Why if I wrap a sketch on a cylinder it doesn't behave like a Helix?

mko_sc

Sketch wrapped on cylinder with curve pattern i have problems

I need to have multiple helices on a cylinder on which to add Curve pattern components.

but if I create a helix with its function, the curve pattern alignment is correct

while if it creates a helix obtained from a "wrap" the alignment is not right, there is no concentricity.(clearly Keep orientation is disabled)
Thank you so much
https://cad.onshape.com/documents/8093713ecba17430a2eef231/w/1328a799055f79056bd7a52f/e/66d906cc7c2a70bbecf4123a

mahir

Using the wrap command works fine, but there are a couple things to keep in mind.

1. You were only patterning along the first segment of the wrapped surface's boundary. You need to right-click and create a selection to select the rest of the curve. The picture below shows the result of doing this.
   https://cad.onshape.com/documents/fcad26be1889afb70377be4d/w/2721e8a25185e00ebbdcf774/e/95db55416d290046f513e4c9
   
   
2. The curve feature's orientation control is based on the instantaneous curvature of your curve at each pattern instance. That being said, the helix command creates a true helix with accurate curvature control. While using the wrap command to fold an arbitrary sketch onto a cylinder will only yield an approximation. So the curvature won't be as accurate, and any curve pattern based on that curve will end up having more variation/inaccuracy in orientation from instance to instance.

mko_sc

sorry

mko_sc

Hello,

Sorry if I insist, I also tried to hook the other line for the path to follow,

but the result is not remotely close to my goal and I don't understand why

one thing is approximation but in this case the thing is completely wrong, you can see well from "show curvature".

Thanks

https://cad.onshape.com/documents/74d27d15a017b8b913331b59/w/8d8be167dd9c15120ae16e9a/e/fda9a3f3ac5e1fef4e354a3d

Thanks

matthew_stacy

@mirko_schia, this looks like a spiral staircase that reverses direction halfway up.  Am I understanding your intent correctly?

I approached the problem with a helix (starting halfway up the cylinder) and then mirrored that.  I hung the first step on the helix and then applied a curve pattern.  The upper half above the mirror plane is a second curve pattern (I couldn't make it work with a single pattern).

Let me know it this is what you're looking for:  https://cad.onshape.com/documents?nodeId=dfbe4b7748eaaa199ae75689&resourceType=folder

konstantin_shiriazdanov

I beleve the Helix created by the native feature keeps some additional information about center axis which is extracted and used by patterns and sweep native features. But helix created by wrap is not recognized specifically and may not have specific axis attributes. So you have to give some additional info about instance orientation to curve pattern to make correct transform. In this custom feature you select reference face.

https://cad.onshape.com/documents/0cebf8e996bef572dab50077/w/1abca4baef2f283fdb1917c0/e/e93db49078cefffbed15ab92

mko_sc

Thanks,

I believe the solution is as intuited by KONSTANTIN. now I try it for good and let you know

For Matthew, my aim is to design tools similar to these

thanks a lot to everyone

mko_sc

I confirm that the repetition along a wrapped sketch of a "Part pattern" works well with path pattern

the repetition of a "Feature pattern" is also perfect.

Thank you all