how to model helical compression spring with squared ground ends 1

[abeschneider]

How would I go about modeling a helical compression spring with squared ground ends?

I can easily create the active coils using the helix function in Generative Shape Design. Problem is in creating the squared ends; I think one way to do it would be to create another helix at the end, with a pitch 1/2 the normal pitch, and a height 1/2 of one normal pitch. But now the "end coil" is not tangent to the active coil.

Any suggestions? Thanks.

 

[jackk]

I think you're on the right track, Abe.

For tangency, I suggest you cut back the helix curves and add a connect curve to fill in the gap with a tangent curve. Do the same at the other end. Then join all 5 curves (3 helix and 2 connects) into a single curve for your sweep.

 

[5050t]

To make the end coil curve tangent to active coil curve, I would use "Curve Smooth" option in GSD. Then create your sweep.

 

[solid7]

abeschneider - is this what you're trying to do?

I didn't do either method of blending the curve. I use a spline on a cylindrical work support, for more predictable results with the blend.

Step 1: create a cylinder, and make a parameter that links the helix starting point diameter with the cylinder diameter.

Step 2: make a point "on curve" - for both the main helix, and the second stage pitch, from the point where they intersect. Set it back whatever distance works, (1" worked well for me) and trim to the point.

Step 3: make a spline, with tangency to both helixes, and use the cylinder (with the same diameter as the helix) as the work support. This is the only realistic way to ensure the shape is round, and it's easier to get good results, from what I have experimented with.

Step 4: join the pieces.

Step 5: sweep the spring profile, and make end cutting planes, by running a parallel plane from a plane normal to your axis, and setting it to the center point of your spring profile. Split the ends back to these planes.

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[abeschneider]

Guys,
Thanks for all your (quick) help. I first tried the "Curve Smooth" in GSD, but for some reason, I couldn't create a solid rib in Part Design without Topological errors.

I ended up using Solid7's method (with a couple modifications), which seems to be working very well. A suggestion: I ran into errors when I didn't make the offset of the spline endpoints (the "points on curve") big enough. I found that a parametric value of about 1/(2.5 X the mean helix diameter) gets rid of the errors and yields good results:

 

[solid7]

Not sure how you came up with the formula for determining the point setback, but I like it. Thank you for sharing it.

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CAD design engineering services - Catia V4, Catia V5, and CAD Translation. Catia V5 resources - CATBlog.