On-Ground Personnel
Keeping our warfighters safe and delivering them a competitive advantage is a key goal of departments of defense around the world. It’s a goal shared by embedded computing manufacturers like Abaco: we never forget who we serve.This case study describes how a major international contractor integrated an Abaco single board computer at the heart of its CAS/CSAR solution. Download Now
Datasheet - Top Enhancements Creo 7.0
PTC's Creo 7.0 has breakthrough innovations in the areas of generative design, real-time simulation, multibody design, additive manufacturing, and more! With Creo 7.0, you will be able to design the most innovative products faster than ever before, keeping you on the cutting edge of product design and ahead of your competition. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close