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# Helix with variable pitch

Solution Partner Genius

hello, is there a way to draw a helix (NX11) with variable pitch controlled at given points? I need to have 8 turns, first 2 turns with pitch1, 3rd with pitch2, 4th and5th with pitch3, 6th pitch2, 7th 8th with pitch 1.

I have tried with the option 'linear along a spine', but I only get the first two precise, the others are not (see red arrows, image below). I also tried 'by law curve' but didn't get the expected result.

Thank you for good tips!

13 REPLIES 13

# Re: Helix with variable pitch

Experimenter

I have not really used the Helix feature before, but I have been doing a lot of helix-like geometries by writing equations for x,y and z values and using Larve Curve, by equation. This get quite complicated when dealing with non-constant pitch etc.

But I tried the helix function now. To me the option "linear along spine" for pitch and radius does not make any sense at all. I think NX is doing something else, approximating the linear behavior. If the resulting curve is to be not only continues but also differential (G1 behavior all along the curve), the radius and pitch must be differential too. And a linear behavior between more than two points is not differential.

So this assumed approximation is probably why you don't get precise results. You requirements for the pitch can't describe a pitch at one turn, and then another pitch at the next turn. The curve would not be G1 and could not be used for e.g. Swept feature.

Hope this makes sense.

# Re: Helix with variable pitch

Solution Partner Genius

Yes, that is the perfect explanation of what I 'felt'... I think the best way to get what I need is to use the Wrap Curve command, wrapping a spline through points around a cylinder.

Thank you Erland

# Re: Helix with variable pitch

Creator

Hi,

I had to build a polygonal taper once and I used the Law Curve command, you can see the formulas in the attached screenshot.

So if you could find the proper formula on Google Scholar for example, I think you could use this option as well.

# Re: Helix with variable pitch

Solution Partner Genius
Thank you, Ddzed. I don't understand the formula you attach though, what is 'e' ?

Siemens Phenom

# Re: Helix with variable pitch

Gears Phenom

You can use 'Law Curve' command with the parameters:

n=8 (number of turns)

t=1 (NX parametres)

xt=R*cos(n*t*360)

yt=R*sin(n*t*360)

for zt use By law curve and select a sketch as shown in the picture below

Be shure that the parameters n, t... are 'constant'

# Re: Helix with variable pitch

Solution Partner Genius
grazie Cesare, era proprio quello che cercavo!
Thank you Cesare, it is really what I was looking for!
Laura

# Re: Helix with variable pitch

Creator

Hi Laurus,

The "e" is the eccentricity of the polygon I created while "Dm" is the diameter, "s" is the angle and "t" is a parameter from NX.

# Re: Helix with variable pitch

Phenom

Hi @Cesare,

can you post the prt file to avoid to create ?

Thank you...

Using NX1867
RuleDesigner PDM