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# Why the distance from the helix to the center is not equal

Pioneer

version UG NX 12.0.0.27

I draw a helix and use the command along the spine line. The spine line is shown in Figure 1. The spine line is parallel to the Z-axis. The operating parameters are shown in Figure 2. The resulting of the helix is shown in Figure 3. Take the 1, 2, and 3 points on the helix line, as shown in Figure 4, measure the distance from these points to the spine line. The measurement method is shown in Figure 5. The results obtained are shown in Figure 6. The results show that the three points are to the spine line. The distance is different, the origin file locates in attachments, I hope to get the same radius of the helix, I don't know why, who can tell me?

fig 1

fig 2

fig 3

fig 4

fig 5

fig 6

9 REPLIES 9

# Re: Why the distance from the helix to the center is not equal

Siemens Phenom

Hello @N12X ,

I believe points on helix and the origin are not on same plane, so distances will be different.

Hope it helps.

Thanks,

Amol

# Re: Why the distance from the helix to the center is not equal

Pioneer
Thank you, you know the distance from any point on the helix line to its axis is called the radius of the helix, and the radius of the helix should be exactly equal.

# Re: Why the distance from the helix to the center is not equal

Gears Phenom

Ciao @N12X ,

this is my result.

You must select first any point on the elix, then select 'line'.

Ciao

# Re: Why the distance from the helix to the center is not equal

Siemens Phenom
A helix in NX is not an analytical object but a NURBS spline. - this allows the helix to have varying diameter and non-constant pitch.
A nurbs spline can replicate almost any shape. It mimics the helix shape within an accuracy tolerance, The tolerance governs how much data will be used to create the spline. But it also allows a deviation from the theoretical shape.
the amount of data required to be "very exact" will be much higher than "less exact". You will find the "Distance tolerance" in the helix dialog.
You can see the difference by selecting the spline of the helix, note : select the "spline" and not the "Helix feature", then press Ctrl+i, the number of poles will be reported and highlighted in the graphics.
Press F5 to refresh the graphics. Change the tolerance of the existing helix and repeat the select+ Ctrl+i.

Regards,
Tomas

# Re: Why the distance from the helix to the center is not equal

Pioneer

thank you very much, but sometimes I found the radius is equal, I do not know why? such as fig

# Re: Why the distance from the helix to the center is not equal

Siemens Phenom
If you imagine the spline swaying both in and out within the allowed tolerance, it will also be spot on here and there.
If you try measure slightly besides the points where you get the perfect result, you will probably see the small deviation.

Regards,
Tomas

# Re: Why the distance from the helix to the center is not equal

Gears Esteemed Contributor

In your first case, the spine curve is shorter than your helix length; the distance from the helix end point to the spine picks up some distance in the Z direction (as alluded to by @AmolKadam ). For the first case, try lengthening your spine curve or measuring to the Z datum axis instead of the spine curve.

# Re: Why the distance from the helix to the center is not equal

Pioneer

it is just displaying error, if you click ctrl+i, you will found the difference. such as fig 1, the details information in the below file, I also say thank you for your care.

fig.1

Pioneer
thank you