Sweep with Twist

thomas_kozak

I'm trying to follow a set of instructions for generating a hyperbolic worm gear.  One of the steps involves sweeping a gear profile along a semicircle while also twisting it by x degrees.  Possible in OnShape?  I don't see it on the Sweep tool and trying to fake it with Lofts seems to be imprecise.

Fields

I believe this is what you're looking for. Loft does work, but like using multiple points for a spline on a gear tooth, you need multiple sketches for the loft to follow properly. Also, getting the end conditions right is a pain. It's much easier to loft well past what you need, then cut out all but the middle section. 
Unfortunately this turns into a big file very quickly, and I had to save off a few times to keep my limit down.  

Here's the public file. Just use the rollback bar to follow the idea.
https://cad.onshape.com/documents/56c4e376e4b098490f907d4b/w/208572b740acc9be5daf3838/e/19d350cf90fd4623bf0e8e67

The cutting tool and end result. (I just copied another gear face and rotated a few times for effect)

dennis_20

Sweep with guide curves should do the trick.

thomas_kozak

Can you add guide curves to a sweep? I know you can do it with loft.  However as I understand it the loft guide curves have to intersect the lofted profile at both ends, which means the path for the guide curve would have to be 3-dimensional to describe the correct twisting.

viru

@thomas_kozak , Kindly refer below link in which worm gear is created similar to your requirement.
https://cad.onshape.com/documents/6c5c1d79ed9d4cf9b75fd503/w/84bebcd7159144acbfe4fb8f/e/6a89e4751e7b4324a54d0125
https://cad.onshape.com/documents/49fb27a7c1ea4799bb684a99/w/3ab432355087408aacfa96b9/e/2670f4f809f84c55aa5f4202

øyvind_kaurstad

@viru Those examples are not the same as the OP asked for, it seems. He wants hyperbolic worm gears, those are just regular screws.

thomas_kozak

Thanks for the input viru!  As øyvind kaurstad states, a simple helical screw is doable.  The challenge is sweeping the teeth along a torus rather than along a cylinder, or twisting the sweep which would accomplish the same thing.  I'm leaning towards this is not currently possible in OnShape but I've seen people come up with some really clever workarounds on this forum so I thought I'd put the question out there.

Fields

I believe this is what you're looking for. Loft does work, but like using multiple points for a spline on a gear tooth, you need multiple sketches for the loft to follow properly. Also, getting the end conditions right is a pain. It's much easier to loft well past what you need, then cut out all but the middle section. 
Unfortunately this turns into a big file very quickly, and I had to save off a few times to keep my limit down.  

Here's the public file. Just use the rollback bar to follow the idea.
https://cad.onshape.com/documents/56c4e376e4b098490f907d4b/w/208572b740acc9be5daf3838/e/19d350cf90fd4623bf0e8e67

The cutting tool and end result. (I just copied another gear face and rotated a few times for effect)

thomas_kozak

Thanks, Fields. I think that's the closest possible, although with the variability of end conditions I'm not sure I would trust this to be 100% accurate to the correct twist.  For now i'm sticking with non-enveloping worms which are much easier to create (tooth profile swept along helix).