Spring with different end

[dr_gallup]

I'm trying to model a helical compression spring with a unique end feature. The helical compression spring has one closed coil as the last turn. Then I want to wrap another turn that has no pitch and just touches the last closed coil to make sort of a flange on the end of the spring. I've made a curve by equation and done a swept protrusion just to show what I'm trying to do. This equation is not right but it regenerates and gives the idea:

/* For cylindrical coordinate system, enter parametric equation
/* in terms of t (which will vary from 0 to 1) for r, theta and z
/* For example: for a circle in x-y plane, centered at origin
/* and radius = 4, the parametric equations will be:
/* r = 4
/* theta = t * 360
/* z = 0
/*-------------------------------------------------------------------
z=-1*wire_dia/2
theta=t*360
r=mean_dia/2+1.01*wire_dia*tan(theta/8)
View attachment 6391 View attachment 6392

There are two problems with this equation, the added coil intersects the last turn of the spring and it leaves a small gap where it starts. Looks like I need something more like a variable section sweep where I can control the normal.

I think the last line of the equation should be :

r=mean_dia/2+1.01*(wire_dia^2-(t*wire_dia)^2)^.5

The curve regens with this equation but the swept protrusion fails. This curve increases the radius much more quickly and if my math is right should fix the problem of the dead coil and the flange coil intersecting. However, the problem with the gap caused by the curve normal looks like it will be much worse.

 

[krow72]

I think that you can do that with a datum graph. Check out this video from Leo Green. His website has a lot of good tutorials.

Datum Graphs, Free Pro/E Wildfire Video Tutorial, Consumer Product Design/Development, E-Cognition Inc

 

[dr_gallup]

Thanks for the link. The last model in the video does about the opposite of what I want, the ends turn in instead of out. I think I can use the technique. Unfortunately the models are in WF5 and I need WF4. I can still open it in Creo2 but I'll have to recreate in WF4. Good practice.

 

[dr_gallup]

That is working out pretty well but there are some things about VSS that I don't understand.

If I make my sketch centered on the trajectory cross hairs, it behaves itself quite well.
View attachment 6396 View attachment 6397

However, because I am anal about using part dimensions in my drawings, I want to offset the circle so the trajectory is the OD of the spring.
View attachment 6394

However, I must need some kind of normal or tangent control because this causes the sketch to "orbit" around my trajectory so that the areas where the trajectory has constant diameter, the spring is "bee hived".
View attachment 6395

I can't seem to figure out how to use the X to T controls to make it behave.

 

[krow72]

could you post the model and graphs so I could look at it and play around with it? I am not sure if you will get what you want because your sketch would have to wrap around the curve to stay as the OD of your spring.

 

[dr_gallup]

Here is the file with the sketch centered on the trajectory cross hairs. I would have thought that if the normal follows the trajectory then if the section is offset to the outside than it should always stay outside as it follows the trajectory.

 

[dr_gallup]

Actually, I think I've got it. I changed the section plane control from normal to trajectory to normal to projection and selected the bottom (datum 2) as my direction reference.
View attachment 6399
I find these variable section sweep options clear as mud.

 

[silverado8405]

Glad I'm not the only one befuddled by the options in there and why it doesn't work like I think it should.

 

[krow72]

what I meant about wrapping around the curve is that your wire sketch is on the top of the curve at the bottom of the spring therefore it will be on top of the curve at the top of the spring and your overall dimension will not be correct if you show dimensions in your drawing because the dimension will go to the bottom of the top wire (if that makes sense). You may have to bite the bullet and create your overall dimension for this one.

This VSS is always a headache for me as well. I seem to have to spend way too much time messing with the settings to get what I want when I use it. Since I don't use it that often, I always forget what I learned from the last time anyway.