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Alexandrite

## Spiral curve with uniform pitch

Hi, I am trying to create a spiral curve with uniform pitch along its sweep direction. It seems Creo is only able to control the pitch along its trajectory spine, nothing else.  The pictures below show I am trying to create:

Creo4 part file attached here for your reference.

Anyone has any idea how do I achieve this ? Thanks

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## Re: Spiral curve with uniform pitch

Ok, perhaps I was wrong-ish.  I re-tried an earlier method with a tweak or 2.  Actually simpler than the last one  posted and a lot more like what you want.  It MIGHT be possible to get it perfect, but  I got as close as I think you can reasonably get, with the large arc, middle linear distance (from point to point) being about .030" different from the large arc end distance, with the others falling in the middle.  The distances on the inner arc are exactly equal to 4 decimals.  I don't think you can possibly realistically get closer.  It's got a nice smooooth helix, which I like.

What's this for out of curiousity?

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Creo4 part file

## Re: Spiral curve with uniform pitch

Can't open the file since I'm on creo 3.  In looking at the pictures instead of a model, I can;t tell what the cross section of the surface is, if it's circular or not.  But, it looks like you can get CLOSE, but not quite what you want.  Why? because the cross section of the helix is always going to be normal to the spine trajectory, when in reality you need it to change from one angle relative to the spine to another smoothly from one end, to the center, back to the angle at the start.

So, how exact does it need to be?

## Re: Spiral curve with uniform pitch

Also, even if you got it even closer, the pitch would ONLY be correct at the point where it intersects the 2 curves.  The rotation of the spiral along the trajectory would have to be nowhere near linear to make it work...

## Re: Spiral curve with uniform pitch

The base quilt was created using sweep and its cross section is circular along its spine (the middle curve). I would like to have uniform pitch along the sweep dir, as uniform as possible.

One idea i have is to generate a set of equally spaced points on the outer and inner curves using pattern, and join the corresponding points using datum curve on surface. I can then create the final spiral sweep using those curves. This method is tedious and hard to modify, not good.

What idea you have in your mind?

## Re: Spiral curve with uniform pitch

can you model it out and share. It's hard for me to understand from your description above. Thanks in advance.

## Re: Spiral curve with uniform pitch

Thanks, I will try it out.

## Re: Spiral curve with uniform pitch

Yes you could put a ton of points on the surface, and approximate a true spiral, but that's not only tedious, but it'll give you a "spiral" that is not smooth.  Also, you won't be able to force the curve onto the surface, you'd have to use that as a trajectory, and then do another intersection.  Not good.

I'm assuming that the guiding curves shown are both TRUE arcs, and not some spline, conic, or ellipse?

I've got one more trick that didn't work the first time, but I'm going to try it a little differently this time.

## Re: Spiral curve with uniform pitch

If you are a genius at programming with graph features driving the rotation of the spiral as it's being driven along the curves, are able to create a curve that exactly bisects the distance between the 2 curves to use as the spine trajectory (as I was able to do with some personal trickery), you MIGHT be able to do it, but as I said, the geometry simply does not work as you envision it, it simply CAN'T geometrically.  The spiral would not be a smooth rotation, it would have to slow down, then speed up, then slow down again every 180deg of rotation to make the points on the intersecting plane that would give the even spacing at those points you show.

It was an interesting puzzle but one that, ultimately, really can't be solved in Pro/E (creo).  Have fun with the file, and please pardon the extra curves, I wasn't able to quickly delete those.  The quilt is the one I'm most happy with.  Enjoy!

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