Law curve help

[SiW979]

If I want to create a helix that is of a fixed arc length, but can have the radius/diameter modified so basically the smaller the diameter, the more over lap there is after the first 360 degrees and as the diameter increases, then the over lap reduces, then how could I define this using expressions please? (anyone else smell a deformable worm drive clip?)

Cheers

Si

Best regards

Simon NX 7.5.4.4 MP8 and NX 8.5 (native) - TC 8

http://www.jcb.com

 

[FrankMalone]

Define a new expression with the length of the helix (for instance LH=300)
Now define the number of turns like this: n=LH/sqrt((pi()*D)^2+pitch^2) where D is the helix diameter, pitch is the pitch (this is obvious) and LH is the length defined above. That's it.

You can note a subtle difference between the length calculated by NX and this one. If you unwrap the helix you can see the length is the same.

Regards
Frank.

 

[SiW979]

Hi Frank

Not quite what I was looking for, I should have said that the helix is 2D and when viewed from above should not be a perfect circle, but and spiral which is gradually increasing in radius.


Best regards

Simon NX 7.5.4.4 MP8 and NX 8.5 (native) - TC 8

http://www.jcb.com

 

[cowski]

Here's my take on it (NX 8 part file attached).

www.nxjournaling.com

 

[cowski]

Forgot to mention the expressions: in the part navigator, expand the user expressions folder and you can edit the starting diameter, thickness, and total length directly.

www.nxjournaling.com

 

[aluminum2]

I did something similar, but a linear relationship of r and pitch. From memory you have to make your radius a function of t. like (r+r^2/t) * sin() or cos().

 

[cowski]

The radius in the attached file increases linearly for 360°, then the "extra length" is a fixed radius. In reality, the clip would conform much more closely to the diameter of the item it is clamped to, then diverge near the overlap. I think it could be modeled more accurately using only lines & arcs, but the OP mentioned law curves...

www.nxjournaling.com