How to create a variable pitch helix in NX? 3

[imti7]

In solidworks i was having a variable pitch option to create a helix with pitch n revolution and then sweep long the path to create screw(i have attached the images n .x_t model file for reference!, Kindly tell me how create the same in NX

 

[JohnRBaker]

Use the 'Law Curve' function. In the video below, go to about the 5:00 point and there will be some information about how you can get to a library of predefined 'Law Curves' which you can start with and then edit:

https://www.youtube.com/watch?v=oT6OeBug9Sw

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[Toost]

You can also use a "law" in the helix feature.

Regards,
Tomas

The more you know about a subject, the more you know how little you know about that subject.

 

[imti7]

thank you

 

[cowski]

I uploaded an example file in your other, related thread.
thread561-510003

www.nxjournaling.com

 

[mmauldin]

You can also draw a 2D layout of the pitch and wrap it around the cylinder. Useful approach when you don't want to do math. I usually add fillets to the sketch to make the transitions smoother.

 

[JohnRBaker]

Or use a Spline through a Sketch made-up of Points...

John R. Baker, P.E. (ret)
Irvine, CA
Siemens PLM:

The secret of life is not finding someone to live with
It's finding someone you can't live without

 

[mmauldin]

Here is an example of the wrap method in use:

 

[imti7]

Hi guys,
Using wrap method i have one doubt ,on what basis we have to define the angle of our 2D sketch layout to wrap it on the cylinder, because in below cylinder i tried creating 200mm Pitch helix onto Ø40mm cylinder, when the angle is 45° it gives 1.5 turn & when angle is 17.5° it gives 4 turns, how angle is calucalted?

Suppose let's say we have our objective to create below parameter helical curve
we have a cylinder of 40mm dia and 945mm Height.
we have variable ptiches like below on that cylinder:
1. Height 0mm-240mm = 98mm ptich Helix turns on Ø40mm cylinder = 2.44 turns should be there on cyl btwen this distnce.
2. Height 240mm-320mm = 80mm pitch helix turns on Ø40mm cylinder= 01 turn should be there on cyl btwen this distnce.
3. Height 320mm- 945mm= 75mm pitch helix turns Ø40mm cylinder=8.33 turns should be there on cyl btwen this distnce.

Please show me how would you bring above parameter helix onto cylinder exactly at required distances.
Thanks for the support,
Imtiyaz

 

[cowski]

In short, the horizontal leg of your triangle is the circumference of your cylinder (or OD * pi) and the vertical leg is the desired pitch. The angle you are looking for is atan(OD*pi/pitch). Check out the NX12 file that I posted in your other thread, it shows one way of creating the sketch and using wrap curve to create the spline.

If I have time, I'll create another version according to your spec above.

Edit: file attached. If you are going to sweep the thread geometry along the helix, you will want to leave some room to transition between the linear pitch portions of the screw.
The first helix (near the origin) has no transitions and is modeled as described in your post. The resulting helix is not smooth and cannot be used as a guide curve for a sweep.
The 2nd helix (middle) uses the 240-320mm section as a transition; it uses a simple arc between the linear portions.
The 3rd helix (right) uses the "cubic along spine" pitch law in the helix command. The pitch is a constant 98mm in the first section (0-240mm). It uses cubic interpolation to transition from 98mm pitch to 75mm pitch from 240-320mm. Finally, it has a constant pitch of 75mm from 320mm to the end.

www.nxjournaling.com

 

[imti7]

Dear cowski,
My apologies for the delayed response!

Thank you for the formula and files,

I understood all of your points,

both wrap using smooth transition arc and Helix using cubic along spine options are reliable to use swept.

specially Helix using cubic along spine is great method to create variable pitches it seemed to me after seeing your work.

In your wrap method,i still have a question for an angle. kindly tell me what formula you have used to calculate angle for 98mm ptich helix in 240mm height for 2.44 turns.

the formula told in your previous thread will work for one complete revolution of helix but how we calculate angle when we have both height and pitch of the helix.

 

[mmauldin]

If you know the pitch then you don't need to figure out the angle. In the example below, all that is needed is the circumference (measured as the length of the cylinders edge), the pitch, and the number of turns. A line drawn from the base of the cylinder through a point 1 pitch horizontal and 1 circumference vertical establishes the angle. The end of the line can be determined by a explicit horizontal value or, as in this example, the number of turns multiplied by the pitch.

 

[cowski]

kindly tell me what formula you have used to calculate angle for 98mm ptich helix in 240mm height for 2.44 turns

There are multiple ways to get what you need. Mmauldin gives one alternative to what I did.
To answer your question, I found the angle by taking the atan(OD*pi/pitch) (see my previous post and/or the expressions in the NX file I posted).

In your question, you are specifying pitch, height, and number of turns. These three values are related, 2 of the values are independent and the third can be calculated from the 2 given values. Pick 2 of the values that you want to control; if you try to control all 3 simultaneously, you will end up with an over constrained system of equations.

www.nxjournaling.com

 

[imti7]

Dear cowski and mmauldin

both of you thank you so much , by here it solves my all questions for variable pitch helix


thank you so much you guys