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Variable Pitch Helix

Shyam Podishett

New member
<DIV =postcolor id=post-12290>Hi,

Can any body tell me to create a Variable Pitch Helix. I just know that, it is possible by using option " Use Law".

But if anybody can tell, how exactly we can create this???

Shyam Podishetti
TCS, India</DIV>
 
Hello Shyam,


u can follow these steps to create variable pitch helix


1.Create these expressions (Tools->Expression...)


Dia_helix=10


Num_turns=5


t=0


xt=Dia_helix*sin(360*Num_turns*t)


yt=Dia_helix*cos(360*Num_turns*t)


zt=10*(t*(t+1)/2)


Note that u can use zt=t*t which also creates variable pitch helix, but the one mentioned above will create helixwhose pitch varies linearly.


2.Insert->Curve->LawCurve...


Select 'By Equation' optionto define X,Y & Z values.
 
Thank you

The post helped a lot. But this function gives the linear variation in pitch from 0 to the pitch defined. Is there any way to define the starting pitch and ending pitch & also start Helix dia and end helix dia for varying helix diameter

Many thanks in advance.
 
1. you can create a law curve based on expressions for x and y and a separate law curve for you z values. The expressions for the x and y values are formulas for the x and y values of a circle multiplied by the number of coils, i.e. x=rad*cos(t*360*number_coils) and y=rad*sin(t*360*number_coils). "t" is a built in expression that tells NX to evaluate the formula from 0 to 1. For the z value you can create a sketch that directly plots the values of z. Look at the attached part for an example.

2. create a cylinder whose diameter equals the diameter the spring minus the diameter of the wire and whose length is equal to the spring length. Then, on a datum plane that is tangent to the cylinder create a sketch that is the "unwound" path of the coil. Use "wrap curve" to map this sketch onto the cylinder and then create a "tube" using the wrapped curve. You can get rid of the cylinder and create flattened ends by offsetting the cylindrical wall to make it larger than the spring and doing a boolean intersection of the cylinder and tube. Example part attached.

download the model :
https://www.dropbox.com/s/msu2mebkc49z0eb/variable helix template.rar
 

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