Constraing a sketch line to a cylinders edge 3

[gedkins]

New to UG NX. Took the online course and the Design course. How do you constrain a sketch line to be colinear with a cylinders edge (Silhouette edge) in a sketch. After entering the constraints mode to add the constraint I cannot pick the edge of the model. Do I need to convert the edge?

Guy

Guy Edkins
Managing Partner
Delta Group Ltd

http://www.deltagl.com

 

[cowski]

Silhouette edges are for visualization only, they are not true edges (ie can't use them for geometry construction).

In my limited experience with the sketcher, I would create a datum plane tangent to the side of the cylinder and use that for the sketch plane. I don't know exactly what your end goal is, so my method may not be applicable for you. Hopefully a sketcher guru will come along and educate both of us.

 

[Xwheelguy]

I think cowski's advice pretty much sums it up. I'm not very experience with datum planes, so I'm not sure as to what all methods are available to make a datum tangent to a cylinder's silhouette.

Using a 20mm diameter cylinder, I created a datum through the center of the cylinder then created an offset datum plane. Taking it a step further, I used the expression that controls the cylinder diameter (p0=20)to control the offset distance of the datum (p0/2). That way, if the cylinder changes shape or location, the datums should move with it.

A simpler method would be to create a line through the center of the cylinder's end faces & associatively project the line onto the cylinder's surface. I didn't know if more geometry would be tagged to the line once it is projected.

Hope this makes some sense.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[gedkins]

Thanks guys for the help. I was hoping it was a little simpler but it looks like it isn't. I will be coming to the well for advice often as I am supporting about 6 new users. Its slow and painful, somehow we will prevail.

Guy

Guy Edkins
Managing Partner
Delta Group Ltd

http://www.deltagl.com

 

[NXPERSON]

When I want to constrain an sketch object to the end face of a cylindrical object, I create a projected line.

1. Select PROJECT GEOMETRY command in sketcher.
2. Make sure the ASSOCIATIVE link is depressed.
3. Select the desired edge of cylinder to reference (Note: More than one edge can be selected).
4. Select OK to create the lines.
5. Turn the projected lines into reference lines using the CONVERT TO/FROM REFERENCE command.
6. Now constrain the sketch object to the referenced
object(s) using the colinear constraint.

By having the associativity turn on when projecting the cylinders edge, it will resize itself if the cylinders diameter changes. Also, other constraint types or new lines can be used with the referenced/projected line(s).

 

[richb71]

i would do what you want by creating an associative line at your desired point on the cyl. you will need a tangent datum to make an associative intersection line:

you can create a datum plane tangent to the cyl face by:
create a first datum pl (DP1) thru the cylinder center by clicking the cyl face. then create the tangent datum pl (DP2) by clicking the cyl face, then DP1. use the alternate soln (1-2-3) button to go to quad pt u want. if you need a DP tangent at a non-90 deg angle, create a third plane by clicking on a datum axis thru the center, then DP2, then input an angle.

create the "silhouette" line by using insert - curve op - Intersect. turn on asoociative output. pick the datum plane as "fist set" and then the cyl face as the 'second set".
you can now create a sketch and add geo constraints back to the associative intersection curve.

-rich

 

[MSPBenson]

As always with UG there's more than 1 way to skin a cat so here's another option to throw into the pot.
Using the datum or face you are positioning your sketch on, create an associative section curve of the cylinder face using the "section curve" function. Use this to create a "colinear" constraint in the sketch.

Mark Benson
CAD Support Engineer