How do I constrain a face to a cylinder?

[Anonymous]

I am trying to CAD a model rocket I just made so I can test the aerodynamics of it.  I have all of the individual parts made in inventor, but I am having trouble getting the fins on the rocket.

How can I constrain the fins (which have a flat face) to the outside of the cylindrical rocket tube?  The photo shows the fin and the face (the narrow and long face) that I am trying to constrain to the tube.

Thank you!

[Curtis_Waguespack · Accepted solution]

Hi mccarthyk,

There are many ways you might do this, but my preference it just to create some helper geometry in the part model (the fin in this case). The helper geometry is simply a surface extrusion that can be toggled off once it's been used to constrain the fin to the rocket body (edit the fin and right click on the surface feature and choose Visibility).

Attached is an example file that you can refer to.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[Anonymous]

Thanks a lot for making that file!

However, I am a complete noob with everything but the basics, and I don't know what helper geometry is.  I did a quick google search and not so much came up.  Could you please give a breif description of what that is?

[Curtis_Waguespack]

Hi mccarthyk,

Sorry for the confusion. You'll just sketch and constrain the circle as normal, but instead of extruding and making it a Solid feature, you'll cick the Surface button in the Extrude dialog box to make the output a surface.

The key here is that you will create the surface in the correct position and orientation so that when you constrain the surface to the rocket body in the assembly file it is correct.

I hope this helps.
Best of luck to you in all of your Inventor pursuits,
Curtis
http://inventortrenches.blogspot.com

[Anonymous]

Sorry.  I think my problem is a lot simpler than you think.  I would just like to constrain the fin to the rocket, and I'm not sure how to do that.  Every time I try it doesn't work.

I have attached the .ipt of the fins, and the .ipt of the rocket.  If someone could please show me how I can constrain 3 of them them so they are spaced 120 degrees apart, with the short straight edge parallel to the rocket and ligned up at the bottom so it will look something like the picture below, I would really appreciate it.

Thank you.

P.S. Curtis, I really do appreciate the file that you made an posted, but I don't really understand it (not that it matters, but the fins are actually flat - it's an optical illusion from the shape that maked them look curved in the 2D photo!)

[Anonymous]

I found out a good way to do this, I took my fin .ipt and created a cylider around it and then rotated it.  I this this is what Curtuis was telling me to do - but I acheived it in a different way.

[JDMather]

What you should have done is modeled as multi-body solid and then push out (Manage>Make Components) the individual parts and assembly.  The parts would have been grounded in proper location.

Use of origin workplanes and modeled in position would be another technique.

[Anonymous]

use the tangent constraint after you use flushes or mates to center it on the tube.