Variable Helix

shaun_3

Any plans for the ability to have a variable helix where pitch and diameter can be controlled independently? (Like the SW tool)
Barring that, any ideas on how to accurately model the thread form for self tapping screws tapering off into the gimlet point? 

pete_yodis

@shaun_3 There is no compound curve function in Onshape at the moment.  To get around that, you have to create edges of either surfaces or solids and reference them in your sweep to get what you want...

andrew_troup

shaun_3 said:

Possible to use intersection between a revolved surface - representing the body of the screw - and a swept helical surface as the path for a new swept solid?

Absolutely. This is actually how I would do it even in Solidworks

(variable helix, AFAIK, is still confined to varying the pitch at constant diameter; it was not possible last time I checked to combine a tapered helix with a variable pitch. Plus a tapered helix did not support a transition from parallel to tapered, so it would not be a realistic representation of most self tapping screws. However I'm a couple of years behind the play in SW, so please correct me if wrong)

pete_yodis

@shaun_3 There is no compound curve function in Onshape at the moment.  To get around that, you have to create edges of either surfaces or solids and reference them in your sweep to get what you want...

shaun_3

Possible to use intersection between a revolved surface - representing the body of the screw - and a swept helical surface as the path for a new swept solid?

andrew_troup

shaun_3 said:

Possible to use intersection between a revolved surface - representing the body of the screw - and a swept helical surface as the path for a new swept solid?

Absolutely. This is actually how I would do it even in Solidworks

(variable helix, AFAIK, is still confined to varying the pitch at constant diameter; it was not possible last time I checked to combine a tapered helix with a variable pitch. Plus a tapered helix did not support a transition from parallel to tapered, so it would not be a realistic representation of most self tapping screws. However I'm a couple of years behind the play in SW, so please correct me if wrong)

shaun_3

andrew_troup said:

shaun_3 said:

Possible to use intersection between a revolved surface - representing the body of the screw - and a swept helical surface as the path for a new swept solid?

Absolutely. This is actually how I would do it even in Solidworks

(variable helix, AFAIK, is still confined to varying the pitch at constant diameter; it was not possible last time I checked to combine a tapered helix with a variable pitch. Plus a tapered helix did not support a transition from parallel to tapered, so it would not be a realistic representation of most self tapping screws. However I'm a couple of years behind the play in SW, so please correct me if wrong)

Not sure when it started, but in SW2015 you have very fine control over the end product. (see below)
This kind of control allows you to sweep a thread form such that it disappears into the point.

nav

Hi @shaun_3 just trying to do something similar in OS, when using different pitches the transitions is not very smooth (See images below). in order to make the variable diameter helix, not sure if it's the same procedure as above I just used the diameters from your post in parallel planes, then used the loft feature to create the body where to place the helix, I still haven't figured out the calculations (Reasoning--maybe OS guys can help) behind the onshape helix start point placement, the first two helix I created the (bottom ones), were coincident, but the third one was in the same pitch example 180 degrees apart and in the variable pitch example 60 degrees apart, that`s why i had to use the Transform tool to rotate the las helix into position.






EDIT : using turns instead of pitch in the helix command performs a smooth transition


EDIT 2 : There is no actual smooth transition when using the number of turns instead of pitch either, it was just an optical effect and I got lucky with the number of turns i selected randomly, when using a different # of turns I get the same result as in the second image above. Is very likely we need tools like andrew_troup said:

@nav: I don't right now have an idea for a workaround for the problem of how to transition smoothly between different pitches. It's a bit difficult, in the absence of 3D sketches with fillet or tangent spline or 'fitted spline' ability

andrew_troup

@shaun_3 : Thanks for the update re SW2015. That does look remarkably comprehensive.
Is it possible to specify transition radii when the diameter changes (ie, the radius of the tangent arcs, if using a revolved surface intersecting a helical surface, per your alternative method?)

@nav: I don't right now have an idea for a workaround for the problem of how to transition smoothly between different pitches. It's a bit difficult, in the absence of 3D sketches with fillet or tangent spline or 'fitted spline' ability

For variable diameter, though, it seems relatively straightforward. I would tend to use a revolve to create the surface, rather than a loft, because it's dead easy to use fillet to create the necessary tangent arcs in the profile, but I think there are other ways which would also work.

Nickolas_Lockard

I am trying to engineer a locking slot-and-tab for a collar that fits over this part. I couldn't figure out how to do a compound path along the surface, so tried 3 helixes, each on separate surfaces. But where helixes intersect part is really bad. I need the tabs to engage smoothly and not hang up. Any ideas? (Edit: I haven't bothered to add the entrance shaft for the tab yet. No point until I can get a smooth path.) I wish I could create an 'S' path along a curved surface (so it would be an S bent through 15 degrees of arc of a cylinder surface.) Any way to do it or other ideas?

shaun_3

You might try extruding a surface, with the 's' path that you want, through the cylinder, then use the intersection of the the cylindrical surface and the 's' surface as the path for a swept cut