Helix direction parameter; datum axis as helix axis? 3

[abeschneider]

Is it possible to parametrically change the helix direction (ie: parametrically define the helix axis)?

Also, why can't one select an actual datum axis as the helix direction when in the "define orientation" dialogue? (or can you?)

Thank you.

 

[kevklem]

I believe the short answer is no. After playing with it some, I found that it takes the input WCS or line/point for creation and then its direction is fixed, hence the simplistic axis definition as well.

 

[abeschneider]

Wow, that seems pretty limited.

In Catia, one has the option of selecting any axis or line to define/redefine the direction of the helix, which is quite handy.

Wonder if there's some other way of making helixes in NX than the default?

 

[JohnRBaker]

The only approach that I've used for something like this is to create a swept surface in the form of a helical shape and then extract the outer edge.

To do this first draw 2 line at right angles (probably best to use a Sketch, that way you can attach the sketch Datum and such that you can manipulate them to control the direction of the final helix as well as providing a means to edit the length of the lines) forming a sort of "L" shape. Make one line the length of the desired helix (this line will also represent the "axis" or direction of the helix) and the other the desired "radius". Now using the Insert/Sweep/Swept... function, select the "axis" line as "Guide String 1" and hit "OK" twice. Now select the "radius" line as "Section String 1" and again hit "OK" twice. Now select the "Alignment Method" of "Arclength" and the "Section Location" to be "Ends of guides". Now for the "Orientation Method" select "Angular Law" and choose the "Law Option" of "Linear". Now enter a start value of "0" and an end value as the number of turns X 360 (for example, if the helix is to have 2 complete turns - enter 720, 3 compelte turns - enter 1080, and so on) and hit "OK" . Now chose a "Scaling Method" of "Constant" (note that you could at this point use another "Law", the "Parimeter Law" to create a variable radius helix again using a "Linear" law and entering the values for the start and end radius of the desired helix) and accept the default value of "1" by hitting "OK" and then chose "Create" for the "Boolean Operation".

Now that you have a helical shape, just use Insert/Associative Copy/Extract... and using the "Curve" option select the outer edge of the helical surface and then either Blank or move to an invisible Layer the surface, and you now have a fully parametric AND associative Helical Curve.

Anyway, I know it sounds like a kludge, but it does work and it allows for lots of options (for example, who says the "axis" even has to be a line. It could be a spline representing the centerline of a "curved" helix).

John R. Baker, P.E.
Product "Evangelist"
NX Product Line
UGS Corp
Cypress, CA

http://www.ugs.com

 

[abeschneider]

John,
Thank you very much for such a great, informative, and easy to follow post!

Couldn't UGS encapsulate this method into an actual feature command? It'd be more useful than the current "Helix" command, IMHO.

 

[abeschneider]

John,

Question: how do you make the # of turns (ie: the 720 or 1080) parametric; controllable by a variable input?

I tried to do this following your method but the law input box allows only manual input.

Thanks

 

[JohnRBaker]

OK, instead of using the "Linear" law, use the one labled "By Equation", but before you create your helix you need to create a couple of expressions. Now these can be any name that you wish, but the system will assume these names unless you tell it otherwise. Anyway create the following expressions:

Angle=360
t=0
xt=Angle*t

Now if you wish to actually enter the number turns rather that calc out the final angle all of the time, you could use the following expressions:

Turns=1
t=0
xt=(360*Turns)*t

Now when you create the helical surface when you use the "By Equation" angular law, it will ask for two expressions, but as I said it's defaulted to "t" and "xt" so if you use those names you don't have to do anything but keep hitting "OK". Of course you can also create these expressions afterwards and then edit the helical surface and change the orientation method by selecting "Change Law Type" and selecting "By Equation" and following the steps above.

Anyway, now you have complete control over ALL "parameters" of your "associative" helix.

John R. Baker, P.E.
Product "Evangelist"
NX Product Line
UGS Corp
Cypress, CA

http://www.ugs.com

 

[abeschneider]

John,
Thank you. Perfect explanation.

Any comment on why you can't enter the parameter into the linear law option box? Seems like that would be a logical place for a knowledge input...

 

[JohnRBaker]

It's just some really old parts of the code that have not been fully 'updated' yet.

Now that being said, despite the fact that it's not using expressions, the 'parameters' of those laws can be 'edited' using Edit Feature, so while they may not have met the exact definition of what constitutes being 'parametric', a user can change the 'numerical' values and get an updated model.


John R. Baker, P.E.
Product "Evangelist"
NX Product Line
UGS Corp
Cypress, CA

http://www.ugs.com

 

[abeschneider]

John,
Is UGS going to 'update' these old parts of the code? Maybe in NX5?

Thing about being driven by parameters vs being able to be edited is (as you know of course) that manually editing a box becomes unfeasible when you may have many such instances in a machine - how can one be expected to manually update them all one at a time? Parameters make this much more flexible (of course this is a totally redundant comment that is common knowledge here - but then why doesn't UGS have a consistent parametric interface yet?)

 

[JohnRBaker]

There are no changes to this area, at least none that I've been able to determine, in NX 5.

John R. Baker, P.E.
Product "Evangelist"
NX Product Line
UGS Corp
Cypress, CA

http://www.ugs.com

 

[cbrn]

Hi,
just a question: instead of building a swept surface and then extract the edge, wouldn't it be simpler to define the curve directly by law (in fact, the parametric explicit expressions which define an helix in 3D are pretty simple)? Or is there something that won't let use this approach?

Regards

 

[cowski]

cbrn,
The original poster was looking for a way to associate the helix axis to the helix. The extract edge method will allow this, ie change the axis direction, the swept will update, hence the extract edge will update. Is there an easy way to do this using only equations? If so, please share.

 

[cbrn]

Hi,
Cowski, you're right: the use of the axis is what I was missing... Thank you.
Anyway, it seems to me that in UG freeform curves can have indipendent definitions for each u,v,w direction, i.e. one can be based upon another curve (a straight line, in this case) while the others are defined by equation.
I once struggled on this matter, and then went to a full-equation definition of what I was looking for, so I don't have deeper information.

Regards